AU2012200830A1 - Clostridial toxin activity assays - Google Patents

Abstract

Compositions useful for detecting Clostridial toxin activity comprising a cell that contains an exogenous Clostridial toxin substrate comprises a fluoroscent member, a membrane targeting domain and a Clostridial toxin recognition sequence comprising a cleavage site, where the cleavage site intervenes between said fluorescent member and said membrane localization domain and methods useful for determining Clostridial toxin activity using such Clostridial toxin substrates. WO 2008/036060 PCTIUS2006/012825 U-+

Description

Australian Patents Act 1990 - Regulation 3.2A ORIGINAL COMPLETE SPECIFICATION STANDARD PATENT Invention Title "Clostridial toxin activity assays" The following statement is a full description of this invention, including the best method of performing it known to us:- WO 2008/036060 PCTIUS2006/012825 CLOSTRIDIAL TOXIN ACTIVITY ASSAYS [01] This patent application claims priority pursuant to 35 U.S.C. §119(e) to United States provisional patent application Serial No. 60/668,909 filed on April 5, 2005, which is hereby incorporated by reference in its entirety. [02] All of the publications cited in this application are hereby incorporated by reference herein in their entirety. All GeneBank sequence listings cited this application, as identified by their GenBank accession numbers, are available from the National Center for Biotechnological Information and are all hereby incorporated by reference in their entirety. [03] The myorelaxant properties of Clostridial toxins (CoNTs) are being exploited in a wide variety of therapeutic and cosmetic applications, see e.g., William J. Lipham, COSMETIC AND CUNICAL APPLICATIONS OF BOTULINUM TOXIN (Slack, Inc., 2004). For example, CoNTs therapies are proposed for treating dystonia, see e.g., Kei Roger Aoki, et al., Method for treating Dystonia with Botulinum Toxin C to G, U.S. Patent No. 6,319,505 (Nov. 20, 2001); pain, see e.g., Kei Roger Aoki, et al., Method for Treating Pain by Peripheral Administration of a Neurotoxin, U.S. Patent No. 6,464,986 (Oct. 15, 2002); muscle injuries, see e.g., Gregory F. Brooks, Methods for Treating Muscle Injuries, U.S. Patent No. 6,423,319 (Jul. 23, 2002); cardiovascular diseases, see e.g., Gregory F. Brooks, Methods for Treating Cardiovascular Diseases with Botulinum Toxins, U.S. Patent Publication No. 2003/0185860 (Oct. 2, 2003); neuropsychiatric disorders, see e.g., Steven Donovan, Therapeutic Treatments for Neuropsychiatric Disorders, U.S. Patent Publication No. 2003/0211121 (Nov. 13, 2003); lower back pain, see e.g., Kei Roger Aoki, et al., Botulinum Toxin Therapy for Lower Back Pain, U.S. Patent Publication No. 2004/0037852 (Feb. 26, 2004); as well as other neuromuscular disorders, see e.g., Kei Roger Aoki, et al., Multiple Botuilnum Toxins for Treating Neuromuscular Disorders and Conditions, U.S. Patent Publication No. 2001/0021695 (Sep. 13, 2001); Kei Roger Aoki, et al., Treatment of Neuromuscular Disorders and Conditions with Different Botulinum, U.S. Patent Publication No. 2002/0010138 (Jan. 24, 2002); Kei Roger Aoki, et al., Use of Botulinum Toxins for Treating Various Disorders and Conditions and Associated Pain, U.S. Patent Publication No. 2004/0013692 (Jan. 22, 2004) all of which are hereby incorporated by reference. Additional proposed uses of CoNTs as biopharmaceutical neuromodulators has expanded to cover a wide variety of treatments targeting certain disorders that lack a neuromuscular basis. For example, the effects on the autonomic nervous system has allowed the development of a Botulinum toxin serotype A (BoNT/A) therapy for treating axillary hyperhydrosis or sweating, and reports indicate BoNT/A may be an effective treatment for myofascial pain and tension, stroke, traumatic brain injury, cerebral palsy, gastrointestinal motility disorders, urinary incontinence cancer and migraine headaches. Lastly, cosmetic and other therapeutic applications are widely known. In fact, the expected use of CoNTs in both therapeutic and cosmetic treatments of humans is anticipated to expand to an ever widening range of diseases and aliments that can benefit from the myorelaxant properties of these toxins. [04] The growing clinical and therapeutic use of Clostridial toxins necessitates the pharmaceutical industry to use accurate assays for Clostridial toxin activity in order to, for example, ensure accurate 1 of 168 WO 2008/036060 PCT/US2006/012825 pharmaceutical formulations and monitor established quality control standards. In addition, given the potential danger associated with small quantities of Clostridial toxins in foodstuffs, the food industry requires Clostridial toxin assays, for example, to validate new food packaging methods and to ensure food safety. The present invention provides novel Clostridial toxin assays for determining the presence or activity of a Clostridial toxin useful for various industries, such as, e.g.. the pharmaceutical and food industries, and provides related advantages as well. BRIEF DESCRIPTION OF THE DRAWINGS [05] FIG. 1 shows a schematic of the current paradigm of the intoxication mechanism for tetanus and botulinum toxin activity in central and peripheral neuron. This intoxication process can be described as comprising four steps: 1) receptor binding, where Clostridial toxin binds to a Clostridial receptor system initiates the intoxication process; 2) complex internalization, where after toxin binding, a vesicle containing a toxin/receptor system complex is endocytosised into the cell; 3) light chain translocation, where multiple events are thought to occur, including changes in the internal pH of the vesicle, formation of a channel pore comprising the HN domain of Clostridial toxin heavy chain, separation of the Clostridial toxin light chain from the heavy chain, enzymatic activation of the light chain; and release of the activated light chain and 4) enzymatic target modification, where the activated light chain of Clostridial toxin proteolytically cleaves its target SNARE substrates, such as, e.g., SNAP-25, VAMP or Syntaxin. [06] FIG. 2 shows a schematic of SNARE proteins. Figure la shows the general domain organization of SNAP-25, VAMP and Syntaxin depicting approximate locations of the a-helical resions (white boxs), SNARE motifs (Hatched boxes with S1, S2, S3, S4, V1, V2, X1 or X2 designations) and the membrane anchoring domains (white boxes designated MA). Figure 1b shoes the helical organization of a SNARE motif. [07] FIG. 3 shows a schematic of the the subcellular localization and cleavage sites of SNAP-25, VAMP and Syntaxin. VAMP is localized to synaptic vesicle membrane, whereas SNAP-25 and Syntaxin are localized to the plasma membrane. BoNT/A and BoNT/E cleave SNAP-25 close to the carboxy-terminus, releasing nine or 26 residues, respectively. BoNT/B, BoNT /D, BoNT /F, BoNT /G and TeNT act on the conserved central portion of VAMP (white box) and release the amino-terminal cytosolic half of VAMP into the cytosol. BoNT/C1 cleaves SNAP-25 close to the carboxy-terminus as well as cleaving Syntaxin at a single site near the cytosolic membrane surface. The action of BoNT/ C1 results in release of a large portion of the cytosolic domain of Syntaxin, while only a small portion of SNAP-25 is released by selective proteolysis of BoNT/C1. [08] FIG. 4 shows PC12 cells transfected with a plasmid encoding a green fluorescent protein alone (GFP, transfected with a plasmid encoding a Clostridial toxin substrate alone (GFP-SNAP252o), or co transfected a plasmid encoding a Clostridial toxin substrate alone (GFP-SNAP252s) and a plasmid encoding the light chain of BoNT/A (BoNT/A-LC). Cells expressing green fluorescent protein alone (GFP) had fluorescence dispersed throughout the cell including the nuclei. Confocal pictures were taken with 2 of 168 WO 2008/036060 PCT/US2006/012825 the plane in the middle of the cell. Cells expressing the Clostridial toxin substrate alone (GFP SNAP2520) demonstrated fluorescence in the plasma membrane of the cell body and neurites. Cells co expressing the Clostridial toxin substrate and the BoNT/A light chain (GFP-SNAP252, BoNT/A-LC) exhibit a loss of plasma membrane localization of the GFP fluorescence. The GFP fluorescence instead accumulates in some areas of the cytoplasm. [09] FIG. 5 shows Western blot analysis identifying cells with high affinity uptake for a Clostridial toxin. FIG. 5a shows a Western blot analysis used to identify cells capable of BoNT/A uptake. The blot shows five cell lines treated with 1 nM of Pure BoNT/A overnight, with equal amounts of protein loaded per lane and probed with an antibody that detects the BoNT/A SNAP-25 1 97 cleavage product. FIG. 5b shows Western blot analysis used to evaluate the time necessary for BoNT/A uptake. The blots show either Neuro-2A cells or SH-SY5Y cells treated with 1 nM of Pure BoNT/A for various lengths of time, with equal amounts of protein loaded per lane and probed with an antibody that detects the BoNT/A SNAP-25 1 97 cleavage product. FIG. 5c shows a Western blot analysis used to evaluate the concentration range necessary of BoNT/A uptake. The blots show Neuro-2A cells treated with a range of Pure BoNT/A concentrations overnight, with equal amounts of protein loaded per lane and probed with an antibody that detects the BoNT/A SNAP-25 1 9 7 cleavage product. [010] FIG. 6 shows Western blot analysis identifying cells with high affinity uptake for a Clostridial toxin. FIG. 6a shows a Western blot analysis used to identify cells capable of BoNT/E uptake. The top blot show Neuro-2A cells and SH-SY5Y cells treated with either 10 nM or 100 nM of BoNT/E di-chain overnight, with equal amounts of protein loaded per lane and probed with an antibody (SMI-81; Sternberger Monoclonals, Lutherville, MD) that detects the uncleaved SNAP-252s substrate and the BoNT/E SNAP-25 1 0o cleavage product. The bottom blot show various cells treated with 20 nM of BoNT/E di-chain, with equal amounts of protein loaded per lane and probed with an antibody for the uncleaved SNAP-25206 substrate and the BoNT/E SNAP-25 1 80 cleavage product. FIG. 6b shows Western blot analysis used to determine a time course for BoNT/E uptake. The blots show SH-SY5Y cells treated with either 5 nM or 20 nM of BoNT/E di-chain for either 4 hours or 8 hours, with equal amounts of protein loaded per lane and probed with an antibody (SMI-81; Stemberger Monoclonals, Lutherville, MD) that detects the uncleaved SNAP-25206 substrate and the BoNT/E SNAP-25 1 80 cleavage product. FIG. 6c shows a Western blot analysis used to evaluate the the concentration range necessary of BoNT/E uptake. The blots show SK-N-DZ cells treated with a range of BoNT/E di-chain concentrations for approximately 6 hours, with equal amounts of protein loaded per lane and probed with an antibody (SMI 81; Stemberger Monoclonals, Lutherville, MD) that detects the uncleaved SNAP-252N substrate and the BoNT/E SNAP-25 1 jO cleavage product. [011] FIG. 7 shows Western blot analysis evaluating the effects of treatments used to increase uptake of a Costridial toxin. FIG. 7a shows a Western blot analysis evaluating the effects of ganglioside treatment on the uptake of BoNT/A.. The blot shows Neuro-2A cells treated without or with 25 pg/mL of GT1b (- or +) and exposed overnight to three different concentrations of BoNT/A (12.5 pM. 25 pM or 50 pM), with equal amounts of protein loaded per lane and probed with an antibody that detects the BoNT/A 3 of 168 WO 2008/036060 PCT/US2006/012825 SNAP-25 1 97 cleavage product. FIG. 7b shows Westem blot analysis evaluating the effects of cell differentiation on the uptake of BoNT/A. The blots show either Neuro-2A cells or SH-SYSY cells treated 2 nM of Pure BoNT/A overnight that where either grown in serum-free media or with various differentiation reagents (lonomycin, db-cAMP, Retinoic acid, Neuraminidase or N2), with equal amounts of protein loaded per lane and probed with an antibody (SMI-81; Stemberger Monoclonals, Lutherville, MD) that detects the uncleaved SNAP-25206 substrate and the BoNT/A SNAP-25 1 97 cleavage product. [012] FIG. 8 shows Western blot analysis evaluating the effects of treatments used to Increase uptake of a Costridial toxin. FIG. 8a shows a Western blot analysis evaluating the effects of ganglioside treatment on the uptake of BoNT/E.. The blot shows Neuro-2A cells treated with either 25 pg/mL of GT1b, GQ1b, GD1a, GD1b or GD3 and exposed for approximately 5 hours to 14 nM of BoNT/E di-chain, with equal amounts of protein loaded per lane and probed with an antibody (SMI-81; Stemberger Monoclonals, Lutherville, MD) that detects the uncleaved SNAP-252om substrate and the BoNT/E SNAP 251so cleavage product. FIG. 7b shows Western blot analysis evaluating the effects of cell differentiation on the uptake of BoNT/E. The blots show either N1 E-1 15 cells, SH-SY5Y cells, SK-N-DZ cells or NG108 15 cells treated with either 0 nM, 2 nM or 20 nM of BoNT/E di-chain for approximately 6 hours that where grown in serum-free media, with equal amounts of protein loaded per lane and probed with an antibody (SMI-81; Sternberger Monoclonals, Lutherville, MD) that detects the uncleaved SNAP-252 substrate and the BoNT/E SNAP-25 1 eo cleavage product. FIG. 9 shows a schematic of a fluorescent-based Clostridial toxin activity assay which relies on cell lines containing a Clostridial toxin substrate localized to the cell membrane. FIG. la shows an assay scenario where the uncleaved Clostridial toxin substrate, comprising a fluorescent member (FM), a membrane targeting domain (MTD) and a Clostridial toxin recognition sequence comprising a Clostridial toxin cleavage site (RS), is detected. Upon excitation, the fluorescent member emits fluorescent light at a characteristic wavelength that is localized to the membrane. FIG. 1b shows an assay scenario where the cleaved Clostridial toxin substrate is detected. Upon excitation, the fluorescent member emits fluorescent light at a characteristic wavelength. However, because the cleavage product containing the fluorescent member is released into the cytoplasm, detection of fluorescence is in a different subcellular localization. Thus, a decrease in fluorescent member emissions in the membrane, or an increase in fluorescent member emissions in the cytoplasm is indicative of the presence of Clostridial toxin activity. DETAILED DESCRIPTION OF THE INVENTION [013] The present invention provides novel assays for determining the presence or absence of an active Clostridial toxin in a sample and for determining the activity of a Clostridial toxin, including botulinum toxins of all serotypes and tetanus toxin. The novel assays of the invention rely on the cellular localization of the uncleaved Clostridial toxin substrate, the cellular localization of the cleaved Clostridial toxin substrate, or the cellular localization of both the uncleaved and cleaved Clostridial toxin substrate. The present invention further provides novel compositions, including cells and cell lines containing Clostridial toxin substrates, useful for the assays disclosed in the specification. The novel cells and 4 of 168 WO 2008/036060 PCT/US2006/012825 assays of the invention reduce the need for animal toxicity studies, yet serve to analyze multiple toxin functions, namely, binding and cellular uptake of toxin, translocation into the cell cytosol, and protease activity. As discussed further below, the novel cells and methods of the invention can be used to analyze crude and bulk samples as well as highly purified dichain toxins and formulated toxin products and further are amenable to automated high throughput assay formats. [014] The assays disclosed in the present specification use cells which are capable of efficient Clostridial toxin uptake and which include a membrane localized Clostridial toxin substrate containing a fluorescent marker. As an example, a cell useful in the invention can express a SNAP2520-enhanced green fluorescent protein (EGFP) fusion protein (absorbance 484 nM, emission 510 nM), which localizes to the plasma membrane (FIG. 9). Upon BoNT/A treatment of this cell, cleavage of the membrane localized SNAP2520-EGFP substrate occurs, releasing the EGFP containing fragment into the cytoplasm. Upon excitation of the treated cell with a 484 nM laser, the EGFP is excited and emits light at 510 nM. However, because a portion of the EGFP is now cytoplasmic, a distribution change between the uncleaved, membrane localized SNAP25 2 06-EGFP toxin substrate and the cleaved, cytoplasmic localized EGFP fragment can be observed in BoNT/A treated cells. [015] Aspects of the present invention provide for an exogenous Clostridial toxin substrate capable of being localized to the plasma membrane of a cell. These substrates comprise a fluorescent member, a membrane targeting domain and a Clostridial toxin recognition sequence comprising a cleavage site, where the cleavage site intervenes between the fluorescent member and the membrane localization domain. [016] Other aspects of the present invention provide compositions comprising a cell containing an exogenous Clostridial toxin substrate capable of being localized to the plasma membrane of the cell wherein the cell is capable of Clostridial toxin intoxication, and wherein the exogenous Clostridial toxin substrate comprises a fluorescent member, a membrane targeting domain and a Clostridial toxin recognition sequence comprising a cleavage site, where the cleavage site intervenes between the fluorescent member and the membrane localization domain. The exogenous Clostridial toxin substrate can be transiently or stably contained in the cell. [017] Other aspects of the present invention provide compositions comprising a cell population, said cell population comprsing cells that contain an exogenous Clostridial toxin substrate capable of being localized to the plasma membrane of the cells wherein the cells are capable of Clostridial toxin intoxication, and wherein the exogenous Clostridial toxin substrate comprises a fluorescent member, a membrane targeting domain and a Clostridial toxin recognition sequence comprising a cleavage site, where the cleavage site intervenes between the fluorescent member and the membrane localization domain and wherein greater than 50% of the cell population comprise the cells containing the exogenous Clostridial toxin substrate. [018] Other aspects of the present invention provide compositions comprising a cell population, said 5 of 168 WO 2008/036060 PCT/US2006/012825 cell population comprising cells that transiently contain an exogenous Clostridial toxin substrate capable of being localized to the plasma membrane of the cells wherein the cells are capable of Clostridial toxin intoxication, and wherein the exogenous Clostridial toxin substrate comprises a fluorescent member, a membrane targeting domain and a Clostridial toxin recognition sequence comprising a cleavage site, where the cleavage site intervenes between the fluorescent member and the membrane localization domain and wherein greater than 50% of the cell population comprise the cells containing the exogenous Clostridial toxin substrate. [019] Other aspects of the present invention provide compositions comprising a cell population, the cell population comprising cells that stably contain an exogenous Clostridial toxin substrate capable of being localized to the plasma membrane of the cells wherein the cells are capable of Clostridial toxin intoxication, and wherein the exogenous Clostridial toxin substrate comprises a fluorescent member, a membrane targeting domain and a Clostridial toxin recognition sequence comprising a cleavage site, where the cleavage site intervenes between the fluorescent member and the membrane localization domain. 1020] Other aspects of the present invention provide methods of determining Clostridial toxin activity by contacting with a sample a cell population, the cell population comprsing cells that contain an exogenous Clostridial toxin substrate capable of being localized to the plasma membrane of the cells wherein the cell are capable of Clostridial toxin intoxication, wherein the exogenous Clostridial toxin substrate comprises a fluorescent member, a membrane targeting domain and a Clostridial toxin recognition sequence comprising a cleavage site, where the cleavage site intervenes between the fluorescent member and the membrane localization domain and wherein greater than 50% of the cell population comprises the cells containing the exogenous Clostridial toxin substrate; exciting the fluorescent member; and determining the fluorescence of the contacted cell population relative to a control cell population, where a difference in fluorescence of the contacted cell population as compared to the control cell population is indicative of Clostridial toxin activity. [021] Other aspects of the present invention provide methods of determining Clostridial toxin activity by contacting with a sample a cell population, the cell population comprsing cells that transiently contains an exogenous Clostridial toxin substrate capable of being localized to the plasma membrane of the cells wherein the cells are capable of Clostridial toxin intoxication, wherein the exogenous Clostridial toxin substrate comprises a fluorescent member, a membrane targeting domain and a Clostridial toxin recognition sequence comprising a cleavage site, where the cleavage site intervenes between the fluorescent member and the membrane localization domain and wherein greater than 50% of the cell population comprises the cells containing the exogenous Clostridial toxin substrate; exciting the fluorescent member; and determining the fluorescence of the contacted cell population relative to a control cell population, where a difference in fluorescence of the contacted cell population as compared to the control cell population is indicative of Clostridial toxin activity. [022] Other aspects of the present invention provide methods of determining Clostridial toxin activity by 6 of 168 WO 2008/036060 PCT/US2006/012825 contacting with a sample a cell population, the cell population comprising cells that stably contain an exogenous Clostridial toxin substrate capable of being localized to the plasma membrane of the cells wherein the cells are capable of Clostridial toxin intoxication, wherein the exogenous Clostridial toxin substrate comprises a fluorescent member, a membrane targeting domain and a Clostridial toxin recognition sequence comprising a cleavage site, where the cleavage site intervenes between the fluorescent member and the membrane localization domain and wherein greater than 50% of the cell population comprises the cells containing the exogenous Clostridial toxin substrate; exciting the fluorescent member; and determining the fluorescence of the contacted cell population relative to a control cell population, where a difference in fluorescence of the contacted cell population as compared to the control cell population is indicative of Clostridial toxin activity. [023] Bacteria of the genus Clostridia are strictly anaerobic to aero-tolerant spore-forming bacilli found In soil, freshwater and saltwater sediments, household dust, the surface of foods, feces as well as in the normal intestinal flora of humans and animals. While the majority of isolates are gram-positive, a few gram-negative species exist. Members of this genus produce sophisticated exotoxins that are among the most potent toxins known in the world. Exposure to these toxins during the course of Clostridia infection is the primary cause underlying disease pathogenesis. Clostridia are a major threat to human and animal health, being responsible for many diseases including botulism, tetanus, gas gangrene, pseudomembranous colitis and food poisoning. For example, Clostridium argentinense, C. bifermentans, C. histolyticum, C. novyi, C. septicum, C. sporogenes and C. tertium are etiological agents for gas gangrene. C. perfringens is responsible for foodbome illness, enteritis necroticans where as C. difficile is responsible for pseudomembranous enterocolitis. Both C. baratil and C. butyricum are causative agents for a form of foodborne, intestinal and wound botulism. Interestingly, only a few species of these bacteria are pathogenic for humans, most are saprophytic. Thus, in most cases, Clostridia are opportunistic pathogens that infect a host whose health is compromised. [024] Of all Clostridia, Clostridium botulinum and Clostridium tetani produce the most potent biological toxins known and are the causative agents of the neuroparalytic syndromes botulism and tetanus. Seven antigenically-distinct types of Botulinum toxins (BoNTs) have been identified by investigating botulism outbreaks in man (BoNT/A, /B, /E and /F), animals (BoNT/C1 and /D), or isolated from soil (BoNT/G). BoNTs possess approximately 35% amino acid identity with each other and share the same functional domain organization and overall structural architecture. The amino acid sequences of eight Clostridial toxin serotypes have been derived from the corresponding genes (Niemann, "Molecular Biology of Clostridial Neurotoxins" in Sourcebook of Bacterial Protein Toxins Alouf and Freer (Eds.) pp. 303-348 London: Academic Press 1991). It is recognized by those of skill in the art that within each type of Clostridial toxin there can be various strains differing somewhat in their amino acid sequence, and also in the nucleic acids encoding these proteins. While all seven BoNT serotypes have similar structure and pharmacological properties, each also displays heterogeneous bacteriological characteristics. In contrast, tetanus toxin (TeNT) is produced by a uniform group of C. tetani. Two other species of clostridia, C. barati and C. butyricum, also produce toxins similar to BoNT/F and BoNT/E, respectively. 7 of 168 WO 2008/036060 PCT/US2006/012825 [025] Clostridia toxins (CoNTs) are each translated as a single chain polypeptide of approximately 150 kDa that is subsequently cleaved by proteolytic scission within a disulphide loop by bacterial or tissue proteases. This posttranslational processing yields a di-chain molecule comprising an approximately 50 kDa light chain (LC) and an approximately 100 kDa heavy chain (HC) held together by a single disulphide bond and noncovalent interactions. Each mature di-chain molecule comprises three functionally distinct domains: 1) an enzymatic domain located in the LC that includes a metalloprotease region containing a zinc-dependent endopeptidase activity which specifically targets core components of the neurotransmitter release apparatus; 2) a translocation domain contained within the amino-terminal half of the HC (HN) that facilitates release of the toxin from intracellular vesicles into the cytoplasm of the target cell; and 3) a binding domain found within the carboxy-terminal half of the HC (Hc) that determines the binding activity and binding specificity of the toxin to the receptor complex located at the surface of the target cell. [026] The binding, translocation and enzymatic activity of these three functional domains are all necessary for toxicity. While all details of this process are not yet precisely known, the overall cellular intoxication mechanism whereby CoNTs enter a neuron and inhibit neurotransmitter release is similar, regardless of type. Although the applicants have no wish to be limited by the following description, the intoxication mechanism can be described as comprising four steps: 1) receptor binding, 2) complex internalization, 3) light chain translocation, and 4) enzymatic target modification (see FIG. 1). The process is initiated when the Hc domain of a CoNT binds to CoNT-specific receptor complex located on the plasma membrane surface of a target cell. The binding specificity of a receptor complex is thought to be achieved, in part, by specific combinations of gangliosides and protein receptors that appear to distinctly comprise each Clostridial toxin receptor complex. Once bound, the CoNT/receptor complexes are internalized by endocytosis and the internalized vesicles are sorted to specific intracellular routes. The translocation step appears to be triggered by the acidification of the vesicle compartment. This process seems to initiate two important pH-dependent structural rearrangements that increase hydrophobicity and promote enzymatic activation of the toxin. Once activated, light chain endopeptidase of the toxin is released from the intracellular vesicle into the cytosol where it specifically targets one of three known core components of the neurotransmitter release apparatus. There of these core proteins, vesicle-associated membrane protein (VAMP)/synaptobrevin, synaptosomal-associated protein of 25 kDa (SNAP-25) and Syntaxin, are necessary for synaptic vesicle docking and fusion at the nerve terminal and constitute members of the soluble N-ethylmaleimide-sensitive factor-attachment protein-receptor (SNARE) family (see FIG. 2). The selective proteolysis of synaptic SNAREs accounts for the total block of neurotransmitter release caused by Clostridial toxins in vivo. The SNARE protein targets of Clostridial toxins are common to exocytosis in a variety of non-neuronal types; in these cells, as in neurons, light chain peptidase activity inhibits exocytosis, see, e.g., Yann Humeau et al., How Botulinum and Tetanus Neurotoxins Block Neurotransmitter Release, 82(5) Biochimie. 427-446 (2000); Kathryn Turton et al., Botulinum and Tetanus Neurotoxins: Structure, Function and Therapeutic Utility, 27(11) Trends Biochem. Sci. 552-558. (2002); M. Zouhair Atassi, Basic and Therapeutic Aspects of Botulinum and Tetanus Toxins, (Dirk W. Dresser & Joseph J. Jankovic eds., 2003); Giovanna Lalli et al., The Journey of Tetanus and Botulinum Neurotoxins in Neurons, 11(9) Trends Microbiol. 431-437, (2003) which are hereby incorporated by reference. 8 of 168 WO 2008/036060 PCTIUS2006/012825 [027] TeNT and BoNT /B, /D, /F, and /G specifically recognize VAMP (also known as synaptobrevin), an integral protein of the synaptic vesicle membrane. VAMP is cleaved at distinct bonds depending on the toxin. BoNT /A and /E recognize and specifically cleave SNAP-25, a protein of the presynaptic membrane, at two different sites in the carboxy-terminal portion of the protein. BoNT/C1 cleaves syntaxin, a protein of the nerve plasmalemma, in addition to SNAP-25. The three protein targets of the CoNTs are conserved from yeast to humans although cleavage sites and toxin susceptibility are not necessarily conserved, see below; see, also, e.g., Humeau, supra, (2000); Heiner Niemann et al., Clostridial neurotoxins: new tools for dissecting exocytosis, 4(5) Trends Cell Biol. 179-185 (1994); and Rossella Pellizzari et al., Tetanus and botulinum neurotoxins: mechanism of action and therapeutic uses, 354(1381) Philos. Trans. R. Soc. Lond. B Biol. Sci. 259-268 (1999). [028] The natural targets of the Clostridial toxins include VAMP, SNAP-25, and syntaxin. VAMP is associated with the synaptic vesicle membrane, whereas SNAP-25 and syntaxin are associated with the plasma membrane (see FIG. 3). BoNT/A and BoNTIE cleave SNAP-25 in the carboxy-terminal region, releasing a nine or twenty-six amino acid segment, respectively, and BoNT/Ci also cleaves SNAP-25 near the carboxy-terminus. The botulinum serotypes BoNT/B, BoNT/D, BoNT/F and BoNT/G, and tetanus toxin, act on the conserved central portion of VAMP, and release the amino-terminal portion of VAMP into the cytosol. BoNT/Ci cleaves syntaxin at a single site near the cytosolic membrane surface. Thus, BoNT/B, BoNT/C1, BoNT/D, BoNT/F, BoNT/G or TeNT proteolysis results in release of a large portion of the cytosolic domain of VAMP or syntaxin, while only a small portion of SNAP-25 is released by BoNT/A, BoNT/Cl or BoNT/E cleavage, see, e.g., Humeau et al., supra, (2000); Turton et al., supra, (2002); Lalli et al., supra (2003). [029] Naturally occurring SNAP-25, a protein of about 206 residues lacking a transmembrane segment, is associated with the cytosolic surface of the nerve plasmalemma (see FIG. 3). SNAP-25 Is required for axonal growth during development and may be required for nerve terminal plasticity in the mature nervous system. SNAP-25 has been isolated from a variety of vertebrate and invertebrate species including, e.g., species belonging to the genera Homo, Macaca, Bos, Rattus, Mus, Gallus, Carassius, Danio, Torpedo, Xenopus, Strongylocentrotus, Drosophila, Hirudo, Loligo, Lymnaea and Caenorhabdiis. In humans, at least two isoforms are differentially expressed during development; isoform a is constitutively expressed during fetal development, while isoform b appears at birth and predominates in adult life. SNAP-25 analogues such as SNAP-23 also are expressed outside the nervous system, for example, in pancreatic cells. [030] Naturally occurring VAMP is a protein of about 120 residues, with the exact length depending on the species and isoform. As shown in FIG. 3, VAMP contains a short carboxy-terminal segment inside the vesicle lumen while most of the molecule is exposed to the cytosol. The proline-rich amino-terminal thirty residues are divergent among species and isoforms while the central portion of VAMP (residues 30 to 96), which is rich in charged and hydrophilic residues and includes known cleavage sites, is highly conserved. VAMP colocalizes with synaptophysin on synaptic vesicle membranes. VAMP has been 9 of 168 WO 2008/036060 PCT/US2006/012825 isolated from a variety of vertebrate and invertebrate species including, e.g., species belonging to the genera Homo, Macaca, Bos, Rattus, Mus, Gallus, Danio, Torpedo, Xenopus, Strongylocentrotus, Drosophila, Hirudo, Loligo, Lymnaea, Aplysia and Caenorhabditis. In addition, multiple isoforms of VAMP have been identified including VAMP-1, VAMP-2 and VAMP-3/cellubrevin, and forms insensitive to toxin cleavage have been identified in non-neuronal cells. VAMP appears to be present in all vertebrate tissues although the distribution of VAMP-1 and VAMP-2 varies in different cell types. Chicken and rat VAMP-1 are not cleaved by TeNT or BoNT/B. These VAMP-1 orthologs have a valine in place of the glutamine present in human and mouse VAMP-1 at the TeNT or BoNT/B cleavage site. The substitution does not affect BoNT/D, /F or /G, which cleave both VAMP-1 and VAMP-2 with similar rates. [031] Naturally occurring Syntaxin is located on the cytosolic surface of the nerve plasmalemma and Is membrane-anchored via a carboxy-terminal segment, with most of the protein exposed to the cytosol (see FIG. 3). Syntaxin colocalizes with calcium channels at the active zones of the presynaptic membrane, where neurotransmitter release takes place. In addition, syntaxin interacts with synaptotagmin, a protein of the SSV membrane that forms a functional bridge between the plasmalemma and the vesicles. Syntaxin has been isolated from a variety of vertebrate and invertebrate species including, e.g., species belonging to the genera Homo, Bos, Rattus, Mus, Gallus, Danic, Strongylocentrotus, Drosophila, Hirudo, Loligo, Lymnaea and Aplysia. Three Isoforms of slightly different length (285 and 288 residues) have been identified in nerve cells (isoforms 1A, 181 and 1B2), with isoforms 2, 3, 4 and 5 expressed in other tissues. The different isoforms have varying sensitivities to BoNT/C1, with the 1A, 1B1, 1 B2, 2 and 3 syntaxin isoforms cleaved by this toxin. [0321 Aspects of the present invention provide for compositions comprising an exogenous Clostridial toxin substrate capable of being localized to the plasma membrane of a cell. These substrates are comprised of a fluorescent member, a membrane targeting domain and a Clostridial toxin recognition sequence comprising a cleavage site, where the cleavage site intervenes between the fluorescent member and the membrane localization domain. [033] The Clostridial toxin substrates disclosed in the present specification include, in part, a Clostridial toxin recognition sequence including a cleavage site. By definition, a Clostridial toxin substrate is susceptible to cleavage by at least one Clostridial toxin under conditions suitable for Clostridial toxin protease activity. A variety of Clostridial toxin substrates are discussed herein below. Additional Clostridial toxin substrates are described in, e.g., Lance E. Steward, et al., FRET Protease Assays for Clostridial Toxins, U.S. Patenmt Publication 2003/0143651 (Jul. 31, 2003); Lance E. Steward, et al., FRET Protease Assays for Botulinum Serotype A/E Toxins, U.S. Patenmt Publication 2003/0143650 (Jul. 31, 2003); and Ester Fernandez-Salas, et al., Cell-based Fluorescence Resonance Energy Transfer (FRET) Assays for Clostridial Toxins, U.S. Patent Publication 2004/0072270 (Apr. 15, 2004). [034] The Clostridial toxin substrates disclosed in the present specification comprise, in part, a Clostridial toxin recognition sequence including a cleavage site. As used herein, the term "Clostridial toxin recognition sequence" means a scissile bond together with adjacent or non-adjacent recognition 10 of 168 WO 2008/036060 PCT/US2006/012825 elements, or both, sufficient for detectable proteolysis at the scissile bond by a Clostridial toxin under conditions suitable for Clostridial toxin protease activity. A variety of Clostridial toxin recognition sequences are discussed herein below. [035] Clostridial toxin substrates useful in aspects of the invention include peptides and peptidomimetics as well as derivatized forms thereof. As used herein, the term "peptidomimetic" is used broadly to mean a peptide-like molecule that is cleaved by the same Clostridial toxin as the peptide substrate upon which it is structurally based. Such peptidomimetics include chemically modified peptides, peptide-like molecules containing non-naturally occurring amino acids, and peptoids, which are peptide like molecules resulting from oligomeric assembly of N-substituted glycines, and are cleaved by the same Clostridial toxin as the peptide substrate upon which the peptidomimetic is derived (see, for example, Goodman and Ro, Peptidomimetics for Drug Design, in "Burger's Medicinal Chemistry and Drug Discovery" Vol. 1 (ed. M.E. Wolff; John Wiley & Sons 1995), pages 803-861). [036] A variety of peptidomimetics are known in the art including, for example, peptide-like molecules which contain a constrained amino acid, a non-peptide component that mimics peptide secondary structure, or an amide bond isostere. A peptidomimetic that contains a constrained, non-naturally occurring amino acid can include, for example, an a-methylated amino acid; an a,a-dialkyl-glycine or a aminocycloalkane carboxylic acid; an N" -C" cylized amino acid; an N"-methylated amino acid; a P- or y amino cycloalkane carboxylic acid; an a,p-unsaturated amino acid; a p, p-dimethyl or P-methyl amino acid; a -substituted-2,3-methano amino acid; an NC* or C" -CO cyclized amino acid; or a substituted proline or another amino acid mimetic. In addition, a peptidomimetic which mimics peptide secondary structure can contain, for example, a nonpeptidic P-tum mimic; y-tum mimic; mimic of p-sheet structure; or mimic of helical structure, each of which is well known in the art. A peptidomimetic also can be a peptide-like molecule which contains, for example, an amide bond isostere such as a retro-inverso modification; reduced amide bond; methylenethioether or methylenesulfoxide bond; methylene ether bond; ethylene bond; thloamide bond; trans-olefin or fluoroolefin bond; 1,5-disubstituted tetrazole ring; ketomethylene or fluoroketomethylene bond or another amide isostere. One skilled in the art understands that these and other peptidomimetics are encompassed within the meaning of the term "peptidomimetic" as used herein. [037] In other embodiments, a Clostridial toxin substrate useful in the invention is a peptide or peptidomimetic having a defined length. A Clostridial toxin substrate can be, for example, a peptide or peptidomimetic having at least 100, at least 150, at least 200, at least 250, at least 300, at least 350 or at least 500 residues. In other embodiments, a Clostridial toxin substrate has at most 20 residues, at most 30 residues, at most 40 residues, at most 50 residues, at most 100 residues, at most 150 residues, at most 200 residues, at most 250 residues, at most 300 residues, at most 350 residues or at most 400 residues. [038] A wide variety of Clostridial toxin recognition sequence are useful in aspects of the invention. 11 of 168 WO 2008/036060 PCT/US2006/012825 Specific and distinct cleavage sites for different Clostridial toxins are well known in the art. BoNT/A cleaves a GIn-Arg bond; BoNT/B and TeNT cleave a GIn-Phe bond; BoNT/Ci cleaves a Lys-Ala or Arg-Ala bond; BoNT/D cleaves a Lys-Leu bond; BoNT/E cleaves an Arg-Ile bond; BoNT/F cleaves a Gln-Lys bond; and BoNT/G cleaves an Ala-Ala bond (see Table 1). In standard nomenclature, the sequence surrounding a Clostridial toxin cleavage site is denoted P 5 -P4-P 3

-P

2

.P

1

-P

1 '-P2'-P3'-P 4 '-P5', with P 1

-P

1 ' representing the scissile bond. It is understood that a P 1 or P 1 ' site, or both, can be substituted with another amino acid or amino acid mimetic in place of the naturally occurring residue. As an example, BoNT/A substrates have been prepared in which the P 1 position (Gin) is modified to be an alanine, 2-aminobutyric acid or asparagine residue; these substrates were hydrolyzed by BoNT/A at the

P

1 .Arg bond, see, e.g., James J. Schmidt & Karen A Bostian, Endoproteinase activity of type A botulinum neurotoxin: substrate requirements and activation by serum albumin, 16(1) J. Protein Chem. 19-26 (1997). While it is recognized that substitutions can be introduced at the P 1 position of the scissile bond, for example, a BoNT/A scissile bond, it is further recognized that conservation of the P 1 ' residue can be advantageous, see, e.g., Vadakkanchery V. Vaidyanathan et al., Proteolysis of SNAP-25 isoforms by botulinum neurotoxin types A, C, and E: domains and amino acid residues controlling the formation of enzyme-substrate complexes and cleavage, 72(1) J Neurochem. 327-337 (1999). BoNT/A SNAP-25 Glu-Ala-Asn-Gin-Arg*-Ala-Thr-Lys 96 BoNT/B VAMP-2 Gly-Ala-Ser-Gln-Phe*-Glu-Thr-Ser 97 BoNT/C1 Syntaxin-1 Asp-Thr-Lys-Lys-Ala'- Val-Lys-Tyr 98 BoNT/Cl SNAP-25 Ala-Asn-Gn-Arg-Ala*-Thr-Lys-Met 99 BoNT/D VAMP-2 Arg-Asp-Gin-Lys-Leu*-Ser-Glu-Leu 100 BoNT/E SNAP-25 Gln-Ile-Asp-Arg-lIe*- Met-Glu-Lys 101 BoNT/F VAMP-2 Glu-Arg-Asp-Gin-Ly-Leu-Ser-Glu 102 BoNT/G VAMP-2 Glu-Thr-Ser-Ala--Ala-Lys-Leu-Lys 103 TeNT VAMP-2 Gly-Ala-Ser-Gin-Phe*-Glu-Thr-Ser 104 * Scissile bond shown in bold [039] Thus, an embodiment, is a composition comprising an exogenous Clostridial toxin substrate capable of being localized to the plasma membrane of a cell wherein said substrate comprises a fluorescent member, a membrane targeting domain and a Clostridial toxin recognition sequence comprising a cleavage site, where the cleavage site Intervenes between said fluorescent member and said membrane localization domain. In an aspect of this embodiment, a Clostridial toxin substrate comprises a Clostridial toxin recognition sequence in which the Pj' residue is not modified or substituted relative to the naturally occurring residue in a target protein cleaved by the Clostridial toxin. In another aspect of this embodiment, a Clostridial toxin substrate comprises a Clostridial toxin recognition sequence in which the P 1 residue is modified or substituted relative to the naturally occurring residue in a target protein cleaved by the Clostridial toxin; such a Clostridial toxin substrate retains susceptibility to peptide 12 of 168 WO 2008/036060 PCT/US2006/012825 bond cleavage between the P 1 and P 1 ' residues. [040] Any of a variety of Clostridial toxin recognition sequences are useful in the cells of the invention including, without limitation, botulinum toxin recognition sequences such as BoNT/A recognition sequences, BoNT/B recognition sequences, BoNT/C1 recognition sequences, BoNT/D recognition sequences, BoNT/E recognition sequences, BoNT/F recognition sequences, BoNT/G recognition sequences and TeNT recognition sequences. [041] A variety of BoNT/A recognition sequences are well known in the art and are useful in the invention, see, e.g., Mark A. Breidenbach & Axel T. Brunger, Substrate recognition strategy for botulinum neurotoxin serotype A, 432(7019) Nature 925-929 (2004). A BoNT/A recognition sequence can have, for example, residues 46-206, residues 134 to 206, residues 137 to 206 or 146-206 of human SNAP-25, see, e.g., Teresa A. Ekong et al., Recombinant SNAP-25 is an effective substrate for Clostridium botulinum type A toxin endopeptidase activity in vitro, 143 (Pt 10) Microbiology 3337-3347 (1997); Clifford C. Shone et al., Toxin Assays, U.S. Patent No. 5,962,637 (Oct. 5, 1999); and Vaidyanathan et al., supra, (1999). A BoNT/A recognition sequence also can include, without limitation, the sequence Thr-Arg-ile-Asp-Glu-Ala Asn-Gln-Arg-Ala-Thr-Lys-Met (SEQ ID NO: 105) or a peptidomimetic thereof, which corresponds to residues 190 to 202 of human SNAP-25; Ser-Asn-Lys-Thr-Arg- lle-Asp-Glu-Ala-Asn-Gln-Arg-Ala-Thr-Lys (SEQ ID NO: 106) or a peptidomimetic thereof, which corresponds to residues 187 to 201 of human SNAP-25; Ser-Asn-Lys-Thr-Arg-Ile-Asp-Glu-Ala-Asn-Gln-Arg-Ala-Thr-Lys-Met (SEQ ID NO: 107) or a peptidomimetic thereof, which corresponds to residues 187 to 202 of human SNAP-25; Ser-Asn-Lys-Thr Arg-lle-Asp-Glu-Ala-Asn-Gln-Arg-Ala-Thr-Lys-Met-Leu (SEQ ID NO: 108) or a peptidomimetic thereof, which corresponds to residues 187 to 203 of human SNAP-25; Asp-Ser-Asn-Lys-Thr-Arg-Ile-Asp-Glu-Ala Asn-Gln-Arg-Ala-Thr-Lys-Met (SEQ ID NO: 109) or a peptidomimetic thereof, which corresponds to residues 186 to 202 of human SNAP-25; or Asp-Ser-Asn-Lys-Thr-Arg-lie-Asp-Glu-Ala-Asn-Gn-Arg-Ala Thr-Lys-Met-Leu (SEQ ID NO: 110) or a peptidomimetic thereof, which corresponds to residues 186 to 203 of human SNAP-25. See, for example, James J. Schmidt & Karen A Bostian, Proteolysis of synthetic peptides by type A botulinum neurotoxin, 14(8) J. Protein Chem. 703-708 (1995); Schmidt & Bostian, supra, (1997); James J. Schmidt et al., Type A botulinum neurotoxin proteolytic activity: development of competitive inhibitors and implications for substrate specificity at the S1' binding subsite, 435(1) FEBS Lett. 61-64 (1998); and James J. Schmidt & Karen A Bostian, Assay for the proteolytic activity of serotype a from clostridium botulinum, U.S. Patent No. 5,965,699 (Oct. 12, 1999). [042] A BoNT/A recognition sequence useful in aspects of the invention can correspond to a segment of a protein that is sensitive to cleavage by botulinum toxin serotype A, or can be substantially similar to a segment of a BoNT/A-sensitive protein. As shown in Table 2, a variety of naturally occurring proteins sensitive to cleavage by BoNT/A are known in the art and include, for example, human, rat, mouse, Danio, Carassius, SNAP-25A and SNAP-25B; and Torpedo SNAP-25. Thus, a BoNT/A recognition sequence can correspond, for example, to a segment of human SNAP-25A or SNAP-25B; bovine SNAP 25A or SNAP-25B; rat SNAP-25A or SNAP-25B; mouse SNAP-25A or SNAP-25B; Xenopus SNAP-25A or SNAP-25B; Danio SNAP-25A or SNAP-25B; Carassius SNAP-25A or SNAP-25B; Torpedo SNAP-25; 13 of 168 WO 2008/036060 PCT/US2006/012825 Strongylocentrotus SNAP-25; Loligo SNAP-25; Lymnaea SNAP-25; Aplysia SNAP-25, isoforms thereof, or another naturally occurring protein sensitive to cleavage by BoNT/A. Furthermore, comparison of native SNAP-25 amino acid sequences cleaved by BoNT/A reveals that such sequences are not absolutely conserved (see Table 2), indicating that a variety of amino acid substitutions and modifications relative to a naturally occurring BoNT/A-sensitive SNAP-25 sequence can be tolerated In a BoNT/A recognition sequence useful in the invention. It is understood that a similar BoNT/A recognition sequence can be prepared, if desired, from a corresponding (homologous) segment of another BoNT/A-sensitive SNAP-25 isoform, paralog or ortholog, such as, the BoNT/A recognition sequence contain in the SNAP 25 proteins identified in the organisms listed above and in Table 2. 14 of 168 WO 2008/036060 PCTIUS2006/012825 C2 CSC SzC (8 z~ Z Z Z 0 CS zI I I I I I - . o a c co 0 0 0oO O O cn co . (a Zo z w z Z R Z 0< 0e 0 0 0 z co) C W < z z z z iz z z z z B 0 z0~ 0 z z zO(zOO0t0 A 01 00 000 :. Z Z Z Z9 CZ Z Z E2 > < C~ M c o a: . IL~ 0nn g3 CO ) U) ) a n C3 w U ) n ) LLI0 0.0 a aC80 BL E EL i L 0 cc z 2II L* 0o 0. z 'W (2 WO 2008/036060 PCT/US2006/012825 [043] Table 2 - Cleavage of SNAP-25 and related proteins. Primate: Human SNAP-25A residues 163-206 of SEQ ID NO: 1; Human SNAP-25B residues 163-206 of SEQ ID NO: 2; Human SNAP-23A residues 169-211 of SEQ ID NO: 3; Human SNAP-23B residues 116-158 of SEQ ID NO: 4; Monkey SNAP-25B residues 163-206 of SEQ ID NO: 5; Rodent: Rat SNAP-25A residues 163-206 of SEQ ID NO: 6; Rat SNAP-25B residues 163-206 of SEQ ID NO: 7; Mouse SNAP-25B residues 163-206 of SEQ ID NO: 8; Rat SNAP-23 residues 168-210 of SEQ ID NO: 9; Mouse SNAP-23 residues 168-210 of SEQ ID NO: 10; Bird: Chicken SNAP-25B residues 163-206 of SEQ ID NO: 11; Fish: Goldfish SNAP-25A residues 161-204 of SEQ ID NO: 12; Goldfish SNAP-25B residues 160-203 of SEQ ID NO: 13; Zebrafish SNAP-25A residues 161-204 of SEQ ID NO: 14; Zebrafish SNAP-25B residues 160-203 of SEQ ID NO: 15; Zebrafish SNAP-23 residues 174-214 of SEQ ID NO: 16; Ray: marbled electric ray SNAP-25 residues 170-210 of SEQ ID NO: 17; Amphibian: Frog SNAP-25A residues 163-206 of SEQ ID NO: 18: Frog SNAP-25B residues 163-206 of SEQ ID NO: 19; Frog SNAP-23 residues 163-204 of SEQ ID NO: 20; Sea urchin SNAP-25 residues 169-212 of SEQ ID NO: 21; Insect: Fruit fly SNAP-25 residues 171-212 of SEQ ID NO: 22 212; Fruit fly SNAP-24 residues 170-212 of SEQ ID NO: 23; Segmented worm: Leech SNAP 25 residues 170-212 of SEQ ID NO: 24; Cephalopod: squid SNAP-25 residues 245-267 of SEQ ID NO: 25; Gastropod: Pond snail SNAP-25 residues 244-266 of SEQ ID NO: 26; Round worm: Nematode worm SNAP-25 residues 165-207 of SEQ ID NO: 27. [044] A Clostridial toxin substrate, such as a substrate containing a BoNT/A recognition sequence, can have one or multiple modifications as compared to a naturally occurring sequence that is cleaved by the corresponding Clostridial toxin. As an example, as compared to a 17-mer corresponding to residues 187 to 203 of human SNAP-25, substitution of Asp193 with Asn in the BoNT/A substrate resulted in a relative rate of proteolysis of 0.23; substitution of Glu194 with Gin resulted in a relative rate of 2.08; substitution of Ala195 with 2-aminobutyric acid resulted in a relative rate of 0.38; and substitution of Gln197 with Asn, 2 aminobutyric acid or Ala resulted in a relative rate of 0.66, 0.25, or 0.19, respectively (see Table 3). Furthermore, substitution of Ala199 with 2-arninobutyric acid resulted in a relative rate of 0.79; substitution of Thr200 with Ser or 2-aminobutyric acid resulted in a relative rate of 0.26 or 1.20, respectively; substitution of Lys201 with Ala resulted in a relative rate of 0.12; and substitution of Met202 with Ala or norleucine resulted in a relative rate of 0.38 or 1.20, respectively, see, e.g., Schmidt & Bostian, supra, (1997). These results indicate that a variety of residues can be substituted in a Clostridial toxin substrate as compared to a naturally occurring toxin-sensitive sequence. In the case of BoNT/A, these results indicate that residues including but not limited to Glu194, Ala195, GIn197, Ala199, Thr200 and Met202, Leu203, Gly204, Ser205, and Gly206, as well as residues more distal from the GIn-Arg scissile bond, can be substituted or conjugated to a fluorophore, bulking group, donor fluorophore or acceptor in a BoNT/A substrate useful in the invention. Such a BoNT/A substrate is detectably proteolyzed at the scissile bond by BoNT/A under conditions suitable for Clostridial toxin protease activity. Thus, a BoNT/A substrate can include, if desired, one or several amino acid substitutions, additions or deletions relative to a naturally occurring SNAP-25 sequence. [045] Thus, in an embodiment, a composition comprises an exogenous BoNT/A substrate capable of 16 of 168 WO 2008/036060 PCT/US2006/012825 being localized to the plasma membrane of a cell wherein said substrate comprises a fluorescent member, a membrane targeting domain and a BoNT/A recognition sequence comprising a cleavage site, where the cleavage site intervenes between said fluorescent member and said membrane localization domain. As used herein, the term "botulinum toxin serotype A recognition sequence" is synonymous with "BoNT/A recognition sequence" and means a scissile bond together with adjacent or non-adjacent recognition elements, or both, sufficient for detectable proteolysis at the scissile bond by a BoNT/A under conditions suitable for Clostridial toxin protease activity. A scissile bond cleaved by BoNT/A can be, for example, Gln-Arg. [046] In an aspect of this embodiment, the Clostridial toxin substrate includes, in part, a BoNT/A recognition sequence comprising a BoNT/A recognition sequence containing at least six consecutive residues of SNAP-25 including GIn-Arg. In another aspect of this embodiment, the Clostridial toxin substrate includes, in part, a BoNT/A recognition sequence comprising the BoNT/A recognition sequence Glu-Ala-Asn-GIn-Arg-Ala-Thr-Lys (SEQ ID NO: 96). In other aspects of this embodiment, the Clostridial toxin substrate includes, in part, a BoNT/A recognition sequence comprising a portion of SNAP-25 such as, e.g., residues 1 to 206 of SEQ ID NO: 1; residues 46 to 206 of SEQ ID NO: 1; residues 134 to 206 of SEQ ID NO: 1; residues 137 to 206 of SEQ ID NO: 1; residues 146 to 206 of SEQ ID NO: 1, or a peptidomimetic thereof. In still other aspects of this embodiment, the Clostridial toxin substrate includes, in part, a BoNT/A recognition sequence comprising SEQ ID NO: 105, SEQ ID NO: 106, SEQ ID NO: 107, SEQ ID NO: 108, SEQ ID NO: 109, or SEQ ID NO: 110, or a peptidomimetic thereof. [115 SNKTRIDEANQRATK 106 0.03 [1-16] SNKTRIDEANQRATKM 107 1.17 [1-17] SNKTRIDEANORATKML 108 1.00 M16A SNKTRIDEANORATKAL 114 0.38 M16X SNKTRIDEANQRATKML 112 1.20 K15A SNKTRIDEANORATAML 113 0.12 T14S SNKTRIDEANQRATKML 114 0.26 Tl4B SNKTRIDEANORATKML 115 1.20 A13B SNKTRIDEANORBTKML 116 0.79 Q11A SNKTRIDEANARATKML 117 0.19 Q11B SNKTRIDEANBRATKML 118 0.25 011N SNKTRIDEANNRATKML 119 0.66 N10A SNKTRIDEAAQRATKML 120 0.06 A9B SNKTRIDEBNORATKML 121 0.38 E8Q SNKTRIDOANQRATKML 122 2.08 D7N SNKTRINEANORATKML 123 0.23 a Nonstandard abbreviations: B, 2-aminobutyric acid; X, 2-aminohexanoic acid (norleucine) b Initial hydrolysis rates relative to peptide [1-17]. Peptide concentrations were 1.0 mM. 17 of 168 WO 2008/036060 PCT/US2006/012825 [047] A variety of BoNT/B recognition sequences are well known in the art or can be defined by routine methods. Such BoNT/B recognition sequences can include, for example, a sequence corresponding to some or all of the hydrophilic core of a VAMP protein such as human VAMP-1 or human VAMP-2. A BoNT/B recognition sequence can include, without limitation, residues 33 to 94, residues 45 to 94, residues 55 to 94, residues 60 to 94, residues 65 to 94, residues 60 to 88 or residues 65 to 88 of human VAMP-2 (SEQ ID NO: 31), or residues 60 to 94 of human VAMP-1-1 (SEQ ID NO: 28), VAMP-1-2 (SEQ ID NO: 29) and VAMP-1-3 (SEQ ID NO: 30) see, e.g., Shone et al., Eur. J. Biochem. 217: 965-971 (1993); and Shone et al., supra, (Oct. 5, 1999). A BoNT/B recognition sequence also can include, without limitation, the sequence Leu-Ser-Glu-Leu-Asp-Asp-Arg-Ala-Asp-Ala-Leu-Gln-Ala-Gly-Ala-Ser-Gln-Phe Glu-Thr-Ser-Ala-Ala-Lys-Leu-Lys-Arg-Lys-Tyr-Trp-Trp-Lys-Asn-Leu-Lys (SEQ ID NO: 124) or a peptidomimetic thereof, which corresponds to residues 60 to 94 of human VAMP-2, see, e.g., James J. Schmidt & Robert G. Stafford, High Throughput Assays for the Proteolytic Activities of Clostridial Neurotoxins, U.S. Patent No. 6,762,280 (Jul. 13, 2004) and the BoNT/B recognition sequence Leu-Ser Glu-Leu-Asp-Asp-Arg-Ala-Asp-Ala-Leu-Gn-Aa-Gly-Ala-Ser-Gn-Phe-Glu-Ser-Ser-Ala-Ala-Lys-Leu-Lys Arg-Lys-Tyr-Trp-Trp-Lys-Asn-Cys-Lys (SEQ ID NO: 125) or a peptidomimetic thereof, which corresponds to residues 62 to 96 of human VAMP-1. [048] A BoNT/B recognition sequence useful in aspects of the invention can correspond to a segment of a protein that is sensitive to cleavage by botulinum toxin serotype B, or can be substantially similar to a segment of a BoNT/B-sensitive protein. As shown in Table 4, a variety of naturally occurring proteins sensitive to cleavage by BoNT/B are known in the art and include, for example, human and mouse VAMP-1, VAMP-2 and VAMP-3/cellubrevin; bovine VAMP-2; rat VAMP-2 and VAMP-3; chicken VAMP-2; Torpedo VAMP-1; Strongylocentrotus VAMP; Drosophila sybA, synB, synC, synD and synE; Hirudo VAMP; and Caenorhabditis SNB1-like. Thus, a BoNTIB recognition sequence can correspond, for example, to a segment of human VAMP-1, VAMP-2 or VAMP-3; bovine VAMP-2; rat VAMP-2 or VAMP-3; mouse VAMP-1, VAMP-2 or VAMP-3; chicken VAMP-1, VAMP-2 or VAMP-3; Xenopus VAMP-2 or VAMP-3; Danio VAMP-1 or VAMP-2; Torpedo VAMP-1; Strongylocentrotus VAMP; Drosophila sybA, synB, synC, synD or synE; Hirudo VAMP; Loligo VAMP; Lymnaea VAMP; Aplysia VAMP; Caenorhabditis SNB1, isoforms thereof, or another naturally occurring protein sensitive to cleavage by BoNT/B. Furthermore, as shown in Table 4, comparison of native VAMP amino acid sequences cleaved by BoNT/B reveals that such sequences are not absolutely conserved, indicating that a variety of amino acid substitutions and modifications relative to a naturally occurring VAMP sequence can be tolerated in a BoNT/B substrate of the invention. It is understood that a similar BoNT/B recognition sequence can be prepared, if desired, from a corresponding (homologous) segment of another BoNT/B-sensitive VAMP-1 or VAMP-2 isoform, paralog or ortholog, such as, the BoNT/B recognition sequence contain in the VAMP 1 and VAMP-2 proteins identified in the organisms listed above and in Table 4. 18 of 168 WO 2008/036060 PCTIUS2006/012825 P- I- I- I. - I ~ I..I I-t z z z z ZI- . 08 cs 0sc z8 c 8 co o o o SCSIC 8 z z z ZIZIc E18 <2 < C < ' <' <<< < < C < -~ Cf) (a~ Clo ) to CO o 0 Rz~~c acaa a [No0a 0 co aa 000000a000a0 CO o oco 0 co( Cl) Co Cl) CO C03 w co ( <C <' < <C <C co<' C C) -j -i -i -j C-1 O-j C-J -J j <C <' < C < C <C <C < << << < ui0 0 0 000 00 Z i 0 00a0a0a0 0 z zz zz z W WL >C 5! -! -j Ni -j 'C ' 'C « <'C 'C C ' ><< ' >C ' > y a 0 a 0 in 0 02 > ~ ~ ~ ~ ~ ~ . > > > >> L *z 88 z z >. >. >. > > 1< L>u> > >)> WO 2008/036060 PCTJUS2006/OI 2825 z C2 18 12 0 z z 0_ 0 a ai C? m czzc Sw A 0 - a acc a: a - 6cc w 0 w 0 w< < c L LL LL LL 0o C- 0 091~ 0 a ~ 00C *w z WO 2008/036060 PCT/US2006/012825 [049] Table 4 - Cleavage of VAMP and related proteins. Primate: Human VAMP-1-1 residues 49 92 of SEQ ID NO: 28; Human VAMP-1-2 residues 49-92 of SEQ ID NO: 29; Human VAMP-1 -3 residues 49-92 of SEQ ID NO: 30; Human VAMP-2 residues 47-90 of SEQ ID NO: 31; Monkey VAMP-2 residues 47-90 of SEQ ID NO: 32; Human VAMP-3/cellubrevin residues 30-73 of SEQ ID NO: 33; Bovine: Cow VAMP-2 residues 47-90 of SEQ ID NO: 34; Rodent: Rat VAMP-1 residues 49-92 of SEQ ID NO: 35; Rat VAMP-1-b residues 49-92 of SEQ ID NO: 36; Mouse VAMP-1 residues 49-92 of SEQ ID NO: 37; Rat VAMP-2 residues 47-90 of SEQ ID NO: 38; Rat VAMP-2-b residues 47-90 of SEQ ID NO: 39; Mouse VAMP-2 residues 47-90 of SEQ ID NO: 40; Rat VAMP-3/cellubrevin residues 34-77 of SEQ ID NO: 41; Mouse VAMP-3/cellubrevin residues 34-77 of SEQ ID NO: 42; Bird: Chicken VAMP-1 residues 190-233 of SEQ ID NO: 43; Chicken VAMP-2 residues 47-88 of SEQ ID NO: 44; Chicken VAMP-3/cellubrevin residues 34-77 of SEQ ID NO: 45; Fish: Zebrafish VAMP-1 residues 50-93 of SEQ ID NO: 46; Zebrafish VAMP-2 residues 41-84 of SEQ ID NO: 47; Zebrafish VAMP-3 residues 33-60 of SEQ ID NO: 48; Ray: marbled electric ray VAMP-1 residues 51-94 of SEQ ID NO: 49; Amphibian: Frog VAMP-2 residues 45-88 of SEQ ID NO: 50; Frog VAMP-3 residues 32-75 of SEQ ID NO: 51; Sea urchin VAMP residues 31-74 of SEQ ID NO: 52; Insect: Fruit fly SynAl residues 40-83 of SEQ ID NO: 53; Fruit fly SynA2 residues 63-106 of SEQ ID NO: 54; Fruit fly SynB1 residues 63-106 of SEQ ID NO: 55; Fruit fly SynB2 residues 63-106 of SEQ ID NO: 56; Fruit fly SynC residues 57-100 of SEQ ID NO: 57; Fruit fly SynD residues 66-109 of SEQ ID NO: 58; Fruit fly SynE residues 57-100 of SEQ ID NO: 59; Segmented worm: Leech VAMP residues 45-88 of SEQ ID NO: 60; Cephalopod: squid VAMP residues 56-99 of SEQ ID NO: 61; Gastropod: Pond snail VAMP residues 49-92 of SEQ ID NO: 62; sea hare VAMP residues 37-80 of SEQ ID NO: 63; Round worm: Nematode worm SNB1 residues 72-115 of SEQ ID NO: 64; Nematode worm SNB-like residues 82 115 of SEQ ID NO: 65. [050] Thus, in an embodiment, a composition comprises an exogenous BoNT/B substrate capable of being localized to the plasma membrane of a cell wherein said substrate comprises a fluorescent member, a membrane targeting domain and a BoNT/B recognition sequence comprising a cleavage site, where the cleavage site intervenes between said fluorescent member and said membrane localization domain. As used herein, the term "botulinum toxin serotype B recognition sequence" is synonymous with "BoNT/B recognition sequence" and means a scissile bond together with adjacent or non-adjacent recognition elements, or both, sufficient for detectable proteolysis at the scissile bond by a BoNT/B under appropriate conditions. A scissile bond cleaved by BoNTIB can be, for example, GIn-Phe. [051] In an aspect of this embodiment, the Clostridial toxin substrate includes, in part, a BoNT/B recognition sequence comprising a BoNT/B recognition sequence containing at least six consecutive residues of VAMP including Gln-Phe. In another aspect of this embodiment, the Clostridial toxin substrate includes, in part, a BoNT/B recognition sequence comprising the BoNT/B recognition sequence Gly-Ala-Ser-Gin-Phe-Glu-Thr-Ser (SEQ ID NO: 97). In other aspects of this embodiment, the Clostridial toxin substrate includes, in part, a BoNT/B recognition sequence comprising a portion of VAMP-1-1 such as, e.g., residues 1 to 118 of SEQ ID NO: 28; residues 62 to 96 of SEQ ID NO: 28, or a peptidomimetic thereof. In other aspects of this embodiment, the Clostridial toxin substrate includes, In part, a BoNT/B recognition sequence comprising a portion of VAMP-1-2 such as, e.g., residues 1 to 117 of SEQ ID NO: 21 of 168 WO 2008/036060 PCT/US2006/012825 29; residues 62 to 96 of SEQ ID NO: 29, or a peptidomimetic thereof. In other aspects of this embodiment, the Clostridlal toxin substrate includes, in part, a BoNT/B recognition sequence comprising a portion of VAMP-1-3 such as, e.g., residues 1 to 116 of SEQ ID NO: 30; residues 62 to 96 of SEQ ID NO: 30, or a peptidomimetic thereof. In other aspects of this embodiment, the Clostridial toxin substrate includes, in part, a BoNT/B recognition sequence comprising a portion of VAMP-2 such as, e.g., residues 1 to 116 of SEQ ID NO: 31; residues 33 to 94 of SEQ ID NO: 31; residues 45 to 94 of SEQ ID NO: 31; residues 55 to 94 of SEQ ID NO: 31; residues 60 to 94 of SEQ ID NO: 31; residues 65 to 94 of SEQ ID NO: 31; residues 60 to 88 of SEQ ID NO: 31; residues 65 to 88 of SEQ ID NO: 31, or a peptidomimetic thereof. [052] It is understood that a BoNT/C1 recognition sequence can correspond to a segment of a protein that is sensitive to cleavage by botulinum toxin serotype C1, or can be substantially similar to a segment of a BoNT/C1-sensitive protein. As further shown in Table 5, a variety of naturally occurring proteins sensitive to cleavage by BoNT/C1 are known in the art and include, for example, human and mouse Syntaxin 1A, Syntaxin 1B1 and Syntaxin 1B2; bovine and rat Syntaxin 1A and Syntaxin 1B2; rat Syntaxin 2 and Rat syntaxin 3; Strongylocentrotus Syntaxin; Drosophila Syntaxin 1A; Hirudo Syntaxin1A; Loligo Syntaxin 1A; Aplysia Syntaxin 1A. Thus, a BoNT/C1 recognition sequence can correspond, for example, to a segment of human Syntaxin 1 A, Syntaxin 1B1, Syntaxin 1 B2, Syntaxin 2-1, Syntaxin 2-2, Syntaxin 2 3 or Syntaxin 3A; bovine Syntaxin 1A, Syntaxin 1B1 or Syntaxin 1B2; rat Syntaxin 1A, Syntaxin 181, Syntaxin 1 B2, Syntaxin 2 or Syntaxin 3A; mouse Syntaxin 1 A, Syntaxin 11B1, Syntaxin 1B2, Syntaxin 2, Syntaxin 3A, Syntaxin 38 or Syntaxin 3C; chicken Syntaxin 1A or Syntaxin 2; Xenopus Syntaxin 1A or Syntaxin 1B; Danio Syntaxin 1A, Syntaxin 1B or Syntaxin 3; Torpedo Syntaxin 1A or Syntaxin 1B; Strongylocentrotus Syntaxin 1A or Syntaxin 1B; Drosophila Syntaxin 1A or Syntaxin 1B; Hirudo Syntaxin 1 A or Syntaxin 1B; Loligo Syntaxin 1 A or Syntaxin 1 B; Lymnaea Syntaxin 1 A or Syntaxin 1 B, isoforms thereof, or another naturally occurring protein sensitive to cleavage by BoNT/C1. Furthermore, comparison of native syntaxin amino acid sequences cleaved by BoNT/C1 reveals that such sequences are not absolutely conserved (see Table 5), indicating that a variety of amino acid substitutions and modifications relative to a naturally occurring BoNT/C1-sensitive syntaxin sequence can be tolerated in a BoNT/C1 substrate useful in the invention. It is understood that a similar BoNT/C1 recognition sequence can be prepared, if desired, from a corresponding (homologous) segment of another BoNT/C1-sensitive syntaxin isoform, paralog or ortholog, such as, the BoNT/C1 recognition sequence contain in the syntaxin proteins identified in the organisms listed above and in Table 5. [053] Table 5 - Cleavage of Syntaxin and related proteins. Primate: Human Syntaxin1A residues 242-264 of SEQ ID NO: 66; Human Syntaxin1B1 residues 241-263 of SEQ ID NO: 67; Human SyntaxinlB2 residues 241-263 of SEQ ID NO: 68; Human Syntaxin2-1 residues 241-263 of SEQ ID NO: 69; Human Syntaxin2-2 residues 241-263 of SEQ ID NO: 70; Human Syntaxin2-3 residues 241-263 of SEQ ID NO: 71; Human Syntaxin3 residues 241-263 of SEQ ID NO: 72; Bovine: Cow Syntaxin1A residues 242-264 of SEQ ID NO: 73; Cow Syntaxin1B2 residues 241-263 of SEQ ID NO: 74; Rodent: Rat Syntaxin1A residues 242-264 of SEQ ID NO: 75; Rat Syntaxin1B2 residues 241-263 of SEQ ID NO: 76; Mouse Syntaxin1A residues 242-264 of SEQ ID NO: 77; Mouse SyntaxiniB1 residues 241-263 of SEQ 22 of 168 WO 2008/036060 PCT/US2006/012825 ID NO: 78; Mouse Syntaxin1 B2 residues 241-263 of SEQ ID NO: 79; Rat Syntaxin2 residues 243-265 of SEQ ID NO: 80; Mouse Syntaxin2 residues 242-264 of SEQ ID NO: 81; Rat Syntaxin3A residues 241-263 of SEQ ID NO: 82; Mouse Syntaxin3A residues 241-263 of SEQ ID NO: 83; Mouse Syntaxin3B residues 241-263 of SEQ ID NO: 84; Mouse Syntaxin3C residues 223-245 of SEQ ID NO: 85; Bird: Chicken Syntaxini B residues 235-257 of SEQ ID NO: 86; Chicken Syntaxin2 residues 240-262 of SEQ ID NO: 87; Fish: Zebrafish Syntaxin1B residues 241-263 of SEQ ID NO: 88; Zebrafish Syntaxin3 residues 239-261 of SEQ ID NO: 89; sea urchin SyntaxinlB residues 241-263 of SEQ ID NO: 90; Insect: Fruit fly Syntaxin1A residues 245-267 of SEQ ID NO: 91; Segmented worm: leech SyntaxinlA residues 248-270 of SEQ ID NO: 92; Cephalopod: squid Syntaxin1A residues 245-267 of SEQ ID NO: 93; Gastropod: Pond snail Syntaxin1A residues 244-266 of SEQ ID NO: 94; sea hare SyntaxinlA residues 244-266 of SEQ ID NO: 95. Syntaxin1A Primate Syntaxin181 DYVERAVSDTKK * AVKYOSKARRK BoNT/C1 Syntaxin1 B2 Syntaxin2-1 Primate Syntaxin2-2 DYVEHAKEETKK ND AIKYQSKARRK ND Syntaxin2-3 Primate Syntaxin3A DHVEKARDESKK ND AVKYOSQARKK ND Bovine SyntaxinlB2 DYVERAVSDTKK AVKYOSKARRK BoNT/C1 Syntaxin1A2 SyntaxinlA Rodent Syntaxin1 B1 DYVERAVSDTKK AVKYOSKARRK BoNT/C1 Syntaxin1 B2 Rodent Syntadn2 DYVEHAKEETKK * AIKYOSKARRK BoNT/Ci Rodent Syntaxin3A DHVEKARDETK * AMKYQGQARKK BoNT/C1 Rodent Syntaxin3B GFVERAVADTKK ND AVKYQSEARRK ND Bird Syntaxin1 B DYVEPVVFVTK4 ND AVMYQCKSRRK ND Bird Syntaxin2 DYVEHAKEETKK ND AVKYQSKARRK ND Fish Syntaxin1B DYVERAVSDTKK * AVKYQSQARKK BoNT/C1 Fish Syntaxin3 DHVEAARDETKK ND AVRYOSKARKK ND Sea urchin Syntaxin1B DYVRRQNDTKK * AVKYQSKARRK BoNTICI Insect Syntaxin1A DYVQTATQDTKK * ALKYQSKARRK BoNT/C1 Segmented SyntaxinlA DYVETAAADTKK * AMKYQSAARKK BoNT/Ci worm Cephalopod Syntaxin1A DYIETAKVDTKK * AVKYOSKAROK BoNT/C1 Gastropod Syntaxin1A DYIETAKMDTKK * AVKYQSKARRK BoNT/C1 Proteolytic cleavage occurs at this site (*); Proteolytic cleavage not detected at this site (-); Proteolytic cleavage not determined at this site (ND) [054] As further shown in Table 2, a variety of naturally occurring proteins sensitive to cleavage by BoNT/C1 are known in the art and include, for example, human, rat, mouse, Danio, Carassius SNAP-25A 23 of 168 WO 2008/036060 PCTIUS2006/012825 and SNAP-258; and Drosophila SNAP-25. Thus, a BoNT/Ci recognition sequence can correspond, for example, to a segment of human SNAP-25A or SNAP-25B; bovine SNAP-25A or SNAP-25B; rat SNAP 25A or SNAP-25B; mouse SNAP-25A or SNAP-25B; Xenopus SNAP-25A or SNAP-25B; Danio SNAP 25A or SNAP-25B; Carassius SNAP-25A or SNAP-25B; Torpedo SNAP-25; Strongylocentrotus SNAP 25; Drosophila SNAP-25 or SNAP-24; Hirudo SNAP-25; Loligo SNAP-25; Lymnaea SNAP-25, isoforms thereof, or another naturally occurring protein sensitive to cleavage by BoNT/C1. As discussed above in regard to variants of naturally occurring syntaxin sequences, comparison of native SNAP-25 amino acid sequences cleaved by BoNT/Cl reveals significant sequence variability (Table 2), indicating that a variety of amino acid substitutions and modifications relative to a naturally occurring BoNT/C1-sensitive SNAP-25 sequence can be tolerated in a BoNT/C1 substrate useful in the invention. It is understood that a similar BoNT/C1 recognition sequence can be prepared, if desired, from a corresponding (homologous) segment of another BoNT/C1-sensitive SNAP-25 isoform, paralog or ortholog, such as, the BoNT/A recognition sequence contain in the SNAP-25 proteins identified in the organisms listed above and in Table 2. [055] Thus, in an embodiment, a composition comprises an exogenous BoNT/C1 substrate capable of being localized to the plasma membrane of a cell wherein said substrate comprises a fluorescent member, a membrane targeting domain and a BoNT/C1 recognition sequence comprising a cleavage site, where the cleavage site intervenes between said fluorescent member and said membrane localization domain. As used herein, the term "botulinum toxin serotype C1 recognition sequence" is synonymous with "BoNT/Cl recognition sequence" and means a scissile bond together with adjacent or non-adjacent recognition elements, or both, sufficient for detectable proteolysis at the scissile bond by a BoNT/C1 under appropriate conditions. A scissile bond cleaved by BoNTICi can be, for example, Lys-Ala or Arg-Ala. [056] In an aspect of this embodiment, the encoded Clostridial toxin substrate includes, in part, a BoNT/C1 recognition sequence comprising a BoNT/C1 recognition sequence containing at least six consecutive residues of Syntaxin including Lys-Ala. In another aspect of this embodiment, the Clostridial toxin substrate includes, in part, a BoNT/Cl recognition sequence comprising the BoNT/C1 recognition sequence Asp-Thr-Lys-Lys-Ala-Val-Lys-Tyr (SEQ ID NO: 98). In another aspect of this embodiment, the Clostridial toxin substrate includes, in part, a BoNT/Cl recognition sequence comprising a BoNT/C1 recognition sequence containing at least six consecutive residues of SNAP-25 including Arg-Ala. In another aspect of this embodiment, the Clostridial toxin substrate includes, in part, a BoNT/Cl recognition sequence comprising the BoNT/C1 recognition sequence Ala-Asn-Gin-Arg-Ala-Thr-Lys-Met (SEQ ID NO: 99). In yet another aspect of this embodiment, the Clostridial toxin substrate includes, in part, a BoNT/C1 recognition sequence comprising a BoNT/Ci recognition sequence containing at least six consecutive residues of Syntaxin Including Lys-Ala and a BoNT/C1 recognition sequence comprising a BoNT/C1 recognition sequence containing at least six consecutive residues of SNAP-25 including Arg-Ala. [057] In other aspects of this embodiment, the Clostridial toxin substrate includes, in part, a BoNT/C1 recognition sequence comprising a portion of Syntaxin-1A such as, e.g., residues 1 to 288 of SEQ ID NO: 24 of 168 WO 2008/036060 PCTIUS2006/012825 66, or a peptidomimetic thereof. In other aspects of this embodiment, the Clostridial toxin substrate includes, in part, a BoNT/Cl recognition sequence comprising a portion of Syntaxin-IBI such as, e.g., residues 1 to 288 of SEQ ID NO: 67, or a peptidomimetic thereof. In other aspects of this embodiment, the Clostridial toxin substrate includes, in part, a BoNT/Ci recognition sequence comprising a portion of Syntaxin-11B2 such as, e.g., residues 1 to 288 of SEQ ID NO: 68, or a peptidomimetic thereof. In other aspects of this embodiment, the Clostridial toxin substrate includes, in part, a BoNT/Cl recognition sequence comprising a portion of Syntaxin 2-1 such as, e.g., residues 1 to 287 of SEQ ID NO: 69, or a peptidomimetic thereof. In other aspects of this embodiment, the Clostridial toxin substrate includes, in part, a BoNT/C1 recognition sequence comprising a portion of Syntaxin-2-2 such as, e.g., residues 1 to 288 of SEQ ID NO: 70, or a peptidomimetic thereof. In other aspects of this embodiment, the Clostridial toxin substrate includes, in part, a BoNT/C1 recognition sequence comprising a portion of Syntaxin-2-3 such as, e.g., residues 1 to 289 of SEQ ID NO: 71, or a peptidomimetic thereof. In other aspects of this embodiment, the Clostridial toxin substrate includes, in part, a BoNT/C1 recognition sequence comprising a portion of Syntaxin-3A such as, e.g., residues 1 to 289 of SEQ ID NO: 83, or a peptidomimetic thereof. In other aspects of this embodiment, the Clostridial toxin substrate includes, in part, a BoNT/Cl recognition sequence comprising a portion of Syntaxin-3B such as, e.g., residues 1 to 283 of SEQ ID NO: 84, or a peptidomimetic thereof. In other aspects of this embodiment, the Clostridial toxin substrate includes, in part, a BoNT/C1 recognition sequence comprising a portion of Syntaxin-3C such as, e.g., residues 1 to 269 of SEQ ID NO: 85, or a peptidomimetic thereof. [058] In other aspects of this embodiment, the Clostridial toxin substrate includes, in part, a BoNT/C1 recognition sequence comprising a portion of SNAP-25 such as, e.g., residues 1 to 206 of SEQ ID NO: 1; residues 93 to 206 of SEQ ID NO: 1; residues 134 to 206 of SEQ ID NO: 1; residues 137 to 206 of SEQ ID NO: 1: residues 146 to 206 of SEQ ID NO: 1; residues 137 to 202 of SEQ ID NO: 1, or a peptidomimetic thereof. In still other aspects of this embodiment, the Clostridial toxin substrate includes, in part, a BoNT/C1 recognition sequence comprising SEQ ID NO: 105, SEQ ID NO: 106, SEQ ID NO: 107, SEQ ID NO: 108, SEQ ID NO: 109, or SEQ ID NO: 110, or a peptidomimetic thereof. [059] A variety of BoNT/D recognition sequences are well known in the art or can be defined by routine methods. A BoNT/D recognition sequence can include, for example, residues 27 to 116; residues 37 to 116; residues 1 to 86; residues 1 to 76; or residues 1 to 69 of rat VAMP-2, see, e.g., Shinji Yamasaki et al., Cleavage of members of the synaptobrevinNAMP family by types D and F botulinum neurotoxins and tetanus toxin, 269(17) J. Biol. Chem. 12764-12772 (1994). Thus, a BoNT/D recognition sequence can include, for example, residues 27 to 69 or residues 37 to 69 of rat VAMP-2. A BoNT/D recognition sequence also can include, without limitation, the sequence Ala-Gln-Val-Asp-Glu-Val-Val-Asp-Ile-Met Arg-Val-Asn-Val-Asp-Lys-Val-Leu-Glu-Arg-Asp-Gin-Lys-Leu-Ser-Glu-Leu-Asp-Asp-Arg-Ala-Asp-Ala-Leu Gin-Ala-Gly-Ala-Ser (SEQ ID NO: 126) or a peptidomimetic thereof, which corresponds to residues 37 to 75 of human VAMP-2, see, e.g., Schmidt & Stafford, supra, (Jul. 13, 2004) and the BoNT/D recognition sequence Ala-Gln-Val-Glu-Glu-Val-Val-Asp-lle-Ile-Arg-Val-Asn-Val-Asp-Lys-Val-Leu-Glu-Arg-Asp-Gln Lys-Leu-Ser-Glu-Leu-Asp-Asp-Arg-Ala-Asp-Ala-Leu-Gn-Ala-Gly-Ala-Ser (SEQ ID NO: 127) or a peptidomimetic thereof, which corresponds to residues 39 to 77 of the human VAMP-1 isoforms, VAMP 25 of 168 WO 2008/036060 PCTIUS2006/012825 1-1, VAMP-1 -2 and VAMP-1-3. [060] A BoNT/D recognition sequence can correspond to a segment of a protein that is sensitive to cleavage by botulinum toxin serotype D, or can be substantially similar to a segment of a BoNT/D-sensitive protein. As shown in Table 4, a variety of naturally occurring proteins sensitive to cleavage by BoNT/D are known in the art and include, for example, human, rat and mouse VAMP-1, VAMP-2 and VAMP-3/cellubrevin; bovine VAMP-2; chicken VAMP-1, VAMP-2 and VAMP-3; Xenopus VAMP-2 or VAMP-3; Danio VAMP-1 or VAMP-2; Torpedo VAMP-1; Strongylocentrotus VAMP; Drosophila sybA, synB, synC, synD, synE; Hirudo VAMP; Loligo VAMP; Lymnaea VAMP; Aplysia VAMP; and Caenorhabditis SNB1. Thus, a BoNT/D recognition sequence can correspond, for example, to a segment of human VAMP-1, VAMP-2 or VAMP-3; bovine VAMP-2; rat VAMP-1, VAMP-2 or VAMP-3; mouse VAMP-1, VAMP-2 or VAMP-3; chicken VAMP-1, VAMP-2 or VAMP-3; Xenopus VAMP-2 or VAMP-3; Danio VAMP-1 or VAMP-2; Torpedo VAMP-1; Strongylocentrotus VAMP: Drosophila sybA, synB, synC, synD, synE; Hirudo VAMP; Loligo VAMP; Lymnaea VAMP: Aplysia VAMP: Caenorhabditis SNB1, isoforms thereof, or another naturally occurring protein sensitive to cleavage by BoNT/D. Furthermore, as shown in Table 4 above, comparison of native VAMP amino acid sequences cleaved by BoNT/D reveals significant sequence variability, indicating that a variety of amino acid substitutions and modifications relative to a naturally occurring BoNT/D-sensitive VAMP sequence can be tolerated in a BoNT/D substrate useful in the invention. It is understood that a similar BoNT/D recognition sequence can be prepared, if desired, from a corresponding (homologous) segment of another BoNT/D-senstive VAMP-1 or VAMP-2 isoform, paralog or ortholog, such as, the BoNT/B recognition sequence contain in the VAMP-1 and VAMP-2 proteins identified in the organisms listed above and in Table 4. [061] Thus, in an embodiment, a composition comprises an exogenous BoNT/D substrate capable of being localized to the plasma membrane of a cell wherein said substrate comprises a fluorescent member, a membrane targeting domain and a BoNT/D recognition sequence comprising a cleavage site, where the cleavage site intervenes between said fluorescent member and said membrane localization domain. The term "botulinum toxin serotype D recognition sequence" is synonymous with "BoNT/D recognition sequence" and means a scissile bond together with adjacent or non-adjacent recognition elements, or both, sufficient for detectable proteolysis at the scissile bond by a BoNT/D under appropriate conditions. A scissile bond cleaved by BoNT/D can be, for example, Lys-Leu. [062] In an aspect of this embodiment, the Clostridial toxin substrate includes, in part, a BoNT/D recognition sequence comprising a BoNT/D recognition sequence containing at least six consecutive residues of VAMP including Lys-Leu. In another aspect of this embodiment, the Clostridial toxin substrate includes, in part, a BoNT/D recognition sequence comprising the BoNT/D recognition sequence Arg-Asp Gin-Lys-Leu-Ser-Glu-Leu (SEQ ID NO: 100). In other aspects of this embodiment, the Clostridial toxin substrate includes, in part, a BoNT/D recognition sequence comprising a portion of VAMP-1-1 such as, e.g., residues 1 to 118 of SEQ ID NO: 28; residues 39 to 77 of SEQ ID NO: 28, or a peptidomimetic thereof. In other aspects of this embodiment, the Clostridial toxin substrate includes, in part, a BoNT/D recognition sequence comprising a portion of VAMP-1-2 such as, e.g., residues 1 to 117 of SEQ ID NO: 26 of 168 WO 2008/036060 PCT/US2006/012825 29; residues 39 to 77 of SEQ ID NO: 29, or a peptidomimetic thereof. In other aspects of this embodiment, the Clostridial toxin substrate includes, in part, a BoNT/D recognition sequence comprising a portion of VAMP-1-3 such as, e.g., residues 1 to 116 of SEQ ID NO: 30; residues 39 to 77 of SEQ ID NO: 30, or a peptidomimetic thereof. In other aspects of this embodiment, the Clostridial toxin substrate includes, in part, a BoNT/D recognition sequence comprising a portion of VAMP-2 such as, e.g., residues 1 to 116 of SEQ ID NO: 31; residues 1 to 86 of SEQ ID NO: 31; residues 1 to 76 of SEQ ID NO: 31; residues 1 to 69 of SEQ ID NO: 31; residues 27 to 116 of SEQ ID NO: 31; residues 37 to 116 of SEQ ID NO: 31; residues 27 to 68 of SEQ ID NO: 31; residues 37 to 69 of SEQ ID NO: 31, or a peptidomimetic thereof. (063] One skilled in the art appreciates that a BoNT/E recognition sequence can correspond to a segment of a protein that is sensitive to cleavage by botulinum toxin serotype E, or can be substantially similar to a segment of a BoNT/E-sensitive protein. A BoNT/E recognition sequence can have, for example, residues 46-206, residues 92 to 206, residues, residues 134 to 206, residues, 137 to 206; 146 206 or 156-206 of human SNAP-25, see, e.g., Vaidyanathan et al., supra, (1999); and Schmidt & Stafford, supra, (Jul. 13, 2004). [064] A BoNT/E recognition sequence useful in aspects of the invention can correspond to a segment of a protein that is sensitive to cleavage by botulinum toxin serotype E, or can be substantially similar to a segment of a BoNT/E-sensitive protein. As shown in Table 2, a variety of naturally occurring proteins sensitive to cleavage by BoNT/E are known in the art and include, for example, human, chicken, Danio, Carassius SNAP-25A and SNAP-25B; rat and mouse SNAP-25A, SNAP-25B and SNAP-23; and Caenorhabditis SNAP-25. Thus, a BoNT/E recognition sequence can correspond, for example, to a segment of human SNAP-25A or SNAP-25B; bovine SNAP-25A or SNAP-25B; rat SNAP-25A, SNAP 25B or SNAP-23; mouse SNAP-25A, SNAP-25B or SNAP-23; Xenopus SNAP-25A or SNAP-25B; Danio SNAP-25A or SNAP-25B; Carassius SNAP-25A or SNAP-25B; Strongylocentrotus SNAP-25; Drosophila SNAP-24; Hirudo SNAP-25; Loligo SNAP-25; Lymnaea SNAP-25; Caenorhabditis SNAP-25, isoforms thereof, or another naturally occurring protein sensitive to cleavage by BoNT/C1. Furthermore, as shown in Table 2, comparison of native SNAP-23 and SNAP-25 amino acid sequences cleaved by BoNT/E reveals that such sequences are not absolutely conserved, indicating that a variety of amino acid substitutions and modifications relative to a naturally occurring BoNT/E-sensitive SNAP-23 or SNAP-25 sequence can be tolerated in a BoNT/E substrate useful in the invention. It is understood that a similar BoNT/E recognition sequence can be prepared, if desired, from a corresponding (homologous) segment of another BoNTIE-sensitive SNAP-25 isoform, paralog or ortholog, such as, the BoNT/E recognition sequence contain in the SNAP-25 proteins identified in the organisms listed above and in Table 2. [065] Thus, in an embodiment, a composition comprises an exogenous BoNT/E substrate capable of being localized to the plasma membrane of a cell wherein said substrate comprises a fluorescent member, a membrane targeting domain and a BoNT/E recognition sequence comprising a cleavage site, where the cleavage site intervenes between said fluorescent member and said membrane localization domain. As used herein, the term "botulinum toxin serotype E recognition sequence" is synonymous with 27 of 168 WO 2008/036060 PCT/US2006/012825 "BoNT/E recognition sequence" and means a scissile bond together with adjacent or non-adjacent recognition elements, or both, sufficient for detectable proteolysis at the scissile bond by a BoNT/E under appropriate conditions. A scissile bond cleaved by BoNT/E can be, for example, Arg-Ile. [066] In an aspect of this embodiment, the Clostridial toxin substrate includes, in part, a BoNT/E recognition sequence comprising a BoNT/E recognition sequence containing at least six consecutive residues of SNAP-25 including Arg-Ile. In another aspect of this embodiment, the Clostridial toxin substrate includes, in part, a BoNT/E recognition sequence comprising the BoNT/E recognition sequence Gln-lie-Asp-Arg-ile-Met-Glu-Lys (SEQ ID NO: 101). In other aspects of this embodiment, the Clostridial toxin substrate includes, in part, a BoNT/E recognition sequence comprising a portion of SNAP-25 such as, e.g., residues 1 to 206 of SEQ ID NO: 1; residues 46 to 206 of SEQ ID NO: 1; residues 92 to 206 of SEQ ID NO: 1; residues 134 to 206 of SEQ ID NO: 1; residues 137 to 206 of SEQ ID NO: 1, residues 146 to 206 of SEQ ID NO: 1; residues 156 to 206 of SEQ ID NO: 1, or a peptidomimetic thereof. [067] A variety of BoNT/F recognition sequences are well known in the art or can be defined by routine methods. A BoNT/F recognition sequence can include, for example, residues 27 to 116; residues 37 to 116; residues 1 to 86; residues 1 to 76; or residues 1 to 69 of rat VAMP-2, see, e.g., Yamasaki et al., supra, (1994). A BoNT/F recognition sequence also can include, for example, residues 27 to 69 or residues 37 to 69 of rat VAMP-2. It is understood that a similar BoNTIF recognition sequence can be prepared, if desired, from a corresponding (homologous) segment of another BoNT/F-sensitive VAMP isoform, paralog or ortholog, such as, e.g., human VAMP-1 or human VAMP-2. A BoNT/F recognition sequence also can include, without limitation, the sequence Ala-Gln-Val-Asp-Glu-Val-Val-Asp-Ile-Met Arg-Val-Asn-Val-Asp-Lys-Val-Leu-Glu-Arg-Asp-Gln-Lys-Leu-Ser-Glu-Leu-Asp-Asp-Arg-Ala-Asp-Ala-Leu Gin-Ala-Gly-Ala-Ser (SEQ ID NO: 126) or a peptidomimetic thereof, which corresponds to residues 37 to 75 of human VAMP-2, see, e.g., Schmidt & Stafford, supra, (Jul. 13, 2004) and the BoNT/F recognition sequence Ala-Gln-Val-Glu-Glu-Val-Val-Asp-Ile-le-Arg-Val-Asn-Val-Asp-Lys-Val-Leu-Glu-Arg-Asp-Gln Lys-Leu-Ser-Glu-Leu-Asp-Asp-Arg-Ala-Asp-Ala-Leu-Gln-Ala-Gly-Ala-Ser (SEQ ID NO: 127) or a peptidomimetic thereof, which corresponds to residues 39 to 77 of human VAMP-1. [068] A BoNT/F recognition sequence can correspond to a segment of a protein that is sensitive to cleavage by botulinum toxin serotype F, or can be substantially similar to a segment of a BoNT/F sensitive protein. As shown in Table 4, a variety of naturally occurring proteins sensitive to cleavage by BoNT/F are known in the art and include, for example, human, rat and mouse VAMP-1, VAMP-2 and VAMP-3/cellubrevin; bovine VAMP-2; chicken VAMP-1 and VAMP-2; Torpedo VAMP-1; and Drosophila sybA and synB. Thus, a BoNT/F recognition sequence can correspond, for example, to a segment of human VAMP-1, VAMP-2 or VAMP-3; bovine VAMP-2; rat VAMP-1, VAMP-2 or VAMP-3; mouse VAMP 1, VAMP-2 or VAMP-3: chicken VAMP-1, VAMP-2 or VAMP-3; Xenopus VAMP-2 or VAMP-3; Danio VAMP-1 or VAMP-2; Torpedo VAMP-1; Drosophila sybA and synB; Hirudo VAMP; Loligo VAMP; Lymnaea VAMP; Aplysia VAMP; Caenorhabditis SNB1, isoforms thereof, or another naturally occurring protein sensitive to cleavage by BoNT/F. Thus, a BoNT/F recognition sequence can correspond, for example, to a segment of human VAMP-1 or VAMP-2, mouse VAMP-1 or VAMP-2, bovine VAMP-1 or 28 of 168 WO 2008/036060 PCT/US2006/012825 VAMP-2, rat VAMP-1 or VAMP-2, rat cellubrevin, chicken VAMP-1 or VAMP-2, Torpedo VAMP-1, Aplysia VAMP, Drosophila syb, leech VAMP, or another naturally occurring protein sensitive to cleavage by BoNT/F. Furthermore, as shown in Table 4 above, comparison of native VAMP amino acid sequences cleaved by BoNT/F reveals that such sequences are not absolutely conserved, indicating that a variety of amino acid substitutions and modifications relative to a naturally occurring BoNT/F-sensitive VAMP sequence can be tolerated in a BoNT/F substrate useful in the invention. It is understood that a similar BoNT/F recognition sequence can be prepared, if desired, from a corresponding (homologous) segment of another BoNT/F-sensitive VAMP-1 or VAMP-2 isoform, paralog or ortholog, such as, the BoNT/F recognition sequence contain in the VAMP-1 and VAMP-2 identified in the organisms listed above and In Table 4. [069] Thus, in an embodiment, a composition comprises an exogenous BoNT/F substrate capable of being localized to the plasma membrane of a cell wherein said substrate comprises a fluorescent member, a membrane targeting domain and a BoNT/F recognition sequence comprising a cleavage site, where the cleavage site intervenes between said fluorescent member and said membrane localization domain. The term "botulinum toxin serotype F recognition sequence," as used herein, is synonymous with "BoNT/F recognition sequence" and means a scissile bond together with adjacent or non-adjacent recognition elements, or both, sufficient for detectable proteolysis at the scissile bond by a BoNT/F under appropriate conditions. A scissile bond cleaved by BoNT/F can be, for example, Gin-Lys. [070] In an aspect of this embodiment, the Clostridial toxin substrate includes, in part, a BoNT/F recognition sequence comprising a BoNT/F recognition sequence containing at least six consecutive residues of VAMP including GIn-Lys. In another aspect of this embodiment, the Clostridial toxin substrate includes, in part, a BoNT/F recognition sequence comprising the BoNT/F recognition sequence Glu-Arg Asp-Gln-Lys-Leu-Ser-Glu (SEQ ID NO: 102). In other aspects of this embodiment, the Clostridial toxin substrate includes, in part, a BoNT/F recognition sequence comprising a portion of VAMP-1-1 such as, e.g., residues 1 to 118 of SEQ ID NO: 28; residues 39 to 77 of SEQ ID NO: 28, or a peptidomimetic thereof. In other aspects of this embodiment, the Clostridial toxin substrate includes, in part, a BoNT/F recognition sequence comprising a portion of VAMP-1-2 such as, e.g., residues 1 to 117 of SEQ ID NO: 29; residues 39 to 77 of SEQ ID NO: 29, or a peptidomimetic thereof. In other aspects of this embodiment, the Clostridial toxin substrate includes, in part, a BoNT/F recognition sequence comprising a portion of VAMP-1-3 such as, e.g., residues I to 116 of SEQ ID NO: 30; residues 39 to 77 of SEQ ID NO: 30, or a peptidomimetic thereof. In other aspects of this embodiment, the Clostridial toxin substrate includes, in part, a BoNT/F recognition sequence comprising a portion of VAMP-2 such as, e.g., residues 1 to 116 of SEQ ID NO: 31; residues 1 to 86 of SEQ ID NO: 31; residues 1 to 76 of SEQ ID NO: 31; residues 1 to 69 of SEQ ID NO: 31; residues 27 to 116 of SEQ ID NO: 31; residues 37 to 116 of SEQ ID NO: 31; residues 27 to 68 of SEQ ID NO: 31; residues 37 to 75 of SEQ ID NO: 31; residues 37 to 69 of SEQ ID NO: 31, or a peptidomimetic thereof. [071] A BoNT/G recognition sequence can correspond to a segment of a protein that is sensitive to cleavage by botulinum toxin serotype G, or can be substantially similar to such a BoNT/G-sensitive 29 of 168 WO 2008/036060 PCTIUS2006/012825 segment. As shown in Table 4, a variety of naturally occurring proteins sensitive to cleavage by BoNT/G are known in the art and include, for example, human, rat and mouse VAMP-1, VAMP-2 and VAMP 3/cellubrevin; bovine VAMP-2; chicken VAMP-1, and VAMP-2; and Torpedo VAMP-1. Thus, a BoNT/G recognition sequence can correspond, for example, to a segment of human VAMP-1, VAMP-2 or VAMP-3; bovine VAMP-2; rat VAMP-1, VAMP-2 or VAMP-3; mouse VAMP-1, VAMP-2 or VAMP-3; chicken VAMP-1, VAMP-2 or VAMP-3; Xenopus VAMP-2 or VAMP-3; Danio VAMP-1 or VAMP-2; Torpedo VAMP-1; Caenorhabditis SNBI, isoforms thereof, or another naturally occurring protein sensitive to cleavage by BoNT/G. Furthermore, as shown in Table 4 above, comparison of native VAMP amino acid sequences cleaved by BoNT/G reveals that such sequences are not absolutely conserved, indicating that a variety of amino acid substitutions and modifications relative to a naturally occurring BoNT/G sensitive VAMP sequence can be tolerated in a BoNT/G substrate useful in the invention. It is understood that a similar BoNT/G recognition sequence can be prepared, if desired, from a corresponding (homologous) segment of another BoNT/G-sensitive VAMP-1 or VAMP-2 isoform, paralog or ortholog, such as, the BoNT/G recognition sequence contain in the VAMP-1 and VAMP-2 identified in the organisms listed above and in Table 4. [072] Thus, in an embodiment, a composition comprises an exogenous BoNT/G substrate capable of being localized to the plasma membrane of a cell wherein said substrate comprises a fluorescent member, a membrane targeting domain and a BoNT/G recognition sequence comprising a cleavage site, where the cleavage site intervenes between said fluorescent member and said membrane localization domain. As used herein, the term "botulinum toxin serotype G recognition sequence" is synonymous with "BoNT/G recognition sequence" and means a scissile bond together with adjacent or non-adjacent recognition elements, or both, sufficient for detectable proteolysis at the scissile bond by a BoNT/G under appropriate conditions. A scissile bond cleaved by BoNT/G can be, for example, Ala-Ala. [073] In an aspect of this embodiment, the Clostridial toxin substrate includes, in part, a BoNT/G recognition sequence comprising a BoNT/G recognition sequence containing at least six consecutive residues of VAMP including Ala-Ala. In another aspect of this embodiment, the Clostridial toxin substrate includes, in part, a BoNT/G recognition sequence comprising the BoNT/G recognition sequence Glu-Thr Ser-Ala-Ala-Lys-Leu-Lys (SEQ ID NO: 103). In other aspects of this embodiment, the Clostridial toxin substrate includes, in part, a BoNT/G recognition sequence comprising a portion of VAMP-1-1 such as, e.g.. residues 1 to 118 of SEQ ID NO: 28, or a peptidomimetic thereof. In other aspects of this embodiment, the Clostridial toxin substrate includes, in part, a BoNT/G recognition sequence comprising a portion of VAMP-1-2 such as, e.g., residues 1 to 117 of SEQ ID NO: 29, or a peptidomimetic thereof. In other aspects of this embodiment, the Clostridial toxin substrate includes, in part, a BoNT/G recognition sequence comprising a portion of VAMP-1-3 such as, e.g., residues 1 to 116 of SEQ ID NO: 30, or a peptidomimetic thereof. In other aspects of this embodiment, the Clostridial toxin substrate includes, in part, a BoNT/G recognition sequence comprising a portion of VAMP-2 such as, e.g., residues 1 to 116 of SEQ ID NO: 31, or a peptidomimetic thereof. [074] A variety of TeNT recognition sequences are well known in the art or can be defined by routine 30 of 168 WO 2008/036060 PCT/US2006/012825 methods and Include sequences corresponding to some or all of the hydrophilic core of a VAMP protein such as human VAMP-1 or human VAMP-2. A TeNT recognition sequence can include, for example, residues 25 to 93 or residues 33 to 94 of human VAMP-2 (SEQ ID NO: 31; F. Comille et al., Solid-phase synthesis, conformational analysis and in vitro cleavage of synthetic human synaptobrevin 11 1-93 by tetanus toxin L chain, 222(1) Eur. J. Biochem. 173-181 (1994); Patrick Foran et al., Differences in the protease activities of tetanus and botulinum B toxins revealed by the cleavage of vesicle-associated membrane protein and various sized fragments, 33(51) Biochemistry 15365-15374 (1994); residues 51 to 93 or residues 1 to 86 of rat VAMP-2, see, e.g., Yamasaki et al., supra, (1994); or residues 33 to 94 of human VAMP-1-1 (SEQ ID NO: 28), residues 33 to 94 of human VAMP-1-2 (SEQ ID NO: 29) and residues 33 to 94 of human VAMP-1-3 (SEQ ID NO: 30). A TeNT recognition sequence also can include, for example, residues 25 to 86, residues 33 to 86 or residues 51 to 86 of human VAMP-2 (SEQ ID NO: 31) or rat VAMP-2 (SEQ ID NO: 38). It is understood that a similar TeNT recognition sequence can be prepared, if desired, from a corresponding (homologous) segment of another TeNT-sensitive VAMP isoform or species homolog such as human VAMP-1 or sea urchin or Aplysia VAMP. (075] Thus, a TeNT recognition sequence can correspond to a segment of a protein that is sensitive to cleavage by tetanus toxin, or can be substantially similar to a segment of a TeNT-sensitive protein. As shown in Table 4, a variety of naturally occurring proteins sensitive to cleavage by TeNT are known in the art and include, for example, human and mouse VAMP-1, VAMP-2 and VAMP-3/cellubrevin; bovine VAMP-2; rat VAMP-2 and VAMP-3; chicken VAMP-2; Torpedo VAMP-1; Strongylocentrotus VAMP; Drosophila sybA, synB, synC, synD and synE; Hirudo VAMP; and Caenorhabditis SNB1-like. Thus, a TeNT recognition sequence can correspond, for example, to a segment of human VAMP-1, VAMP-2 or VAMP-3; bovine VAMP-2; rat VAMP-2 or VAMP-3; mouse VAMP-1, VAMP-2 or VAMP-3; chicken VAMP-1, VAMP-2 or VAMP-3; Xenopus VAMP-2 or VAMP-3; Danio VAMP-1 or VAMP-2; Torpedo VAMP-1; Strongylocentrotus VAMP; Drosophila sybA, synB, synC, synD or synE; Hirudo VAMP; Loiigo VAMP; Lymnaea VAMP; Aplysia VAMP; Caenorhabditis SNB1 and SNB-like, isoforms thereof, or another naturally occurring protein sensitive to cleavage by TeNT. Furthermore, comparison of native VAMP amino acid sequences cleaved by TeNT reveals that such sequences are not absolutely conserved (Table 4). This finding indicates that a variety of amino acid substitutions and modifications relative to a naturally occurring TeNT-sensitive VAMP sequence can be tolerated in a TeNT substrate useful in the invention. It is understood that a similar TeNT recognition sequence can be prepared, if desired, from a corresponding (homologous) segment of another TeNT-sensitive VAMP-1 or VAMP-2 isoform, paralog or ortholog, such as, the TeNT recognition sequence contain in the VAMP-1 and VAMP-2 identified in the organisms listed above and in Table 4. [076] Thus, in an embodiment, a composition comprises an exogenous TeNT substrate capable of being localized to the plasma membrane of a cell wherein said substrate comprises a fluorescent member, a membrane targeting domain and a TeNT recognition sequence comprising a cleavage site, where the cleavage site intervenes between said fluorescent member and said membrane localization domain. As used herein, the term "tetanus toxin recognition sequence" means a scissile bond together with adjacent or non-adjacent recognition elements, or both, sufficient for detectable proteolysis at the 31 of 168 WO 2008/036060 PCT/US2006/012825 scissile bond by a tetanus toxin under appropriate conditions. A scissile bond cleaved by TeNT can be, for example, Gln-Phe. [077] In an aspect of this embodiment, the Clostridial toxin substrate includes, in part, a TeNT recognition sequence comprising a TeNT recognition sequence containing at least six consecutive residues of VAMP including Gin-Phe. In another aspect of this embodiment, the Clostridial toxin substrate includes, in part, a TeNT recognition sequence comprising the TeNT recognition sequence Gly Ala-Ser-Gln-Phe-Glu-Thr-Ser (SEQ ID NO: 104). In other aspects of this embodiment, the Clostridial toxin substrate includes, in part, a TeNT recognition sequence comprising a portion of VAMP-1-1 such as, e.g., residues 1 to 118 of SEQ ID NO: 28 or residues 33 to 94 of SEQ ID NO: 28. In other aspects of this embodiment, the Clostridial toxin substrate includes, in part, a TeNT recognition sequence comprising a portion of VAMP-1-2 such as, e.g., residues 1 to 117 of SEQ ID NO: 29 or residues 33 to 94 of SEQ ID NO: 29. In other aspects of this embodiment, the Clostridial toxin substrate includes, in part, a TeNT recognition sequence comprising a portion of VAMP-1-3 such as, e.g., residues 1 to 116 of SEQ ID NO: 30 or residues 33 to 94 of SEQ ID NO: 30. In other aspects of this embodiment, the Clostridial toxin substrate includes, in part, a TeNT recognition sequence comprising a portion of VAMP-2 such as, e.g., residues 1 to 116 of SEQ ID NO: 31; residues 25 to 94 of SEQ ID NO: 31; residues 33 to 94 of SEQ ID NO: 31; residues 51 to 93 of SEQ ID NO: 31; residues 1 to 86 of SEQ ID NO: 31; residues 25 to 86 of SEQ ID NO: 31; residues 33 to 86 of SEQ ID NO: 31; residues 51 to 86 of SEQ ID NO: 31, or a peptidomimetic thereof. [0781 SNAP-25, VAMP and Syntaxin share a short motif usually located within regions predicted to adopt an a-helical conformation called the SNARE motif. This motif ususally comprises a nine amino acid motif with the general formula of H-e-G-X-H-9-X-H-P (see FIG. 2b), where H is a aliphatic residue, 9 is a carboxylate residue, P is a polar residue and X is any amino acid, see e.g., Omella Rossetto et al., SNARE motif and neurotoxins, 372(6505) Nature 415-416 (1994); Rossella Pellizzari et al., Structural determinants of the specificity for synaptic vesicle-associated membrane protein/synaptobrevin of tetanus and botulinum type B and G neurotoxins, 271(34) J. Biol. Chem. 20353-20358 (1996); Rossella Pellizzari et al., The interaction of synaptic vesicle-associated membrane protein/synaptobrevin with botulinum neurotoxins D and F, 409(3) FEBS Lett. 339-342 (1997); and Philip Washboume et al., Botulinum neurotoxin types A and E require the SNARE motif in SNAP-25 for proteolysis, 418(1-2) FEBS Lett. 1-5 (1997). This motif is present in SNAP-25, VAMP and syntaxin isoforms expressed in animals sensitive to the toxins. In contrast, Drosophila and yeast SNAP-25 proteins are resistant to these toxins. In additon, VAMP and syntaxin isoforms not involved in exocytosis contain sequence variations in these a-helical motif regions. [079] Multiple repetitions of the a-helical motif are present in proteins sensitive to cleavage by Clostridial toxins: Four copies are naturally present in SNAP-25, designated S1-S4; two copies are naturally present in VAMP, designated V1 and V2; and two copies are naturally present in syntaxin, designated X1 and X2, see, e.g., Humeau et al., supra, (2000). Furthermore, peptides corresponding to the specific sequence of the a-helical motifs can inhibit toxin activity in vitro and in vivo, and such 32 of 168 WO 2008/036060 PCT/US2006/012825 peptides can cross-Inhibit different toxins. In addition, antibodies raised against such peptides can cross-react among the three target proteins, indicating that this a-helical motif is exposed on the protein surface and adopts a similar configuration in each of the three target proteins. Consistent with these findings, SNAP-25-specific, VAMP-specific and syntaxin-specific toxins cross-inhibit each other by competing for the same binding site, although they do not cleave targets non-specifically. These results indicate that a Clostridial toxin recognition sequence can include, if desired, at least one a-helical motif. It is recognized that an a-helical motif is not required for cleavage by a Clostridial toxin, as evidenced by 16-mer and 17-mer substrates for BoNT/A known in the art, see, e.g., Schmidt & Bostian, supra, (1997); Schmidt & Bostian, supra, (Oct. 12,1999); and Schmidt & Stafford, supra, (Jul. 13, 2004). [080] Although multiple a-helical motifs are found in the naturally occurring SNAP-25, VAMP and syntaxin target proteins, a Clostridial toxin recognition sequence useful in a Clostridial toxin substrate can have a single a-helical motif. In particular embodiments, a method of the invention relies on a Clostridial toxin recognition sequence including two or more a-helical motifs. A BoNT/A or BoNT/E recognition sequence can include, for example, the S4 a-helical motif, alone or combined with one or more additional a-helical motifs; a BoNT/B, BoNT/G or TeNT recognition sequence can include, for example, the V2 a helical motif, alone or combined with one or more additional a-helical motifs; a BoNT/C1 recognition sequence can include, for example, the S4 a-helical motif, alone or combined with one or more additional a-helical motifs, or the X2 a-helical motif, alone or combined with one or more additional a-helical motifs; and a BoNT/D or BoNT/F recognition sequence can include, for example, the V1 a-helical motif, alone or combined with one or more additional a-helical motifs. Representative SNARE motifs are presented in Tables 6, 7 and 8. 33 of 168 WO 2008/036060 PCT/US2006/012825 Primate SNP2A ADESLESTR VEESKDAGI IL EGEL MDENLEQVS SNAP-25B3AOEL mate SNAP-23B TDESLESTR AIESQDAGI LDEQKEQLN MEENLTQVG SNAP-23BLEQEL Rodent ADESLESTR VEESKDAGI LDEQGEQLE MDENLEOVS dent SNAP-23 TDESLESTR AIESODAGI LDEQGEQLN MEENLTQVG Bird SNAP-25B ADESLESTR VEESKDAGI LDEQGEQLE MDENLEQVS Amphibian 5 ADESLESTR VEGSKDAGI IE EQL MDENLEQVG AmpibanSNAP-25B LDEQGEQLE _______ Amphibian SNAP-23 ADESLESTR ALESODAGI LDEOGEQLD MDENLVQVG Fish SNAP-25A ADESLESTR VEESKDAGI LDEQGELE MDENLEQVG SNAP-25B GDESLESTR MDENLEQVG Fish SNAP-23 TDESLESTR AEESRETGV LDEQGEQLR MEENLDQVG Ray SNAP-25 TDESLESTR VEESKDAGI LDEQGEQLE MEENLDQVG Sea urchin SNAP-25 TDESLESTR AEESKEAGI LDEQGEOLD MDENLTQVS Insect SNAP-25 ADESLESTR CEESKEAGI LDDQGEQLD MEENMGQVN Insect SNAP-24 ADESLESTR MDESKEAGI LDDQGEQLD MDENLGQVN Segmented worm SNAP-25 TDDSLESTR CEESKDAGI LDEQGEQLD MEQNMGEVS Cephalopod SNAP-25 TDDSLESTR CEESKEAGI LDEQGEQLD MENNMKEVS Gastropod SNAP-25 TNESLESTR CEESKEAGI LDEQGEQLD MEONIGEVA Round worm SNAP-25 TDDSLESTR CEESKEAGI LDDQGEQLE MDENVQQVS Proteolytic cleavage occurs at this site (*); Proteolytic cleavage not detected at this site (-); Proteolytic cleavage not determined at this site (ND) [081] Table 6 - SNARE motifs of SNAP-25 and Related Proteins. Primate: Human SNAP-25A residues 22-30, 36-44, 50-58 and 146-154 of SEQ ID NO: 1; Human SNAP-25B residues 22-30, 36-44, 50-58 and 146-154 of SEQ ID NO: 2; Human SNAP-23A residues 17-25, 31-39, 45-53, and 152-160 of SEQ ID NO: 3; Human SNAP-23B residues 17-25, 31-39, 45-53 and 152-160 of SEQ ID NO: 4; Monkey SNAP-25B residues 22-30, 36-44, 50-58 and 146-154 of SEQ ID NO: 5; Rodent: Rat SNAP-25A residues 22-30, 36-44, 50-58 and 146-154 of SEQ ID NO: 6; Rat SNAP-25B residues 22-30, 36-44, 50-58 and 146-154 of SEQ ID NO: 7; Mouse SNAP-25B residues 22-30, 36-44, 50-58 and 146-154 of SEQ ID NO: 8; Rat SNAP-23 residues 17-25, 31-39, 45-53 and 151-159 of SEQ ID NO: 9; Mouse SNAP-23 residues 17-25, 31-39, 45-53 and 151-159 of SEQ ID NO: 10; Bird: Chicken SNAP-25B residues 22-30, 36-44, 50-58 and 146-154 of SEQ ID NO: 11; Fish: Goldfish SNAP-25A residues 22-30, 36-44, 50-58 and 144-152 of SEQ ID NO: 12; Goldfish SNAP-25B residues 22-30, 36-44, 50-58 and 143-151 of SEQ ID NO: 13; Zebrafish SNAP-25A residues 22-30, 36-44, 50-58 and 144-152 of SEQ ID NO: 14; Zebrafish SNAP-25B residues 22-30, 36-44, 50-58 and 143-151 of SEQ ID NO: 15; Zebrafish SNAP-23 residues 17-25, 31-39, 45-53 and 157-165 of SEQ ID NO: 16; Ray: marbled electric ray SNAP-25 residues 26-34, 40-48, 54-62 and 153-161 of SEQ ID NO: 17; Amphibian: Frog SNAP-25A residues 22-30, 36-44, 50-58 and 146-154 of SEQ ID NO: 18; Frog SNAP-25B residues 22-30, 36-44, 50-58 and 146-154 of SEQ ID NO: 19; Frog SNAP-23 residues 17-25, 31-39, 45-53 and 146-154 of SEQ ID NO: 20; Sea urchin SNAP 34 of 168 WO 2008/036060 PCT/US2006/012825 25 residues 24-32, 38-46, 52-60 and 152-160 of SEQ ID NO: 21; Insect: Fruit fly SNAP-25 residues 29 37, 43-51, 57-65 and 154-163 of SEQ ID NO: 22 212; Fruit fly SNAP-24 residues 24-32, 38-46, 52-60 and 153-162 of SEQ ID NO: 23; Segmented worm: Leech SNAP-25 residues 30-38, 44-52, 58-66 and 153 161 of SEQ ID NO: 24; Cephalopod: squid SNAP-25 residues 25-33, 39-47, 53-61 and 153-161 of SEQ ID NO: 25; Gastropod: Pond snail SNAP-25 residues 32-40, 46-54, 60-68 and 160-168 of SEQ ID NO: 26; Round worm: Nematode worm SNAP-25 residues 22-30, 36-44, 50-58 and 148-156 of SEQ ID NO: 27. VAMP1-1 Primate VAMP1-2 VEEWDIMR LDDRADALQ VAMP1 -3 Primate VAMP2 VDEVVDIMR LDDRADALQ Primate VAMP3 VDEWDIMR LDDRADALQ Bovine VAMP2 VDEVVDIMR LDDRADALQ VAMP12EW~l Rodent VAMP1/b VEEWDIMR LDDRADALQ Rodent VAMP3 VDEWDIMR LDDRADALQ Rodent VAMP3 VDEVVDIMR LDDRADALQ Bird VAMP1 VDEVVDIMR LDDRADALQ Bird VAMP3 VDEWDIMR LDDRADALQ Bird VAMP2 VDEVVDIMR LDDRADALQ Amphibian VAMP2 VDEWDIMR LDDRADALQ Amphiban VAMP3 VDEWDIMR LDDRADALQ Fish VAMP1 VDEWDIMR LDDRADALQ Fish VAMP2 VDEVVDIMR LDDRADALQ Fish VAMP-3 VDEWVDIMR LDDRADALQ Ray VAMPI VEEWDIIR LDDRADALQ Sea urchin VAMP VDEVVDIMR LDDRADALQ Insect Syn-Al VDEVVGIMR LGERADQLE Syn-A21 Insect Syn-B2 VDEVVGIMR LGERADOLE insect ~~~Syn-D DVDIRLDRDL Syn-C Insect Syn-D VDEWVDIMR LODRADALO ___________________ Syn-E Segmented worm VAMP VDEWGMMR LDGRADALQ Cephalopod VAMP VEEWGIMR LDDRADALQ Gastropod VAMP VDEWGIMR LDDRAEALQ SNBI VDEWGIMK LDDRADALQ Round worm SNB-Iike VNEVIDVMR LDHRAEVLO [082] Table 7 - SNARE motifs of VAMP and Related Proteins. Primate: Human VAMP-1-1 residues 40-48 and 56-64 of SEQ ID NO: 28; Human VAMP-1-2 residues 40-48 and 56-64 of SEQ ID NO: 29; 35 of 168 WO 2008/036060 PCT/US2006/012825 Human VAMP-1-3 residues 40-48 and 56-64 of SEQ ID NO: 30; Human VAMP-2 residues 39-47 and 63 71 of SEQ ID NO: 31; Monkey VAMP-2 residues 39-47 and 63-71 of SEQ ID NO: 32; Human VAMP 3/cellubrevin residues 22-30 and 46-54 of SEQ ID NO: 33; Bovine: Cow VAMP-2 residues 39-47 and 63 71 of SEQ ID NO: 34; Rodent: Rat VAMP-1 residues 40-48 and 56-64 of SEQ ID NO: 35; Rat VAMP-1-b residues 40-48 and 56-64 of SEQ ID NO: 36; Mouse VAMP-1 residues 40-48 and 56-64 of SEQ ID NO: 37; Rat VAMP-2 residues 39-47 and 63-71 of SEQ ID NO: 38; Rat VAMP-2-b residues 39-47 and 63-71 of SEQ ID NO: 39; Mouse VAMP-2 residues 39-47 and 63-71 of SEQ ID NO: 40; Rat VAMP-3/cellubrevin residues 26-34 and 50-58 of SEQ ID NO: 41; Mouse VAMP-3/cellubrevin residues 26-34 and 50-58 of SEQ ID NO: 42; Bird: Chicken VAMP-1 residues 182-190 and 198-206 of SEQ ID NO: 43; Chicken VAMP-2 residues 37-45 and 61-69 of SEQ ID NO: 44; Chicken VAMP-3/cellubrevin residues 26-34 and 50-58 of SEQ ID NO: 45; Fish: Zebrafish VAMP-1 residues 41-49 and 57-65 of SEQ ID NO: 46; Zebrafish VAMP-2 residues 33-41 and 57-65 of SEQ ID NO: 47; Zebrafish VAMP-3 residues 25-33 and 49-57 of SEQ ID NO: 48; Ray: marbled electric ray VAMP-1 residues 42-50 and 58-66 of SEQ ID NO: 49; Amphibian: Frog VAMP-2 residues 37-45 and 61-69 of SEQ ID NO: 50; Frog VAMP-3 residues 24-32 and 48-56 of SEQ ID NO: 51; Sea urchin VAMP residues 23-31 and 39-47 of SEQ ID NO: 52; Insect: Fruit fly SynAl residues 31-39 and 47-55 of SEQ ID NO: 53; Fruit fly SynA2 residues 54-62 and 70-78 of SEQ ID NO: 54; Fruit fly SynB1 residues 54-62 and 70-78 of SEQ ID NO: 55; Fruit fly SynB2 residues 54-62 and 70-78 of SEQ ID NO: 56; Fruit fly SynC residues 48-56 and 64-72 of SEQ ID NO: 57; Fruit fly SynD residues 67-75 and 83-91 of SEQ ID NO: 58; Fruit fly SynE residues 67-75 and 83-91 of SEQ ID NO: 59; Segmented worm: Leech VAMP residues 37-45 and 53-61 of SEQ ID NO: 60; Cephalopod: squid VAMP residues 47-55 and 63-71 of SEQ ID NO: 61; Gastropod: Pond snail VAMP residues 40-48 and 56-64 of SEQ ID NO: 62; sea hare VAMP residues 30-38 and 46-54 of SEQ ID NO: 63; Round worm: Nematode worm SNB1 residues 34-42 and 50-58 of SEQ ID NO: 64; Nematode worm SNB-like residues 40-48 and 56-64 of SEQ ID NO: 65. 36 of 168 WO 2008/036060 PCTIUS2006/012825 Syntaxin1A2 MDEFFEQVE LEDMLESGN Syntaxn2-1 Primate Syntaxin2-2 MDDFFHQVE LEEMLESGK Syntaxin2-3__________ _____ _____ Primate Syntaxin3A MDEFFSEIE LEEMLESGN Syntaxin1 A MEFQELEDMLESGN Bovinle Syntain1B82 MEFVELEDMLESGK Syntaxin1A MDEFFEQVE LEDMLESGN Rodent Syntaxin1B61 MAEFFEQVE LEDMLESGK Syntaxin182 MDEFFEQVE LEDMLESGK Rodent Syntaxin2 MDGFFHQVE LEEMLESGK Rodentn3BMDEFFSEIE LEEMLESGN Rodent Syntaxin3C MDEFFSENF LEEMLESGN Bird Syntaxin 18 MDEFFEQVE LEDMLESGK Bird Syntaxin2 MDDFFQQVE LEEMLESGN Fish Syntaxin1 B MDEFFEQVE LED MLESGK Fish Syntaxin3 MDEFFSQIE LEEMLEGGN Sea urchin Syntaxin1B MEEFFEOVE LEDMLESGN Insect Syntaxin1A MDDFFAQVE LEKMLEEGN Segmented worm Syntaxin1A MEEFFEQVN LEDMLESGN Cephalopod SyntaxinlA MEEFFEQVE LEDMLESGN Gastropod Syntaxin1A MEEFFEQVD LEDMIESGN [063] Table 8 - SNARE motifs of Syntaxin and Related Proteins. Primate: Human Syntaxin1A residues 30-38 and 165-173 of SEQ ID NO: 66; Human Syntaxin1B1 residues 29-37 and 164-172 of SEQ ID NO: 67; Human Syntaxin1B2 residues 29-37 and 164-172 of SEQ ID NO: 68; Human Syntaxin2-1 residues 29-37 and 168-176 of SEQ ID NO: 69; Human Syntaxin2-2 residues 29-37 and 168-176 of SEQ ID NO: 70; Human Syntaxin2-3 residues 29-37 and 168-176 of SEQ ID NO: 71; Human Syntaxin3 residues 32-40 and 165-173 of SEQ ID NO: 72; Bovine: Cow Syntaxin1A residues 30-38 and 165-173 of SEQ ID NO: 73; Cow Syntaxin1B2 residues 29-37 and 164-172 of SEQ ID NO: 74; Rodent: Rat Syntaxin1A residues 30-38 and 165-173 of SEQ ID NO: 75; Rat SyntaxinLB2 residues 29-37 and 164 172 of SEQ ID NO: 76; Mouse Syntaxin1A residues 30-38 and 165-173 of SEQ ID NO: 77; Mouse Syntaxin1B1 residues 29-37 and 164-172 of SEQ ID NO: 78; Mouse SyntaxinLB2 residues 29-37 and 164-172 of SEQ ID NO: 79; Rat Syntaxin2 residues 31-39 and 170-178 of SEQ ID NO: 80; Mouse Syntaxin2 residues 30-38 and 169-177 of SEQ ID NO: 81; Rat Syntaxin3A residues 32-40 and 165-173 of SEQ ID NO: 82; Mouse Syntaxin3A residues 32-40 and 165-173 of SEQ ID NO: 83: Mouse Syntaxin3B residues 32-40 and 165-173 of SEQ ID NO: 84; Mouse Syntaxin3C residues 32-40 and 147-155 of SEQ ID NO: 85; Bird: Chicken Syntaxin1B residues 29-37 and 157-165 of SEQ ID NO: 86; Chicken Syntaxin2 residues 28-36 and 167-175 of SEQ ID NO: 87; Fish: Zebrafish Syntaxin1B residues 29-37 and 164-172 37 of 168 WO 2008/036060 PCTIUS2006/012825 of SEQ ID NO: 88; Zebrafish Syntaxin3 residues 29-37 and 163-171 of SEQ ID NO: 89; sea urchin Syntaxin1B residues 29-37 and 164-172 of SEQ ID NO: 90: Insect: Fruit fly SyntaxinlA residues 33-41 and 168-176 of SEQ ID NO: 91; Segmented worm: leech SyntaxinlA residues 36-44 and 171-179 of SEQ ID NO: 92; Cephalopod: squid SyntaxinlA residues 33-41 and 168-176 of SEQ ID NO: 93; Gastropod: Pond snail Syntaxin1A residues 32-40 and 167-175 of SEQ ID NO: 94; sea hare Syntaxin1A residues 32-40 and 167-175 of SEQ ID NO: 95. [084] As discussed above, the SNARE complex is comprised of the t-SNARE SNAP-25 along with another t-SNARE, syntaxin 1 and a v-SNARE VAMP/synaptobrevin. Members of the SNAP-25 family of proteins can be divided into three structural domains and amino-terminal a-helix of approximately 84 residues, an approximately 36 amino acid interhelical loop and a carboxy-terminal a-helix of approximately 86 residues, depending on the individual member. As will be discussed below, all three of these regions may be used to target SNAP-25 to the plasma membrane either alone or in any combination of the three. [085] The interhelical loop of SNAP-25 appears to be important for conferring targeting specificity of this SNARE protein to the membrane. For example, in one study a membrane-targeting domain comprising residues 85-120 of SNAP-25 was shown to localize to the cell membrane Susana Gonzalo et al., SNAP-25 is targeted to the plasma membrane through a novel membrane-binding domain, 274(30) J. Biol. Chem.21313-21318 (1999). This region represents two-thirds of the interhelical loop that connects the amino- and carboxy-terminal a-helices of SNAP-25. The function of this targeting domain appears to be independent of SNARE protein-protein interactions since remove of the SNAP-25 regions that associate with either syntaxin or synaptobrevin did not interfere with proper targeting of SNAP-25 to the membrane. [086] Alignment of SNAP-25 family members revealed two conserved motifs present within the interhelical loop region responsible for membrane targeting. The first is a cysteine-rich region present at the amino-terminal boundary of the membrane-targeting interhelical loop domain. One or more of the cysteines present in this motif is fatty acylated via a thioester linkage of palmitate. Palmitoylation of this cysteine-rich may be important for membrane insertion because elimination of these cysteine residues results in a loss of SNAP-25 membrane-targeting. [0871 The second is a five-amino acid motif located at the carboxy-terminal boundary of the membrane targeting interhelical loop domain (QPXR(V/l)). This motif is believed to play a role in membrane association, see, e.g., Gonzalo et al., supra, (1999); Philip Washbourne et al., Cysteine residues of SNAP-25 are required for SNARE disassembly and exocytosis, but not for membrane targeting, 357(Pt 3) Biochem. J. 625-634 (2001). [088] The a-helices of the various SNARE complex members seems to be involved in protein-protein interactions between members. For example, solution of the crystal structure of the SNARE complex reveals that SNAP-25, syntaxin and synaptobrevin appear to favor a heterotrimeric, parallel four-helix 38 of 168 WO 2008/036060 PCT/US2006/012825 bundle association, see, e.g., R. Bryan Sutton et al., Crystal structure of a SNARE complex involved in synaptic exocytosis at 2.4 A resolution, 395(6700) Nature 347-353 (1998). This analysis indicated an extensive intertwining of the a-helices with the amino-terminal region of the bundle comprising interactions between the amino-terminal a-helix of SNAP-25 with syntaxin, several central associations amongst all three members and an association between syntaxin and synaptobrevin at the carboxyl terminal portion of the four-helix bundle. [089] Protein-protein interactions between the a-helices of SNARE complex members appear to be another way of localizing SNAP-25 to the membrane. For example, co-expression of SNAP-25 with syntaxin results in targeting SNAP-25 to the membrane in the absence of a functional interhelical loop suggesting that protein-protein interactions between these two t-SNAREs can target Clostridial toxin substrates to the membrane, see, e.g., Washboume et al., supra, (2001). [090] Members of the Syntaxin family of proteins can be divided into several structural domains. In the amino-terminal half of the protein contains an Habc region comprising three a-helix domains located at amino acids 30-60, 69-104 and 110-154. The carboxy-terminal half of Syntaxin-1 contains an a-helix of approximately 52-69 residues, depending on the individual member and an approximately 23 amino acid membrane anchoring domain. As will be discussed below, regions comprising the membrane anchoring domain of Syntaxin may be used to target Clostridial toxin substrates to the plasma membrane. [091] The Clostridial toxin substrates disclosed in the present specification include, in part, a membrane targeting domain. As used herein, the term "membrane targeting domain' is synonymous with "MTD" and means a SNAP-25 or Syntaxin peptide which directs a Clostridial toxin substrate to the cell membrane. Any and all SNAP-25 or Syntaxin membrane targeting domains can be used in aspects of the present invention, with the proviso that the Clostridial toxin substrate maintains the property to be cleaved by a Clostridial toxin. Non-limiting examples include, without limitation, naturally occurring membrane targeting domains present in SNAP-25, naturally occurring SNAP-25 MTD variants, and non naturally occurring SNAP-25 MTD variants, such as, e.g., genetically engineered SNAP-25 MTD variants, produced, e.g., by random mutagenesis or rational designed and SNAP-25 MTD peptidomimetics; and naturally occurring membrane targeting domains present in Syntaxin, naturally occurring Syntaxin MTD variants, and non-naturally occurring Syntaxin MTD variants, such as, e.g., genetically engineered Syntaxin MTD variants, produced, e.g., by random mutagenesis or rational designed and Syntaxin MTD peptidomimetics. [0921 Thus, in an embodiment a Clostridial toxin substrate comprises, in part, the membrane targeting domain comprising a region from SNAP-25 sufficient to target a toxin substrate disclosed in the present specification to the membrane. In an aspect of this embodiment, the membrane targeting domain comprising a region from the interhelical region of SNAP-25 sufficient to target a toxin substrate disclosed in the present specification to the membrane. In an aspect of this embodiment the membrane targeting domain comprises the amino acids 85-120 of SEQ ID NO: 1. It is envisioned that an interhelical loop region from SNAP-25 of any and all lengths can comprise the membrane targeting domain with the 39 of 168 WO 2008/036060 PCTIUS2006/012825 proviso that the loop region is sufficient to target a toxin substrate disclosed in the present specification to the membrane. Thus, aspects of this embodiment may include an interhelical loop region comprising, e.g., at least 35 residues from amino acids 85-120 of SEQ ID NO: 1, at least 30 residues from amino acids 85-120 of SEQ ID NO: 1, at least 25 residues from amino acids 85-120 of SEQ ID NO: 1, at least 20 residues from amino acids 85-120 of SEQ ID NO: 1, at least 15 residues from amino acids 85-120 of SEQ ID NO: 1, at least 10 residues from amino acids 85-120 of SEQ ID NO: 1 or at least 5 residues from amino acids 85-120 of SEQ ID NO: 1. Further aspects of this embodiment may include an interhelical loop region comprising, e.g., at most 35 residues from amino acids 85-120 of SEQ ID NO: 1, at most 30 residues from amino acids 85-120 of SEQ ID NO: 1, at most 25 residues from amino acids 85-120 of SEQ ID NO: 1, at most 20 residues from amino acids 85-120 of SEQ ID NO: 1, at most 15 residues from amino acids 85-120 of SEQ ID NO: 1, at most 10 residues from amino acids 85-120 of SEQ ID NO: 1 or at most 5 residues from amino acids 85-120 of SEQ ID NO: 1. [093] In another aspect of this embodiment a Clostridial toxin substrate comprises, in part, the membrane targeting domain comprises amino acids CGLCVCPCNK (SEQ ID NO: 128). In another aspect of this embodiment the membrane targeting domain comprises amino acids CGLFICPCNK (SEQ ID NO: 129). In another aspect of this embodiment the membrane targeting domain comprises amino acids CGLCSCPCNK (SEQ ID NO: 130). In another aspect of this embodiment the membrane targeting domain comprises amino acids CGLCPCPCNK(SEQ ID NO: 131). In another aspect of this embodiment the membrane targeting domain comprises amino acids CGICVCPWKK(SEQ ID NO: 132). In another aspect of this embodiment the membrane targeting domain comprises amino acids CGICVLPCNK(SEQ ID NO: 133). In another aspect of this embodiment the membrane targeting domain comprises amino acids CGLCVLPWNK(SEQ ID NO: 134). [094] In another embodiment a Clostridial toxin substrate comprises, in part, the membrane targeting domain comprises the amino acids QPXRV (SEQ ID NO: 135), where X is any amino acid. In another aspect of this embodiment the membrane targeting domain comprises amino acids QPXRI (SEQ ID NO: 136), where X is any amino acid. In another aspect of this embodiment the membrane targeting domain comprises amino acids QPARV (SEQ ID NO: 137). In another aspect of this embodiment the membrane targeting domain comprises amino acids QPQRV (SEQ ID NO: 138). In another aspect of this embodiment the membrane targeting domain comprises amino acids QPGRV (SEQ ID NO: 139). In another aspect of this embodiment the membrane targeting domain comprises amino acids QPSRI (SEQ ID NO: 140). In another aspect of this embodiment the membrane targeting domain comprises amino acids QPMRM (SEQ ID NO: 141). In another aspect of this embodiment the membrane targeting domain comprises amino acids OPRI (SEQ ID NO: 142). [095] In another embodiment a Clostridial toxin substrate comprises, in part, the membrane targeting domain comprises amino acids from the amino-terminal a-helix of SNAP-25 sufficient to target a toxin substrate disclosed in the present specification to the membrane. In an aspect of this embodiment the membrane targeting domain comprises the amino acids 1-84 of SEQ ID NO: 1. It is envisioned that an amino-terminal a-helix from SNAP-25 of any and all lengths can comprise the membrane targeting 40 of 168 WO 2008/036060 PCT/US2006/012825 domain with the proviso that the loop region is sufficient to target a toxin substrate disclosed in the present specification to the membrane. Thus, aspects of this embodiment may include an amino-terminal a-helix region comprising, e.g., at least 80 residues from amino acids 1-84 of SEQ ID NO: 1, at least 75 residues from amino acids 1-84 of SEQ ID NO: 1, at least 70 residues from amino acids 1-84 of SEQ ID NO: 1, at least 65 residues from amino acids 1-84 of SEQ ID NO: 1, at least 60 residues from amino acids 1-84 of SEQ ID NO: 1, at least 55 residues from amino acids 1-84 of SEQ ID NO: 1, at least 50 residues from amino acids 1-84 of SEQ ID NO: 1, at least 45 residues from amino acids 1-84 of SEQ ID NO: 1, at least 40 residues from amino acids 1-84 of SEQ ID NO: 1, at least 35 residues from amino acids 1-84 of SEQ ID NO: 1, at least 30 residues from amino acids 1-84 of SEQ ID NO: 1, at least 25 residues from amino acids 1-84 of SEQ ID NO: 1, at least 20 residues from amino acids 1-84 of SEQ ID NO: 1, at least 15 residues from amino acids 1-84 of SEQ ID NO: 1, at least 10 residues from amino acids 1-84 of SEQ ID NO: 1 or at least 5 residues from amino acids 1-84 of SEQ ID NO: 1. Further aspects of this embodiment may include an amino-terminal a-helix region comprising, e.g., at most 80 residues from amino acids 1-84 of SEQ ID NO: 1, at most 75 residues from amino acids 1-84 of SEQ ID NO: 1, at most 70 residues from amino acids 1-84 of SEQ ID NO: 1, at most 65 residues from amino acids 1-84 of SEQ ID NO: 1, at most 60 residues from amino acids 1-84 of SEQ ID NO: 1, at most 55 residues from amino acids 1-84 of SEQ ID NO: 1, at most 50 residues from amino acids 1-84 of SEQ ID NO: 1, at most 45 residues from amino acids 1-84 of SEQ ID NO: 1, at most 40 residues from amino acids 1-84 of SEQ ID NO: 1, at most 35 residues from amino acids 1-84 of SEQ ID NO: 1, at most 30 residues from amino acids 1-84 of SEQ ID NO: 1, at most 25 residues from amino acids 1-84 of SEQ ID NO: 1, at most 20 residues from amino acids 1-84 of SEQ ID NO: 1, at most 15 residues from amino acids 1-84 of SEQ ID NO: 1, at most 10 residues from amino acids 1-84 of SEQ ID NO: 1 or at most 5 residues from amino acids 1-84 of SEQ ID NO: 1. [096] In yet another embodiment a Clostridial toxin substrate comprises, in part, the membrane targeting domain comprises amino acids from the carboxy-terminal a-helix of SNAP-25 sufficient to target a toxin substrate disclosed in the present specification to the membrane. In an aspect of this embodiment the membrane targeting domain comprises the amino acids 121-206 of SEQ ID NO: 1. It is envisioned that an carboxy-terminal a-helix from SNAP-25 of any and all lengths can comprise the membrane targeting domain with the proviso that the loop region is sufficient to target a toxin substrate disclosed In the present specification to the membrane. Thus, aspects of this embodiment may include an carboxy terminal a-helix region comprising, e.g., at least 80 residues from amino acids 121-206 of SEQ ID NO: 1; at least 75 residues from amino acids 121-206 of SEQ ID NO: 1, at least 70 residues from amino acids 121-206 of SEQ ID NO: 1, at least 65 residues from amino acids 121-206 of SEQ ID NO: 1, at least 60 residues from amino acids 121-206 of SEQ ID NO: 1, at least 55 residues from amino acids 121-206 of SEQ ID NO: 1, at least 50 residues from amino acids 121-206 of SEQ ID NO: 1, at least 45 residues from amino acids 121-206 of SEQ ID NO: 1, at least 40 residues from amino acids 121-206 of SEQ ID NO: 1, at least 35 residues from amino acids 121-206 of SEQ ID NO: 1, at least 30 residues from amino acids 121-206 of SEQ ID NO: 1, at least 25 residues from amino acids 121-206 of SEQ ID NO: 1, at least 20 residues from amino acids 121-206 of SEQ ID NO: 1, at least 15 residues from amino acids 121-206 of SEQ ID NO: 1, at least 10 residues from amino acids 121-206 of SEQ ID NO: 1 or at least 5 residues 41 of 168 WO 2008/036060 PCTIUS2006/012825 from amino acids 121-206 of SEQ ID NO: 1. Further aspects of this embodiment may include an carboxy-terminal a-helix region comprising, e.g., at most 85 residues from amino acids 121-206 of SEQ ID NO: 1; at most 80 residues from amino acids 121-206 of SEQ ID NO: 1; at most 75 residues from amino acids 121-206 of SEQ ID NO: 1, at most 70 residues from amino acids 121-206 of SEQ ID NO: 1, at most 65 residues from amino acids 121-206 of SEQ ID NO: 1, at most 60 residues from amino acids 121-206 of SEQ ID NO: 1, at most 55 residues from amino acids 121-206 of SEQ ID NO: 1, at most 50 residues from amino acids 121-206 of SEQ ID NO: 1, at most 45 residues from amino acids 121-206 of SEQ ID NO: 1, at most 40 residues from amino acids 121-206 of SEQ ID NO: 1, at most 35 residues from amino acids 121-206 of SEQ ID NO: 1, at most 30 residues from amino acids 121-206 of SEQ ID NO: 1, at most 25 residues from amino acids 121-206 of SEQ ID NO: 1, at most 20 residues from amino acids 121-206 of SEQ ID NO: 1, at most 15 residues from amino acids 121-206 of SEQ ID NO: 1, at most 10 residues from amino acids 121-206 of SEQ ID NO: 1 or at most 5 residues from amino acids 121-206 of SEQ ID NO: 1. [097] In another embodiment a Clostridial toxin substrate comprises, in part, the membrane targeting domain comprising a region from Syntaxin sufficient to target a toxin substrate disclosed in the present specification to the membrane. In an aspect of this embodiment, the membrane targeting domain comprising a region from the membrane anchoring domain of Syntaxin sufficient to target a toxin substrate disclosed in the present specification to the membrane. In an aspect of this embodiment the membrane targeting domain comprises the amino acids 266-288 of SEQ ID NO: 66. It is envisioned that an membrane anchoring domain from Syntaxin of any and all lengths can comprise the membrane targeting domain with the proviso that the loop region is sufficient to target a toxin substrate disclosed in the present specification to the membrane. Thus, aspects of this embodiment may include an interhelical loop region comprising, e.g., at least 20 residues from amino acids 266-288 of SEQ ID NO: 66; at least 15 residues from amino acids 266-288 of SEQ ID NO: 66, Or at least 10 residues from amino acids 266-288 of SEQ ID NO: 66. Further aspects of this embodiment may include an membrane anchoring domain comprising, e.g., at most 20 residues from amino acids 266-288 of SEQ ID NO: 66; at most 15 residues from amino acids 266-288 of SEQ ID NO: 66 or at most 10 residues from amino acids 266-288 of SEQ ID NO: 66. [098] In an aspect of this embodiment, a Clostridial toxin substrate comprises, in part, the membrane targeting domain of human Syntaxin-1A of SEQ ID NO: 66. In another aspect of this embodiment, a Clostridial toxin substrate comprises, in part, the membrane targeting domain compriing amino acids IMIIICCVILGIVIASTVGGIFA, which corresponds to residues 266-288 of SEQ ID NO: 66. In another aspect of this embodiment, a Clostridial toxin substrate comprises, in part, the membrane targeting domain of human Syntaxin-1 B1 of SEQ ID NO: 67. In another aspect of this embodiment, a Clostridial toxin substrate comprises, in part, the membrane targeting domain compriing amino acids IIIIICCVVLGVVLASSIGCTLGL, which corresponds to residues 265-288 of SEQ ID NO: 67. In another aspect of this embodiment, a Clostridial toxin substrate comprises, in part, the membrane targeting domain of human Syntaxin-1 B2 of SEQ ID NO: 68. In another aspect of this embodiment, a Clostridial toxin substrate comprises, in part, the membrane targeting domain compriing amino acids 42 of 168 WO 2008/036060 PCTIUS2006/012825 IMIIICCVVLGVVLASSIGGTLGL, which corresponds to residues 265-288 of SEQ ID NO: 67. In another aspect of this embodiment, a Clostridial toxin substrate comprises, in part, the membrane targeting domain of human Syntaxin-2-1 of SEQ ID NO: 69. In another aspect of this embodiment, a Clostridial toxin substrate comprises, in part, the membrane targeting domain compriing amino acids LMFIIICVIVLLVILGIILATTLS, which corresponds to residues 264-287 of SEQ ID NO: 69. In another aspect of this embodiment, a Clostridial toxin substrate comprises, in part, the membrane targeting domain of human Syntaxin-2-2 of SEQ ID NO: 70. In another aspect of this embodiment, a Clostridial toxin substrate comprises, in part, the membrane targeting domain compriing amino acids WIIIAVSVVLVVIIVLIIGLSVGK, which corresponds to residues 264-288 of SEQ ID NO: 70. In another aspect of this embodiment, a Clostridial toxin substrate comprises, in part, the membrane targeting domain of human Syntaxin-2-3 of SEQ ID NO: 71. In another aspect of this embodiment, a Clostridial toxin substrate comprises, in part, the membrane targeting domain compriing amino acids WIIIAVSVVLVAIIALIIGLSVGK, which corresponds to residues 264-288 of SEQ ID NO: 71. In another aspect of this embodiment, a Clostridial toxin substrate comprises, in part, the membrane targeting domain of human Syntaxin-3 of SEQ ID NO: 72. In another aspect of this embodiment, a Clostridial toxin substrate comprises, in part, the membrane targeting domain compriing amino acids LilllVLVVVLLGILALIIGISVGLN, which corresponds to residues 264-289 of SEQ ID NO: 72. [099] In another aspect of this embodiment, a Clostridial toxin substrate comprises, in part, the membrane targeting domain of cow Syntaxin-1A of SEQ ID NO: 73. In another aspect of this embodiment, a Clostridial toxin substrate comprises, in part, the membrane targeting domain compriing amino acids IMIVICCVVLGIVIASTFGGIFG, which corresponds to residues 266-288 of SEQ ID NO: 67. [0100] In an aspect of this embodiment, a Clostridial toxin substrate comprises, in part, the membrane targeting domain of rat Syntaxin-1A of SEQ ID NO: 75. In another aspect of this embodiment, a Clostridial toxin substrate comprises, in part, the membrane targeting domain compriing amino acids IMIIICCVILGIIIASTIGGIFG, which corresponds to residues 266-288 of SEQ ID NO: 75. In an aspect of this embodiment, a Clostridial toxin substrate comprises, in part, the membrane targeting domain of rat Syntaxin-1B2 of SEQ ID NO: 76. In another aspect of this embodiment, a Clostridial toxin substrate comprises, in part, the membrane targeting domain compriing amino acids IMIIICCVVLGVVLASSIGGTLGL, which corresponds to residues 265-288 of SEQ ID NO: 76. In an aspect of this embodiment, a Clostridial toxin substrate comprises, in part, the membrane targeting domain of rat Syntaxin-2 of SEQ ID NO: 80. In another aspect of this embodiment, a Clostridial toxin substrate comprises, in part, the membrane targeting domain compriing amino acids WIIAAVVVAVIAVLALIIGLSVGK, which corresponds to residues 267-290 of SEQ ID NO: 80. In an aspect of this embodiment, a Clostridial toxin substrate comprises, in part, the membrane targeting domain of mouse Syntaxin-2 of SEQ ID NO: 81. In another aspect of this embodiment, a Clostridial toxin substrate comprises, in part, the membrane targeting domain compriing amino acids WIIAAVAVAVIAVLALIIGLSVGK, which corresponds to residues 266-289 of SEQ ID NO: 81. In an aspect of this embodiment, a Clostridial toxin substrate comprises, in part, the membrane targeting domain of rat Syntaxin-3A of SEQ ID NO: 82. In another aspect of this embodiment, a Clostridial toxin substrate 43 of 168 WO 2008/036060 PCT/US2006/012825 comprises, in part, the membrane targeting domain compriing amino acids LilllVIVVVLLGILALIIGISVGLK, which corresponds to residues 264-289 of SEQ ID NO: 82. In an aspect of this embodiment, a Clostridial toxin substrate comprises, in part, the membrane targeting domain of mouse Syntaxin-3A of SEQ ID NO: 83. In another aspect of this embodiment, a Clostridial toxin substrate comprises, in part, the membrane targeting domain compriing amino acids LIIIIVVVVVLLGILALIIGLSVGLK, which corresponds to residues 264-289 of SEQ ID NO: 83. In an aspect of this embodiment, a Clostridial toxin substrate comprises, in part, the membrane targeting domain of mouse Syntaxin-3B of SEQ ID NO: 84. In another aspect of this embodiment, a Clostridial toxin substrate comprises, in part, the membrane targeting domain compriing amino acids IMIMICCIILAIILASTIG, which corresponds to residues 265-283 of SEQ ID NO: 84. In an aspect of this embodiment, a Clostridial toxin substrate comprises, in part, the membrane targeting domain of mouse Syntaxin-3C of SEQ ID NO: 85. In another aspect of this embodiment, a Clostridial toxin substrate comprises, in part, the membrane targeting domain compriing amino acids IMIMICCIILAIILASTIGGIFA, which corresponds to residues 247 269 of SEQ ID NO: 85. [0101] In an aspect of this embodiment, a Clostridial toxin substrate comprises, in part, the membrane targeting domain of chicken Syntaxin-1A of SEQ ID NO: 86. In another aspect of this embodiment, a Clostridial toxin substrate comprises, in part, the membrane targeting domain compriing amino acids IMIIIFVVVLGVVLSPVICGTLGL, which corresponds to residues 259-282 of SEQ ID NO: 86. In an aspect of this embodiment, a Clostridial toxin substrate comprises, in part, the membrane targeting domain of chicken Syntaxin-2 of SEQ ID NO: 87. In another aspect of this embodiment, a Clostridial toxin substrate comprises, in part, the membrane targeting domain compriing amino acids WIIIIVSLVLIAVIGIIIGLSVGIR, which corresponds to residues 263-288 of SEQ ID NO: 87. [0102] In an aspect of this embodiment, a Clostridial toxin substrate comprises, in part, the membrane targeting domain of zebrafish Syntaxin-1A of SEQ ID NO: 88. In another aspect of this embodiment, a Clostridial toxin substrate comprises, in part, the membrane targeting domain comparing amino acids IMIIICCVILGVVLRSSIGGTLGF, which corresponds to residues 265-288 of SEQ ID NO: 88. In an aspect of this embodiment, a Clostridial toxin substrate comprises, in part, the membrane targeting domain of zebrafish Syntaxin-3 of SEQ ID NO: 89. In another aspect of this embodiment, a Clostridial toxin substrate comprises, in part, the membrane targeting domain comparing amino acids IllliVSVVLVILAIIALIVGISVGLKR, which corresponds to residues 262-288 of SEQ ID NO: 89. [0103] In an aspect of this embodiment, a Clostridial toxin substrate comprises, in part, the membrane targeting domain of sea urchin Syntaxin-1A of SEQ ID NO: 90. In another aspect of this embodiment, a Clostridial toxin substrate comprises, in part, the membrane targeting domain compriing amino acids YIAICCGVALGILILVLIIVLA, which corresponds to residues 264-286 of SEQ ID NO: 90. [0104] in an aspect of this embodiment, a Clostridial toxin substrate comprises, in part, the membrane targeting domain of fruit fly Syntaxin-11A of SEQ ID NO: 91. In another aspect of this embodiment, a Clostridial toxin substrate comprises, in part, the membrane targeting domain comparing amino acids 44 of 168 WO 2008/036060 PCT/US2006/012825 IMILICLTVLGILAASYVSSYFM, which corresponds to residues 269-291 of SEQ ID NO: 91. [0105] In an aspect of this embodiment, a Clostridial toxin substrate comprises, in part, the membrane targeting domain of leech Syntaxin-1A of SEQ ID NO: 92. In another aspect of this embodiment, a Clostridial toxin substrate comprises, in part, the membrane targeting domain compriing amino acids IIILICVSVLILIVGGSLLGIFIP, which corresponds to residues 272-295 of SEQ ID NO: 92. [0106] In an aspect of this embodiment, a Clostridial toxin substrate comprises, in part, the membrane targeting domain of squid Syntaxin-1A of SEQ ID NO: 93. In another aspect of this embodiment, a Clostridial toxin substrate comprises, in part, the membrane targeting domain compriing amino acids IAILVCLVILVLVIVSTVGGVFGG, which corresponds to residues 269-292 of SEQ ID NO: 93. [0107] In an aspect of this embodiment, a Clostridial toxin substrate comprises, in part, the membrane targeting domain of snail Syntaxin-1A of SEQ ID NO: 94. In another aspect of this embodiment, a Clostridial toxin substrate comprises, in part, the membrane targeting domain compriing amino acids IMIIICVCVLIIILVGILGGTFG, which corresponds to residues 268-290 of SEQ ID NO: 94. [0108] In an aspect of this embodiment, a Clostridial toxin substrate comprises, in part, the membrane targeting domain of sea hare Syntaxin-1A of SEQ ID NO: 95. In another aspect of this embodiment, a Clostridial toxin substrate comprises, in part, the membrane targeting domain compriing amino acids IMILVCLAILIIILVGVIGGTLG, which corresponds to residues 268-290 of SEQ ID NO: 95. (0109] Clostridial toxin substrates disclosed in the present specification include, in part, a fluorescent member. As used herein, the term "fluorescent member" means any peptide that can either inherently absorbs light energy of a certain wavelength and emits light energy of a different wavelength or is part of a complex that absorbs light energy of a certain wavelength and emits light energy of a different wavelength. Non-limiting examples of a fluorescent member include fluorescent proteins and fluorophore binding proteins. [0110] Clostridial toxin substrates disclosed in the present specification include, in part, a fluorescent proetin. As used herein, the term "fluorescent protein" means a peptide which absorbs light energy of a certain wavelength and emits light energy of a different wavelength and encompass those which emit in a variety of spectra, including violet, blue, cyan, green, yellow, orange and red, see Table 9. It is envisioned that fluorescent proteins derived from any of a variety of species can be useful in aspects of the present invention including, but not limited to, Aequorea fluorescent proteins, Anemonia fluorescent proteins, Anthozoa fluorescent proteins, Discosoma fluorescent proteins, Entacmeae fluorescent proteins, Heteractis fluorescent proteins, Montastrea fluorescent proteins, Renilla fluorescent proteins, Zoanthus fluorescent proteins, and fluorescent proteins from other organisms. Fluorescent proteins useful in the invention encompass, without limitation, wild type fluorescent proteins, naturally occurring variants, and genetically engineered variants, produced, e.g., by random mutagenesis or rational designed, and active peptide fragments derived from an organism. Fluorescent proteins useful in aspects of the invention 45 of 168 WO 2008/036060 PCT/US2006/012825 include, e.g., those which have been genetically engineered for superior performance such as, without limitation, altered excitation or emission wavelengths; enhanced brightness, pH resistance, stability or speed of fluorescent protein formation; photoactivation; or reduced oligomerization or photobleaching, see, e.g., Brendan P. Cormack et al., FACS-optimized Mutants of the Green Fluorescent Protein (GFP), U.S. Patent No. 5,804,387 (Sep. 8, 1998); Roger Y. Tsien & Roger Heim, Modified Green Fluorescent Proteins, U.S. Patent No. 6,800,733 (Oct. 5, 2004); Roger Y. Tsien et al., Long Wavelength Engineered Fluorescent Proteins, U.S. Patent 6,780,975 (Aug. 24, 2004); and Roger Y. Tsien et al., Fluorescent Protein Sensors For Measuring the pH of a Biological Sample, U.S. Patent 6,627,449 (Sep. 30, 2003). It is understood that a fluorescent protein can be engineered for improved protein expression by converting wild type codons to other codons more efficiently utilized in the cells which serve to express the Clostridial toxin substrate, see, e.g., Brian Seed & Jurgen Haas, High Level Expression of Proteins, U.S. Patent No. 5,795,737 (Aug. 18, 1998). [0111] It is also envisioned that any of a variety of active protein fragments can be useful in aspects of the present invention with the proviso that these active fragments retain the ability to emit light energy in a range suitable for the proper operation of aspects of the present invention, such as, e.g. 420-460 nm for blue emitting fluorescent proteins, 460-500 nm for cyan emitting fluorescent proteins, 500-520 nm for green emitting fluorescent proteins, 520-550 nm for yellow emitting fluorescent proteins and for 550-740 nm for red emitting fluorescent proteins. Thus, aspects of this embodiment can include active fragments of fluorescent proteins that retain the ability to emit light energy in a range suitable for the proper operation of aspects of the present invention having a length of, e.g., at least 50 amino acids, at least 60 amino acids, at least 70 amino acids, at least 80 amino acids, at least 90 amino acids, at least 100 amino acids, at least 125 amino acids, at least 150 amino acids, at least 175 amino acids and at least 200 amino acids. Other aspects of this embodiment, can include active fragments of fluorescent proteins that retain the ability to emit light energy in a range suitable for the proper operation of aspects of the present invention having a length of, e.g., at most 50 amino acids, at most 60 amino acids, at most 70 amino acids, at most 80 amino acids, at most 90 amino acids, at most 100 amino acids, at most 125 amino acids, at most 150 amino acids, at most 175 amino acids and at most 200 amino acids. [0112] Non-limiting examples of fluorescent proteins that may be operably-linked to a CoNT substrate disclosed in the specification include, e.g., photoproteins, such as, e.g., aequorin; obelin; Aequorea fluorescent proteins, such, e.g., green fluorescent proteins (GFP, EGFP, AcGFP1), cyan fluorescent proteins (CFP, ECFP), blue fluorescent proteins (BFP, EBFP), red fluorescent proteins (RFP), yellow fluorescent proteins (YFP, EYFP), ultraviolet fluorescent protein (GFPuv), their fluorescence enhancement variants, their peptide destabilization variants, and the like; coral reef fluorescent proteins, such, e.g., Discosoma red fluorescent proteins (DsRed, DsRedl, DsRed2, and DsRed-Express), Anemonia red fluorescent proteins (AsRed and AsRed2), Heteractis far-red fluorescent proteins (HcRed, HcRedl), Anemonia cyan fluorescent proteins (AmCyan, AmCyanl), Zoanthus green fluorescent proteins (ZsGreen, ZsGreenl), Zoanthus yellow fluorescent proteins (ZsYellow, ZsYellowl), their fluorescence enhancement variants, their peptide destabilization variants, and the like; Renilla reniformis green fluorescent protein (Vitality hrGFP), its fluorescence-enhancement variants, its peptide destabilization 46 of 168 WO 2008/036060 PCT/US2006/012825 variants, and the like; and Great Star Coral fluorescent proteins, such, e.g., Montastrea cavemosa fluorescent protein (Monster Greene Fluorescent Protein), its fluorescence-enhancement variants, its peptide destabilization variants, and the like. One skilled in the art understands that these and a variety of other fluorescent proteins can be useful as a fluorescent protein in aspects of the invention, see, e.g., Jennifer Lippincott-Schwartz & George H. Patterson, Development and Use of Fluorescent Protein Markers in Living Cells, 300(5616) Science 87-91 (2003); and Jin Zhang et al., 3(12) Nat. Rev. Mol. Cell Biol. 906-918 (2002). One skilled in the art understands that these and many other fluorescent proteins, including species orthologs and paralogs of the above described naturally occurring fluorescent proteins as well as engineered fluorescent proteins can be useful as a fluorescent protein disclosed in aspects of the present specification. CoNT substrates disclosed in the present specification containing, in part, such fluorescent proteins can be prepared and expressed using standard methods see, e.g., Living Colors* User Manual PT2040-1 (PRI1Y691), BD Biosciences-Clontech, (Nov. 26 2001); BD Living ColorsTM User Manual Volume 11: Reef Coral Fluorescent Proteins, PT3404-1 (PR37085), BD Biosciences-Clontech, (Jul. 17, 2003); Monster Green Florescent Protein pHMCFP Vector, TB320, Promega Corp., (May, 2004); and Vitality hrGFP Mammalian Expression Vectors, Instruction Manual (rev. 064007g), Stratagene, Inc.. Expression vectors suitable for bacterial, mammalian and other expression of fluorescent proteins are available from a variety of commercial sources including BD Biosciences Clontech (Palo Alto, CA); Promega Corp. (Madison, WI) and Stratagene, Inc. (La Jolla, CA). (0113] In an embodiment, the fluorescent protein is a green fluorescent protein. As used herein, the term "green fluorescent protein" is synonymous with "GFP" and means a protein which absorbs light of a certain wavelength and emits peak light energy of wavelengths in the range of 500-520 nm. Green fluorescent proteins useful in the invention include, without limitation, the AcGFP1 of SEQ ID NO: 143, genetically engineered AcGFP1 variants and active AcGFP1 fragments thereof that retain the ability to emit peak light energy in the range of 500-520 nm, the ZsGreen of SEQ ID NO: 144, genetically engineered ZsGreen variants and active ZsGreen fragments thereof that retain the ability to emit peak light energy in the range of 500-520 nm, the EGFP of SEQ ID NO: 145, genetically engineered ECFP variants and active ECFP fragments thereof that retain the ability to emit peak light energy in the range of 500-520 nm, the Monster Green Fluorescent Protein (MGFP) of SEQ ID NO: 146, genetically engineered MGFP variants and active MGFP fragments thereof that retain the ability to emit peak light energy in the range of 500-520 nm, the Vitality* hrGFP of SEQ ID NO: 147, genetically engineered hrGFP variants and active hrGFP fragments thereof that retain the ability to emit peak light energy in the range of 500-520 nm, as well as, naturally-occurring GFPs, naturally occurring GFP variants, genetically engineered GFP variants and active GFP fragments thereof that retain the ability to emit peak light energy in the range of 500-520 nm. As non-limiting examples, Reni//a-derived fluorescent proteins such as, e.g., the dimeric Renilla mulled GFP, which has narrow excitation (498 nm) and emission (509 nm) peaks, see, e.g., Beau Peelle et al., Characterization and use of green fluorescent proteins from Renilla muller and Ptilosarcus guemyi for the human cell display of functional peptides, 20(6) J. Protein Chem. 507-519 (2001); and Aequorea-derived fluorescent proteins as described in, e.g., Roger Y. Tsien & Roger Heim, Modified Green Fluorescent Proteins, U.S. Patent Nos. 5,625,048 (Apr. 29, 1997), 6,319,669 (Nov. 20, 2001), 6,066,476 (May 23, 2000) and 6,800,733 (Oct. 5, 2004). 47 of 168 WO 2008/036060 PCT/US2006/012825 [0114] Thus, in aspects of this embodiment, the fluorescent protein can be a GFP that emits peak s light in the range of 500-520 nm which has, e.g., at least 70% amino acid Identity with the AcGFP1 of SEQ ID NO: 143, at least 75% amino acid identity with the AcGFP1 of SEQ ID NO: 143, at least 80% amino acid identity with the AcGFP1 of SEQ ID NO: 143, at least 85% amino acid identity with the AcGFP1 of SEQ ID NO: 143, at least 90% amino acid identity with the AcGFP1 of SEQ ID NO: 143 or at least 95% amino acid Identity with the AcGFP1 of SEQ ID NO: 143. In other aspects of this embodiment, the fluorescent protein is a GFP that emits light in the range of 500-520 nm which has, e.g., at most one, two, three, four, five, six, seven, eight, nine, or ten amino acid substitutions relative to the AcGFP1 of SEQ ID NO: 143. [0115] In other aspects of this embodiment, the fluorescent protein can be a GFP that emits light in the range of 500-520 nm which has, e.g., at least 70% amino acid identity with the ZsGreen of SEQ ID NO: 144, at least 75% amino acid identity with the ZsGreen of SEQ ID NO: 144, at least 80% amino acid identity with the ZsGreen of SEQ ID NO: 144, at least 85% amino acid identity with the ZsGreen of SEQ ID NO: 144, at least 90% amino acid identity with the ZsGreen of SEQ ID NO: 144 or at least 95% amino acid Identity with the ZsGreen of SEQ ID NO: 144. In still other aspects of this embodiment, the fluorescent protein is a GFP that emits light in the range of 500-520 nm which has, e.g., at most one, two, three, four, five, six, seven, eight, nine, or ten amino acid substitutions relative to the ZsGreen of SEQ ID NO: 144. [0116] In other aspects of this embodiment, the fluorescent protein can be a GFP that emits light in the range of 500-520 nm which has, e.g., at least 70% amino acid identity with the EGFP of SEQ ID NO: 145, at least 75% amino acid identity with the EGFP of SEQ ID NO: 145, at least 80% amino acid identity with the EGFP of SEQ ID NO: 145, at least 85% amino acid identity with the EGFP of SEQ ID NO: 145, at least 90% amino acid identity with the EGFP of SEQ ID NO: 145 or at least 95% amino acid identity with the EGFP of SEQ ID NO: 145. In still other aspects of this embodiment, the fluorescent protein is a GFP that emits light in the range of 500-520 nm which has, e.g., at most one, two, three, four, five, six, seven, eight, nine, or ten amino acid substitutions relative to the EGFP of SEQ ID NO: 145. [0117] In other aspects of this embodiment, the fluorescent protein can be a GFP that emits light In the range of 500-520 nm which has, e.g., at least 70% amino acid identity with the MGFP of SEQ ID NO: 146, at least 75% amino acid identity with the MGFP of SEQ ID NO: 146, at least 80% amino acid identity with the MGFP of SEQ ID NO: 146, at least 85% amino acid identity with the MGFP of SEQ ID NO: 146, at least 90% amino acid identity with the MGFP of SEQ ID NO: 146 or at least 95% amino acid identity with the MGFP of SEQ ID NO: 146. In still other aspects of this embodiment, the fluorescent protein is a GFP that emits light in the range of 500-520 nm which has, e.g., at most one, two, three, four, five, six, seven, eight, nine, or ten amino acid substitutions relative to the MGFP of SEQ ID NO: 146. [0118] In other aspects of this embodiment, the fluorescent protein can be a GFP that emits light in the range of 500-520 nm which has, e.g., at least 70% amino acid identity with the hrGFP of SEQ ID NO: 147, at least 75% amino acid identity with the hrGFP of SEQ ID NO: 147, at least 80% amino acid identity 48 of 168 WO 2008/036060 PCTIUS2006/012825 with the hrGFP of SEQ ID NO: 147, at least 85% amino acid identity with the hrGFP of SEQ ID NO: 147, at least 90% amino acid identity with the hrGFP of SEQ ID NO: 147 or at least 95% amino acid identity with the hrGFP of SEQ ID NO: 147. In still other aspects of this embodiment, the fluorescent protein is a GFP that emits light in the range of 500-520 nm which has, e.g., at most one, two, three, four, five, six, seven, eight, nine, or ten amino acid substitutions relative to the hrGFP of SEQ ID NO: 147. [0119] In another embodiment, the fluorescent protein is a cyan fluorescent protein. As used herein, the term "cyan fluorescent protein" is synonymous with "CFP" and means a protein which absorbs light of a certain wavelength and emit peak light energy of wavelengths in the range of 460-500 nm. Cyan fluorescent proteins useful In the invention include, without limitation, the ECFP of SEQ ID NO: 148, genetically engineered ECFP variants and active ECFP fragments thereof that retain the ability to emit peak light energy in the range of 460-500 nm, the AmCyan of SEQ ID NO: 149, genetically engineered AmCyan variants and active AmCyan fragments thereof that retain the ability to emit peak light energy in the range of 460-500 nm, as well as, naturally-occurring cyan fluorescent proteins, naturally occurring CFP variants, genetically engineered CFP variants and active CFP fragments thereof that retain the ability to emit peak light energy in the range of 460-500 nm. As a non-limiting example, the CFP variant known as "CGFP" contains a Thr203Tyr substitution that changes the excitation and emission wavelengths of the ECFP of SEQ ID NO: 148 to a range between CFP and EGFP; and Aequorea-derived fluorescent proteins as described in, e.g., Roger Y. Tsien & Roger Heim, Modified Green Fluorescent Proteins, U.S. Patent Nos. 5,625,048 (Apr. 29, 1997), 6,319,669 (Nov. 20, 2001), 6,066,476 (May 23, 2000) and 6,800,733 (Oct. 5, 2004). [0120] Thus, in aspects of this embodiment, the fluorescent protein is a CFP that emits light in the range of 460-500 nm which has, e.g., at least 70% amino acid identity with the ECFP of SEQ ID NO: 148, at least 75% amino acid identity with the ECFP of SEQ ID NO: 148, at least 80% amino acid identity with the ECFP of SEQ ID NO: 148, at least 85% amino acid identity with the ECFP of SEQ ID NO: 148, at least 90% amino acid identity with the ECFP of SEQ ID NO: 148 or at least 95% amino acid Identity with the ECFP of SEQ ID NO: 148. In other aspects of this embodiment, the fluorescent protein is a CFP that emits light in the range of 460-500 nm which has, e.g., at most one, two, three, four, five, six, seven, eight, nine, or ten amino acid substitutions relative to the ECFP of SEQ ID NO: 148. [0121] In other aspects of this embodiment, the fluorescent protein is a CFP that emits light in the range of 460-500 nm which has, e.g., at least 70% amino acid identity with the AmCyan of SEQ ID NO: 149, at least 75% amino acid identity with the AmCyan of SEQ ID NO: 149, at least 80% amino acid Identity with the AmCyan of SEQ ID NO: 149, at least 85% amino acid identity with the AmCyan of SEQ ID NO: 149, at least 90% amino acid identity with the AmCyan of SEQ ID NO: 149 or at least 95% amino acid identity with the AmCyan of SEQ ID NO: 149. In still other aspects of this embodiment, the fluorescent protein Is a CFP that emits light in the range of 460-500 nm which has, e.g., at most one, two, three, four, five, six, seven, eight, nine, or ten amino acid substitutions relative to the AmCyan of SEQ ID NO: 149. [01221 In yet another embodiment, the fluorescent protein is a blue fluorescent protein. As used herein, 49 of 168 WO 2008/036060 PCTIUS2006/012825 the term "blue fluorescent protein" is synonymous with "BFP" and means a protein which absorbs light of a certain wavelength and emit peak light energy of wavelengths in the range of 420-460 nm. Blue fluorescent proteins useful In the invention include, without limitation, the EBFP of SEQ ID NO: 150, genetically engineered EBFP variants and active EBFP fragments thereof that retain the ability to emit peak light energy in the range of 420-460 nm, as well as, naturally-occurring blue fluorescent proteins, naturally occurring BFP variants, genetically engineered BFP variants and active BFP fragments thereof that retain the ability to emit peak light energy in the range of 420-460 nm. As non-limiting examples, see Aequorea-derived fluorescent proteins as described In, e.g., Roger Y. Tsien & Roger Heim, Modified Green Fluorescent Proteins, U.S. Patent Nos. 5,625,048 (Apr. 29, 1997), 6,319,669 (Nov. 20, 2001), 6,066,476 (May 23, 2000) and 6,800,733 (Oct. 5, 2004). [01231 Thus, in aspects of this embodiment, the fluorescent protein is a BFP that emits light in the range of 420-460 nm which has, e.g., at least 70% amino acid identity with the EBFP of SEQ ID NO: 150, at least 75% amino acid identity with the EBFP of SEQ ID NO: 150, at least 80% amino acid identity with the EBFP of SEQ ID NO: 150, at least 85% amino acid identity with the EBFP of SEQ ID NO: 150, at least 90% amino acid identity with the EBFP of SEQ ID NO: 150 or at least 95% amino acid identity with the EBFP of SEQ ID NO: 150. In other aspects of this embodiment, the fluorescent protein is a BFP that emits light in the range of 420-460 nm which has, e.g., at most one, two, three, four, five, six, seven, eight, nine, or ten amino acid substitutions relative to the EBFP of SEQ ID NO: 150. [0124] In yet another embodiment, the fluorescent protein is a yellow fluorescent protein. As used herein, the term "yellow fluorescent protein" is synonymous with "YFP" and means a protein which absorbs light of a certain wavelength and emit peak light energy of wavelengths in the range of 520-550 nm. Yellow fluorescent proteins useful in the invention include, without limitation, the EYFP of SEQ ID NO: 151, genetically engineered EYFP variants and active EYFP fragments thereof that retain the ability to emit peak light energy in the range of 520-550 nm, the ZsYellow of SEQ ID NO: 152, genetically engineered ZsYellow variants and active ZsYellow fragments thereof that retain the ability to emit peak light energy in the range of 520-550 nm, as well as, naturally-occurring YFPs, naturally occurring YFP variants, genetically engineered YFP variants and active YFP fragments thereof that retain the ability to emit peak light energy in the range of 520-550 nm. As non-limiting examples, the YFP variants "Citrine," which contain Val68Leu and Gln69Met substitutions in the YFP of SEQ ID NO: 151, and "Venus," which contain Phe46Leu, Met153Thr, Val163Ala and Ser175Gly substitutions in the YFP of SEQ ID NO: 151, are extremely bright and fast-maturing YFPs, see, e.g., Oliver Griesbeck et al., Reducing the environmental sensitivity of yellow fluorescent protein. Mechanism and applications, 276(31) J. Biol. Chem. 29188-29194 (2001); and Takeharu Nagai et al., A variant of yellow fluorescent protein with fast and efficient maturation for cell-biological applications, 20(1) Nat. Blotechnol. 87-90 (2002); and Aequorea-derived fluorescent proteins as described in, e.g., Roger Y. Tsien et al., Long Wavelength Engineered Fluorescent Proteins, U.S. Patent Nos. 6,124,128 (Sep. 26, 2000), 6,054,321 (Apr. 25, 2000), 6,077,707 (Jun. 20, 2000), 6,403,374 (Jun. 11, 2002) and 6,780,975 (Aug. 24, 2004). [0125] Thus, in aspects of this embodiment, the fluorescent protein is a YFP that emits light in the range 50 of 168 WO 2008/036060 PCT/US2006/012825 of 520-550 nm which has, e.g., at least 70% amino acid identity with the YFP of SEQ ID NO: 151, at least 75% amino acid identity with the YFP of SEQ ID NO: 151, at least 80% amino acid identity with the YFP of SEQ ID NO: 151, at least 85% amino acid identity with the YFP of SEQ ID NO: 151, at least 90% amino acid identity with the YFP of SEQ ID NO: 151 or at least 95% amino acid identity with the YFP of SEQ ID NO: 151. In other aspects of this embodiment, the fluorescent protein is a YFP that emits light in the range of 520-550 nm which has, e.g., at most one, two, three, four, five, six, seven, eight, nine, or ten amino acid substitutions relative to the YFP of SEQ ID NO: 151. [0126] In other aspects of this embodiment, the fluorescent protein is a YFP that emits light in the range of 520-550 nm which has, e.g., at least 70% amino acid identity with the ZsYellow of SEQ ID NO: 152, at least 75% amino acid Identity with the ZsYellow of SEQ ID NO: 152, at least 80% amino acid identity with the ZsYellow of SEQ ID NO: 152, at least 85% amino acid identity with the ZsYellow of SEQ ID NO: 152, at least 900/ amino acid identity with the ZsYellow of SEQ ID NO: 152 or at least 95% amino acid identity with the ZsYellow of SEQ ID NO: 152. In still other aspects of this embodiment, the fluorescent protein is a YFP that emits light In the range of 520-550 nm which has, e.g., at most one, two, three, four, five, six, seven, eight, nine, or ten amino acid substitutions relative to the ZsYellow of SEQ ID NO: 152. [0127] In yet embodiment, the fluorescent protein is a red fluorescent protein. As used herein, the term "red fluorescent protein" is synonymous with "RFP" and means a protein which absorbs light of a certain wavelength and emit peak light energy of wavelengths in the range of 550-740 nm. Red fluorescent proteins useful in the invention include, without limitation, the Discosoma striate RFP DsRed of SEQ ID NO: 153, DsRedl of SEQ ID NO: 154, DsRed2 of SEQ ID NO: 155 and DsRed Express of SEQ ID NO: 156, genetically engineered DsRed, DsRedl, DsRed2 and DsRed Express variants and active DsRed, DsRedl, DsRed2 and DsRed Express fragments thereof that retain the ability to emit peak light energy in the range of 550-740 nm; the Heteractis crispa RFP HcRed of SEQ ID NO: 157, genetically engineered HcRed variants and active HcRed fragments thereof that retain the ability to emit peak light energy in the range of 550-740 nm; the Anemonia sulcata RFP AsRed of SEQ ID NO: 158, genetically engineered AsRed variants and active AsRed fragments thereof that retain the ability to emit peak light energy in the range of 550-740 nm, as well as, naturally-occurring RFPs, naturally occurring RFP variants, genetically engineered RFP variants and active RFP fragments thereof that retain the ability to emit peak light energy in the range of 550-740 nm. As a non-limiting example, Entacmeae quadricolor fluorescent proteins including red fluorescent proteins such as, e.g., eqFP61 1, see, e.g., J6rg Wiedenmann et al., A far-red fluorescent protein with fast maturation and reduced oligomerization tendency from Entacmaea quadricolor (Anthozoa, Actinaria), 99(18) Proc. Natl. Acad. Sci. U. S. A. 11646-11651 (2002). [0128] Thus, in aspects of this embodiment, the fluorescent protein can be a RFP that emits light in the range of 550-740 nm which has, e.g., at least 70% amino acid identity with the DsRed of SEQ ID NO: 153, at least 75% amino acid identity with the DsRed of SEQ ID NO: 153, at least 80% amino acid identity with the DsRed of SEQ ID NO: 153, at least 85% amino acid identity with the DsRed of SEQ ID NO: 153, at least 90% amino acid identity with the DsRed of SEQ ID NO: 153 or at least 95% amino acid identity with the DsRed of SEQ ID NO: 153. In other aspects of this embodiment, the fluorescent protein is a 51 of 168 WO 2008/036060 PCTIUS2006/012825 RFP that emits light in the range of 550-740 nm which has, e.g., at most one, two, three, four, five, six, seven, eight, nine, or ten amino acid substitutions relative to the DsRed of SEQ ID NO: 153. [0129] In other aspects of this embodiment, the fluorescent protein can be a RFP that emits light in the range of 550-740 nm which has, e.g., at least 70% amino acid identity with the DsRedi of SEQ ID NO: 154, at least 75% amino acid identity with the DsRed1 of SEQ ID NO: 154, at least 80% amino acid identity with the DsRed1 of SEQ ID NO: 154, at least 85% amino acid identity with the DsRedl of SEQ ID NO: 154, at least 90% amino acid identity with the DsRed1 of SEQ ID NO: 154 or at least 95% amino acid identity with the DsRedl of SEQ ID NO: 154. In still other aspects of this embodiment, the fluorescent protein is a RFP that emits light in the range of 550-740 nm which has, e.g., at most one, two, three, four, five, six, seven, eight, nine, or ten amino acid substitutions relative to the DsRedl of SEQ ID NO: 154. [0130] In other aspects of this embodiment, the fluorescent protein can be a RFP that emits light in the range of 550-740 nm which has, e.g., at least 70% amino acid identity with the DsRed2 of SEQ ID NO: 155, at least 75% amino acid identity with the DsRed2 of SEQ ID NO: 155, at least 80% amino acid identity with the DsRed2 of SEQ ID NO: 155, at least 85% amino acid identity with the DsRed2 of SEQ ID NO: 155, at least 90% amino acid identity with the DsRed2 of SEQ ID NO: 155 or at least 95% amino acid identity with the DsRed2 of SEQ ID NO: 155. In still other aspects of this embodiment, the fluorescent protein is a RFP that emits light in the range of 550-740 nm which has, e.g., at most one, two, three, four, five, six, seven, eight, nine, or ten amino acid substitutions relative to the DsRed2 of SEQ ID NO: 155. [0131] In other aspects of this embodiment, the fluorescent protein can be a RFP that emits light in the range of 550-740 nm which has, e.g., at least 70% amino acid identity with the DsRed2 of SEQ ID NO: 156, at least 75% amino acid identity with the DsRed Express of SEQ ID NO: 156, at least 80% amino acid identity with the DsRed Express of SEQ ID NO: 156, at least 85% amino acid identity with the DsRed Express of SEQ ID NO: 156, at least 90% amino acid identity with the DsRed Express of SEQ ID NO: 156 or at least 95% amino acid identity with the DsRed Express of SEQ ID NO: 156. In still other aspects of this embodiment, the fluorescent protein is a RFP that emits light in the range of 550-740 nm which has, e.g., at most one, two, three, four, five, six, seven, eight, nine, or ten amino acid substitutions relative to the DsRed Express of SEQ ID NO: 156. [0132] In other aspects of this embodiment, the fluorescent protein can be a RFP that emits light in the range of 550-740 nm which has, e.g., at least 70% amino acid identity with the AsRed of SEQ ID NO: 158, at least 75% amino acid identity with the AsRed of SEQ ID NO: 158, at least 80% amino acid identity with the AsRed of SEQ ID NO: 158, at least 85% amino acid identity with the AsRed of SEQ ID NO: 158, at least 90% amino acid identity with the AsRed of SEQ ID NO: 158 or at least 95% amino acid identity with the AsRed of SEQ ID NO: 158. In still other aspects of this embodiment, the fluorescent protein is a RFP that emits light in the range of 550-740 nm which has, e.g., at most one, two, three, four, five, six, seven, eight, nine, or ten amino acid substitutions relative to the AsRed of SEQ ID NO: 158. 52 of 168 WO 2008/036060 PCT/US2006/012825 [0133] In other aspects of this embodiment, the fluorescent protein can be a RFP that emits light in the range of 550-740 nm which has, e.g., at least 70% amino acid identity with the HcRed of SEQ ID NO: 157, at least 75% amino acid identity with the HcRed of SEQ ID NO: 157, at least 80% amino acid identity with the HcRed of SEQ ID NO: 157, at least 85% amino acid identity with the HcRed of SEQ ID NO: 157, at least 90% amino acid Identity with the HcRed of SEQ ID NO: 157 or at least 95% amino acid identity with the HcRed of SEQ ID NO: 157. In still other aspects of this embodiment, the fluorescent protein is a RFP that emits light in the range of 550-740 nm which has, e.g., at most one, two, three, four, five, six, seven, eight, nine, or ten amino acid substitutions relative to the HcRed of SEQ ID NO: 157. EB3FP 380 440 ECFP 439 476 AmCyan 458 489 AcGFP 475 505 ZsGreen 493 505 Vitality hrGFP 500 506 EGFP 484 510 Monster Green* 505 515 EYFP 512 529 ZsYellow 529 539 DsRed-Express 557 579 DsRed2 563 582 DsRed 558 583 AsRed2 576 592 HcRedl 588 618 [0134] Clostridial toxin substrates disclosed in the present specification include, in part, a fluorophore binding protein. As used herein, the term "fluorophore binding protein" means a peptide that can covalently or non-covalently associate with a fluorophore. A fluorophore binding protein can establish a covalent bond, or strong non-covalent interaction, with a fluorophore in a selective chemical or biochemical reaction. Nonlimitng examples of such fluorophore binding proteins and corresponding fluorophores include the bis-arsenical tetracysteine system, see, e.g., B. Albert Griffin et al., Specific covalent labeling of recombinant protein molecules inside live cells, 281(5374) Science 269-272 (1998); and B. Albert Griffin et al., Fluorescent labeling of recombinant proteins in living cells with FlAsH, 327 Methods Enzymol. 565-578 (2000); the alkylguanine-DNA-alkyltransferase (AGT) system, see. e.g., Antje Keppler et al, A General Method for the Covalant Labeling of Fusion proteins with Small Molecules in vivo, 21(1) Nat. Biotech 86-89 (2003); Antje Keppler et al, Labeling of fusion proteins of 06-alkylguanine DNA alkyltransferase with small molecules in vivo and in vitro, 32(4) Methods 437-444 (2004); and Antje Keppler et al, Labeling of Fusion Proteins with Synthetic Fluorophores in Live Cells, 101(27) Proc. NatI. Acad. Sci. USA 9955-9959 (2004); and the dehalogenase system. In addition, non-limiting examples of 53 of 168 WO 2008/036060 PCT/US2006/012825 fluorophore binding proteins and corresponding fluorophores, as well as well-characterized reagents, conditions and protocols are readily available from commercial vendors that include, without limitation, TC-FIAsH" TC-ReAsHTO In-Cell Tetracysteine Tag Detection Kit (Invitrogin Corp., Carlsbad, CA); SNAP tagTm multi-purpose protein tag system (Covalys Biosciences AG, Switzerland); and HaloTagrm Interchangeable Labeling Technology (Promega Corp., Madison WI). These protocols are routine procedures well within the scope of one skilled in the art and from the teaching herein. ReAsH resorufin arsenical hairpin binding dye 593____________ 608_______ . AGT/SNAP-Tag System BG-430 para-benzyl guanine 421 444 and 484 _____________diethylaminocoumarin___________ BG-DAF para-benzyl guanine diacetylfluorescein 500 524 BG-505 para-benzyl guanine dyomic DY-505-05 504 . 532 BG-488 para-benzyl guanine ATTO 488 506 526 BG-532 para-benzyl guanine ATTO 532 536 554 BG-547 para-benzyl guanine dyomic DY-547 554 568 TMR-Star para-benzyl guanine 554 580 _____________tetramethylrhodamine___________ BG-600 para-benzyl guanine ATTO 600 606 626 BG-632 para-benzyl guanine dyomic DY-632 636 656 BG-647 para-benzyl guanine dyomic DY-647 660 673 BG-732 para-benzyl guanine dyomic DY-732 732 747 BG-747 para-benzyl guanine dyomic DY-747 752 763 Dehalogenase/HaloTagT" System HaloTag Coumarian derivative 353 434 Coumarian HaloTag nonfluorescent diacetyl fluorescein 494 526 diAcFAM derivative HaloTag TMR tetramethyl rhodamine derivative 555 585 [0135] The bis-arsenical tetracysteine system comprises a fusion protein including the protein of interest and a tetracysteine hexapeptide comprising the amino acid sequence C-C-X-X-C-C (SEQ ID NO: 182) and a bis-arsenical fluorophore complexed with two dithiol residues. In the labeling reaction, the tetracysteine peptide displaces the dithiols from the arsenic residues of the fluorophore. This interaction strongly couples the fluorophore with the fluorophore binding protein and significantly Increases the signal by reducing the quenching of the fluorophore. Nonlimiting examples of bis-arsenical fluorophores include nonfluorescent biarsenical derivitives of fluorescein, such as, e.g., FlAsH and nonfluorescent blarsenical derivitives of resorufin, such as, e.g., ReAsH. [0136] The AGT system comprises a fusion protein including the protein of interest and a modified AGT 22 kDa polypeptide (SEQ ID NO: 183) and a benzyl guanine modified in the para-position by a 54 of 168 WO 2008/036060 PCT/US2006/012825 fluorescent label. In the labeling reaction, the 06-position of the para-substituted benzyl guanine irreversibly binds to a reactive csyteine in the active center of AGT. Nonlimiting examples of modifed benzylguanine fluorophores listed in Table 10. [0137] The dehalogenase system comprises a fusion protein including the protein of interest and a modified dehalogenase and a modified fluorophore comprising an alkyl residue. In the labeling reaction, the modified fluorophore strongly interacts with the active site of the modified dehalogenase. The modified dehalogenase is a 33 kDa polypeptide (SEQ ID NO: 184) comprising a mutation in the active center that significantly slows the catalytic activity of the enzyme, effectively creating an irreversible interaction. Nonlimiting examples of modifed benzylguanine fluorophores listed in Table 10. [0138] Thus, in an embodiment, a fluorophore binding protein is a tetracysteine peptide which strongly interacts with a fluorophore. In an aspect of this embodiment, the fluorophore binding protein is a tetracysteine peptide comprises SEQ ID NO: 182 which strongly interacts with a fluorophore. In another aspect of this embodiment, the fluorophore binding protein is a tetracysteine peptide that strongly interacts with a nonfluorescent biarsenical derivitives of fluorescein. In another aspect of this embodiment, the fluorophore binding protein is a tetracysteine peptide that strongly interacts with a nonfluorescent biarsenical derivitives of resorufin. [0139] Thus, in an embodiment, a fluorophore binding protein is an AGT polypeptide which strongly interacts with a fluorophore. In an aspect of this embodiment, the fluorophore binding protein is an AGT which strongly interacts with a fluorophore comprises SEQ ID NO: 183. In other aspects of this embodiment, the fluorophore binding protein can be a AGT which strongly interacts with a fluorophore that has, e.g., at least 70% amino acid identity with the AGT of SEQ ID NO: 183, at least 75% amino acid identity with the AGT of SEQ ID NO: 183, at least 80% amino acid identity with the AGT of SEQ ID NO: 183, at least 85% amino acid identity with the AGT of SEQ ID NO: 183, at least 90% amino acid identity with the AGT of SEQ ID NO: 183 or at least 95% amino acid identity with the AGT of SEQ ID NO: 183. In still other aspects of this embodiment, the fluorophore binding protein is a AGT which strongly interacts with a fluorophore that has, e.g., at most one, two, three, four, five, six, seven, eight, nine, or ten amino acid substitutions relative to the AGT of SEQ ID NO: 183. In other aspects of this embodiment, the fluorophore binding protein is an AGT that strongly interacts with a para-substituted benzyl guanine derivitive comprising a diethylaminocoumarin, a diacetylfluorescein, a dyomic DY-505-05, an ATTO 488, an ATTO 532, a DY-547, a tetramethylrhodamine, an ATTO 600, a dyomic DY-632, a dyomic DY-647, a dyomic DY-732 or a dyomic DY-747. [0140] Thus, In an embodiment, a fluorophore binding protein is a dehalogenase polypeptide which strongly interacts with a fluorophore. In an aspect of this embodiment, the fluorophore binding protein is a dehalogenase which strongly interacts with a fluorophore comprises SEQ ID NO: 184. In other aspects of this embodiment, the fluorophore binding protein can be a dehalogenase which strongly interacts with a fluorophore that has, e.g., at least 70% amino acid identity with the dehalogenase of SEQ ID NO: 184, at least 75% amino acid identity with the dehalogenase of SEQ ID NO: 184, at least 80% amino acid identity 55 of 168 WO 2008/036060 PCT/US2006/012825 with the dehalogenase of SEQ ID NO: 184, at least 85% amino acid identity with the dehalogenase of SEQ ID NO: 184, at least 90% amino acid identity with the dehalogenase of SEQ ID NO: 184 or at least 95% amino acid identity with the dehalogenase of SEQ ID NO: 184. In still other aspects of this embodiment, the Iluorophore binding protein is a dehalogenase which strongly interacts with a fluorophore that has, e.g., at most one, two, three, four, five, six, seven, eight, nine, or ten amino acid substitutions relative to the dehalogenase of SEQ ID NO: 184. In other aspects of this embodiment, the fluorophore binding protein is an dehalogenase that strongly interacts with a coumarian derivitive such as HaloTag Coumarian, a fluorescein derivitive such as HaloTag diAcFAM or a tetramethyl rhodamine derivitive such as HaloTag TMR. [0141] It is understood that a Clostridial toxin substrate useful in the invention optionally can include one or more additional components. As a non-limiting example, a flexible spacer sequence such as GGGGS (SEQ ID NO: 159) can be included in a Clostridial toxin substrate useful in the invention. A useful Clostridial toxin substrate further can include, without limitation, one or more of the following: epitope binding tags, such as. e.g., FLAG, ExpressTM, human Influenza virus hemagluttinin (HA), human p62"'" protein (c-MYC), Vesicular Stomatitis Virus Glycoprotein (VSV-G), glycoprotein-D precursor of Herpes simplex virus (HSV), V5, and AU1; affinity-binding , such as. e.g., polyhistidine (HIS), streptavidin binding peptide (strep), and biotin or a biotinylation sequence; peptide-binding regions, such as. e.g., the glutathione binding domain of glutathione-S-transferase, the calmodulin binding domain of the calmodulin binding protein, and the maltose binding domain of the maltose binding protein; immunoglobulin hinge region; an N-hydroxysuccinimide linker; a peptide or peptidomimetic hairpin turn; or a hydrophilic sequence or another component or sequence that, for example, promotes the solubility or stability of the Clostridial toxin substrate. Non-limiting examples of specific protocols for selecting, making and using an appropriate binding peptide are described in, e.g., Epitope Tagging, pp. 17.90-17.93 (Sambrook and Russell, eds., Molecular Cloning A Laboratory Manual, Vol. 3, 3d ed. 2001); Antibodies: A Laboratory Manual (Edward Harlow & David Lane, eds., Cold Spring Harbor Laboratory Press, 2"d ed. 1998); and Using Antibodies: A Laboratory Manual: Portable Protocol No. I (Edward Harlow & David Lane, Cold Spring Harbor Laboratory Press, 1998), which are hereby incorporated by reference. In addition, non limiting examples of binding peptides as well as well-characterized reagents, conditions and protocols are readily available from commercial vendors that include, without limitation, BD Biosciences-Clontech, Palo Alto, CA; BD Biosciences Pharmingen, San Diego, CA; Invitrogen, Inc, Carlsbad, CA; QIAGEN, Inc., Valencia, CA; and Stratagene, La Jolla, CA. These protocols are routine procedures well within the scope of one skilled in the art and from the teaching herein. [0142] Aspects of the present invention provide compositions comprising a cell that contains an exogenous Clostridial toxin substrate capable of being localized to the plasma membrane of said cell wherein said cell is capable of Clostridial toxin intoxication, and wherein said substrate comprises a fluorescent member, a membrane targeting domain and a Clostridial toxin recognition sequence comprising a cleavage site, where the cleavage site intervenes between said fluorescent member and said membrane localization domain. 56 of 168 WO 2008/036060 PCT/US2006/012825 [0143] Other aspects of the present invention provide compositions comprising a cell that transiently contains an exogenous Clostridial toxin substrate capable of being localized to the plasma membrane of said cell wherein said cell is capable of Clostridial toxin intoxication, wherein said substrate comprises a fluorescent member, a membrane targeting domain and a Clostridial toxin recognition sequence comprising a cleavage site, where the cleavage site intervenes between said fluorescent member and said membrane localization domain. [0144] Other aspects of the present invention provide compositions comprising a cell that stably contains an exogenous Clostridial toxin substrate capable of being localized to the plasma membrane of said cell wherein said cell is capable of Clostridial toxin intoxication, and wherein said substrate comprises a fluorescent member, a membrane targeting domain and a Clostridial toxin recognition sequence comprising a cleavage site, where the cleavage site intervenes between said fluorescent member and said membrane localization domain. [0145] Yet other aspects of the present invention provide compositions comprising a cell population, the cell population comprising cells that contain an exogenous Clostridial toxin substrate capable of being localized to the plasma membrane of said cells wherein said cells are capable of Clostridial toxin intoxication, and wherein said substrate comprises a fluorescent member, a membrane targeting domain and a Clostridial toxin recognition sequence comprising a cleavage site, where the cleavage site intervenes between said fluorescent member and said membrane localization domain and wherein greater than 50% of said cell population comprises said cells containing said exogenous Clostridial toxin substrate. [0146] Yet other aspects of the present invention provide compositions comprising a cell population, the cell population comprising cells that transiently contain an exogenous Clostridial toxin substrate capable of being localized to the plasma membrane of said cells wherein said cells are capable of Clostridial toxin intoxication, wherein said substrate comprises a fluorescent member, a membrane targeting domain and a Clostridial toxin recognition sequence comprising a cleavage site, where the cleavage site intervenes between said fluorescent member and said membrane localization domain and wherein greater than 50% of said cell population comprises said cells containing said exogenous Clostridial toxin substrate. [0147] Yet other aspects of the present invention provide compositions comprising a cell population, said cell population comprising cells that stably contain an exogenous Clostridial toxin substrate capable of being localized to the plasma membrane of said cells wherein said cells are capable of Clostridial toxin intoxication, and wherein said substrate comprises a fluorescent member, a membrane targeting domain and a Clostridial toxin recognition sequence comprising a cleavage site, where the cleavage site intervenes between said fluorescent member and said membrane localization domain. [0148] The cell compositions disclosed in the present specification include, in part, a cell capable of Clostridial toxin intoxication. As used herein, the term "cell," means any eukaryotic cell that expresses, or can be engineered to express, at least one receptor that binds a Clostridial toxin. The term cell 57 of 168 WO 2008/036060 PCTIUS2006/012825 encompasses cells from a variety of organisms, such as, e.g., murine, rat, porcine, bovine, equine, primate and human cells; from a variety of cell types such as, e.g., neural and non-neural; and can be isolated from or part of a heterogeneous cell population, tissue or organism. It is understood that cells useful in aspects of the invention can included, without limitation, primary cells; cultured cells; established cells; normal cells; transformed cells; tumor cells; infected cells; proliferating and terminally differentiated cells; and stably or transiently transfected cells, including stably and transiently transfected cells. It is further understood that cells useful in aspects of the invention can be in any state such as proliferating or quiescent; intact or permeabilized such as through chemical-mediated transfection such as, e.g., calcium phosphate-mediated, diethy-laminoethyl (DEAE) dextran-mediated, lipid-mediated, polyethyleneimine (PEI)-mediated and polybrene-mediated; physical-mediated tranfection, such as, e.g., biolistic particle delivery, microinjection and electroporation; and viral-mediated transfection, such as, e.g., retroviral mediated transfection. It is further understood that cells useful in aspects of the invention may include those which express a Clostridial toxin substrate under control of a constitutive, tissue-specific, cell specific or inducible promoter element, enhancer element or both. It further is understood that cells useful in aspects of the invention may or may not express one or more endogenous Clostridial toxin target proteins such as, e.g., SNAP-25, VAMP and syntaxin. (0149] As used herein, the term "cell capable of Clostridial toxin intoxication" means a cell that can enable the overall cellular mechanism whereby a Clostridial toxin proteolytically cleaves a substrate and encompasses the binding of a Clostridial toxin to a low or high affinity receptor, the internalization of the toxin/receptor complex, the translocation of the Clostridial toxin light chain into the cytoplasm and the enzymatic target modification of a Clostridial toxin substrate. By definition, a cell capable of Clostridial toxin intoxication must express one or more endogenous low or high affinity Clostridial toxin receptors for one or more Clostridial toxin serotypes; express one or more exogenous low or high affinity Clostridial toxin receptors for one or more Clostridial toxin serotypes; or express a combination of endogenous low or high affinity Clostridial toxin receptors and exogenous low or high affinity Clostridial toxin receptors for one or more Clostridlal toxin serotypes. [0150] Thus, in an embodiment, a cell capable of Clostridial toxin intoxication can be a cell expressing a Clostridial toxin receptor. In aspects of this embodiment, the Clostridial toxin receptor can be a low affinity Clostridial toxin receptor, a high affinity Clostridial toxin receptor, an endogenous Clostridial toxin receptor, an exogenous Clostridial toxin receptor, or any combination thereof. In other aspects of this embodiment, the Clostridial toxin receptor can be a BoNT/A receptor, a BoNT/B receptor, a BoNT/Ci receptor, a BoNT/D receptor, a BoNT/E receptor, a BoNT/F receptor, a BoNT/G receptor or a TeNT receptor. [0151] In another embodiment, a cell capable of Clostridial toxin intoxication can be a cell expressing a plurality of Clostridial toxin receptors. In aspects of this embodiment, a plurality of Clostridial toxin receptor can comprise low affinity Clostridial toxin receptors, high affinity Clostridial toxin receptors, endogenous Clostridial toxin receptors, exogenous Clostridial toxin receptors, or any combination thereof. In aspects of this embodiment, a plurality of Clostridial toxin receptor can comprise, e.g., two or more 58 of 168 WO 2008/036060 PCTIUS2006/012825 Clostridial toxin receptors, three or more Clostridial toxin receptors, four or more Clostridial toxin receptors, five or more Clostridial toxin receptors, six or more Clostridial toxin receptors, seven or more Clostridial toxin receptors and eight or more Clostridial toxin receptors. In other aspects of this embodiment, cell capable of Clostridial toxin intoxication can express two or more of the following receptors a BoNT/A receptor, a BoNT/B receptor, a BoNT/C1 receptor, a BoNT/D receptor, a BoNTE receptor, a BoNT/F receptor, a BoNT/G receptor or a TeNT receptor. In other aspects of this embodiment, cell capable of Clostridial toxin intoxication can express three or more of the following receptors a BoNT/A receptor, a BoNT/B receptor, a BoNT/C1 receptor, a BoNT/D receptor, a BoNT/E receptor, a BoNT/F receptor, a BoNT/G receptor or a TeNT receptor. In other aspects of this embodiment, cell capable of Clostridial toxin intoxication can express four or more of the following receptors a BoNT/A receptor, a BoNT/B receptor, a BoNT/C1 receptor, a BoNT/D receptor, a BoNT/E receptor, a BoNT/F receptor, a BoNT/G receptor or a TeNT receptor. In other aspects of this embodiment, cell capable of Clostridial toxin intoxication can express five or more of the following receptors a BoNT/A receptor, a BoNT/B receptor, a BoNT/C1 receptor, a BoNT/D receptor, a BoNT/E receptor, a BoNT/F receptor, a BoNT/G receptor or a TeNT receptor. In other aspects of this embodiment, cell capable of Clostridial toxin intoxication can express six or more of the following receptors a BoNT/A receptor, a BoNT/B receptor, a BoNT/Cl receptor, a BoNT/D receptor, a BoNT/E receptor, a BoNT/F receptor, a BoNT/G receptor or a TeNT receptor. In other aspects of this embodiment, cell capable of Clostridial toxin intoxication can express seven or more of the following receptors a BoNT/A receptor, a BoNT/B receptor, a BoNT/C1 receptor, a BoNT/D receptor, a BoNT/E receptor, a BoNT/F receptor, a BoNT/G receptor or a TeNT receptor. [0152] Cells that express one or more endogenous or exogenous Clostridial toxin receptors can be identified by routine methods including direct and indirect assays for toxin uptake. Assays that determine Clostridial toxin binding or uptake properties can be used to assess whether a cell is expressing a Clostridial toxin receptor. Such assays include, without limitation, cross-linking assays using labeled Clostridial toxins, such as, e.g., [1251] BoNT/A, [1251 BoNT/B, [1211] BoNT/C1, [1251] BoNT/D, [1251] BoNT/E, [1251] BoNT/F, [1251] BoNT/G and [123 1] TeNT, see, e.g., Noriko Yokosawa et al., Binding of Clostridium botulinum type C neurotoxin to different neuroblastoma cell lines, 57(1) Infect. Immun. 272-277 (1989); Noriko Yokosawa et al., Binding of botulinum type Cl, D and E neurotoxins to neuronal cell lines and synaptosomes, 29(2) Toxicon 261-264 (1991); and Tei-ichi Nishiki et al., Identification of protein receptor for Clostridium botulinum type B neurotoxin in rat brain synaptosomes, 269(14) J. Biol. Chem. 10498 10503 (1994). Other non-limiting assays include immunocytochemical assays that detect toxin binding using labeled or unlabeled antibodies, see, e.g., Atsushi Nishikawa et al., The receptor and transporter for internalization of Clostridlum botulinum type C progenitor toxin into HT-29 cells, 319(2) Biochem. Biophys. Res. Commun. 327-333 (2004) and immunoprecipitation assays, see, e.g., Yukako Fujinaga et al., Molecular characterization of binding subcomponents of Clostridium botulinum type C progenitor toxin for intestinal epithelial cells and erythrocytes, 150(Pt 5) Microbiology 1529-1538 (2004), that detect bound toxin using labeled or unlabeled antibodies. Antibodies useful for these assays include, without limitation, antibodies selected against a Clostridial toxin, such as, e.g., BoNT/A, BoNT/B, BoNT/C1, BoNT/D, BoNT/E, BoNT/F, BoNT/G or TeNT , antibodies selected against a CoNT receptor, such as, e.g., FGFR3 59 of 168 WO 2008/036060 PCT/US2006/012825 or synaptotagmin, and/or antibodies selected against a ganglioside, such as, e.g., GD1a, GD1b, GD3, GQ1b, or GT1b. If the antibody is labeled, the binding of the molecule can be detected by various means, including Western blotting, direct microscopic observation of the cellular location of the antibody, measurement of cell or substrate-bound antibody following a wash step, or electrophoresis, employing techniques well-known to those of skill in the art. If the antibody is unlabeled, one may employ a labeled secondary antibody for indirect detection of the bound molecule, and detection can proceed as for a labeled antibody. It is understood that these and similar assays that determine Clostridial toxin uptake properties or characteristics can be useful in selecting a neuron or other cells useful in aspects of the invention. [01531 Assays that monitor the release of a molecule after exposure to a Clostridial toxin can also be used to assess whether a cell is expressing a Clostridial toxin receptor. In these assays, inhibition of the molecule's release would occur in cells expressing a Clostridial toxin receptor after Clostridial toxin treatment. Well known assays include methods that measure inhibition of radio-labeled catecholamine release from neurons, such as, e.g., [3H] noradrenaline or [H] dopamine release, see e.g., A Fassio et al., Evidence for calcium-dependent vesicular transmitter release insensitive to tetanus toxin and botulinum toxin type F, 90(3) Neuroscience 893-902 (1999); and Sara Stigliani et al., The sensitivity of catecholamine release to botulinum toxin C1 and E suggests selective targeting of vesicles set into the readily releasable pool, 85(2) J. Neurochem. 409-421 (2003), or measures catecholamine release using a fluorometric procedure, see, e.g., Anton de Paiva et al., A role for the interchain disulfide or its participating thiols in the internalization of botulinum neurotoxin A revealed by a toxin derivative that binds to ecto-acceptors and inhibits transmitter release intracellularly, 268(28) J. Biol. Chem. 20838-20844 (1993); Gary W. Lawrence et al., Distinct exocytotic responses of intact and permeabilised chromaffin cells after cleavage of the 25-kDa synaptosomal-associated protein (SNAP-25) or synaptobrevin by botulinum toxin A or B, 236(3) Eur. J. Biochem. 877-886 (1996); and Patrick Foran et al., Botulinum neurotoxin C1 cleaves both syntaxin and SNAP-25 in intact and permeabilized chromaffin cells: correlation with its blockade of catecholamine release, 35(8) Biochemistry 2630-2636 (1996). Other non limiting examples include assays that measure inhibition of hormone release from endocrine cells, such as, e.g., anterior pituitary cells or ovarian cells. It is understood that these and similar assays for molecule release can be useful in selecting a neuron or other cells useful in aspects of the invention. [0154] Assays that detect the cleavage of a Clostridial toxin substrate after exposure to a Clostridial toxin can also be used to assess whether a cell is expressing a Clostridial toxin receptor. In these assays, generation of a Clostridial toxin substrate cleavage-product would be detected in cells expressing a Clostridial toxin receptor after Clostridial toxin treatment. Non-limiting examples of specific Western blotting procedures, as well as well-characterized reagents, conditions and protocols are readily available from commercial vendors that include, without limitation, Amersham Biosciences, Piscataway, NJ; Bio Rad Laboratories, Hercules, CA; Pierce Biotechnology, Inc., Rockford, IL; Promega Corporation, Madison, WI, and Stratagene, Inc., La Jolla, CA. It is understood that these and similar assays for Clostridial toxin substrate cleavage can be useful in selecting a neuron or other cells useful in aspects of the invention. 60 of 168 WO 2008/036060 PCT/US2006/012825 [0155] As non-limiting examples, western blot analysis using an antibody that specifically recognizes BoNT/A SNAP-25-cleaved product can be used to assay for uptake of BoNT/A; western blot analysis using an antibody that specifically recognizes BoNT/C1 SNAP-25-cleaved product can be used to assay for uptake of BoNT/C1; and western blot analysis using an antibody that specifically recognizes a BoNT/E SNAP-25-cleaved product can be used to assay for uptake of BoNT/E. Examples of anti-SNAP-25 antibodies useful for these assays include, without limitation, rabbit polyclonal anti-SNAP251 97 antiserum pAb anti-SNAP25197 #1 (Allergan, Inc., Irvine, CA), mouse monoclonal anti-SNAP-25 antibody SMI-81 (Stemberger Monoclonals, Lutherville, MD), mouse monoclonal anti-SNAP-25 antibody Cl 71.1 (Synaptic Systems, Goettingen, Germany), mouse monoclonal anti-SNAP-25 antibody Cl 71.2 (Synaptic Systems, Goettingen, Germany), mouse monoclonal anti-SNAP-25 antibody SP12 (Abcam, Cambridge, MA), rabbit polyclonal anti-SNAP-25 antiserum (Synaptic Systems, Goettingen, Germany), and rabbit polyclonal anti SNAP-25 antiserum (Abcam, Cambridge, MA). [0156] As additional non-limiting examples, western blot analysis using an antibody that specifically recognizes a BoNT/B VAMP-cleaved product can be used to assay for uptake of BoNT/B; western blot analysis using an antibody that specifically recognizes BoNT/D VAMP-cleaved product can be used to assay for uptake of BoNT/D; western blot analysis using an antibody that specifically recognizes BoNT/F VAMP-cleaved product can be used to assay for uptake of BoNT/F; western blot analysis using an antibody that specifically recognizes BoNT/G VAMP-cleaved product can be used to assay for uptake of BoNT/G; and western blot analysis using an antibody that specifically recognizes TeNT. Examples of anti-VAMP antibodies useful for these assays include, without limitation, mouse monoclonal anti-VAMP-1 antibody Cl 10.1 (Synaptic Systems, Goettingen, Germany), mouse monoclonal anti-VAMP-1 antibody SP10 (Abcam, Cambridge, MA), mouse monoclonal anti-VAMP-1 antibody SP11 (Abcam, Cambridge, MA), rabbit polyclonal anti-VAMP-1 antiserum (Synaptic Systems, Goettingen, Germany), rabbit polyclonal anti-VAMP-1 antiserum (Abcam, Cambridge, MA), mouse monoclonal anti-VAMP-2 antibody Cl 69.1 (Synaptic Systems, Goettingen, Germany), rabbit polyclonal anti-VAMP-2 antiserum (Synaptic Systems, Goettingen, Germany), rabbit polyclonal anti-VAMP-2 antiserum (Abcam, Cambridge, MA), mouse monoclonal anti-VAMP-3 antibody Cl 10.1 (Synaptic Systems, Goettingen, Germany), rabbit polyclonal anti-VAMP-3 antiserum (Synaptic Systems, Goettingen, Germany) and rabbit polyclonal anti VAMP-3 antiserum (Abcam, Cambridge, MA), [01571 As another non-limiting example, western blot analysis using an antibody that specifically recognizes BoNT/C1 Syntaxin-cleaved product can be used to assay for uptake of BoNT/C1. Examples of anti-Syntaxin antibodies useful for these assays include, without limitation, mouse monoclonal anti Syntaxin-1 antibody Cl 78.2 (Synaptic Systems, Goettingen, Germany), mouse monoclonal anti-Syntaxin 1A antibody Cl 78.3 (Synaptic Systems, Goettingen, Germany), rabbit polyclonal anti-Syntaxin-1A antiserum (Synaptic Systems, Goettingen, Germany), rabbit polyclonal anti-Syntaxin-1B antiserum (Synaptic Systems, Goettingen, Germany), rabbit polyclonal anti-Syntaxin antiserum (Abcam, Cambridge, MA), rabbit polyclonal anti-Syntaxin-2 antiserum (Abcam, Cambridge, MA) and rabbit polyclonal anti Syntaxin-3 antiserum (Abcam, Cambridge, MA), 61 of 168 WO 2008/036060 PCTIUS2006/012825 [0158] It is envisioned that an exogenous Clostridial toxin receptor can Include, without limitation, a nucleic acid molecule, such as, e.g., DNA and RNA, that encodes a Clostridial toxin receptor disclosed in the present specification and peptide molecule or peptidomimetic comprising a Clostridial toxin receptor disclosed in the present specification. In is also envisioned that an exogenous Clostridial toxin receptor can be transiently or stably expressed in a cell useful in aspects of the invention. Thus, aspects of this embodiment include a cell that transiently contains a nucleic acid molecule, such as, e.g., DNA and RNA, that encode a Clostridial toxin receptor disclosed in the present specification and a cell that transiently contains a peptide molecule or peptidomimetic comprising Clostridial toxin receptor disclosed in the present specification. Other aspects of this embodiment include a cell that stably contains a nucleic acid molecule, such as, e.g., DNA and RNA, that encode a Clostridial toxin substrate disclosed in the present specification and a cell that stably contains a peptide molecule or peptidomimetic comprising Clostridial toxin substrate disclosed in the present specification. Stably-maintained nucleic acid molecules may be extra-chromosomal and replicate autonomously, or they may be integrated into the chromosomal material of the cell and replicate non-autonomously. [0159] It is understood that the selection of a cell depends, in part, on which Clostridial toxin is to be assayed. As a non-limiting example, to assay for BoNT/A activity, one selects a cell that expresses or can be engineered to express a low or high affinity receptor for BoNT/A. As a further example, to assay for BoNT/B activity, one selects a cell that expresses or can be engineered to express a low or high affinity receptor for BoNT/B. As a still further example, to assay for BoNTIC1 activity, one selects a cell that expresses or can be engineered to express a low or high affinity receptor for BoNT/C1. As a still further example, to assay for BoNT/D activity, one selects a cell that expresses or can be engineered to express a low or high affinity receptor for BoNT/D. As a still further example, to assay for BoNT/E activity, one selects a cell that expresses or can be engineered to express a low or high affinity receptor for BoNT/E. As a still further example, to assay for BoNT/F activity, one selects a cell that expresses or can be engineered to express a low or high affinity receptor for BoNT/F. As a still further example, to assay for BoNT/G activity, one selects a cell that expresses or can be engineered to express a low or high affinity receptor for BoNT/G. As a still further example, to assay for TeNT activity, one selects a cell that expresses or can be engineered to express a low or high affinity receptor for TeNT. [0160] As discussed above, it is understood that a cell useful in the invention expresses endogenous or exogenous low or high affinity Clostridial toxin receptors for one or more Clostridial toxins. Such a cell also generally exhibits inhibition of exocytosis upon exposure to Clostridial toxin with, for example, an ICo of less than 500 nM, less than 100 mM, less than 50 nM, less than 5 nM, less than 0.5 nM, less than 0.05 nM, less than 0.005 nM, less than 0.0005 nM, less than 0.00005 nM or less than 0.000005 nM. In particular embodiments, the invention provides a neuron containing a BoNT/A substrate which exhibits inhibition of exocytosis with an ICo of less than 500 nM, less than 100 mM, less than 50 nM, less than 5 nM, less than 0.5 nM, less than 0.05 nM, less than 0.005 nM, less than 0.0005 nM, less than 0.00005 nM or less than 0.000005 nM upon exposure to BoNT/A. In further embodiments, the invention provides a neuron containing a BoNT/B substrate which exhibits inhibition of exocytosis with an ICso of less than 500 62 of 168 WO 2008/036060 PCT/US2006/012825 nM, less than 100 mM, less than 50 nM, less than 5 nM, less than 0.5 nM, less than 0.05 nM, less than 0.005 nM, less than 0.0005 nM, less than 0.00005 nM or less than 0.000005 nM upon exposure to BoNTIB. In other embodiments, the invention provides a neuron containing a BoNT/C1 substrate which exhibits inhibition of exocytosis with an IC 5 0 of less than 500 nM, less than 100 mM, less than 50 nM, less than 5 nM, less than 0.5 nM, less than 0.05 nM, less than 0.005 nM, less than 0.0005 nM, less than 0.00005 nM or less than 0.000005 nM upon exposure to BoNT/C1. In still further embodiments, the invention provides a neuron containing a BoNT/D substrate which exhibits inhibition of exocytosis with an

IC

50 of less than 500 nM, less than 100 mM, less than 50 nM, less than 5 nM, less than 0.5 nM, less than 0.05 nM, less than 0.005 nM, less than 0.0005 nM, less than 0.00005 nM or less than 0.000005 nM upon exposure to BoNT/D. In additional embodiments, the invention provides a neuron containing a BoNT/E substrate which exhibits inhibition of exocytosis with an IC 5 0 of less than 500 nM, less than 100 mM, less than 50 nM, less than 5 nM, less than 0.5 nM, less than 0.05 nM, less than 0.005 nM, less than 0.0005 nM, less than 0.00005 nM or less than 0.000005 nM upon exposure to BoNT/E. In yet further embodiments, the invention provides a neuron containing a BoNT/F substrate which exhibits inhibition of exocytosis with an IC 50 of less than 500 nM, less than 100 mM, less than 50 nM, less than 5 nM, less than 0.5 nM, less than 0.05 nM, less than 0.005 nM, less than 0.0005 nM, less than 0.00005 nM or less than 0.000005 nM upon exposure to BoNT/F. In further embodiments, the invention provides a neuron containing a BoNT/G substrate which exhibits inhibition of exocytosis with an IC 50 of less than 500 nM, less than 100 mM, less than 50 nM, less than 5 nM, less than 0.5 nM, less than 0.05 nM, less than 0.005 nM, less than 0.0005 nM, less than 0.00005 nM or less than 0.000005 nM upon exposure to BoNT/G. In still further embodiments, the invention provides a neuron containing a TeNT substrate which exhibits inhibition of exocytosis with an IC 50 of less than 500 nM, less than 100 mM, less than 50 nM, less than 5 nM, less than 0.5 nM, less than 0.05 nM, less than 0.005 nM, less than 0.0005 nM, less than 0.00005 nM or less than 0.000005 nM upon exposure to TeNT. It is understood that the same neuron can express two or more receptors for different Clostridial toxin serotypes, with the same or a different IC 50 for each individual toxin serotype. [0161 ] Cells useful in aspects of the invention include both neuronal and non-neuronal cells. Neuronal cells useful in aspects of the invention include, without limitation, primary neuronal cells; immortalized or established neuronal cells; transformed neuronal cells; neuronal tumor cells; stably and transiently transfected neuronal cells and further include, yet are not limited to, mammalian, murine, rat, primate and human neuronal cells. Non-limiting examples of neuronal cells useful in aspects of the invention include, e.g., peripheral neuronal cells, such as, e.g., motor neurons and sensory neurons; and CNS neuronal cells, such as, e.g., spinal cord neurons like embryonic spinal cord neurons, dorsal root ganglia (DRG) neurons, cerebral cortex neurons, cerebellar neurons, hippocampal neurons and motor neurons. Neuronal cells useful in the invention include, without limitation, those described herein below or tabulated in Table 12. Such neuronal cells can be, for example, central nervous system (CNS) neurons; neuroblastoma cells; motor neurons, hippocampal neurons or cerebellar neurons and further can be, without limitation, Neuro-2A, SH-SY5Y, NG108-15, N1E-115 or SK-N-DZ cells. The skilled person understands that these and additional primary and established neurons can be useful in the cells and methods of the invention. 63 of 168 WO 2008/036060 PCT/US2006/012825 [0162] Neurons useful in aspects of the invention include, without limitation, primary cultures such as primary cultures of embryonic dorsal root ganglion (DRG) neurons. As one example, primary cultures of embryonic rat DRG neurons are described in Mary J. Welch et al., Sensitivity of embryonic rat dorsal root ganglia neurons to Clostridium botulinum neurotoxins, 38(2) Toxicon 245 258 (2000); and primary cultures of fetal spinal cord neurons, for example, primary cultures of murine fetal spinal cord neurons are described in Elaine A. Neale et al., Botulinum neurotoxin A blocks synaptic vesicle exocytosis but not endocytosis at the nerve terminal, 147(6) J. Cell Biol. 1249-1260 (1999), and John A. Chaddock et al., Inhibition of vesicular secretion in both neuronal and non-neuronal cells by a retargeted endopeptidase derivative of Clostridium botulinum neurotoxin type A, 68(5) Infect. Immun. 2587-2593 (2000). Thus, in an embodiment, a cell capable of Clostridial toxin intoxication can be a neuron. In aspects of this embodiment, a neuron can be a neuron from, e.g., a primary culture, an embryonic dorsal root ganglion primary culture or a fetal spinal cord primary culture. As non-limiting examples, cells useful for determining Clostridial toxin activity according to a method disclosed in the present specification can include, a primary neuronal cell, such as, e.g., rat embryonic dorsal root ganglion (DRG) neurons or murine fetal spinal cord neurons, that include a Clostridial toxin substrate comprising a SNAP-25 recognition sequence; such as, e.g., a BoNT/A recognition sequence or a BoNT/E recognition sequence; a primary neuronal cell, such as, e.g., rat embryonic dorsal root ganglion (DRG) neurons or murine fetal spinal cord neurons, that include a Clostridial toxin substrate comprising a VAMP recognition sequence; such as, e.g., a BoNT/B recognition sequence or a TeNT recognition sequence; and a primary neuronal cell, such as, e.g., rat embryonic dorsal root ganglion (DRG) neurons or murine fetal spinal cord neurons, that include a Clostridial toxin substrate comprising a Syntaxin recognition sequence; such as, e.g., a BoNT/C1 recognition sequence. [0163] Neuronal cell lines useful in aspects of the invention include, without limitation, neuroblastoma cell lines, neuronal hybrid cell lines, spinal cord cell lines, central nervous system cell lines, cerebral cortex cell lines, dorsal root ganglion cell lines, hippocampal cell lines and pheochromocytoma cell lines. [01641 Neuroblastoma cell lines, such as, e.g., murine, rat, primate or human neuroblastoma cell lines can be useful in aspects of the invention. Neuroblastoma cell lines useful in aspects of the invention include, without limitation, BE(2)-C (ATCC CRL-2268; ECACC 95011817), BE(2)-M17 (ATCC CRL-2267; ECACC 95011816), C1300 (ECACC 93120817), CHP-212 (ATCC CRL-2273), CHP-126 (DSMZ ACC 304), IMR 32 (ATCC CRL-127; ECACC 86041809; DSMZ ACC 165), KELLY (ECACC 92110411; DSMZ ACC 355), LA-N-2, see, e.g., Robert C. Seeger et al., Morphology, growth, chromosomal pattern and fibrinolytic activity of two new human neuroblastoma cell lines, 37(5) Cancer Res. 1364-1371 (1977); and G. J. West et al., Adrenergic, cholinergic, and inactive human neuroblastoma cell lines with the action potential Na+ ionophore, 37(5) Cancer Res. 1372-1376 (1977), MC-IXC (ATCC CRL-2270), MHH-NB-1 1 (DSMZ ACC 157), N18Tg2 (DSMZ ACC 103), N1E-115 (ATCC CCL-2263; ECACC 88112303), N4TG3 (DSMZ ACC 101), Neuro-2A (ATCC CCL-131; ECACC 89121404; DSMZ ACC 148), NB41A3 (ATCC CCL-147; ECACC 89121405), NS20Y (DSMZ ACC 94), SH-SY5Y (ATCC CRL-2266; ECACC 94030304; DSMZ ACC 209), SIMA (DSMZ ACC 164), SK-N-DZ (ATCC CRL-2149; ECACC 94092305), SK-N-F1 64 of 168 WO 2008/036060 PCT/US2006/012825 (ATCC CRL-2142, ECACC 94092304), SK-N-MC (ATCC HTB-10, DSMZ ACC 203) and SK-N-SH (ATCC HTB-1 1, ECACC 86012802). Thus, in an embodiment, a cell capable of Clostridial toxin intoxication can be a neuroblastoma cell. In aspects of this embodiment, a neuroblastoma cell can be, e.g., BE(2)-C, BE(2)-M17, C1300, CHP-212, CHP-126, IMR 32, KELLY, LA-N-2, MC-IXC, MHH-NB-11, N18Tg2, NIE 115, N4TG3, Neuro-2A, NB41A3, NS20Y, SH-SYSY, SIMA, SK-N-DZ, SK-N-F1, SK-N-MC and SK-N-SH. As non-limiting examples, cells useful for determining Clostridial toxin activity according to a method disclosed in the present specification can include, a neuroblastoma cell, such as, e.g., SH-SY5Y cells, that include a Clostridial toxin substrate comprising a SNAP-25 recognition sequence; such as, e.g., a BoNT/A recognition sequence or a BoNT/E recognition sequence; Neuro-2a cells, that include a Clostridial toxin substrate comprising a SNAP-25 recognition sequence; such as, e.g., a BoNT/A recognition sequence; and N1E-115 cells or SK-N-DZ cells, that include a Clostridial toxin substrate comprising a SNAP-25 recognition sequence; such as, e.g., a BoNT/E recognition sequence. [0165] Neuronal hybrid cell lines, such as, e.g., murine, rat, primate and human hybrid neuronal cell lines can be useful In aspects of the invention. Such hybrid cell lines include neuroblastoma/glioma hybrids, such as, e.g., N18 (ECACC 88112301), NG108-15 (ATCC HB-12317, ECACC 88112302) and NG115-401L (ECACC 87032003); neuroblastoma/motor neuron hybrids, such as, e.g., NSC-19 and NSC-34, which express motor neuron characteristics, display a multipolar neuron-like phenotype, express high levels of choline acetyltransferase (CHAT), generate action potentials, express neurofilament triplet proteins and synthesize, store and release acetylcholine., see, e.g., N. R. Cashman et al., Neuroblastoma x spinal cord (NSC) hybrid cell lines resemble developing motor neurons, 194(3) Dev. Dyn. 209-221 (1992); and Christopher J. Eggett et al., Development and characterisation of a glutamate-sensitive motor neuronal cell line, 74(5) J. Neurochem. 1895-1902 (2000); neuroblastoma/dorsal root ganglion neuron hybrids, such as, e.g., F1 1, see, e.g., Doros Platika et al., Neuronal traits of clonal cell lines derived by fusion of dorsal root ganglia neurons with neuroblastoma cells, 82(10) Proc. Nati. Acad. Sci. U. S. A. 3499-3503 (1985), ND-C (ECACC 92090913), ND-E (ECACC 92090915), ND-U1 (ECACC 92090916), ND3 (ECACC 92090901), ND7/23 (ECACC 92090903), ND8/34 (ECACC 92090904), ND8/47, ND15 (ECACC 92090907), ND27 (ECACC 92090912); neuroblastoma/ hippocampal neuron hybrids, such as, e.g., HN-33, see, e.g., Henry J. Lee et al., Neuronal properties and trophic activities of immortalized hippocampal cells from embryonic and young adult mice. 10(6) J. Neurosci. 1779-1787 (1990). Thus, in an embodiment, a cell capable of Clostridial toxin intoxication can be a hybrid neuron. In aspects of this embodiment, a hybrid neuron can be, e.g., a neuroblastoma/glioma hybrid, a neuroblastoma/motor neuron hybrid, a neuroblastoma/root ganglion neuron hybrid and a neuroblastoma/ hippocampal neuron hybrid. In further aspects of this embodiment, a neuroblastoma/glioma hybrid can be, e.g., N18, NG108 15 and NG115-401L. In further aspects of this embodiment, a neuroblastoma/motor neuron hybrid can be, e.g., NSC-19 and NSC-32. In further aspects of this embodiment, a neuroblastoma/dorsal root ganglion neuron hybrid can be, e.g., ND8-47. In further aspects of this embodiment, a neuroblastoma/root ganglion neuron hybrid can be, e.g., Fl1, ND-C, ND-E, ND-U1, ND3, ND7/23, ND8/34, ND8/47, ND1 5 and ND27. In further aspects of this embodiment, a neuroblastoma/hippocampal neuron hybrid can be, e.g., HN-33. 65 of 168 WO 2008/036060 PCT/US2006/012825 [0166] The NG108-15 cell line is a hybrid of mouse neuroblastoma and rat glioma cells that binds BoNT/C1 at subnanomolar concentrations with an ICo of 0.2 nM (0.18 ng of complex per microliter), reaching saturation at 6 nM, see, e.g., Noriko Yokosawa et al., Binding of Clostridium botulinum type C neurotoxin to different neuroblastoma cell lines, 57(1) Infect. Immun. 272-277 (1989); and Noriko Yokosawa et al., Binding of botulinum type Cl, D and E neurotoxins to neuronal cell lines and synaptosomes, 29(2) Toxicon 261-264 (1991). Based on binding data, the NG108-15 cell line may contain both low and high affinity receptors for BoNT/C1. As non-limiting examples, cells useful for determining Clostridial toxin activity according to a method disclosed in the present specification can include, a neuronal hybrid cell, such as, e.g., NG108-15 cells, that include a Clostridial toxin substrate comprising a SNAP-25 recognition sequence; such as, e.g., a BoNT/A recognition sequence, a BoNT/C1 recognition sequence or a BoNT/E recognition sequence; and NG108-15 cells, that include a Clostridial toxin substrate comprising a Syntaxin recognition sequence; such as, e.g., a BoNT/C1 recognition sequence. [0167] Spinal cord cell lines, such as, e.g., murne, rat, primate or human spinal cord cell lines can be useful in aspects of the invention and include, without limitation, TE 189.T (ATCC CRL-7947) and M4b, see, e.g., Ana M. Cardenas et al., Establishment and characterization of immortalized neuronal cell lines derived from the spinal cord of normal and trisomy 16 fetal mice, an animal model of Down syndrome, 68(1) J. Neurosci. Res. 46-58 (2002). As an example, a human spinal cord cell line can be generated from precursors of human embryonic spinal cord cells (first trimester embryos) that are immortalized with a tetracycline repressible v-myc oncogene as described in Ronghao Li et al., Motoneuron differentiation of immortalized human spinal cord cell lines, 59(3) J. Neurosci. Res. 342-352 (2000). Such cells can be expanded indefinitely in proliferative growth conditions before rapid differentiation (4-7 days) into functional neurons that express neuronal phenotypic markers such as choline acetyltransferase. As another example, a murine spinal cord cell line can be prepared by immortalizing an embryonic spinal cord culture using transforming media. Such a spinal cord cell line can be, for example, the murine M4b line and can express neuronal markers such as NSE, synaptophysin, MAP 2 and choline acetyltransferase, and can release acetylcholine upon appropriate stimulation, see, e.g., Cardenas et al., supra, (2002).Thus, in an embodiment, a cell capable of Clostridial toxin intoxication can be a spinal cord cell. In aspects of this embodiment, a spinal cord cell can be, e.g., TE 189.T and M4b. [0168] Central nervous system (CNS) cell lines, such as, e.g., murine, rat, primate and human CNS cell lines, can be useful in aspects of the invention. A useful CNS cell line can be, for example, a human CNS cell line immortalized with a tetracycline repressible v-myc oncogene as described in Dinah W. Sah et al., Bipotent progenitor cell lines from the human CNS, 15(6) Nat. Biotechnol. 574-580 (1997). Upon repression of the oncogene, the cells differentiate into neurons. Thus, in an embodiment, a cell capable of Clostridial toxin intoxication can be a CNS cell. [0169] Cerebral cortex cell lines, such as, e.g., murine, rat, primate and human cerebral cortex cell lines, can be useful in aspects of the invention and Include, without limitation, CNh, see, e.g., Ana M. Cardenas et al., Calcium signals In cell lines derived from the cerebral cortex of normal and trisomy 16 mice, 10(2) 66 of 168 WO 2008/036060 PCT/US2006/012825 Neuroreport 363-369 (1999), HCN-1a (ATCC CRL-10442) and HCN-2 (ATCC CRL-10742). As an example, urine cortex primary cultures from 12-16 days embryos can be immortalized, for example, by culturing the cells in conditioned media from a rat thyroid cell line that induces transformation in vitro. The immortalized cells can be differentiated into neurons expressing neuronal markers using the appropriate media; these differentiated cells express choline acetyltransferase and secrete acetylcholine and glutamate in response to depolarization and nicotine stimulation, see, e.g., David D. Allen et al., Impaired cholinergic function in cell lines derived from the cerebral cortex of normal and trisomy 16 mice, 12(9) Eur. J. Neurosci. 3259-3264 (2000). Thus, in an embodiment, a cell capable of Clostridial toxin intoxication can be a cerebral cortex cell. In aspects of this embodiment, a cerebral cortex cell can be, e.g., CNh, HCN-1a and HCN-2. [0170] Dorsal root ganglia cell lines, such as, e.g., urine, rat, primate and human dorsal root ganglia cell lines, can be useful in aspects of the invention and include, without limitation, G4b, see, e.g., David D. Allen et al., A dorsal root ganglia cell line derived from trisomy 16 fetal mice, a model for Down syndrome, 13(4) Neuroreport 491-496 (2002). Embryonic dorsal root ganglia primary cultures can be immortalized with transforming conditioned media as described above. Upon differentiation, the cell line exhibits neuronal traits and lacks glial markers by immunohistochemistry. Release of neurotransmitters such as acetylcholine can be induced in response to potassium and nicotine, see, e.g., Allen et al., supra, (2002). Thus, in an embodiment, a cell capable of Clostridial toxin intoxication can be a dorsal root ganglia cell. In aspects of this embodiment, a dorsal root ganglia cell can be, e.g., G4b. [0171] Hippocampal cell lines, such as, e.g., murine, rat, primate and human hippocampal lines can be useful in aspects of the invention and include, without limitation, HT-4, see, e.g., K. Frederiksen et al., Immortalization of precursor cells from the mammalian CNS, 1(6) Neuron 439-448 (1988) and HT-22, see, e.g., John B. Davis and Pamela Maher, Protein kinase C activation inhibits glutamate-induced cytotoxicity in a neuronal cell line, 652(1) Brain Res. 169-173 (1994). As a non-limiting example, the murine hippocampal cell line HT-22 can be useful in the invention. As a further non-limiting example, the immortalized HN33 hippocampal cell line can be useful in the invention. This hippocampal cell line was derived from the fusion of primary neurons from the hippocampus of postnatal day 21 mice with the N18TG2 neuroblastoma cell line, and, when differentiated, shares membrane properties with adult hippocampal neurons in primary culture, see, e.g., Henry J. Lee et al., Neuronal Properties and Trophic Activities of Immortalized Hippocampal Cells from Embryonic and Young Adult Mice, 19(6) J. Neurosci. 1779-1787 (1990); and Henry J. Lee et al., Immortalized young adult neurons from the septal region: generation and characterization, 52(1-2) Brain Res. Dev Brain Res. 219-228 (1990). Thus, in an embodiment, a cell capable of Clostridial toxin intoxication can be a hippocampal cell. In aspects of this embodiment, a hippocampal cell can be, e.g., HT-4, HT-22 and HN33. [0172] A variety of non-neuronal cells are useful in aspects of the invention. Non-neuronal cells useful in aspects of the invention include, without limitation, primary non-neuronal cells; immortalized or established non-neuronal cells; transformed non-neuronal cells; non-neuronal tumor cells; stably and transiently transfected non-neuronal cells and further include, yet are not limited to, mammalian, murine, 67 of 168 WO 2008/036060 PCTIUS2006/012825 rat, primate and human non-neuronal cells. Non-neuronal cells useful in aspects of the invention further include, without limitation, any of the following primary or established cells: anterior pituitary cells; adrenal cells, such as. e.g., chromaffin cells of the adrenal medulla; pancreatic cells, such as. e.g., pancreatic acinar cells, pancreatic islet P cells and insulinoma HIT or INS-1 cells; ovarian cells, such as. e.g., steroid producing ovarian cells; kidney cells, such as. e.g., inner medullary collecting duct (IMCD) cells; stomach cells, such as, e.g., enterochromaffin cells; blood cells, such as. e.g., eurythrocytes, leucocytes, platelets, neutrophils, eosinophils, mast cells; epithelial cells, such as. e.g., those of the apical plasma membrane; fibroblasts; thyroid cells; chondrocytes; muscle cells; hepatocytes; glandular cells such as, e.g., pituitary cells, adrenal cells, chromaffin cells; and cells involved in glucose transporter (GLUT4) translocation. Thus, in an embodiment, a cell capable of Clostridial toxin intoxication can be a non-neuronal cell. In aspects of this embodiment, a non-neuronal cell can be from a primary or established non-neuronal cell line from the, e.g., anterior pituitary cells, adrenal cells, pancreatic cells, ovarian cells, kidney cells, stomach cells, blood cells, epithelial cells, fibroblasts, thyroid cells, chondrocytes, muscle cells, hepatocytes and glandular cells. [0173] As non-limiting examples, cells useful for determining Clostridial toxin activity according to a method disclosed in the present specification can include, a primary or established non-neuronal cell, such as, e.g., chromaffin cells or pancreatic acinar cells, that include a Clostridial toxin substrate comprising a SNAP-25 recognition sequence; such as, e.g., a BoNT/A recognition sequence or a BoNT/E recognition sequence; a primary neuronal cell, such as, e.g., chromaffin cells or pancreatic acinar cells, that include a Clostridial toxin substrate comprising a VAMP recognition sequence; such as, e.g., a BoNT/B recognition sequence or a TeNT recognition sequence; and a primary neuronal cell, such as, e.g., chromaffin cells or pancreatic acinar cells, that include a Clostridial toxin substrate comprising a Syntaxin recognition sequence; such as, e.g., a BoNT/C1 recognition sequence. [0174] As discussed above, cells useful in the invention include neuronal and non-neuronal cells that express low or undetectable levels of endogenous receptor but which have been transfected with, or otherwise engineered to express, one or more exogenous nucleic acid molecules encoding one or more Clostridial toxin receptors. The selection of the Clostridial toxin receptor depends on which Clostridial toxin is to be assayed. As a non-limiting example, a neuronal or non-neuronal cell can be transiently or stably engineered to express an exogenous nucleic acid molecule encoding the fibroblast growth factor 3 receptor (FGFR3), which serves as a BoNT/A receptor, see, e.g., PCT Patent Application No. 2005/006421. As another non-limiting example, a neuronal or non-neuronal cell can be transiently or stably engineered to express an exogenous nucleic acid molecule encoding a synaptic vesicle glycoprotein 2 (SV2) isoform, which serves as a BoNT/A receptor, see, e.g., Min Dong et al., SV2 Is the Protein Receptor for Botulinum Neurotoxin A, Science (2006); S. Mahrhold et al, The Synaptic Vesicle Protein 2C Mediates the Uptake of Botulinum Neurotoxin A into Phrenic Nerves, 580(8) FEBS Lett. 2011 2014 (2006). Additionjally, a neuronal or non-neuronal cell can be transiently or stably engineered to express multiple exogenous nucleic acid molecules encoding FGFR3 and an SV2 isoform. As another non-limiting example, a neuronal or non-neuronal cell can be transiently or stably engineered to express 68 of 168 WO 2008/036060 PCTIUS2006/012825 an exogenous nucleic acid molecule encoding the synaptotagmin I, which serves as a BoNT/B receptor and as a BoNT/G receptor, see, e.g., Min Dong et al., Synaptotagmins I and Il mediate entry of botulinum neurotoxin B into cells, 162(7) J. Cell Biol. 1293-1303 (2003); and Andreas Rummel et al., Synaptotagmins I and 11 act as nerve cell receptors for botulinum neurotoxin G, 279(29) J. Biol. Chem. 30865-30870 (2004). As another non-limiting example, a neuronal or non-neuronal cell can be transiently or stably engineered to express an exogenous nucleic acid molecule encoding the synaptotagmin 11, which serves as a BoNT/B receptor and as a BoNT/G receptor, see, e.g., Min Dong et al., supra, (2003); and Andreas Rummel et al., supra, (2004). [0175] Thus in an embodiment, a neuronal or non-neuronal cell is transiently or stably engineered to express an exogenous nucleic acid molecule encoding a FGFR3. In aspects of this embodiment, a neuronal or non-neuronal cell is transiently or stably engineered to express an exogenous nucleic acid molecule encoding the FGFR3 of SEQ ID NO: 173, the FGFR3 of SEQ ID NO: 174 or the FGFR3 of SEQ ID NO: 175. [0176] In another embodiment, a neuronal or non-neuronal cell is transiently or stably engineered to express an exogenous nucleic acid molecule encoding a SV2. In aspects of this embodiment, a neuronal or non-neuronal cell is transiently or stably engineered to express an exogenous nucleic acid molecule encoding the SV2 of SEQ ID NO: 176, the SV2 of SEQ 10 NO: 177, the SV2 of SEQ ID NO: 178 or the SV2 of SEQ ID NO: 179. [0177] In another embodiment, a neuronal or non-neuronal cell is transiently or stably engineered to express an exogenous nucleic acid molecule encoding a FGFR3 and an exogenous nucleic acid molecule encoding a SV2. In aspects of this embodiment, a neuronal or non-neuronal cell is transiently or stably engineered to express an exogenous nucleic acid molecule encoding the FGFR3 of SEQ ID NO: 173, the FGFR3 of SEQ ID NO: 174 or the FGFR3 of SEQ ID NO: 175 and an exogenous nucleic acid molecule encoding the SV2 of SEQ ID NO: 176, the SV2 of SEQ ID NO: 177, the SV2 of SEQ ID NO: 178 or the SV2 of SEQ ID NO: 179. [0178] In another embodiment, a neuronal or non-neuronal cell is transiently or stably engineered to express an exogenous nucleic acid molecule encoding a Synaptotagmin I. In aspects of this embodiment, a neuronal or non-neuronal cell is transiently or stably engineered to express an exogenous nucleic acid molecule encoding the Synaptotagmin of SEQ ID NO: 180. [0179] In another embodiment, a neuronal or non-neuronal cell is transiently or stably engineered to express an exogenous nucleic acid molecule encoding a Synaptotagmin 11. In aspects of this embodiment, a neuronal or non-neuronal cell is transiently or stably engineered to express an exogenous nucleic acid molecule encoding the Synaptotagmin of SEQ ID NO: 181. [0180] Cells useful in aspects of the present invention further include, without limitation, transformed, tumor or other cells which over-express one or more endogenous Clostridial toxin receptors or which 69 of 168 WO 2008/036060 PCTIUS2006/012825 express one or more endogenous Clostridial toxin receptors. It is understood that the over-expressed receptor can be a wild type form of the receptor or can include one or more amino acid modifications as compared to the wild type receptor, with the proviso that the process of Clostridial toxin intoxication can still occur. As a non-limiting example, cells useful for determining BoNT/A activity encompass those which express or over-express a form of the fibroblast growth factor 3 receptor (FGFR3). As another non-limiting example, cells useful for determining BoNT/B activity encompass those which express or over-express a form of synaptotagmin 1. As another non-limiting example, cells useful for determining BoNT/B activity encompass those which express or over-express a form of synaptotagmin 11. As another non-limiting example, cells useful for determining BoNT/G activity encompass those which express or over-express a form of synaptotagmin I. As another non-limiting example, cells useful for determining BoNT/G activity encompass those which express or over-express a form of synaptotagmin 11. [0181] Cells which express or over-express a form of the fibroblast growth factor 3 receptor include, yet are not limited to, naturally occurring and genetically modified as well as primary and established myeloma cells, bladder carcinoma cells, prostate carcinoma cells, thyroid carcinoma cells and cervical carcinoma cells. Such cells useful in aspects of the invention further encompass, without limitation, human myeloma cell lines including H929 (ATCC CRL-9068; ECACC 95050415; DSMZ ACC 163), JIM-3, see, e.g., H. Barker et al., pp. 155-158 (J. RadI & B. van Camp eds., EURAGE Monoclonal Gammopathies IlIl: Clinical Significance and Basic Mechanisms. 1991), KMS-1 1, see, e.g., Masayoshi Namba et al., Establishment of five human myeloma cell lines, 25(8) In Vitro Cell Dev. Biol. 723-729 (1989), KMS-18, see, e.g., Naozo Nakazawa et al., Interphase detection of t(4;14)(p16.3;q32.3) by in situ hybridization and FGFR3 over-expression in plasma cell malignancies, 117(2) Cancer Genet. Cytogenet. 89-96 (2000), LB278, see, e.g., D. Ronchetti et al., Characterization of the t(4;14)(p16.3;q32) in the KMS 18 multiple myeloma cell line, 15(5) Leukemia 864-865 (2001), LB375, see, e.g., Ronchetti et al., supra, (2001), LB1017, see, e.g., Ronchetti et al., supra, (2001), LB2100, see, e.g., Ronchetti et al., supra, (2001), LP-1 (DSMZ ACC 41). OPM-2 (DSMZ ACC 50), PCL1, see, e.g., Ronchetti et al., supra, (2001),UTMC-2, see, e.g., Shuji Ozaki et al., Characterization of a novel interleukin-6 autocrine dependent human plasma cell line, 8(12) Leukemia 2207-2213 (1994), which over-express FGFR3 due to chromosomal translocation t(4;14)(q16.3;q32.3) and other multiple myeloma cells with a t(4:14) translocation; leukemia cells including chronic myeloid leukemia (CML) cells such as CD34+ BCR-ABL+ cells; and bladder carcinoma cells including primary and other urothelial carcinoma cells. One skilled in the art understands that these and other cells which over-express or express a form of the fibroblast growth factor 3 receptor can be useful in determining BoNT/A activity according to a method of the invention. [0182] Thus, in an embodiment, a cell capable of Clostridial toxin intoxication can be a cell expressing an endogenous Clostridial toxin receptor. In aspects of this embodiment, an endogenous Clostridial toxin receptor expressed by a cell is a receptor for, e.g., BoNT/A, BoNT/B, BoNT/C1, BoNT/D, BoNT/E, BoNT/F, BoNT/G and TeNT. In further aspects of this embodiment, an endogenous Clostridial toxin receptor is, e.g., FGFR3, synaptotagmin I or synaptotagmin 11. In another aspect of this embodiment, a cell expressing an endogenous Clostridial toxin receptor can be from, e.g., a primary myeloma cell line, 70 of 168 WO 2008/036060 PCTIUS2006/012825 an established myeloma cell line, a primary bladder carcinoma cell line, an established bladder carcinoma cell line, a primary cervical carcinoma cell line and an established cervical carcinoma cell line. In another embodiment, an FGFR3 expressing cell can be, e.g., a cell containing a t(4;14)(q16.3;q32.3) chromosomal translocation. In further aspects of this embodiment, an FGFR3 expressing cell can be, e.g., H929, JIM-3, KMS-11, KMS-18, LB278, LB375, LB1017, LB2100, LP-1, OPM-2, PCL1 and UTMC 2.In further aspects of this embodiment, an FGFR3 expressing cell can be, e.g., H929, JIM-3, KMS-11, KMS-18, LB278, LB375, LB1017, LB2100, LP-1, OPM-2, PCL1 and UTMC-2. As non-limiting examples, cells useful for determining Clostridial toxin activity according to a method disclosed In the present specification can include, an established myeloma cell, such as, e.g., KMS-11 or H929, that include a Clostridial toxin substrate comprising a SNAP-25 recognition sequence; such as, e.g., a BoNT/A recognition sequence; a primary or established bladder carcinoma cell that includes a Clostridial toxin substrate comprising a SNAP-25 recognition sequence; such as, e.g., a BoNT/A recognition sequence; and a primary or established cervical carcinoma cell that includes a Clostridial toxin substrate comprising a SNAP-25 recognition sequence; such as, e.g., a BoNT/A recognition sequence. [0183] Further such cells useful in aspects of the invention further encompass, without limitation, stably transfected cell lines expressing a Clostridial toxin receptor. including, e.g., B9, see, e.g., Elizabeth E. Plowright et al., Ectopic expression of fibroblast growth factor receptor 3 promotes myeloma cell proliferation and prevents apoptosis, 95(3) Blood 992-998 (2000); TC, see, e.g., Hiroyuki Onose et al., Over-expression of fibroblast growth factor receptor 3 in a human thyroid carcinoma cell line results in overgrowth of the confluent cultures, 140(2) Eur. J. Endocrinol. 169-173 (1999); L6, see, e.g., M. Kana et al., Signal transduction pathway of human fibroblast growth factor receptor 3. Identification of a novel 66 kDa phosphoprotein, 272(10) J. Biol. Chem. 6621-6628 (1997); and CFK2, see, e.g., Janet E. Henderson et al., Expression of FGFR3 with the G380R achondroplasia mutation inhibits proliferation and maturation of CFK2 chondrocytic cells, 15(1) J. Bone Miner. Res. 155-165 (2000). One skilled in the art understands that these and other cells which over-express or express an activated form of the fibroblast growth factor 3 receptor can be useful in determining BoNT/A activity according to a method of the invention. Thus, in an embodiment, a cell capable of Clostridial toxin Intoxication can be a cell stably expressing an exogenous Clostridial toxin receptor. In aspects of this embodiment, an exogenous Clostridial toxin receptor stably expressed by a cell is a receptor for, e.g., BoNT/A, BoNT/B, BoNT/Cl, BoNT/D, BoNT/E, BoNT/F, BoNT/G and TeNT. In further aspects of this embodiment, an exogenous Clostridial toxin receptor is, e.g., FGFR3. In further aspects of this embodiment, an FGFR3 expressing cell can be, e.g., 89, TC, L6 and CFK2. As non-limiting examples, cells useful for determining Clostridial toxin activity according to a method disclosed in the present specification can include a B9 cell which stably express a nucleic acid molecule encoding a Clostridial toxin substrate, such as, e.g., a BoNT/A substrate; a B9 cell which stably contains a Clostridial toxin substrate, such as, e.g., a BoNT/A substrate; a TC cell which stably express a nucleic acid molecule encoding a Clostridial toxin substrate, such as, e.g., a BoNT/A substrate; a TC cell which stably contains a Clostridial toxin substrate, such as, e.g., a BoNT/A substrate; a L6 cell which stably express a nucleic acid molecule encoding a Clostridial toxin substrate, such as, e.g., a BoNT/A substrate; a L6 cell which stably contains a Clostridial toxin substrate, such as, e.g., a BoNT/A substrate; a CFK2 cell which stably express a nucleic acid molecule encoding a Clostridial toxin 71 of 168 WO 2008/036060 PCT/US2006/012825 substrate, such as, e.g., a BoNT/A substrate; and a CFK2 cell which stably contains a Clostridial toxin substrate, such as, e.g., a BoNT/A substrate. [0184] The cell compositions disclosed in the present specification include, in part, a Clostridial toxin substrate. In is envisioned that any and all Clostridial toxin substrate disclosed in the present specification can be used. Thus, aspects of this embodiment include nucleic acid molecules, such as, e.g., DNA and RNA, that encode a Clostridial toxin substrate disclosed in the present specification and peptide molecule or peptidomimetic comprising a Clostridial toxin substrate disclosed in the present specification. Other aspects of this embodiment include, in part, a Clostridial toxin recognition sequence including, without limitation, a BoNT/A toxin recognition sequence, a BoNT/B toxin recognition sequence, a BoNT/C1 toxin recognition sequence, a BoNT/D toxin recognition sequence, a BoNT/E toxin recognition sequence, a BoNT/F toxin recognition sequence, a BoNT/G toxin recognition sequence and a TeNT toxin recognition sequence. Other aspects of this embodiment include, in part, a membrane targeting domain including, without limitation, naturally occurring membrane targeting domains present in SNAP-25, naturally occurring SNAP-25 MTD variants, and non-naturally occurring SNAP-25 MTD variants, and SNAP-25 MTD peptidomimetics; and naturally occurring membrane targeting domains present in syntaxin, naturally occurring syntaxin MTD variants, and non-naturally occurring syntaxin MTD variants and syntaxin MTD peptidomimetics. Other aspects of this embodiment include, in part, a fluorescent protein including, without limitation, wild-type fluorescent proteins, naturally occurring variants, genetically engineered variants, active peptide fragments derived from Aequorea fluorescent proteins, Anemonia fluorescent proteins, Anthozoa fluorescent proteins, Discosoma fluorescent proteins, Entacmeae fluorescent proteins, Heteractis fluorescent proteins, Montastrea fluorescent proteins, Renilla fluorescent proteins, Zoanthus fluorescent proteins and fluorescent binding proteins. Non-limiting examples of fluorescent proteins include, e.g., EBFP, ECFP, AmCyan, AcGFP, ZsGreen, Vitality hrGFP, EGFP, Monster Green" hMGFP, EYFP, ZsYellow, DsRed-Express, DsRed2, DsRed, AsRed2 and HcRed1. Non-limiting examples of fluorescent binding proteins include, e.g., a tetracysteine peptide, an AGT and a dehalogenase. [0185] The cell compositions disclosed in the present specification include, in part, a cell that transiently contains a Clostridial toxin substrate. As used herein, the term "transiently containing" means a Clostridial toxin substrate that is temporarily introduced into a cell in order to perform the assays disclosed in the present specification. By definition, in order to perform the assays disclosed in the present specification at least 50% of the cells comprising a cell population must contain an exogenous Clostridial toxin substrate. As used herein, the term "cell population" means the total number of cells used in a method that transiently introduces a Clostridial toxin substrate for a given assay. As a non limiting example, given a cell population comprising 1.5x106 cells, at least 7.5x1 04 cells must contain a non-naturally occuring Clostridal toxin substrate after transduction using, e.g., an adenoviral method or a lentiviral method. As another non-limiting example, given a cell population comprising 1.5x10 5 cells, at least 7.5x10 4 cells must contain an exogenous Clostridal toxin substrate after transfection using, e.g., a protein transfection method. Thus, aspects of a cell transiently containing a Clostridial toxin substrate disclosed in the specification may include a cell that contains a substrate for, e.g., at most about one day, 72 of 168 WO 2008/036060 PCT/US2006/012825 at most about two days, at most about three days, at most about four days, at most about five days, and at most about six days, at most about seven days, at most about eight days, at most about nine days and at most about ten days and wherein the cell population containing a Clostridial toxin substrate comprises, e.g., at least 50% of the cells within the cell population, at least 60% of the cells within the cell population, at least 70% of the cells within the cell population, at least 80% of the cells within the cell population, and at least 90% of the cells within the cell population. [0186] Thus, in an embodiment, a composition comprises a cell that transiently contains a nucleic acid molecule that encodes an exogenous Clostridial toxin substrate capable of being localized to the plasma membrane of said cell wherein said cell is capable of Clostridial toxin intoxication, wherein said substrate comprises a fluorescent member, a membrane targeting domain and a Clostridial toxin recognition sequence comprising a cleavage site, where the cleavage site intervenes between said fluorescent member and said membrane localization domain. [0187] In another embodiment, a composition comprises a cell population, said cell population comprsing cells that transiently contains a nucleic acid molecule that encodes an exogenous Clostridial toxin substrate capable of being localized to the plasma membrane of said cells wherein said cells are capable of Clostridial toxin intoxication, wherein said substrate comprises a fluorescent member, a membrane targeting domain and a Clostridial toxin recognition sequence comprising a cleavage site, where the cleavage site intervenes between said fluorescent member and said membrane localization domain and wherein greater than 50% of said cell population comprises said cells containing said exogenous Clostridial toxin substrate. In aspects of this embodiment, the Clostridial toxin substrate capable of being localized to the plasma membrane encoded by the nucleic acid molecule can be, e.g., a BoNT/A substrate, a BoNT/B substrate, a BoNT/C1 substrate, a BoNT/D substrate, a BoNT/E substrate, a BoNT/F substrate, a BoNT/G substrate or a TeNT substrate. As non-limiting examples, cells useful for determining Clostridial toxin activity according to a method disclosed in the present specification can include SH-SY5Y cells such as, e.g., differentiated SH-SY5Y cells and SH-SY5Y cells which transiently express a nucleic acid molecule encoding a Clostridial toxin substrate, such as, e.g., a BoNT/A substrate or a BoNT/E substrate: NG108-15 cells such as, e.g., differentiated NG108-15 cells and NG108-15 cells which transiently express a nucleic acid molecule encoding a Clostridial toxin substrate, such as, e.g., a BoNT/A substrate or a BoNT/E substrate; Neuro-2A cells such as, e.g., differentiated Neuro-2A cells and Neuro-2A cells which transiently express a nucleic acid molecule encoding a Clostridial toxin substrate, such as, e.g., a BoNT/A substrate; N1E-115 cells such as, e.g., differentiated N1E-115 cells and N1E 115 cells which transiently express a nucleic acid molecule encoding a Clostridial toxin substrate, such as, e.g., a BoNT/E substrate; and SK-N-DZ cells such as, e.g., differentiated SK-N-DZ cells and SK-N-DZ cells which transiently express a nucleic acid molecule encoding a Clostridial toxin substrate, such as, e.g., a BoNT/E substrate. [0188] In another embodiment, a composition comprises a cell that transiently contains an exogenous Clostridial toxin substrate capable of being localized to the plasma membrane of said cell wherein said cell Is capable of Clostridial toxin intoxication, wherein said substrate comprises a fluorescent member, a 73 of 168 WO 2008/036060 PCT/US2006/012825 membrane targeting domain and a Clostridial toxin recognition sequence comprising a cleavage site, where the cleavage site intervenes between said fluorescent member and said membrane localization domain. [0189] In another embodiment, a composition comprises a cell population, said cell population comprising cells that transiently contains an exogenous Clostridial toxin substrate capable of being localized to the plasma membrane of said cells wherein said cells are capable of Clostridial toxin intoxication, wherein said substrate comprises a fluorescent member, a membrane targeting domain and a Clostridial toxin recognition sequence comprising a cleavage site, where the cleavage site intervenes between said fluorescent member and said membrane localization domain and wherein greater than 50% of said cell population comprises said cells containing said exogenous Clostridial toxin substrate. In aspects of this embodiment, the Clostridial toxin substrate capable of being localized to the plasma membrane can be, e.g., a BoNT/A substrate, a BoNT/B substrate, a BoNT/C1 substrate, a BoNT/D substrate, a BoNT/E substrate, a BoNT/F substrate, a BoNT/G substrate or a TeNT substrate. As non limiting examples, cells useful for determining Clostridial toxin activity according to a method disclosed in the present specification can include SH-SY5Y cells such as, e.g., differentiated SH-SY5Y cells and SH SY5Y cells which transiently contain a Clostridial toxin substrate, such as, e.g., a BoNT/A substrate or a BoNT/E substrate; NG108-15 cells such as, e.g., differentiated NG108-15 cells and NG108-15 cells which transiently contain a Clostridial toxin substrate, such as, e.g., a BoNT/A substrate or a BoNT/E substrate; Neuro-2A cells such as, e.g., differentiated Neuro-2A cells and Neuro-2A cells which transiently contain a Clostridial toxin substrate, such as, e.g., a BoNT/A substrate; N1 E-1 15 cells such as, e.g., differentiated N1E-1 15 cells and N1 E-1 15 cells which transiently contain a Clostridial toxin substrate, such as, e.g., a BoNT/E substrate; and SK-N-DZ cells such as, e.g., differentiated SK-N-DZ cells and SK-N-DZ cells which transiently contain a Clostridial toxin substrate, such as, e.g., a BoNT/E substrate. [0190] The cell compositions disclosed in the present specification include, in part, a cell that stably contains a Clostridial toxin substrate. As used herein, the term "stably containing" means a Clostridial toxin substrate that is introduced into a cell and maintained for long periods of time in order to perform the fluorescence assays of the present invention. Stably-maintained nucleic acid molecules encompass stably-maintained nucleic acid molecules that are extra-chromosomal and replicate autonomously and stably-maintained nucleic acid molecules that are integrated into the chromosomal material of the cell and replicate non-autonomously. Thus aspects of a cell stably containing a Clostridial toxin substrate disclosed in the specification may include a cell that contains a substrate for, e.g., at least ten days, at least 20 two days, at least 30 days, at least forty days, at least 50 days, and at least 60 days, at least 70 days, at least 80 days, at least 90 days and at least 100 days. Other aspects of a cell stably containing a Clostridial toxin substrate disclosed in the specification may include a cell that contains a substrate for, e.g., at least 100 days, at least 200 days, at least 300 days, at least 400 days, and at least 500 days. Still other aspects of a cell stably containing a Clostridial toxin substrate disclosed in the specification may include a cell that permanently contains a Clostridial toxin substrate. [01911 Thus, in an embodiment, a composition comprises a cell stably containing a nucleic acid 74 of 168 WO 2008/036060 PCTIUS2006/012825 molecule that encodes an exogenous Clostridial toxin substrate capable of being localized to the plasma membrane of said cell wherein said cell is capable of Clostridial toxin intoxication, and wherein said substrate comprises a fluorescent member, a membrane targeting domain and a Clostridial toxin recognition sequence comprising a cleavage site, where the cleavage site intervenes between said fluorescent member and said membrane localization domain. [0192] In another embodiment, a composition comprises a cell population, said cell population comprising cells stably containing a nucleic acid molecule that encodes an exogenous Clostridial toxin substrate capable of being localized to the plasma membrane of said cells wherein said cells are capable of Clostridial toxin intoxication, and wherein said substrate comprises a fluorescent member, a membrane targeting domain and a Clostridial toxin recognition sequence comprising a cleavage site, where the cleavage site intervenes between said fluorescent member and said membrane localization domain. In aspects of this embodiment, the Clostridial toxin substrate capable of being localized to the plasma membrane encoded by the nucleic acid molecule can be, e.g., a BoNT/A substrate, a BoNT/B substrate, a BoNT/C1 substrate, a BoNT/D substrate, a BoNT/E substrate, a BoNT/F substrate, a BoNT/G substrate or a TeNT substrate. As non-limiting examples, cells useful for determining Clostridial toxin activity according to a method disclosed in the present specification can include SH-SY5Y cells such as, e.g., differentiated SH-SY5Y cells and SH-SY5Y cells which stably express a nucleic acid molecule encoding a Clostridial toxin substrate, such as, e.g., a BoNT/A substrate or a BoNT/E substrate; NG108-15 cells such as, e.g., differentiated NG108-15 cells and NG108-15 cells which stably express a nucleic acid molecule encoding a Clostridial toxin substrate, such as, e.g., a BoNT/A substrate or a BoNT/E substrate; Neuro 2A cells such as, e.g., differentiated Neuro-2A cells and Neuro-2A cells which stably express a nucleic acid molecule encoding a Clostridial toxin substrate, such as, e.g., a BoNT/A substrate; KMS-1 1 cells such as, e.g., differentiated KMS-1 1 cells and KMS-1 1 cells which stably express a nucleic acid molecule encoding a Clostridial toxin substrate, such as, e.g., a BoNT/A substrate; N1 E-1 15 cells such as, e.g., differentiated N1E-1 15 cells and N1E-115 cells which stably express a nucleic acid molecule encoding a Clostridial toxin substrate, such as, e.g., a BoNT/E substrate; and SK-N-DZ cells such as, e.g., differentiated SK-N-DZ cells and SK-N-DZ cells which stably express a nucleic acid molecule encoding a Clostridial toxin substrate, such as, e.g., a BoNT/E substrate. [0193] In another embodiment, a composition comprises a cell stably containing an exogenous Clostridial toxin substrate capable of being localized to the plasma membrane of said cell wherein said cell is capable of Clostridial toxin intoxication, and wherein said substrate comprises a fluorescent protein, a membrane targeting domain and a Clostridial toxin recognition sequence comprising a cleavage site, where the cleavage site intervenes between said fluorescent protein and said membrane localization domain. [0194] In another embodiment, a composition comprises a cell population, said cell population comprising cells stably containing an exogenous Clostridial toxin substrate capable of being localized to the plasma membrane of said cells wherein said cells are capable of Clostridial toxin intoxication, and wherein said substrate comprises a fluorescent member, a membrane targeting domain and a Clostridial 75 of 168 WO 2008/036060 PCT/US2006/012825 toxin recognition sequence comprising a cleavage site, where the cleavage site intervenes between said fluorescent member and said membrane localization domain. In aspects of this embodiment, the Clostridial toxin substrate capable of being localized to the plasma membrane can be, e.g., a BoNT/A substrate, a BoNT/B substrate, a BoNT/C1 substrate, a BoNT/D substrate, a BoNT/E substrate, a BoNT/F substrate, a BoNT/G substrate or a TeNT substrate. As non-limiting examples, cells useful for determining Clostridial toxin activity according to a method disclosed in the present specification can include SH-SY5Y cells such as, e.g., differentiated SH-SY5Y cells and SH-SY5Y cells which stably contain a Clostridial toxin substrate, such as, e.g., a BoNT/A substrate or a BoNT/E substrate; NG108-15 cells such as, e.g., differentiated NG108-15 cells and NG108-15 cells which stably contain a Clostridial toxin substrate, such as, e.g., a BoNT/A substrate or a BoNT/E substrate; Neuro-2A cells such as, e.g., differentiated Neuro-2A cells and Neuro-2A cells which stably contain a Clostridial toxin substrate, such as, e.g., a BoNT/A substrate; KMS-11 cells such as, e.g., differentiated KMS-11 cells and KMS-11 cells which stably contain a Clostridial toxin substrate, such as, e.g., a BoNT/A substrate; N1 E-1 15 cells such as, e.g., differentiated N1E-1 15 cells and N1 E-115 cells which stably contain a Clostridial toxin substrate, such as, e.g., a BoNT/E substrate; and SK-N-DZ cells such as, e.g., differentiated SK-N-DZ cells and SK N-DZ cells which stably contain a Clostridial toxin substrate, such as, e.g., a BoNT/E substrate. 10195] As mentioned above, a nucleic acid molecule can be used to express a Clostridial toxin substrate disclosed in the present specification. It is envisioned that any and all methods for introducing a nucleic acid molecule into a cell can be used. Methods useful for introducing a nucleic acid molecule into a cell including, without limitation, calcium phosphate-mediated, DEAE dextran-mediated, lipid-mediated, polybrene-mediated, polylysine-mediated, viral-mediated, microinjection, protoplast fusion, biolistic, electroporation and conjugation to an antibody, gramacidin S, artificial viral envelope or other intracellular carrier such as TAT., see, e.g., Introducing Cloned Genes into Cultured Mammalian Cells, pp. 16.1-16.62 (Sambrook & Russell, eds., Molecular Cloning A Laboratory Manual, Vol. 3, 3'r ed. 2001); Alessia Colosimo et al., Transfer and expression of foreign genes in mammalian cells, 29(2) Biotechniques 314 318, 320-322, 324 (2000); Philip Washbourne & A. Kimberley McAllister, Techniques for gene transfer into neurons, 12(5) Curr. Opin. Neurobiol. 566-573 (2002); and Current Protocols in Molecular Biology, John Wiley and Sons, pp 9.16.4-9.16.11 (2000). One skilled in the art understands that selection of a specific method to introduce a nucleic acid molecule into a cell will depend, in part, on whether the cell will transiently contain the Clostridial toxin substrate or whether the cell will stably contain the Clostridial toxin substrate. [0196] In an aspect of this embodiment, a chemical-mediated method, termed transfection, is used to introduce a nucleic acid molecule expressing a Clostridial toxin substrate into a cell. In chemical mediated methods of transfection the chemical reagent forms a complex with the nucleic acid that facilitates its uptake into the cells. Such chemical reagents include, without limitation, calcium phosphate mediated, see, e.g., Martin Jordan & Florian Worm, Transfection of adherent and suspended cells by calcium phosphate, 33(2) Methods 136-143 (2004): diethy-laminoethyl (DEAE) dextran-mediated, lipid mediated, cationic polymer-mediated like polyethyleneimine (PEI)-mediated and polylysine-mediated and polybrene-mediated, see, e.g., Chun Zhang et al., Polyethylenimine strategies for plasmid delivery to 76 of 168 WO 2008/036060 PCT/US2006/012825 brain-derived cells, 33(2) Methods 144-150 (2004). Such chemical-mediated delivery systems can be prepared by standard methods and are commercially available, see, e.g., CellPhect Transfection Kit (Amersham Biosciences, Piscataway, NJ); Mammalian Transfection Kit, Calcium phosphate and DEAE Dextran, (Stratagene, Inc., La Jolla, CA); LipofectamineTM Transfection Reagent (Invitrogen, Inc., Carlsbad, CA); ExGen 500 Transfection kit (Fermentas, Inc., Hanover, MD), and SuperFect and Effectene Transfection Kits (Qiagen, Inc., Valencia, CA). [0197] In another aspect of this embodiment, a physical-mediated method is used to introduce a nucleic acid molecule expressing a Clostridial toxin substrate into a cell. Physical reagents include, without limitation, electroporation, biolistic and microinjection. Biolistics and microinjection techniques perforate the cell wall in order to introduce the nucleic acid molecule into the cell, see, e.g., Jeike E. Biewenga et al., Plasmid-mediated gene transfer in neurons using the biolistics technique, 71(1) J. Neurosci. Methods. 67-75 (1997); and John O'Brien & Sarah C. R. Lummis, Biolistic and diolistic transfection: using the gene gun to deliver DNA and lipophilic dyes into mammalian cells, 33(2) Methods 121-125 (2004). Electroporation, also termed electropermeabilization, uses brief, high-voltage, electrical pulses to create transient pores in the membrane through which the nucleic acid molecules enter and be used effectively for stable and transient transfections of all cell types, see, e.g., M. Golzio et al., In vitro and in vivo electric field-mediated permeabilization, gene transfer, and expression, 33(2) Methods 126-135 (2004); and Oliver Greschet al., New non-viral method for gene transfer into primary cells, 33(2) Methods 151-163 (2004). [0198] In another aspect of this embodiment, a viral-mediated method, termed transduction, is used to introduce a nucleic acid molecule expressing a Clostridial toxin substrate into a cell. In viral-mediated methods of transient transduction, the process by which viral particles infect and replicate in a host cell has been manipulated in order to use this mechanism to introduce a nucleic acid molecule into the cell. Viral-mediated methods have been developed from a wide variety of viruses Including, without limitation, retroviruses, adenoviruses, adeno-associated viruses, herpes simplex viruses, picornaviruses, alphaviruses and baculoviruses, see, e.g., Armin Blesch, Lentiviral and MLV based retroviral vectors for ex vivo and in vivo gene transfer, 33(2) Methods 164-172 (2004); and Maurizio Federico, From lentiviruses to lentivirus vectors, 229 Methods Mol. Biol. 3-15 (2003); E. M. Poeschla, Non-primate lentiviral vectors, 5(5) Curr. Opin. Mol. Ther. 529-540 (2003); Karim Benihoud et al, Adenovirus vectors for gene delivery, 10(5) Curr. Opin. Biotechnol. 440-447 (1999); H. Bueler, Adeno-associated viral vectors for gene transfer and gene therapy, 380(6) Biol. Chem. 613-622 (1999); Chooi M. Lai et al., Adenovirus and adeno-associated virus vectors, 21(12) DNA Cell Biol. 895-913 (2002); Edward A. Burton et al., Gene delivery using herpes simplex virus vectors, 21(12) DNA Cell Biol. 915-936 (2002); Paola Grandi et al., Targeting HSV amplicon vectors, 33(2) Methods 179-186 (2004); Ilya Frolov et al., Alphavirus-based expression vectors: strategies and applications, 93(21) Proc. Natl. Acad. Sci. U. S. A. 11371-11377 (1996); Markus U. Ehrengruber, Alphaviral gene transfer in neurobiology, 59(1) Brain Res. Bull. 13-22 (2002); Thomas A. Kost & J. Patrick Condreay, Recombinant baculoviruses as mammalian cell gene delivery vectors, 20(4) Trends Biotechnol. 173-180 (2002); and A. Huser & C. Hofmann, Baculovirus vectors: novel mammalian cell gene-delivery vehicles and their applications, 3(1) Am. J. 77 of 168 WO 2008/036060 PCTIUS2006/012825 Pharmacogenomics 53-63 (2003). [0199] Adenoviruses, which are non- enveloped, double-stranded DNA viruses, are often selected for mammalian cell transduction because adenoviruses handle relatively large nucleic acid molecules of about 36 kd, are produced at high titer, and can efficiently infect a wide variety of both dividing and non dividing cells, see, e.g., Wim T. J. M. C. Hermens et al., Transient gene transfer to neurons and glia: analysis of adenoviral vector performance in the CNS and PNS, 71(1) J. Neurosci. Methods 85-98 (1997); and Hiroyuki Mizuguchi et al., Approaches for generating recombinant adenovirus vectors, 52(3) Adv. Drug Deliv. Rev. 165-176 (2001). Transduction using adenoviral-based system do not support prolonged protein expression because the nucleic acid molecule is carried from an episome in the cell nucleus, rather than being integrated into the host cell chromosome. Adenovirual vector systems and specific protocols for how to use such vectors are disclosed in, e.g., ViraPowerTM Adenoviral Expression System (Invitrogen, Inc., Carlsbad, CA) and ViraPowerTM Adenoviral Expression System Instruction Manual 25 0543 version A, Invitrogen, Inc., (Jul. 15, 2002); and AdEasyTM Adenoviral Vector System (Stratagene, Inc., La Jolla, CA) and AdEasyTM Adenoviral Vector System Instruction Manual 064004f, Stratagene, Inc.. [0200] Nucleic acid molecule delivery can also use single-stranded RNA retroviruses viruses, such as, e.g., oncoretroviruses and lentiviruses. Retroviral-mediated transduction often produce transduction efficiencies close to 100%, can easily control the proviral copy number by varying the multiplicity of infection (MOI), and can be used to either transiently or stably transduce cells, see, e.g., Tiziana Tonini et al., Transient production of retroviral- and lentiviral-based vectors for the transduction of Mammalian cells, 285 Methods Mol. Biol. 141-148 (2004); Armin Blesch, Lentiviral and MLV based retroviral vectors for ex vivo and in vivo gene transfer, 33(2) Methods 164-172 (2004); F6lix Recillas-Targa, Gene transfer and expression in mammalian cell lines and transgenic animals, 267 Methods Mol. Biol. 417-433 (2004); and Roland Wolkowicz et al., Lentiviral vectors for the delivery of DNA into mammalian cells, 246 Methods Mol. Biol. 391-411 (2004). Retroviral particles consist of an RNA genome packaged in a protein capsid, surrounded by a lipid envelope. The retrovirus infects a host cell by injecting its RNA Into the cytoplasm along with the reverse transcriptase enzyme. The RNA template is then reverse transcribed into a linear, double stranded cDNA that replicates itself by Integrating into the host cell genome. Viral particles are spread both vertically (from parent cell to daughter cells via the provirus) as well as horizontally (from cell to cell via virions). This replication strategy enables long-term persist expression since the nucleic acid molecules of interest are stably integrated into a chromosome of the host cell, thereby enabling long-term expression of the protein. For instance, animal studies have shown that lentiviral vectors injected into a variety of tissues produced sustained protein expression for more than 1 year, see, e.g., Luigi Naldini et al., In vivo gene delivery and stable transduction of non-dividing cells by a lentiviral vector, 272(5259) Science 263-267 (1996). The Oncoretroviruses-derived vector systems, such as, e.g., Moloney murine leukemia virus (MoMLV), are widely used and infect many different non-dividing cells. Lentiviruses can also infect many different cell types, including dividing and non-dividing cells and possess complex envelope proteins, which allows for highly specific cellular targeting. [0201] Retroviral vector systems and specific protocols for how to use such vectors are disclosed in, 78 of 168 WO 2008/036060 PCTIUS2006/012825 e.g., U.S. Patent Nos. Manfred Gossen & Hermann Bujard, Tight control of gene expression in eukaryotic cells by tetracycline-responsive promoters, U.S. Patent No. 5,464,758 (Nov. 7, 1995) and Hermann Bujard & Manfred Gossen, Methods for regulating gene expression, U.S. Patent No. 5,814,618 (Sep. 29, 1998) David S. Hogness, Polynucleotides encoding insect steroid hormone receptor polypeptides and cells transformed with same, U.S. Patent No. 5,514,578 (May 7, 1996) and David S. Hogness, Polynucleotide encoding insect ecdysone receptor, U.S. Patent 6,245,531 (Jun. 12, 2001); Elisabetta Vegeto et al., Progesterone receptor having C. terminal hormone binding domain truncations, U.S. Patent No. 5,364,791 (Nov. 15, 1994), Elisabetta Vegeto et al., Mutated steroid hormone receptors, methods for their use and molecular switch for gene therapy, U.S. Patent No. 5,874,534 (Feb. 23, 1999) and Elisabetta Vegeto et al., Mutated steroid hormone receptors, methods for their use and molecular switch for gene therapy, U.S. Patent No. 5,935,934 (Aug. 10, 1999). Furthermore, such viral delivery systems can be prepared by standard methods and are commercially available, see, e.g., BDTM Tet-Off and Tet On Gene Expression Systems (BD Biosciences-Clonetech, Palo Alto, CA) and BDTm Tet-Off and Tet-On Gene Expression Systems User Manual, PT3001-1, BD Biosciences Clonetech, (Mar. 14, 2003), GeneSwitchTm System (Invitrogen, Inc., Carlsbad, CA) and GeneSwitchTM System A Mifepristone Regulated Expression System for Mammalian Cells version D, 25-0313, Invitrogen, Inc., (Nov. 4, 2002); ViraPowerTM Lentiviral Expression System (Invitrogen, Inc., Carlsbad, CA) and ViraPowerTM Lentiviral Expression System Instruction Manual 25-0501 version E, Invitrogen, Inc., (Dec. 8, 2003); and Complete Control* Retroviral Inducible Mammalian Expression System (Stratagene, La Jolla, CA) and Complete Control" Retroviral Inducible Mammalian Expression System Instruction Manual, 064005e. [0202] As mentioned above, a Clostridial toxin substrate disclosed in the present specification can be introduced into a cell. It is envisioned that any and all methods using a delivery agent to introduce a Clostridial toxin substrate into a cell population can be used. As used herein, the term "delivery agent" means any molecule that enables or enhances internalization of a covalently-linked, non-covalently-linked or in any other manner associated with a Clostridial toxin substrate into a cell. Thus, the term "delivery agent" encompasses, without limitation, proteins, peptides, peptidomimetics, small molecules, nucleic acid molecules, liposomes, lipids, viruses, retroviruses and cells that, without limitation, transport a covalently or non-covalently linked substrate to the cell membrane, cell cytoplasm or nucleus. It further is understood that the term "delivery agent" encompasses molecules that are internalized by any mechanism, including delivery agents which function via receptor mediated endocytosis and those which are independent of receptor mediated endocytosis. [0203] It is also envisioned that any and all methods useful for introducing a Clostridial toxin substrate with a delivery agent into a cell population can be useful with the proviso that this method introduce a Clostridial toxin substrate disclosed in the present specification in at least 50% of the cells within a given cell population. Thus, aspects of this embodiment can include a cell population in which, e.g., at least 90% of the given cell population contains a Clostridial toxin substrate, at least 80% of the given cell population contains a Clostridial toxin substrate, at least 70% of the given cell population contains a Clostridial toxin substrate, at least 60% of the given cell population contains a Clostridial toxin substrate, at least 50% of the given cell population contains a Clostridial toxin substrate. 79 of 168 WO 2008/036060 PCT/US2006/012825 [0204] It is also envisioned that any and all methods useful for introducing a Clostridial toxin substrate disclosed in the present specification linked to a delivery agent can be useful, including methods that covalently link the delivery agent to the substrate and methods that non-covalently link the delivery agent to the substrate. Covalent linking methods that attach a delivery agent to a Clostridial toxin substrate can include chemical conjugation and genetically produced fusion proteins. In one non-limiting method, a polynucleotide, such as, e.g., a plasmid or oligonucleotide, is attached to a Clostridial toxin substrate by conjugation chemistry and introduced into the cell using a method useful for introducing a nucleic acid molecule into a cell population as described in the present specification. In another non-limiting method, a lipid, such as, e.g., a cationic liposome, is attached to a Clostridial toxin substrate by conjugation chemistry and introduced into the cell using a method useful for introducing a nucleic acid molecule into a cell population as described in the present specification. In yet another non-limiting method, a peptide, is attached to a Clostridial toxin substrate by conjugation chemistry and introduced into the cell using a protein delivery method described below. In yet another non-limiting method, a peptide is attached to a Clostridial toxin substrate by producing a nucleic acid molecule that encodes the peptide delivery agent and substrate as an operationally linked fusion protein and this fusion protein is introduced into the cell using a protein delivery method described below. [0205] In an aspect of the present invention, a Clostridial toxin substrate disclosed in the present specification can be introduced into a cell using a peptide delivery agent to produce a cell transiently containing a Clostridial toxin substrate capable of being localized to the plasma. It is envisioned that a variety of peptide delivery agents can be covalently linked to a Clostridial toxin substrate, including, without limitation, the active fragment of protein transduction peptides; the active fragment of cell permeant peptides; phosphopeptides; the active fragment of membrane-translocating peptides; the active fragment of secreted proteins; the active fragment of nuclear localization signal peptides; predominantly hydrophobic peptides; predominantly a-helical peptides, such as, e.g., amphipathic-helical peptide; predominantly basic peptides, such as, e.g., basic amphipathic peptides; peptides containing D-amino acids; short peptides, such as, e.g., KDEL; denatured peptides linked to a denatured or folded Clostridial toxin substrate as described in, e.g., Steven F. Dowdy, Methods for Transducing Fusion Molecules, PCT Publication No. W099/55899 (Nov. 11, 1999); and Steven F. Dowdy, Novel Transduction Molecules and Methods for Using the Same, PCT Publication No. WOOO/62067 (Oct. 19, 2000); and, and any other denatured or folded, modified or unmodified, naturally occurring or synthetic peptide, peptidomimetics or analogs thereof. [0206] It is envisioned that any and all peptide lengths of a delivery agent can be useful in aspects of the present invention. In aspects of this embodiment, therefore, a delivery agent useful for introducing a Clostridial toxin substrate disclosed in the present specification in a cell can be a peptide or peptidomimetic having a length of less than 10 residues, a length of less than 20 residues, a length of less than 30 residues, a length of less than 40 residues, or a length of less than 50 residues. [0207] As non-limiting examples, delivery agents suitable for introducing a Clostridial toxin substrate 80 of 168 WO 2008/036060 PCTIUS2006/012825 disclosed in the present specification into a cell Include polylysine; ciliary neurotrophic factor (CNTF) or an active fragment thereof; caveolin or an active fragment thereof; interleukin-1 (IL-1) or an active fragment thereof; thioredoxin or an active fragment thereof; homeodomain-derived peptides or an active fragment thereof, such as, e.g., Antennapedia (Antp) or an active fragment thereof, like penetratin-1 (SEQ ID NO: 160), Engrailed 1 (En1) or an active fragment thereof, Engrailed 2 (En2) or an active fragment thereof, Hoxb-4 or an active fragment thereof, Hoxa-5 or an active fragment thereof, Hoxc-8 or an active fragment thereof, and Knotted-1 (KN1) or an active fragment thereof; fibroblast growth factor-1 (FGF-1) or an active fragment thereof; Kaposi fibroblast growth factor (kFGF) or an active fragment thereof, such as, e.g., AAVALLPAVLLALLAP (SEQ ID NO: 169); human 3 integrin or an active fragment thereof such as, e.g., a hydrophobic signal sequence; a nuclear localization sequence (NLS) or an active fragment thereof, such as, e.g., TPPKKKRKVEDP (SEQ ID NO: 170); FGF-2 or an active fragment thereof; transportan or an active fragment thereof, such as, e.g., GWTLNSAGYLLGKINLKALAALAKKIL (SEQ ID NO: 171); lactoferrin or an active fragment thereof: VP22 or an active fragment thereof; HIV type I transactivator (HIV TAT) or an active fragment thereof, such as, e.g., (YGRKKRRQRRR; SEQ ID NO: 168); or a heat shock protein such as HSP70 or an active fragment thereof. These and additional delivery agents are well known in the art as described in , e.g., Steven R. Schwarze and Steven F. Dowdy, In vivo protein transduction: intracellular delivery of biologically active proteins, compounds and DNA, 21(2) Trends Pharmacol. Sci. 45-48 (2000); Dara J. Dunican and Patrick Doherty, Designing cell-permeant phosphopeptides to modulate intracellular signaling pathways, 60(1) Biopolymers 45-60 (2001); K. G. Ford et al., Protein transduction: an alternative to genetic intervention? 8(1) Gene Ther. 1-4 (2001); Alain Prochiantz, Messenger proteins: homeoproteins, TAT and others, 12(4) Curr. Opin. Cell Biol. 400-406 (2000); J. J. Schwartz and S. Zhang, Peptide-mediated cellular delivery, 2(2) Curr. Opin. Mol. Ther. 162-167 (2000); and Steven F. Dowdy, Protein Transduction System and Methods of Use Thereof, PCT Publication No. WOOO/34308 (Jun. 15, 2000). [0208] In an embodiment, a delivery agent can be a homeoprotein or an active fragment thereof, such as, e.g., a homeodomain or an active fragment thereof. Homeoproteins are helix-tum-helix proteins that contain a DNA-binding domain of about 60 residues, denoted the homeodomain. A variety of homeoproteins, homeodomains and active fragments thereof can be delivery agents useful In the invention including, without limitation, Antennapedia, Engrailed1 (En1), Engrailed2 (En2), Hoxa-5, Hoxc-8, Hoxb-4 and Knotted-1 (KN1). As an example, Eni and En1 have been expressed In COS-7 cells, where they are first secreted and then internalized by other cells, see, e.g., Prochiantz, supra, (2000). Delivery agents using peptides derived from homeodomains and methods of using such agents are described in, e.g., Gerard Chassaing & Alain Prochiantz, Peptides which can be Used as Vectors for the Intracellular Addresing of Active Molecuels, U.S. Patent No. 6,080,724 (Jun. 27, 2000). [0209] In an aspect of this embodiment, a substrate composition of the invention includes a delivery agent which is the homeodomain protein, Antennapedia, or an active fragment thereof. Antennapedia is a member of a family of developmentally important Drosophila homeoproteins which translocate across neuronal membranes. The third helix of the Antennapedia homeodomain, the 16 residue peptide "penetratin-1" (SEQ ID NO: 160), is internalized into live cells. The internalization occurs both at 370C 81 of 168 WO 2008/036060 PCT/US2006/012825 and 40C, indicating that delivery is neither receptor-mediated nor energy-dependent. Additional delivery agents include peptides and peptidomimetics related in sequence to Penetratin-1 such as, without limitation, one of the peptides shown below In Table 11 or another penetratin-derived peptide or peptidomimetic, including a retroinverse or all D-amino acid peptide or peptidomimetic, or a related but non-a-helical peptide or peptidomimetic, see, e.g., Chassaing & Prochiantz, supra, (2000). In one embodiment, such a penetratin-derived peptide retains the tryptophan, phenylalanine and glutamine residues of penetratin-1 (SEQ ID NO: 160). -D ,e 43-58 ROiKIWFQNRRMKWKK 160 58-43 KKWKMRRNQFWIKIQR 161 43-58 RQIKIWFONRRMKWKK 162 ProSO ROIKIWFPNRRMKWKK16 3Pro ROPKIWFPNRRMPWKK 164 Met-Arg RQIKWFONMRRKWKK 165 7Arg RQIRIWFQNRRMRWRR 166 W/R RRWRRWWRRWWRRWRR 167 [0210] In another embodiment, a substrate composition of the invention includes a delivery agent which is a HIV trans-activator (TAT) protein or an active fragment thereof. Such a delivery agent can include, for example, a sequence identical or similar to residues 47-57 or 47-59 of HIV TAT, see, e.g., Alan Frankel et al., Fusion Protein Comprising TAT-derived Transport Moiert, U.S. Patent No. 5,674,980 (Oct. 7, 1995); Alan Frankel et al., TAT-derived Transport Polypeptide Conjugates, U.S. Patent No. 5,747,641 (May 5, 1998); and Alan Frankel et al., TAT-derived Transport Polypeptides and Fusion Proteins, U.S. Patent No. 5,804,604 (Sep. 8, 1998). As an example, fusion proteins including residues 47-57 of HIV TAT (YGRKKRRQRRR; SEQ ID NO: 168) cross the plasma membrane of, for example, human and murine cells in vitro and in vivo, see, e.g., Schwartz and Zhang, supra, (2000); a variety of proteins from 15 to 120 KDa have been shown to retain biological activity when fused to a HIV TAT delivery agent. An HIV TAT delivery agent can be positively charged and can function, for example, in an energy-, receptor-, transporter- and endocytosis-independent manner to deliver a covalently linked Clostridial toxin substrate to, for example, 90-100% of target cells. Delivery agents using peptides derived from TAT and methods of using such agents are described in, e.g., Frankel et al., supra, (1995); Frankel et al., supra, (1998); and Frankel et al., supra, (1998). [0211] In another embodiment, a substrate composition of the invention also can include as a delivery agent a herpes simplex virus VP22 protein or active fragment thereof. In an aspect of this embodiment, a substrate composition of the invention includes an HSV type 1 (HSV-1) VP22 protein or active fragment thereof. HSV VP22, a nuclear transcription factor, can cross the plasma membrane through non-classical endocytosis and can enter cells independent of GAP junctions and physical contacts. As a fusion with a variety of different proteins, HSV VP22 results in uptake into cells of different types including terminally 82 of 168 WO 2008/036060 PCT/US2006/012825 differentiated cells and can function to deliver a linked Clostridial toxin substrate to, for example, 90-100% of cultured cells. Delivery agents using peptides derived from TAT and methods of using such agents are described in, e.g., Peter F. J. O'Hare & Gillian D. Elliott, Transport Proteins and Their Uses, PCT Patent Publication No. W097/05265 (Feb. 13, 1997); Peter F. J. O'Hare & Gillian D. Elliott, Fusion Proteins for Intracellular and Intercellular Transport and Their Uses, PCT Patent Publication No. W098/32866 (Jul. 30, 1998); Peter F. J. O'Hare et al., Use of Transport Proteins, U.S. Patent No. 6,734,167 (May 11, 2004). [0212] In another embodiment, a delivery agent useful in the invention corresponds to or is derived from a hydrophobic signal sequence. Such a delivery agent can be, for example, the Kaposi fibroblast growth factor (kFGF) or an active fragment thereof such as AAVALLPAVLLALLAP (SEQ ID NO: 169); human 03 integrin or an active fragment thereof; or another hydrophobic delivery agent such as one of those described in, e.g., Dunican & Doherty, supra, (2001). Delivery agents using peptides derived from hydrophobic signal sequences and methods of using such agents are described in, e.g., Yao-Zhong Lin & Jack J. Hawiger, Method for importing biologically active molecules into cells, U.S. Patent No. 5,807,746 (Sep. 15, 1998); Yao-Zhong Lin & Jack J. Hawiger, Method for importing biologically active molecules into cells, U.S. Patent No. 6,043,339 (Mar. 28, 2000); Yao-Zhong Un et al., Sequence and Method for Genetic Engineering of Proteins with Cell Membrane Translocating Activity, U.S. Patent No. 6,248,558 (Jun. 19, 2001); Yao-Zhong Lin et al., Sequence and Method for Genetic Engineering of Proteins with Cell Membrane Translocating Activity, U.S. Patent No. 6,432,680 (Aug 13, 2002); Jack J. Hawiger et al., Method for importing biologically active molecules into cells, U.S. Patent No. 6,495,518 (Dec. 17, 2002); and Yao-Zhong Lin et al., Sequence and Method for Genetic Engineering of Proteins with Cell Membrane Translocating Activity, U.S. Patent No. 6,780,843 (Aug 24, 2004). [0213] In another embodiment, a delivery agent useful in the invention also can be a synthetic sequence that shares one or more characteristics of a naturally occurring delivery agent such as, e.g., a protein transduction domain (PTD). Such delivery agents include, but are not limited to, L- and D-arginine oligomers, for example, 9-mers of L- or D-arginine and related peptoids, see, e.g., Jonathan B. Rothbard & Paul A Wender, Method and Composition for Enhancing Transport Across Biological Membranes, U.S. Patent No. 6,306,993 (Oct. 23, 2001); and Jonathan B. Rothbard & Paul A Wender, Method and Composition for Enhancing Transport Across Biological Membranes, U.S. Patent No. 6,495,663 (Dec. 17, 2002). Such delivery agents further include basic peptides and peptidomimetics; basic a-helical peptides and peptidomimetics; and peptides and peptidomimetics with optimized arginine alignment or optimized a-helical character as compared to a naturally occurring protein transduction domain such as residues 47-57 of HIV TAT, see, e.g., Rothbard & Wender, supra, (2001); and Rothbard & Wender, supra, (2002). The skilled person understands that these and other naturally occurring and synthetic delivery agents can be useful in the substrate compositions of the invention. [0214] In another embodiment, a protein conjugate consisting of antibody directed at a receptor on the plasma membrane and a Clostridial toxin substrate disclosed in the present specification can be introduced into a cell. Delivery agents using antibodies and methods of using such agents are described in, e.g., Pamela B. Davis et al., Fusion proteins for protein delivery, U.S. Patent No. 6,287,817 (Sep. 11, 83 of 168 WO 2008/036060 PCTIUS2006/012825 2001). [0215] A delivery agent useful in the invention also can be an agent that enables or enhances cellular uptake of a non-covalenily associated Clostridial toxin substrate. In one embodiment, such a delivery agent is peptide containing two independent domains: a hydrophobic domain and a hydrophilic domain. In another embodiment, such a delivery agent is an MPG peptide, which is a peptide derived from both the nuclear localization sequence (NLS) of SV40 large T antigen and the fusion peptide domain of HIV-1 gp41, see, e.g., Virginie Escriou et al., NLS bioconjugates for targeting therapeutic genes to the nucleus, 55(2) Adv. Drug Deliv. Rev. 295-306 (2003). In a further embodiment, such a delivery agent is an MPG peptide having the amino acid sequence GALFLGFLGAAGSTMGAWSQPKSKRKV (SEQ ID NO: 172). In yet a further embodiment, such a delivery agent is an amphipathic peptide such as Pep-1. These and related delivery agents that function in the absence of covalent linkage and methods of using such agents are described in, e.g., Gilles Divita et al, Peptide-mediated Transfection Agents and Methods of Use, U.S. Patent No. 6,841,535 (Jan. 11, 2005); Philip L Feigner and Olivier Zelphati, Intracellular Protein Delivery Compositions and Methods of Use, U.S. Patent Publication No. 2003/0008813); and Michael Karas Intracellular Delivery of Small Molecules, Proteins and Nucleic Acids, U.S. Patent Publication 2004/0209797 (Oct. 21, 2004). Such peptide delivery agents can be prepared and used by standard methods and are commercially available, see, e.g. the Charioti" Reagent (Active Motif, Carlsbad, CA); BioPORTER* Reagent (Gene Therapy Systems, Inc., San Diego, CA), BioTrekTM Protein Delivery Reagent (Stratagene, La Jolla, CA), and Pro-JectTM Protein Transfection Reagent (Pierce Biotechnology Inc., Rockford, IL). [0216] Another aspect of the present invention provides expression construct that allow for expression of a nucleic acid molecule encoding a Clostridial toxin substrate disclosed in the present specification. These expression constructs comprise an open reading frame encoding a Clostridial toxin substrate disclosed in the present specification, operably-linked to control sequences from an expression vector useful for expressing the Clostridial toxin substrate in a cell. The term "operably linked" as used herein, refers to any of a variety of cloning methods that can ligate a nucleic acid molecule disclosed in the present specification into an expression vector such that a peptide encoded by the composition is expressed when introduced into a cell. Well-established molecular biology techniques that may be necessary to make an expression construct disclosed in the present specification including, but not limited to, procedures involving polymerase chain reaction (PCR) amplification restriction enzyme reactions, agarose gel electrophoresis, nucleic acid ligation, bacterial transformation, nucleic acid purification, nucleic acid sequencing are routine procedures well within the scope of one skilled in the art and from the teaching herein. Non-limiting examples of specific protocols necessary to make an expression construct are described in e.g., MOLECULAR CLONING A LABORATORY MANUAL, supra, (2001); and CURRENT PROTOCOLS IN MOLECULAR BIOLOGY (Frederick M. Ausubel et al., eds. John Wiley & Sons, 2004), which are hereby incorporated by reference. These protocols are routine procedures well within the scope of one skilled in the art and from the teaching herein. [0217] A wide variety of expression vectors can be employed for expressing an open reading frame 84 of 168 WO 2008/036060 PCTIUS2006/012825 encoding an Clostridial toxin substrate and include without limitation, viral expression vectors, prokaryotic expression vectors and eukaryotic expression vectors including yeast, insect and mammalian expression vectors and generally are equivalent to the expression vectors disclosed herein in Examples 4-6 and 8 14. Non-limiting examples of expression vectors, along with well-established reagents and conditions for making and using an expression construct from such expression vectors are readily available from commercial vendors that include, without limitation, BD Biosciences-Clontech, Palo Alto, CA; BD Biosciences Pharmingen, San Diego, CA; Invitrogen, Inc, Carlsbad, CA; EMD Biosciences-Novagen, Madison, WI; QIAGEN, Inc., Valencia, CA; and Stratagene, La Jolla, CA. The selection, making and use of an appropriate expression vector are routine procedures well within the scope of one skilled in the art and from the teachings herein. [0218] It is envisioned that any of a variety of expression systems may be useful for expressing construct compositions disclosed in the present specification. An expression system encompasses both cell-based systems and cell-free expression systems. Cell-based systems include, without limited, viral expression systems, prokaryotic expression systems, yeast expression systems, baculoviral expression systems, insect expression systems and mammalian expression systems. Cell-free systems include, without limitation, wheat germ extracts, rabbit reticulocyte extracts and E. coli extracts. Expression using an expression system can include any of a variety of characteristics including, without limitation, inducible expression, non-inducible expression, constitutive expression, viral-mediated expression, stably integrated expression, and transient expression. Expression systems that include well-characterized vectors, reagents, conditions and cells are well-established and are readily available from commercial vendors that include, without limitation, Ambion, Inc. Austin, TX; BD Biosciences-Clontech, Palo Alto, CA; BD Biosciences Pharmingen, San Diego, CA; Invitrogen, Inc, Carlsbad, CA; QIAGEN, Inc., Valencia, CA; Roche Applied Science, Indianapolis, IN; and Stratagene, La Jolla, CA. Non-limiting examples on the selection and use of appropriate heterologous expression systems are described in e.g., PROTEIN EXPRESSION. A PRACTIcAL APPROACH (S. J. Higgins and B. David Hames eds., Oxford University Press, 1999); Joseph M. Fernandez & James P. Hoeffler, GENE EXPRESSION SYSTEMS. USING NATURE FOR THE ART OF EXPRESSION (Academic Press, 1999); and Meena Rai & Harish Padh, Expression Systems for Production of Heterologous Proteins, 80(9) CURRENT SCIENCE 1121-1128, (2001), which are hereby incorporated by reference. These protocols are routine procedures well within the scope of one skilled in the art and from the teaching herein. [0219] An expression construct comprising a nucleic acid molecule encoding a Clostridial toxin substrate disclosed in the present specification can be operationally-linked to a variety of regulatory elements that can positively or negatively modulate, either directly or indirectly, the expression of a nucleic acid molecule, such as, e.g., constitutive, tissue-specific, inducible or synthetic promoters and enhancers. Non-limiting examples of constitutive regulatory elements include, e.g., the cytomegalovirus (CMV), herpes simplex virus thymidine kinase (HSV TK), simian virus 40 (SV40) early, 5' long terminal repeat (LTR), elongation factor-la (EF-1a) and polybiquitin (UbC) regulatory elements. Non-limiting examples of inducible regulatory elements useful in aspects of the present invention include, e.g., chemical-inducible regulatory elements such as, without limitation, alcohol-regulated, tetracycline-regulated, steroid 85 of 168 WO 2008/036060 PCTIUS2006/012825 regulated, metal-regulated and pathogenesis-related; and physical-inducible regulatory elements such as, without limitation, temperature-regulated and light-regulated. Such inducible regulatory elements can be prepared and used by standard methods and are commercially available, including, without limitation, tetracycline-inducible and tetracycline-repressible elements such as, e.g., Tet-On"' and Tet-Off " (BD Biosciences-Clontech, Palo Alto, CA) and the T-REx" (Tetracycline-Regulated Expression) and Flp-In' T-REx h systems (Invitrogen, Inc., Carlsbad, CA); ecdysone-inducible regulatory elements such as, e.g., the Complete Control" Inducible Mammalian Expression System (Stratagene, Inc., La Jolla, CA); isopropyl p-D-galactopyranoside (IPTG)-inducible regulatory elements such as, e.g., the LacSwitch* Inducible Mammalian Expression System (Stratagene, Inc., La Jolla, CA); and steroid-inducible regulatory elements such as, e.g., the chimeric progesterone receptor inducible system, GeneSwitch" (Invitrogen, Inc., Carlsbad, CA). The skilled person understands that these and a variety of other constitutive and inducible regulatory systems are commercially available or well known in the art and can be useful in the invention for controlling expression of a nucleic acid molecule which encodes a Clostridial toxin substrate. [0220] in an embodiment, a nucleic acid molecule encoding the Clostridial toxin substrate can optionally be linked to a regulatory element such as a constitutive regulatory element. [0221] In another embodiment, a nucleic acid molecule encoding the Clostridial toxin substrate can optionally be linked to a regulatory element such as an inducible regulatory element. In an aspect of this embodiment, expression of the nucleic acid molecule is induced using, e.g., tetracycline-inducible, ecdysone-inducible or steroid-inducible. [0222] Aspects of the present invention provide methods of determining Clostridial toxin activity by contacting with a sample a cell population, the cell population comprising cells that contain an exogenous Clostridial toxin substrate capable of being localized to the plasma membrane of said cells wherein said contacted cell population is capable of Clostridial toxin intoxication, wherein said substrate comprises a fluorescent member, a membrane targeting domain and a Clostridial toxin recognition sequence comprising a cleavage site, where the cleavage site intervenes between said fluorescent member and said membrane localization domain and wherein greater than 50% of said cell population comprises said cells containing said exogenous Clostridial toxin substrate; exciting said fluorescent member; and determining the fluorescence of said contacted cell population relative to a control cell population, where a difference in fluorescence of said contacted cell population as compared to said control cell population is indicative of Clostridial toxin activity. [0223] Other aspects of the present invention provide methods of determining Clostridial toxin activity by contacting with a sample a cell population, the cell population comprising cells that transiently contain an exogenous Clostridial toxin substrate capable of being localized to the plasma membrane of said cells wherein said contacted cell population is capable of Clostridial toxin intoxication, and wherein said substrate comprises a fluorescent member, a membrane targeting domain and a Clostridial toxin recognition sequence comprising a cleavage site, where the cleavage site Intervenes between said fluorescent member and said membrane localization domain, wherein greater than 50% of said cell 86 of 168 WO 2008/036060 PCT/US2006/012825 population comprises said cells containing said exogenous Clostridial toxin substrate; exciting said fluorescent member; and determining the fluorescence of said contacted cell population relative to a control cell population, where a difference in fluorescence of said contacted cell population as compared to said control cell population is indicative of Clostridial toxin activity. [0224] Aspects of the present invention provide methods of determining Clostridial toxin activity by contacting with a sample a cell population, the cell population comprsing cells that stably contain an exogenous Clostridial toxin substrate capable of being localized to the plasma membrane of said cells wherein said contacted cell population is capable of Clostridial toxin intoxication, and wherein said substrate comprises a fluorescent member, a membrane targeting domain and a Clostridial toxin recognition sequence comprising a cleavage site, where the cleavage site intervenes between said fluorescent member and said membrane localization domain; exciting said fluorescent member; and determining the fluorescence of said contacted cell population relative to a control cell population, where a difference in fluorescence of said contacted cell population as compared to said control cell population is indicative of Clostridial toxin activity. [0225] In an embodiment, a method of determining Clostridial toxin activity comprises the steps of contacting with a sample a cell population, the cell population comprising cells containing an exogenous Clostridial toxin substrate capable of being localized to the plasma membrane of said cells wherein said contacted cell population is capable of Clostridial toxin intoxication, and wherein said substrate comprises a fluorescent member, a membrane targeting domain and a Clostridial toxin recognition sequence comprising a cleavage site, where the cleavage site intervenes between said fluorescent member and said membrane localization domain; exciting said fluorescent member; and determining the fluorescence of said contacted cell population relative to a control cell population, where a difference in fluorescence of said contacted cell population as compared to said control cell population is indicative of Clostridial toxin activity. In aspects of this embodiment, the Clostridial toxin substrate capable of being localized to the plasma membrane can be, e.g., a BoNT/A substrate, a BoNT/B substrate, a BoNT/C1 substrate, a BoNT/D substrate, a BoNT/E substrate, a BoNT/F substrate, a BoNT/G substrate or a TeNT substrate. [0226] The methods disclosed in the present specification include, in part, a Clostridial toxin substrate. In is envisioned that any and all Clostridial toxin substrate disclosed in the present specification can be used to practice the present methods. Thus, aspects of this embodiment include nucleic acid molecules, such as, e.g., DNA and RNA, that encode a Clostridial toxin substrate disclosed in the present specification and peptide molecule or peptidomimetic comprising a Clostridial toxin substrate disclosed in the present specification. Other aspects of this embodiment include, in part, a Clostridial toxin recognition sequence including, without limitation, a BoNT/A toxin recognition sequence, a BoNT/B toxin recognition sequence, a BoNT/C1 toxin recognition sequence, a BoNT/D toxin recognition sequence, a BoNT/E toxin recognition sequence, a BoNT/F toxin recognition sequence, a BoNT/G toxin recognition sequence and a TeNT toxin recognition sequence. Other aspects of this embodiment include, in part, a membrane targeting domain including, without limitation, naturally occurring membrane targeting domains present in SNAP-25, naturally occurring SNAP-25 MTD variants, and non-naturally occurring SNAP-25 MTD 87 of 168 WO 2008/036060 PCT/US2006/012825 variants, and SNAP-25 MTD peptidomimetics; and naturally occurring membrane targeting domains present in syntaxin, naturally occurring syntaxin MTD variants, and non-naturally occurring syntaxin MTD variants and syntaxin MTD peptidomimetics. Other aspects of this embodiment include, In part, a fluorescent protein including, without limitation, wild type fluorescent proteins, naturally occurring variants, genetically engineered variants, active peptide fragments derived from Aequorea fluorescent proteins, Anemonia fluorescent proteins, Anthozoa fluorescent proteins, Discosoma fluorescent proteins, Entacmeae fluorescent proteins, Heteractis fluorescent proteins, Montastrea fluorescent proteins, Renilla fluorescent proteins, Zoanthus fluorescent proteins and fluorophore binding proteins. Non-limiting examples of fluorescent proteins include, e.g., EBFP, ECFP, AmCyan, AcGFP, ZsGreen, Vitality9 hrGFP, EGFP, Monster Greene hMGFP, EYFP, ZsYellow, DsRed-Express, DsRed2, DsRed, AsRed2 and HcRedl. Non-limiting examples of fluorescent binding proteins include, e.g., a tetracysteine peptide, an AGT and a dehalogenase. [0227] The methods disclosed in the present specification include, in part, a cell capable of Clostridial toxin intoxication. In is envisioned that any and all cells disclosed in the present specification can be used to practice the present methods. Thus, aspects of this embodiment include cells, such as, e.g., cells expressing one or more Clostridial toxin receptors including, without limitation, a low affinity Clostridial toxin receptor, a high affinity Clostridial toxin receptor, an endogenous Clostridial toxin receptor, an exogenous Clostridial toxin receptors, a BoNT/A receptor, a BoNT/B receptor, a BoNT/C1 receptor, a BoNT/D receptor, a BoNT/E receptor, a BoNT/F receptor, a BoNT/G receptor and a TeNT receptor. Other aspects of this embodiment include cells, such as, e.g., neuronal cells including, without limitation, primary neuronal cells; immortalized or established neuronal cells; transformed neuronal cells; neuronal tumor cells; stably and transiently transfected neuronal cells expressing a Clostridial toxin receptor, and further include, yet are not limited to, mammalian, murine, rat, primate and human neuronal cells. Other aspects of this embodiment include cells from, such as, e.g., neuronal cell lines including, without limitation, neuroblastoma cell lines, neuronal hybrid cell lines, spinal cord cell lines, central nervous system cell lines, cerebral cortex cell lines, dorsal root ganglion cell lines, hippocampal cell lines and pheochromocytoma cell lines. Non-limiting examples of neuronal cell lines include, e.g., neuroblastoma cell lines BE(2)-C, BE(2)-M17, C1300, CHP-212, CHP-126, IMR 32, KELLY, LA-N-2, MC-IXC, MHH-NB 11, N18Tg2, N1E-115, N4TG3, Neuro-2A, NB41A3, NS20Y, SH-SY5Y, SIMA, SK-N-DZ, SK-N-F1, SK-N MC and SK-N-SH; neuroblastoma/glioma hybrid cell lines N18, NG108-15 and NG115-401L; neuroblastoma/motor neuron hybrid cell lines NSC-19 and NSC-32; neuroblastoma/root ganglion neuron hybrid cell lines F11, ND-C, ND-E, ND-U1, ND3, ND7/23, ND8/34, ND8/47, ND15 and ND27; the neuroblastomalhippocampal neuron hybrid cell line HN-33; spinal cord cell lines TE 189.T and M4b; cerebral cortex cell lines CNh, HCN-1a and HCN-2; dorsal root ganglia cell line G4b; hippocampal cell lines HT-4, HT-22 and HN33; FGFR3 expressing cell lines H929, JIM-3, KMS-11, KMS-18, LB278, LB375, LB1017, LB2100, LP-1, OPM-2, PCL1 and UTMC-2.In further aspects of this embodiment, an FGFR3 expressing cell can be, e.g., H929, JIM-3, KMS-1 1, KMS-18, LB278, LB375, LB1017, LB2100, LP-1, OPM-2, PCLI UTMC-2, B9, TC, L6 and CFK2. Other aspects of this embodiment include cells, such as, e.g., non-neuronal cells including, without limitation, primary non-neuronal cells; immortalized or established non-neuronal cells; transformed non-neuronal cells; non-neuronal tumor cells; stably and 88 of 168 WO 2008/036060 PCT/US2006/012825 transiently transfected non-neuronal cells expressing a Clostridial toxin receptor, and further include, yet are not limited to, mammalian, murine, rat, primate and human non-neuronal cells. Other aspects of this embodiment include cells, such as, e.g., non-neuronal cells useful in aspects of the invention further include, without limitation, anterior pituitary cells; adrenal cells, pancreatic cells, ovarian cells, kidney cells, such as, e.g., HEK293, stomach cell, blood cells, epithelial cells, fibroblasts, thyroid cells, chondrocytes, muscle cells, hepatocytes, glandular cells and cells involved in glucose transporter (GLUT4) translocation. [0228] The methods disclosed in the present specification include, in part, a sample. As used herein, the term "sample" means any biological matter that contains or potentially contains an active Clostridial toxin. A variety of samples can be assayed according to a method disclosed in the present specification including, without limitation, purified, partially purified, or unpurified Clostridial toxin; recombinant single chain or di-chain toxin with a naturally or non-naturally occurring sequence; recombinant Clostridial toxin with a modified protease specificity; recombinant Clostridial toxin with an altered cell specificity; chimeric toxin containing structural elements from multiple Clostridial toxin species or subtypes; bulk Clostridial toxin; formulated Clostridial toxin product, including, e.g., formulated BoNT/A and BoNT/E products; and foods; cells or crude, fractionated or partially purified cell lysates, for example, engineered to include a recombinant nucleic acid encoding a Clostridial toxin; bacterial, baculoviral and yeast lysates; raw, cooked, partially cooked or processed foods; beverages; animal feed; soil samples; water samples; pond sediments; lotions; cosmetics; and clinical formulations. It is understood that the term sample encompasses tissue samples, including, without limitation, mammalian tissue samples, livestock tissue samples such as sheep, cow and pig tissue samples; primate tissue samples; and human tissue samples. Such samples encompass, without limitation, intestinal samples such as infant intestinal samples, and tissue samples obtained from a wound. As non-limiting examples, a method of the invention can be useful for determining the presence or activity of a Clostridial toxin in a food or beverage sample; to assay a sample from a human or animal, for example, exposed to a Clostridial toxin or having one or more symptoms of a Clostridial toxin; to follow activity during production and purification of Clostridial toxin; or to assay formulated Clostridial toxin products such as pharmaceuticals or cosmetics. [0229] The methods disclosed in the present specification include, in part, determining the Clostridial toxin activity from a sample by detecting the fluorescence intensity of a Clostridial toxin substrate from a cell contacted population with the sample. As used herein, with regard to detecting fluorescence intensity the term "contacted cell population" means both detecting the fluorescence intensity of the contacted cell population in the aggregate or detecting the fluorescence intensity of individual cells comprsing the contacted cell population and analysis the obtained data individually or in the aggregate. A variety of means can be useful for determining the fluorescence intensity of a Clostridial toxin substrate contained in a cell contacted population with sample, including, without limitation, detecting the localization of fluorescence intensity within the contacted cell population, detecting fluorescence intensity in the contacted cell population over time, detecting fluorescence intensity in the contacted cell population over time and comparing fluorescence intensity detected in the contacted cell population relative to the fluorescence intensity detected in a control cell population. As used herein, the term "control cell 89 of 168 WO 2008/036060 PCTIUS2006/012825 population" means a cell population of the same or similar type as the contacted cell population and grown under the same conditions but which is not contacted with any sample or is contacted with a defined negative sample or a defined positive sample. As used herein, with regard to detecting fluorescence intensity the term "control cell population" means both detecting the fluorescence intensity of the control cell population in the aggregate or detecting the fluorescence intensity of individual cells comprsing the control cell population and analysis the obtained data individually or in the aggregate. One skilled in the art understands that a variety of control cell populations are useful in the methods of the invention and that a control cell population can be a positive control cell population or a negative control cell population. A control cell population can be, for example, a negative control cell population such as a similar or identical cell population comprising cells containing the same or similar Clostridial toxin substrate that Is contacted with a similar, defined negative sample, which is known to lack active Clostridial toxin, or that is not contacted with any sample. A control cell population also can be, for example, a positive control cell population such as a cell population comprising cells containing one or both cleavage products that result from proteolysis of the Clostridial toxin substrate at the cleavage site or a cell population comprisnig cells containing the same or similar substrate contacted with a defined positive sample, which is known to include active Clostridial toxin. [0230] Fluorescence intensity and, hence, Clostridial toxin activity, can be detected by a variety of means, for example, by detecting increased fluorescence intensity of the cytoplasmic substrate from the contacted cell population; decreased fluorescence intensity of the membrane-localized substrate from the contacted cell population; a shift in fluorescence intensity of the membrane-localized substrate to the cytoplasmic substrate; a decreased fluorescence intensity found in a certain sub-cellular area of cells comprising the contacted cell population; an increased fluorescence intensity found in a certain sub cellular area of cells comprising the contacted cell population. In aspects of this embodiment, a decreased fluorescence intensity can be, e.g., at least two-fold, at least three-fold, at least four-fold, at least five-fold, at least ten-fold, at least twenty-fold or more relative to fluorescence intensity at the same wavelength of the same cell population detected at a different time point, or relative to fluorescence intensity at the same wavelength of a similar cell population not contacted with a sample, such as, e.g., a control cell population. In other aspects of this embodiment, a decreased fluorescence intensity can be, e.g., at most two-fold, at most three-fold, at most four-fold, at most five-fold, at most ten-fold, at most twenty-fold relative to fluorescence Intensity at the same wavelength of the same cell population detected at a different time point, or relative to fluorescence intensity at the same wavelength of a similar cell population not contacted with a sample, such as, e.g., a control cell population. In yet other aspects of this embodiment, an increased fluorescence intensity can be, e.g., at least two-fold, at least three-fold, at least four-fold, at least five-fold, at least ten-fold, at least twenty-fold or more relative to fluorescence intensity at the same wavelength of the same cell population detected at a different time point, or relative to fluorescence intensity at the same wavelength of a similar cell population not contacted with a sample, such as, e.g., a control cell. In yet other aspects of this embodiment, an increased fluorescence intensity can be, e.g., at most two-fold, at most three-fold, at most four-fold, at most five-fold, at most ten-fold, at most twenty-fold relative to fluorescence intensity at the same wavelength of the same cell population detected at a different time point, or relative to fluorescence intensity at the same wavelength of a similar 90 of 168 WO 2008/036060 PCTIUS2006/012825 cell population not contacted with a sample, such as, e.g., a control cell. [02311 It is understood that the relevant fluorescence intensities are detected at the appropriate wavelength or range of wavelengths. As an example, where the fluorescence intensity of the membrane localized substrate is detected, the appropriate wavelength is at or near the emission maxima of the fluorescent member comprising the membrane-localized substrate, or is a range of wavelengths encompassing or near to the emission maxima of the fluorescent member comprising the membrane localized substrate. It is recognized that changes in the absolute amount of Clostridial toxin substrate in the cell, fluorescence intensity, and turbidity or other background absorbance at the excitation wavelength effects the fluorescence intensities of the fluorescent membeer comprising the Clostridial toxin substrate roughly in parallel. Thus, it is understood that a ratio of emission fluorescence intensities is independent of the absolute amount of substrate, fluorescence intensity, and turbidity or other background absorbance, and can be a useful indicator of Clostridial toxin activity. [0232] In one embodiment, Clostridial toxin activity from a sample is determined by detecting the fluorescence intensity of the membrane-localized Clostridial toxin substrate from the contacted cell population, where a decreased in fluorescence intensity over time of the membrane-localized substrate from the contacted cell population is indicative of Clostridial toxin activity. Detection of fluorescence intensity can be practiced as "fixed-time" assays or as continuous-time assays and comparisons can be made using different time points taken from the same contacted cell population or relative to a control cell population.. Thus, aspect of this embodiment include detecting the fluorescence intensity of the membrane-localized Clostridial toxin substrate in, e.g., at least two different time points, at least three different time points, at least four different time points, at least five different time points, at least ten different time points and at least 20 different time points. Other aspects of this embodiment include detecting the fluorescence intensity of the membrane-localized Clostridial toxin substrate over time intervals that are, e.g., no more than 1 minute apart, no more than 5 minutes apart, no more than 10 minutes apart, no more than 15 minutes apart, no more than 30 minutes apart and no more than 30 minutes apart. Other aspects of this embodiment include detecting the fluorescence intensity of the membrane-localized Clostridial toxin substrate over time intervals that are, e.g., no less than 15 minutes apart, no less than 30 minutes apart, no less than 45 minutes apart, no less than 60 minutes apart, no less than 90 minutes apart and no less than 120 minutes apart. Still other aspects of this embodiment include detecting the fluorescence intensity of the membrane-localized Clostridial toxin substrate continuously over time for, e.g., at most about 5 minutes, at most about 10 minutes, at most about 15 minutes, at most about 30 minutes, at most about 45 minutes, at most about 60 minutes, at most about 90 minutes and at most about 120 minutes. Still other aspects of this embodiment include detecting the fluorescence intensity of the membrane-localized Clostridial toxin substrate continuously over time for, e.g., at least about 15 minutes, at least about 30 minutes, at least about 45 minutes, at least about 60 minutes, at least about 90 minutes and at least about 120 minutes. [0233] In another embodiment, Clostridial toxin activity from a sample is determined by detecting the fluorescence intensity of the cytoplasmic Clostridial toxin substrate from the contacted cell population, 91 of 168 WO 2008/036060 PCT/US2006/012825 where increased fluorescence intensity over time of the cytoplasmic substrate from the contacted cell population is indicative of Clostridial toxin activity. Detection of fluorescence intensity can be practiced as a "fixed-time" assay or as a continuous-time assay and comparisons can be made using different time points taken from the same contacted cell population or relative to a control cell population...Thus, aspect of this embodiment include detecting the fluorescence intensity of the cytoplasmic Clostridial toxin substrate in, e.g., at least two different time points, at least three different time points, at least four different time points, at least five different time points, at least ten different time points and at least 20 different time points. Other aspects of this embodiment include detecting the fluorescence intensity of the cytoplasmic Clostridial toxin substrate over time intervals that are, e.g., no more than 1 minute apart, no more than 5 minutes apart, no more than 10 minutes apart, no more than 15 minutes apart, no more than 30 minutes apart and no more than 30 minutes apart. Other aspects of this embodiment include detecting the fluorescence intensity of the cytoplasmic Clostridial toxin substrate over time intervals that are, e.g., no less than 15 minutes apart, no less than 30 minutes apart, no less than 45 minutes apart, no less than 60 minutes apart, no less than 90 minutes apart and no less than 120 minutes apart. Still other aspects of this embodiment include detecting the fluorescence intensity of the cytoplasmic Clostridial toxin substrate continuously over time for, e.g., at most about 5 minutes, at most about 10 minutes, at most about 15 minutes, at most about 30 minutes, at most about 45 minutes, at most about 60 minutes, at most about 90 minutes and at most about 120 minutes. Still other aspects of this embodiment include detecting the fluorescence intensity of the cytoplasmic Clostridial toxin substrate continuously over time for, e.g., at least about 15 minutes, at least about 30 minutes, at least about 45 minutes, at least about 60 minutes, at least about 90 minutes and at least about 120 minutes. [0234] In another embodiment, Clostridial toxin activity from a sample is determined by detecting the fluorescence intensity of the membrane-localized Clostridial toxin substrate from the contacted cell population, where a decreased in fluorescence intensity of the membrane-localized substrate from the contacted cell population, as compared to the control cell population, is indicative of Clostridial toxin activity. It is understood that fluorescence intensity can be detected from a single time point or a plurality of time points. It is envisioned that comparison of the fluorescence intensity detected from the contacted cell population to the fluorescence intensity detected from the control cell population can be made using the values obtained from the same, or similar time point or from different time points. Thus, aspect of this embodiment include detecting the fluorescence intensity of the membrane-localized Clostridial toxin substrate from the contacted cell population and control cell population in, e.g., at least one different time point, at least two different time points, at least three different time points, at least four different time points, at least five different time points, at least ten different time points and at least 20 different time points. Other aspects of this embodiment can include comparison of the fluorescence intensity detected from the contacted cell population obtained from a single time point to the fluorescence intensity detected from the control cell population obtained, e.g., at the same time point, at a similar time point, at a time point later than the time point obtained from the contact cell population, at a time point earlier than the time point obtained from the contact cell population, at a plurality time points later than the time point obtained from the contact cell population, at a plurality time points earlier than the time point obtained from the contact cell population and at a plurality time point both later than and earlier than the time point 92 of 168 WO 2008/036060 PCTIUS2006/012825 obtained from the contact cell population, Other aspects of this embodiment can include comparison of the fluorescence intensity detected from the contacted cell population obtained from a plurality of time points to the fluorescence intensity detected from the control cell population obtained, e.g., from a single time point, at the same time points, at a similar time points, at a time point later than the time points obtained from the contact cell population, at a time point earlier than the time points obtained from the contact cell population, at a plurality time points later than the time points obtained from the contact cell population, at a plurality time points earlier than the time points obtained from the contact cell population and at a plurality time point both later than and earlier than the time points obtained from the contact cell population, [0235] In another embodiment, Clostridial toxin activity from a sample is determined by detecting the fluorescence intensity of the cytoplasmic Clostridial toxin substrate from the contacted cell population, where an increased in fluorescence intensity of the cytoplasmic substrate from the contacted cell population, as compared to the control cell population, is indicative of Clostridial toxin activity. It is understood that fluorescence intensity can be detected from a single time point or a plurality of time points. It is envisioned that comparison of the fluorescence intensity detected from the contacted cell population to the fluorescence intensity detected from the control cell population can be made using the values obtained from the same, or similar time point or from different time points. Thus, aspect of this embodiment include detecting the fluorescence intensity of the cytoplasmic Clostridial toxin substrate from the contacted cell population and control cell population in, e.g., at least one different time point, at least two different time points, at least three different time points, at least four different time points, at least five different time points, at least ten different time points and at least 20 different time points. Other aspects of this embodiment can include comparison of the fluorescence intensity detected from the contacted cell population obtained from a single time point to the fluorescence intensity detected from the control cell population obtained, e.g., at the same time point, at a similar time point, at a time point later than the time point obtained from the contact cell, population at a time point earlier than the time point obtained from the contact cell population, at a plurality time points later than the time point obtained from the contact cell population, at a plurality time points earlier than the time point obtained from the contact cell population and at a plurality time point both later than and earlier than the time point obtained from the contact cell population, Other aspects of this embodiment can include comparison of the fluorescence intensity detected from the contacted cell population obtained from a plurality of time points to the fluorescence intensity detected from the control cell population obtained, e.g., from a single time point, at the same time points, at a similar time points, at a time point later than the time points obtained from the contact cell population, at a time point earlier than the time points obtained from the contact cell population, at a plurality time points later than the time points obtained from the contact cell population, at a plurality time points earlier than the time points obtained from the contact cell population and at a plurality time point both later than and earlier than the time points obtained from the contact cell population, [0236] In another embodiment, Clostridial toxin activity from a sample is determined by detecting the fluorescence intensity of the Clostridial toxin substrate found in a certain sub-cellular area of cells 93 of 168 WO 2008/036060 PCTIUS2006/012825 comprising the contacted cell population. Aspects of this embodiment can include detecting a decreased in fluorescence intensity of the Clostridial toxin substrate found in a certain sub-cellular area of the cells comprsing the contacted cell population, detecting an increase in fluorescence intensity of the Clostridial toxin substrate found in a certain sub-cellular area of the cells comprsing the contacted cell population, or both. In other aspects of this embodiment, the sub-cellular region can be, e.g., the cell membrane, the cytoplasm, the endoplasmic reticulum, an organelle and a vesicle. [0237] In a method of the invention, fluorescence of a contacted cell typically is determined using a fluorimeter. In general, excitation radiation from an excitation source having a first wavelength passes through excitation optics. The excitation optics cause the excitation radiation to excite the substrate in the cell. In response, the fluorescent member in the substrate emit radiation which has a wavelength that is different from the excitation wavelength. Collection optics then collect the emission; if desired, the device includes a temperature controller to maintain the cell at a specific temperature while being scanned. If desired, a multi axis translation stage moves a microtiter plate containing a plurality of samples in order to position different wells to be exposed. It is understood that the multi-axis translation stage, temperature controller, auto-focusing feature, and electronics associated with imaging and data collection can be managed by the appropriate digital computer. 10238] It is further understood that the methods of the invention can be automated and can be configured in a high throughput or ultra high-throughput format using, without limitation, 96-well, 384-well or 1536-well plates. As one non-limiting example, fluorescence emission can be detected using the SpectraMax M5 microplate reader (Molecular Devices, Sunnyvale, CA), a dual-monochromator, multi detection microplate reader with a wavelength range of 250-850 nm and a 6-384 microplate reading capability. As another non-limiting example, fluorescence emission can be detected using the Typhoon T M 9410 system (Amersham Biosciences, Piscataway, NJ). Designd for microplate assays, this system utilizes is capable of excitation fluorescence at 488 nm, 532 nm or 633 nm and has a semiconfocal optimal system with a charge coupled device (CCD) camera to illuminate and image the entire plate. The FPM-2 96-well plate reader (Folley Consulting and Research, Round Lake, IL) also can be useful in detecting fluorescence emission in the methods of the invention. One skilled in the art understands that these and other automated systems with the appropriate spectroscopic compatibility such as the ECLIPSE cuvette reader (Varian-Cary; Walnut Creek, CA) and the FLIPR@ and Gemini XPS spectrofluorometer systems (Molecular Devices, Sunnyvale, CA). [0239] It is envisioned that a variety of conditions suitable for determining Clostridial toxin activity in a sample can be useful according to the methods disclosed in the present specification. In aspects of this embodiment, conditions suitable for determining Clostridial toxin activity can be provided such that, e.g., at least 10% of the substrate is cleaved, at least 20% of the substrate is cleaved, at least 30% of the substrate is cleaved, at least 40% of the substrate is cleaved, at least 50% of the substrate is cleaved, at least 60% of the substrate is cleaved, at least 70% of the substrate is cleaved, at least 80% of the substrate is cleaved or at least 90% of the substrate is cleaved. In other aspects of this embodiment, conditions suitable for determining Clostridial toxin activity can be provided such that, e.g., at most 10% of 94 of 168 WO 2008/036060 PCT/US2006/012825 the substrate is cleaved, at most 20% of the substrate is cleaved, at most 30% of the substrate is cleaved, at most 40% of the substrate is cleaved, at most 50% of the substrate is cleaved, at most 60% of the substrate is cleaved, at most 70% of the substrate is cleaved, at most 80% of the substrate is cleaved or at most 90% of the substrate is cleaved. In another aspect of this embodiment, conditions suitable for determining Clostridial toxin activity can be provided such that 100% of the substrate is cleaved. In another aspect of this embodiment, the conditions suitable for determining Clostridial toxin activity are provided such that the assay is linear. In another aspect of this embodiment, the conditions suitable for determining Clostridial toxin activity are provided such that the assay is non-linear. [0240] Clostridial toxins are zinc metalloproteases, and a source of zinc, such as zinc chloride or zinc acetate, typically in the range of I to 500 pM, for example, 5 to 10 pM can be included, if desired, as part of the conditions suitable for determining Clostridial toxin activity. One skilled in the art understands that zinc chelators such as EDTA generally are excluded from a buffer for determining the presence or activity of a Clostridial toxin. [0241] The concentration of purified or partially purified Clostridial toxin to be assayed in a method of the invention generally is in the range of about 0.0001 ng/ml to 500 pg/ml toxin, for example, about 0.0001 ng/ml to 50 pg/ml toxin, 0.001 ng/ml to 500 pg/ml toxin, 0.001 ng/ml to 50 pg/ml toxin, 0.0001 to 5000 ng/ml toxin, 0.001 ng/ml to 5000 ng/ml, 0.01 ng/ml to 5000 ng/ml, 0.1 ng/ml to 5000 ng/ml, 0.1 ng/ml to 500 ng/ml, 0.1 ng/ml to 50 ng/ml, 1 ng/ml to 5000 ng/ml, 1 ng/ml to 500 ng/ml, 1 ng/ml to 50 ng/ml, 10 ng/ml to 5000 ng/ml, 10 ng/ml to 500 ng/ml, 50 ng/ml to 5000 ng/ml, 50 ng/ml to 500 ng/ml or 100 ng/ml to 5000 ng/ml toxin, which can be, for example, purified recombinant dichain or single chain toxin or formulated Clostridial toxin product containing human serum albumin and excipients. In aspects of this embodiment, the concentration of purified or partially purified Clostridial toxin assayed results in cleavage of, e.g., at least 10% of the total substrate present, at least 20% of the total substrate present, at least 30% of the total substrate present, at least 40% of the total substrate present, at least 50% of the total substrate present, at least 60% of the total substrate present, at least 70% of the total substrate present, at least 80% of the total substrate present or at least 90% of the total substrate present. In further aspects of this embodiment, the concentration of purified or partially purified Clostridial toxin assayed results in cleavage of, e.g., at most 10% of the total substrate present, at most 20% of the total substrate present, at most 30% of the total substrate present, at most 40% of the total substrate present, at most 50% of the total substrate present, at most 60% of the total substrate present, at most 70% of the total substrate present, at most 80% of the total substrate present or at most 90% of the total substrate present. In another aspect of this embodiment, the concentration of purified or partially purified Clostridial toxin assayed results in cleavage of 100% of the total substrate present. [02421 The concentration of purified or partially purified Clostridial toxin assayed in a method of the invention can be, for example, in the range of about 0.1 pM to 500 pM, 0.1 pM to 100 pM, 0.1 pM to 10 pM, 0.1 pM to 1 pM, 0.1 pM to 500 nM, 0.1 pM to 100 nM, 0.1 pM to 10 nM, 0.1 pM to 1 nM, 0.1 pM to 500 pM, 0.1 pM to 100 pM, 0.1 pM to 50 pM, 0.1 pM to 10 pM, 1 pM to 500 pM, 1 pM to 100 pM, 1 pM to 10 pM, 1 pM to 1 pM, 1 pM to 500 nM, 1 pM to 100 nM, 1 pM to 10 nM, 1 pM to 1 nM, 1 pM to 500 pM, 1 95 of 168 WO 2008/036060 PCTIUS2006/012825 pM to 100 pM, 1 pM to 50 pM, 1 pM to 10 pM, 10 pM to 500 PM, 10 pM to 100 PM, 10 pM to 10 pM, 10 pM to 10 pM, 10 pM to 500 nM, 10 pM to 100 nM, 10 pM to 10 nM, 10 pM to 1 nM, 10 pM to 500 pM, 10 pM to 100 pM, 10 pM to 50 pM, 100 pM to 500 pM, 100 pM to 100 pM, 100 pM to 10 pM, 100 pM to 1 pM,100 pM to 500 nM, 100 pM to 100 nM, 100 pM to 10 nM, 100 pM to 1 nM, 100 pM to 500 pM1 nM to 500 pM, 1 nM to 100 pM, 1 nM to 10 pM, 1 nM to 1 pM, 1 nM to 500 nM, 1 nM to 100 nM, 1 nM to 50 nM, 1 nM to 10 nM, 3 nM to 100 nM toxin, which can be, for example, purified native or recombinant light chain or dichain toxin or formulated Clostridial toxin product containing human serum albumin and excipients. One skilled in the art understands that the concentration of purified or partially purified Clostridial toxin will depend on the serotype of the toxin assayed, as well as the purity or recombinant sequence of the toxin, the presence of inhibitory components, and the assay conditions. It is additionally understood that purified, partially purified or crude samples can be diluted to within a convenient range for assaying for Clostridial toxin activity against a standard curve. Similarly, it is understood that a sample can be diluted, if desired, such that the assay is linear. In aspects of this embodiment, the concentration of purified or partially purified Clostridial toxin assayed results in cleavage of, e.g., at least 10% of the total substrate present, at least 20% of the total substrate present, at least 30% of the total substrate present, at least 40% of the total substrate present, at least 50% of the total substrate present, at least 60% of the total substrate present, at least 70% of the total substrate present, at least 80% of the total substrate present at least 90% of the total substrate present. In further aspects of this embodiment, the concentration of purified or partially purified Clostridial toxin assayed results in cleavage of, e.g., at most 10% of the total substrate present, at most 20% of the total substrate present, at most 30% of the total substrate present, at most 40% of the total substrate present, at most 50% of the total substrate present, at most 60% of the total substrate present, at most 70% of the total substrate present, at most 80% of the total substrate present at most 90% of the total substrate present. In another aspect of this embodiment, the concentration of purified or partially purified Clostridial toxin assayed results in cleavage of 100% of the total substrate present. [0243] In still another embodiment, it is envisioned that any and all temperatures that allow the function of a Clostridial activity assay can be used in methods disclosed in the present specification. Assay temperatures can be varied as appropriate by one skilled in the art and generally depend, in part, on the concentration, purity and activity of the Clostridial toxin, the sample to be assayed, the assay time or the convience of the artisan. Thus, an assay temperature should not be as low as to cause the solution to freeze and should not be as high as to denature the Clostridial toxin, the Clostridial toxin substrate disclosed in the present specification. In an aspect of this embodiment, the assay is performed within a temperature range above 0 *C, but below 40 *C. In another aspect of this embodiment, the assay is performed within a temperature range of about 4 *C to about 37 CC. In yet another aspect of this embodiment, the assay is performed within a temperature range of about 2 *C to 10 *C. In yet another aspect of this embodiment, the assay is performed at about 4 *C. In still another aspect of this embodiment, the assay is performed within a temperature range of about 10 CC to about 18 CC. In still another aspect of this embodiment, the assay is performed at about 16 *C. In yet another aspect of this embodiment, the assay is performed within a temperature range of about 18 *C to about 32 *C. In yet another aspect of this embodiment, the assay is performed at about 20 *C. In another aspect of this 96 of 168 WO 2008/036060 PCT/US2006/012825 embodiment, the assay is performed within a temperature range of about 32 *C to about 40 *C. In another aspect of this embodiment, the assay is performed at about 37 0C. In aspects of this embodiment, the amount of Clostridial toxin substrate cleaved within a temperature range is, e.g., at least 10% of the total substrate present, at least 20% of the total substrate present, at least 30% of the total substrate present, at least 40% of the total substrate present, at least 50% of the total substrate present, at least 60% of the total substrate present, at least 70% of the total substrate present, at least 80% of the total substrate present or at least 90% of the total substrate present. In further aspects of this embodiment, the amount of Clostridial toxin substrate cleaved within a temperature range is, e.g., at most 10% of the total substrate present, at most 20% of the total substrate present, at most 30% of the total substrate present, at most 40% of the total substrate present, at most 50% of the total substrate present, at most 60% of the total substrate present, at most 70% of the total substrate present, at most 80% of the total substrate present or at most 90% of the total substrate present. In another aspect of this embodiment, the amount of Clostridial toxin substrate cleaved within a temperature range is 100%. [0244] In still another embodiment, it is foreseen that any and all times sufficient for the detection of the presence of Clostridial toxin substrate cleavage products can be used in methods disclosed in the present specification. Assay times can be varied as appropriate by the skilled artisan and generally depend, in part, on the concentration, purity and activity of the Clostridial toxin, the sample to be assayed, incubation temperature or the convience of the artisan. Assay times generally vary, without limitation, in the range of about 15 minutes to about 4 hours, 30 minutes to 8 hours, 1 hours to 12 overs, 2 hours to 24 hours, 4 hours to 48 hours, 6 hours to 72 hours. In aspects of this embodiment, the amount of Clostridial toxin substrate cleaved during an assay time is, e.g., at least 10% of the total substrate present, at least 20% of the total substrate present, at least 30% of the total substrate present, at least 40% of the total substrate present, at least 50% of the total substrate present, at least 60% of the total substrate present, at least 70% of the total substrate present, at least 80% of the total substrate present or at least 90% of the total substrate present. In further aspects of this embodiment, the amount of Clostridial toxin substrate cleaved during an assay time is, e.g., at most 10% of the total substrate present, at most 20% of the total substrate present, at most 30% of the total substrate present, at most 40% of the total substrate present, at most 50% of the total substrate present, at most 60% of the total substrate present, at most 70% of the total substrate present, at most 80% of the total substrate present or at most 90% of the total substrate present. In another aspect of this embodiment, the amount of Clostridial toxin substrate cleaved during an assay time is 100%. It is understood that assays can be terminated, if desired, prior to exciting the fluorescent member. [0245] The following examples are intended to illustrate but not limit aspects of the present invention. EXAMPLES [0246] The following non-limiting examples are provided for illustrative purposes only in order to facilitate a more complete understanding of disclosed embodiments and are in no way intended to limit any of the embodiments disclosed in the present invention. 97 of 168 WO 2008/036060 PCTIUS2006/012825 EXAMPLE I Construction of Clostridial Toxin Substrates 1. Construction of BoNT/A, BoNT/C1 and BoNT/E SNAP-25 substrates 1a. Construction of pQBI25/SNAP-25m-GFP [0247] To construct pOBI-25/GFP-SNAP-25 0 , a pGEX/SNAP-252m construct was digested with BamHI and EcoRi to excise a fragment containing the entire open reading frame of SNAP-252w. The resulting restriction fragment was purified by the QlAquick Gel Extraction Kit (QIAGEN, Inc., Valencia, CA), and subcloned using a T4 DNA ligase procedure into a pQBI-25C3 vector (Obiogene, Inc., Irvine, CA), digested BamHI and EcoRl, to yield pQBI-25/GFP-SNAP-25m. The ligation mixture was transformed into chemically competent E. coli TOP10 cells (Invitrogen, Inc, Carlsbad, CA) using a heat shock method, plated on 1.5% Luria-Bertani agar plates (pH 7.0) containing 100 pg/mL of Ampicillin, and placed in a 37 *C incubator for overnight growth. Ampicillin-resistant colonies were analyzed using an alkaline lysis plasmid mini-preparation procedure and candidate expression constructs were screened by restriction endonuclease mapping to determine the presence and orientation of the correct insert fragment. Cultures containing the desired expression construct were used to inoculate 1 L baffled flasks containing 200 mL of Luria-Bertani media containing 100 pg/mL of Ampicillin and placed in a 37 *C incubator, shaking at 250 rpm, for overnight growth. Purified plasmid DNA corresponding to an expression construct was isolated using the QIAGEN Maxi-prep method (QIAGEN, Inc., Valencia, CA) and sequenced to verify that the correct expression construct was made (service contract with Sequetech Corp., Mountain View, CA). This cloning strategy yielded a pQBI-25 expression construct encoding a GFP-SNAP-252e. [0248] To construct pQBI-25/SNAP-252N-GFP, a nucleic acid fragment encoding the amino acid region comprising SNAP-252w is amplified from pQBI-25/GFP-SNAP25M6 DNA using a polymerase chain reaction method and subcloned into a pCR2.1 vector using the TOPO* TA cloning method (Invitrogen, Inc, Carlsbad, CA). The resulting pCR2.1/SNAP-252e construct is digested with BamHI and EcoRl to excise a fragment containing the entire open reading frame of SNAP-25m. The resulting restriction fragment was purified by the QlAquick Gel Extraction Kit (QIAGEN, Inc., Valencia, CA), and subcloned using a T4 DNA ligase procedure into a pQBI-25A2 vector (Obiogene, Inc., Irvine, CA), digested BamHI and EcoRI, to yield pQBI-25/SNAP-25 2 0-GFP. The ligation mixture was transformed into chemically competent E. collTOP1O cells (Invitrogen, Inc, Carlsbad, CA) using a heat shock method, plated on 1.5% Luria-Bertani agar plates (pH 7.0) containing 100 pg/mL of Ampicillin, and placed In a 37 *C incubator for overnight growth. Ampicillin-resistant colonies were analyzed using an alkaline lysis plasmid mini preparation procedure and candidate expression constructs were screened by restriction endonuclease mapping to determine the presence and orientation of the correct insert fragment. Cunures containing the desired expression construct were used to inoculate 1 L baffled flasks containing 200 mL of Luria-Bertani media containing 100 pg/mL of Ampicillin and placed in a 37 *C incubator, shaking at 250 rpm, for overnight growth. Purified plasmid DNA corresponding to an expression construct was isolated using the QIAGEN Maxi-prep method (QIAGEN, Inc., Valencia, CA) and sequenced to verify that the correct 98 of 168 WO 2008/036060 PCTIUS2006/012825 expression construct was made (service contract with Sequetech Corp., Mountain View, CA). This cloning strategy yielded a pOBI-25 expression construct encoding a SNAP-2520-GFP. 1b. Construction of pQBI25/SNAP-25nr-GFP 10249] To construct pQBI-25/SNAP-25 2 06 -GFP, a nucleic acid fragment encoding the amino acid region comprising SNAP-252m is amplified from pQBI-25/GFP-SNAP25 2 06 DNA using a polymerase chain reaction method and subcloned into a pCR2.1 vector using the TOPO* TA cloning method (Invitrogen, Inc. Carlsbad, CA). The resulting pCR2.1/SNAP-252m construct is digested with BamHl and EcoRI to excise a fragment containing the entire open reading frame of SNAP-252m. The resulting restriction fragment was purified by the QlAquick Gel Extraction Kit (QIAGEN, Inc., Valencia, CA), and subcloned using a T4 DNA ligase procedure into a pQBI-25A2 vector (Obiogene, Inc., Irvine, CA), digested BamHI and EcoRl, to yield pQBI-25/SNAP-25 2 o 6 -GFP. The ligation mixture was transformed into chemically competent E coli TOP10 cells (Invitrogen, Inc, Carlsbad, CA) using a heat shock method, plated on 1.5% Luria-Bertani agar plates (pH 7.0) containing 100 pg/mL of Ampicillin, and placed in a 37 *C incubator for overnight growth. Ampicillin-resistant colonies were analyzed using an alkaline lysis plasmid mini preparation procedure and candidate expression constructs were screened by restriction endonuclease mapping to determine the presence and orientation of the correct insert fragment. Cultures containing the desired expression construct were used to inoculate 1 L baffled flasks containing 200 mL of Luria-Bertani media containing 100 pg/mL of Ampicillin and placed in a 37 *C incubator, shaking at 250 rpm, for overnight growth. Purified plasmid DNA corresponding to an expression construct was isolated using the QIAGEN Maxi-prep method (QIAGEN, Inc., Valencia, CA) and sequenced to verify that the correct expression construct was made (service contract with Sequetech Corp., Mountain View, CA). This cloning strategy yielded a pQBI-25 expression construct encoding a SNAP-25 2 N-GFP. 1c. Subcellular localization of SNAP-25-GFP substrate and cleavage products [0250] In order to determine whether a BoNT/A substrate can localize to the cell membrane, we assessed whether a cell expressing a plasmid encoding a SNAP-25-GFP substrate was able to localized the substrate to the cell membrane. To transiently express a SNAP-25-GFP substrate in a cell line, a suitable density of PC12 cells was plated into the wells of 6-well, poly-D-lysine/Laminin coated, tissue culture plates containing 3 mL of a suitable medium (see Table 12), and grown in a 37 *C incubator under 5% carbon dioxide until cells reach the desired density (see Table 12). A 500 pL transfection solution is prepared by adding 250 pL of OPTI-MEM Reduced Serum Medium containing 15 pL of LipofectAmine 2000 (Invitrogen, Carlsbad, CA) incubated at room temperature for 5 minutes to 250 pL of OPTI-MEM Reduced Serum Medium containing 10 pg of a pQBI-25/GFP-SNAP-252M construct or 10 pg of a QBI 25/SNAP-25 2 o-GFP construct. This transfection was incubated at room temperature for approximately 20 minutes. The media was replaced with fresh unsupplemented media and the 500 pL transfection solution was added to the cells. The cells were then incubated in a 37 *C incubator under 5% carbon dioxide for approximately 6 to 18 hours. Transfection media was replaced with 3 mL of fresh media and incubate cells in a 37 *C incubator under 5% carbon dioxide. After 48 hours, cells were fixed with paraformaldehyde and imaged in a confocal microscope as described in, e.g., Ester Femandez-Salas et al., Plasma membrane localization signals in the light chain of botulinum neurotoxin, 101(9) Proc. Natl. 99 of 168 WO 2008/036060 PCT/US2006/012825 Acad. Sci. U. S. A. 3208-3213 (2004). Both the GFP-SNAP25 2 m and SNAP25M-GFP substrates localized to the plasma membrane (see FIG. 4). [0251] In order to determine whether a cell membrane-localized BoNT/A substrate can be susceptible to BoNT/A cleavage, we assessed whether BoNT/A exposure to a cell containing a membrane-localized SNAP-25-GFP substrate resulted in the cleavage of the substrate. PC12 cells were transiently transfected with pQBI-25-SNAP25 2 N-GFP a plasmid construct that encodes a SNAP252-GFP substrate, and pcDNA3.1-LC/A, a plasmid construct that encodes the light chain of BoNT/A as described above in Example 1, 1b. Observation of living cells 24 to 48 hours post-transfection using a fluorescence inverted microscope indicated that PC12 cells co-expressing SNAP252-GFP and the light chain of BoNT/A resulted in a change in fluorescent intensity relative to control cells expressing only the SNAP252-GFP substrate. The change in fluorescent intensity resulted from a reduced level of fluorescence emitted from the cells, as well as a change in subcellular localization of the GFP fluorescence; fluorescence in the cells co-expressing both substrate and enzyme was observed in the cytoplasm with accumulation in some areas or cytoplasmic structures (see FIG. 4). This cytoplasmic accumulation appears to represent the cleavage product containing the 9 amino acid cleavage fragment from SNAP-25 fused to GFP. These results indicate that there is a distinct fluorescence pattern as well as a different degree of fluorescence in cells containing the uncleaved SNAP252-GFP substrate as compared to cells containing the cleavage products of this substrate (SNAP25 1 m and the remaining 9 residue fragment of SNAP-25 fused to GFP). 1d. Construction of pQBI67/SNAP-25 2 0 -GFP [0252] To construct pQBI-67/SNAP-25 20 6 -GFP, a nucleic acid fragment encoding the amino acid region comprising SNAP-25m 6 -GFP substrate is amplified from pQBI-25/SNAP25 2 M-GFP DNA using a polymerase chain reaction method and subcloned into a pCR2.1 vector using the TOPO* TA cloning method (Invitrogen, Inc, Carlsbad, CA). The forward and reverse oligonucleotide primers used for this reaction are designed to include unique restriction enzyme sites useful for subsequent subcloning steps. The resulting pCR2.1/SNAP-252o-GFP construct is digested with restriction enzymes that 1) excise the insert containing the entire open reading frame encoding the SNAP-252-GFP peptide; and 2) enable this insert to be operably-linked to a pQBI-67 vector (Obiogene, Inc., Irvine, CA). This insert is subcloned using a T4 DNA ligase procedure into a pQBI-67 vector that is digested with appropriate restriction endonucleases to yield pQBI-67/ SNAP-252-GFP. The ligation mixture is transformed into chemically competent E. coli BL21 (DE3) cells (Invitrogen, Inc, Carlsbad, CA) using a heat shock method, plated on 1.5% Luria-Bertani agar plates (pH 7.0) containing 100 pg/mL of Ampicillin, and placed In a 37 *C incubator for overnight growth. Bacteria containing expression constructs are identified as Ampicillin resistant colonies. Candidate constructs are isolated using an alkaline lysis plasmid mini-preparation procedure and analyzed by restriction endonuclease digest mapping to determine the presence and orientation of the inset. This cloning strategy yields a mammalian expression construct encoding the SNAP-25 206 -GFP operably-linked to the expression elements of the pQBI-67 vector. 2. Construction of BoNT/B, BoNT/D, BoNT/F, BoNT/G and TeNT VAMP substrates 100 of 168 WO 2008/036060 PCTIUS2006/012825 2a. Construction of pQB125/VAMP-1-GFP [0253] To make a VAMP-1 substrate suitable for methods disclosed in the present specification, a pQBI 25NAMP-1-GFP construct will be made using a Splicing by Overlapping ends polymerase chain reaction (SOE-PCR) procedure, see, e.g., R. M. Horton et al., Engineering hybrid genes without the use of restriction enzymes: gene splicing by overlapping extension, 77(1) Gene 61-68 (1989); and R. M. Horton, PCR-mediated recombination and mutagenesis. SOEing together tailor-made genes, 3(2) Mol. Biotechnol. 93-99 (1995). A nucleic acid fragment comprising a region encoding amino acids 85 to 120 of SNAP-25 (SEQ ID NO: 1) will be operably-linked by SOE-PCR to a VAMP-1 sequence comprising a region encoding amino acids 49-92 of SEQ ID NO: 28 and subcloned into a pCR2.1 vector using the TOPO* TA cloning method (Invitrogen, Inc, Carlsbad, CA). The forward and reverse oligonucleotide primers used for these reaction are designed to include unique restriction enzyme sites useful for subsequent subcloning steps. The resulting pCR2.NAMP-1 construct is digested with restriction enzymes that 1) excise the insert containing the entire open reading frame encoding amino acids 85-120 of SNAP-25 (SEQ ID NO: 1) and amino acids 49-92 of VAMP-1 (SEQ ID NO: 28); and 2) enable this insert to be operably-linked to a pQBI-25A vector (Qbiogene, Inc., Carlsbad, CA). The resulting restriction fragment will be purified by the QlAquick Gel Extraction Kit (QIAGEN, Inc., Valencia, CA), and will be subcloned using a T4 DNA ligase procedure into a pQBI-25A vector (Qbiogene, Inc., Irvine, CA) to yield pQBI-25NAMP-1-GFP. This cloning strategy yielded a pQBI-25 expression construct encoding a SNAP-25 membrane targeting domain comprising amino acids 85-120 of SNAP-25 (SEQ ID NO: 1), a Clostridial toxin recognition sequence comprising amino acids 49-92 of VAMP-1 (SEQ ID NO: 28) and a GFP all operably-linked and suitable to detect activity from BoNT/B, BoNT/D, BoNT/F, BoNT/G or TeNT [0254] The subcellular localization of VAMP-1-GFP substrates and their cleavage products will be analyzed using the procedures essentially as described above in Example I, 1c, with the exception that the pQBI-25NAMP-1-GFP construct described above in Example I, 2a will be used instead of expression constructs encoding SNAP-2520-GFP. In addition, a suitable expression construct encoding the light chain of an appropriate Clostridial toxin, such as, e.g., the light chain BoNT/B, BoNT/D, BoNT/F, BoNT/G or TeNT will be used instead of the pcDNA3.1-LC/A construct. 2b. Construction of pQB125/VAMP-2-GFP [0255] To make a VAMP-2 substrate suitable for methods disclosed in the present specification, a pQBI 25NAMP-2-GFP construct will be made using a SOE-PCR procedure. A nucleic acid fragment comprising a region encoding amino acids 85 to 120 of SNAP-25 (SEQ ID NO: 1) will be operably-linked by SOE-PCR to a VAMP-2 sequence comprising a region encoding amino acids 47-90 of SEQ ID NO: 31 and subcloned into a pCR2.1 vector using the TOPO* TA cloning method (Invitrogen, Inc, Carlsbad, CA). The forward and reverse oligonucleotide primers used for these reaction are designed to include unique restriction enzyme sites useful for subsequent subcloning steps. The resulting pCR2.1NAMP-2 construct Is digested with restriction enzymes that 1) excise the insert containing the entire open reading frame encoding amino acids 85-120 of SNAP-25 (SEQ ID NO: 1) and amino acids 47-90 of VAMP-2 (SEQ ID NO: 31); and 2) enable this insert to be operably-linked to a pQBI-25A vector (Obiogene, Inc., Carlsbad, 101 of 168 WO 2008/036060 PCTIUS2006/012825 CA). The resulting restriction fragment will be purified by the OlAquick Gel Extraction Kit (QIAGEN, Inc., Valencia, CA), and will be subcloned using a T4 DNA ligase procedure into a pQBI-25A vector (Obiogene, Inc., Irvine, CA) to yield pQBI-25NAMP-2-GFP. This cloning strategy yielded a pQBI-25 expression construct encoding a SNAP-25 membrane targeting domain comprising amino acids 85-120 of SNAP-25 (SEQ ID NO: 1), a Clostridial toxin recognition sequence comprising amino acids 47-90 of VAMP-2 (SEQ ID NO: 31) and a GFP all operably-linked and suitable to detect activity from BoNT/B, BoNT/D, BoNT/F, BoNT/G or TeNT [0256] The subcellular localization of VAMP-2-GFP substrates and their cleavage products will be analyzed using the procedures essentially as described above in Example I, 1c, with the exception that the pQBI-25NAMP-2-GFP construct described above in Example I, 2b will be used instead of expression constructs encoding SNAP-25 206 -GFP. In addition, a suitable expression construct encoding the light chain of an appropriate Clostridial toxin, such as, e.g., the light chain BoNT/B, BoNT/D, BoNT/F, BoNT/G or TeNT will be used instead of the pcDNA3.1-LC/A construct. 2c. Construction of pQBI25/VAMP-3-GFP [0257] To make a VAMP-3 substrate suitable for methods disclosed in the present specification, a pQBI 25NAMP-3-GFP construct will be made using a SOE-PCR procedure. A nucleic acid fragment comprising a region encoding amino acids 85 to 120 of SNAP-25 (SEQ ID NO: 1) will be operably-linked by SOE-PCR to a VAMP-3 sequence comprising a region encoding amino acids 34-77 of SEQ ID NO: 33 and subcloned into a pCR2.1 vector using the TOPO* TA cloning method (Invitrogen, Inc, Carlsbad, CA). The forward and reverse oligonucleotide primers used for these reaction are designed to include unique restriction enzyme sites useful for subsequent subcloning steps. The resulting pCR2.1NAMP-3 construct is digested with restriction enzymes that 1) excise the insert containing the entire open reading frame encoding amino acids 85-120 of SNAP-25 (SEQ ID NO: 1) and amino acids 34-77 of VAMP-3 (SEQ ID NO: 33); and 2) enable this insert to be operably-linked to a pQBI-25A vector (Qbiogene, Inc., Carlsbad, CA). The resulting restriction fragment will be purified by the QiAquick Gel Extraction Kit (QIAGEN, Inc., Valencia, CA), and will be subcloned using a T4 DNA ligase procedure into a pQBI-25A vector (Obiogene, Inc., Irvine, CA) to yield pQBI-25NAMP-3-GFP. This cloning strategy yielded a pQBI-25 expression construct encoding a SNAP-25 membrane targeting domain comprising amino acids 85-120 of SNAP-25 (SEQ ID NO: 1), a Clostridial toxin recognition sequence comprising amino acids 34-77 of VAMP-3 (SEQ ID NO: 33) and a GFP all operably-linked and suitable to detect activity from BoNT/B, BoNT/D, BoNT/F, BoNT/G or TeNT [0258] The subcellular localization of VAMP-3-GFP substrates and their cleavage products will be analyzed using the procedures essentially as described above in Example 1, 1c, with the exception that the pQBI-25NAMP-3-GFP construct described above in Example I, 2c will be used instead of expression constructs encoding SNAP-2520s-GFP. In addition, a suitable expression construct encoding the light chain of an appropriate Clostridial toxin, such as, e.g., the light chain BoNT/B, BoNT/D, BoNT/F, BoNT/G or TeNT will be used instead of the pcDNA3.1 -LC/A construct. 102 of 168 WO 2008/036060 PCT/US2006/012825 2d. Construction of pQ8I67/VAMP-1-GFP [0259] To construct pQBI-67NAMP-1-GFP, a nucleic acid fragment encoding the amino acid region comprising the VAMP-1-GFP substrate as described above in Example 1, 2a, is amplified from pQBI 25NAMP-1-GFP DNA using a polymerase chain reaction method and subcloned into a pCR2.1 vector using the TOPO* TA cloning method (Invitrogen, Inc, Carlsbad, CA). The forward and reverse oligonucleotide primers used for this reaction are designed to include unique restriction enzyme sites useful for subsequent subcloning steps. The resulting pCR2.1NAMP-1-GFP construct is digested with restriction enzymes that 1) excise the insert containing the entire open reading frame encoding the VAMP-1-GFP peptide; and 2) enable this insert to be operably-linked to a pQBI-67 vector (Obiogene, Inc., Irvine, CA). This insert is subcloned using a T4 DNA ligase procedure into a pQBI-67 vector that is digested with appropriate restriction endonucleases to yield pQBI-67NAMP-1-GFP. The ligation mixture is transformed into chemically competent E. coli BL21 (DE3) cells (Invitrogen, Inc, Carlsbad, CA) using a heat shock method, plated on 1.5% Luria-Bertani agar plates (pH 7.0) containing 100 pg/mL of Ampicillin, and placed in a 37 *C incubator for overnight growth. Bacteria containing expression constructs are identified as Ampicillin resistant colonies. Candidate constructs are isolated using an alkaline lysis plasmid mini-preparation procedure and analyzed by restriction endonuclease digest mapping to determine the presence and orientation of the inset. This cloning strategy yields a mammalian expression construct encoding the VAMP-1 -GFP operably-linked to the expression elements of the pQBI 67 vector. 2e. Construction of p0B167/VAMP-2-GFP [0260] To construct pQBI-67NAMP-2-GFP, a nucleic acid fragment encoding the amino acid region comprising the VAMP-2-GFP substrate as described above in Example I, 2b, Is amplified from pQBI 25NAMP-2-GFP DNA using a polymerase chain reaction method and subcloned into a pCR2.1 vector using the TOPO TA cloning method (Invitrogen, Inc, Carlsbad, CA). The forward and reverse oligonucleotide primers used for this reaction are designed to include unique restriction enzyme sites useful for subsequent subcloning steps. The resulting pCR2.1NAMP-2-GFP construct is digested with restriction enzymes that 1) excise the insert containing the entire open reading frame encoding the VAMP-2-GFP peptide; and 2) enable this insert to be operably-linked to a pQBI-67 vector (Qbiogene, Inc., Irvine, CA). This insert is subcloned using a T4 DNA ligase procedure into a pQBI-67 vector that is digested with appropriate restriction endonucleases to yield pQBI-67NAMP-2-GFP. The ligation mixture is transformed into chemically competent E. coli BL21 (DE3) cells (Invitrogen, Inc, Carlsbad, CA) using a heat shock method, plated on 1.5% Luria-Bertani agar plates (pH 7.0) containing 100 pg/mL of Ampicillin, and placed in a 37 *C incubator for overnight growth. Bacteria containing expression constructs are identified as Ampicillin resistant colonies. Candidate constructs are isolated using an alkaline lysis plasmid mini-preparation procedure and analyzed by restriction endonuclease digest mapping to determine the presence and orientation of the inset. This cloning strategy yields a mammalian expression construct encoding the VAMP-2-GFP operably-linked to the expression elements of the pQBI 67 vector. 103 of 168 WO 2008/036060 PCT/US2006/012825 2f. Construction of pOBI67/VAMP-3-GFP [0261] To construct pQBI-67NAMP-3-GFP, a nucleic acid fragment encoding the amino acid region comprising the VAMP-3-GFP substrate as described above in Example I, 2c, is amplified from pQBI 25NAMP-3-GFP DNA using a polymerase chain reaction method and subcloned into a pCR2.1 vector using the TOPO TA cloning method (Invitrogen, Inc, Carlsbad, CA). The forward and reverse oligonucleotide primers used for this reaction are designed to include unique restriction enzyme sites useful for subsequent subcloning steps. The resulting pCR2.1NAMP-3-GFP construct is digested with restriction enzymes that 1) excise the insert containing the entire open reading frame encoding the VAMP-3-GFP peptide; and 2) enable this insert to be operably-linked to a pQBI-67 vector (Qbiogene, Inc., Irvine, CA). This insert is subcloned using a T4 DNA ligase procedure into a pQBl-67 vector that is digested with appropriate restriction endonucleases to yield pQBI-67NAMP-3-GFP. The ligation mixture is transformed into chemically competent E coil BL21 (DE3) cells (Invitrogen, Inc, Carlsbad, CA) using a heat shock method, plated on 1.5% Luria-Bertani agar plates (pH 7.0) containing 100 pg/mL of Ampicillin, and placed in a 37 *C incubator for overnight growth. Bacteria containing expression constructs are identified as Ampicillin resistant colonies. Candidate constructs are isolated using an alkaline lysis plasmid mini-preparation procedure and analyzed by restriction endonuclease digest mapping to determine the presence and orientation of the inset. This cloning strategy yields a mammalian expression construct encoding the VAMP-3-GFP operably-linked to the expression elements of the pQBl 67 vector. 3. Construction of BoNT/C1 Syntaxin substrates 3a. Construction of pQB125/Syntaxn-1-GFP [0262] To make a Syntaxin-1 substrate suitable for methods disclosed in the present specification, a pQBI-25/Syntaxin-1-GFP construct will be made using a SOE-PCR procedure. A nucleic acid fragment comprising a region encoding amino acids 85 to 120 of SNAP-25 (SEQ ID NO: 1) will be operably-linked by SOE-PCR to a Syntaxin-1 sequence comprising a region encoding amino acids 242-264 of SEQ ID NO: 66 and subcloned into a pCR2.1 vector using the TOPO* TA cloning method (Invitrogen, Inc, Carlsbad, CA). The forward and reverse oligonucleotide primers used for these reaction are designed to include unique restriction enzyme sites useful for subsequent subcloning steps. The resulting pCR2.1/Syntaxin-1 construct is digested with restriction enzymes that 1) excise the insert containing the entire open reading frame encoding amino acids 85-120 of SNAP-25 (SEQ ID NO: 1) and amino acids 242-264 of Syntaxin-1 (SEQ ID NO: 66); and 2) enable this insert to be operably-linked to a pQBI-25A vector (Obiogene, Inc., Carlsbad, CA). The resulting restriction fragment will be purified by the QlAquick Gel Extraction Kit (QIAGEN, Inc., Valencia, CA), and will be subcloned using a T4 DNA ligase procedure into a pQBl-25A vector (Obiogene, Inc., Irvine, CA) to yield pOBI-25/Syntaxin-1-GFP. This cloning strategy yielded a pQBI-25 expression construct encoding a SNAP-25 membrane targeting domain comprising amino acids 85-120 of SNAP-25 (SEQ ID NO: 1), a Clostridial toxin recognition sequence comprising amino acids 242-264 of Syntaxin-1 (SEQ ID NO: 66) and a GFP all operably-linked and suitable to detect activity from BoNT/C1 104 of 168 WO 2008/036060 PCT/US2006/012825 [0263] The subcellular localization of Syntaxin-1-GFP substrates and their cleavage products wim Do analyzed using the procedures essentially as described above in Example 1, 1c, with the exception that the pQBI-25fSyntaxin-1-GFP construct described above in Example I, 2c will be used instead of expression constructs encoding SNAP-25 20 6 -GFP. In addition, a suitable expression construct encoding the light chain of an appropriate Clostridial toxin, such as, e.g., the light chain BoNT/C1 will be used instead of the pcDNA3.1-LC/A construct. 3b. Construction of pQB167/Syntaxln-1-GFP [02641 To construct pQBl-67/Syntaxin-1-GFP, a nucleic acid fragment encoding the amino acid region comprising the Syntaxin-1-GFP substrate as described above in Example 1, 3a, is amplified from pQBI 25/Syntaxin-1-GFP DNA using a polymerase chain reaction method and subcloned Into a pCR2.1 vector using the TOPO* TA cloning method (Invitrogen, Inc, Carlsbad, CA). The forward and reverse oligonucleotide primers used for this reaction are designed to include unique restriction enzyme sites useful for subsequent subcloning steps. The resulting pCR2.1/Syntaxin-1-GFP construct is digested with restriction enzymes that 1) excise the insert containing the entire open reading frame encoding the Syntaxin-1-GFP peptide; and 2) enable this insert to be operably-linked to a pOBl-67 vector (Obiogene, Inc., Irvine, CA). This insert is subcloned using a T4 DNA ligase procedure into a pQBI-67 vector that is digested with appropriate restriction endonucleases to yield pOBl-67/Syntaxin-11-GFP. The ligation mixture is transformed into chemically competent E. coli BL21 (DE3) cells (Invitrogen, Inc, Carlsbad, CA) using a heat shock method, plated on 1.5% Luria-Bertani agar plates (pH 7.0) containing 100 pg/mL of Ampicillin, and placed in a 37 *C incubator for overnight growth. Bacteria containing expression constructs are identified as Ampicillin resistant colonies. Candidate constructs are isolated using an alkaline lysis plasmid mini-preparation procedure and analyzed by restriction endonuclease digest mapping to determine the presence and orientation of the inset. This cloning strategy yields a mammalian expression construct encoding the Syntaxin-1-GFP operably-linked to the expression elements of the pQBI-67 vector. EXAMPLEII Identification of Cell Lines with High Affinity Uptake for CoNTs [02651 Distinct sensitivities to each of the CoNT serotypes might be expected based on the individual receptor systems for each different toxin and toxin serotype and their differing expression in different cell lines. The presence of a high affinity receptor system in a cell for CoNT can be characterized by two attributes: a rapid uptake of the neurotoxin by the cell, and a low neurotoxin concentration needed for cell intoxication. To identify a cell line having a high affinity receptor system for a CoNT, we tested cell lines using one of two different in vitro cleavage assay, one to determine the amount of toxin required for intoxication, the other to determine the length of time necessary for the cell to uptake the neurotoxin. 1. Identification of cell lines with high affinity uptake for BoNT/A 1a. Assay to determine the BoNTA concentration necessary for cell intoxication 105 of 168 WO 2008/036060 PCT/US2006/012825 [0266] In order to assess the amount of BoNTIA needed to intoxicate a cell, a panel of mammalian cell lines of neuronal origin was screened to determine the concentration of toxin necessary to cleave endogenously expressed SNAP-25 (see Table 12). A suitable seed density of cells from each line was plated into individual wells of 6-well, poly-D-lysine/Laminin coated, tissue culture plates containing 3 mL of a suitable medium (see Table 12), and grown in a 37 *C incubator under 5% carbon dioxide for approximately 24 hours. BoNT/A (Metabiologics, Inc., Madison, WI) was added at different concentrations (0 nM, 1 nM, 5 nM, 12.5 nM, 25 nM, 5OnM) in the culture medium containing the cells for approximately 8 or approximately 16 hours. Cells were collected in 15 ml tubes, washed once with 1 ml of phosphate-buffered saline, pH 7.4, and then transferred to 1.5 ml microcentrifuge tubes. Cells were lysed in 0.5 ml of lysis buffer containing 50 mM N-(2-hydroxyethyl) piperazine-N-(2-ethanesufonic acid) (HEPES), pH 6.8, 150 mM sodium chloride, 1.5 mM magnesium chloride, 1mM ethylene glycol bis(p aminoethyl ether) N, N, N' N'-tetraacetic acid (EGTA), 10% glycerol and 1% (v/v) Triton-X* 100 (4 octylphenol polyethoxylate), with rotation for 1 hour at 4 0 C. Lysed cells were centrifuged at 5000 rpm for 10 min at 4 0 C to eliminate debris and the supematants were transferred to fresh siliconized tubes. Protein concentrations were measured by Bradford's method and resuspended in 1 x SDS sample buffer at 1mg/ml or higher concentration. 106 of 168 WO 2008/036060 PCTIUS2006/012825 - - - - -~ - - - - - - o 0 I CD cc cc c, Co ccc c8 c-c c( (D (DJ .. - -a :5 -a -= -= -t CI cc CC aC C C ac -5 A E N7 000~ 'a 16 Z . 0 0- P I .2 - ~ ~ ~ ~ ~ - -~ -<( < ~ ~ . < < < 0 c E- 0 w 0 0 0 0 IL) E O Lo 'aC/ EE w 0 6.9e- U CL L L EU EU -W LL; S' 0 CI E. .0 c C ' 0'U 0.L - - - .1Os 0 C z L LJ w L WO 2008/036060 PCTIUS2006/012825 [0267] To detect for the presence of a cleaved BoNT/A substrate, samples were boiled for 5 min, and 40 VI aliquots were separated by MOPS polyacrylamide gel electrophoresis using NuPAGE* Novex 4-12% Bis-Tris precast polyacrylamide gels (Invitrogen, Inc, Carlsbad, CA) under denaturing, reducing conditions. Separated peptides were transferred from the gel onto polyvinylidene fluoride (PVDF) membranes (Invitrogen, Inc, Carlsbad, CA) by Western blotting using a Trans-Blot* SD semi-dry electrophoretic transfer cell apparatus (Bio-Rad Laboratories, Hercules, CA). PVDF membranes were blocked by incubating at room temperature for 2 hours In a solution containing 25 mM Tris-Buffered Saline (25 mM 2-amino-2-hydroxymethyl-1,3-propanediol hydrochloric acid (Tris-HCI)(pH 7.4), 137 mM sodium chloride, 2.7 mM potassium chloride), 0.1% TWEEN-20, polyoxyethylene (20) sorbitan monolaureate, 2% bovine serum albumin, 5% nonfat dry milk. Blocked membranes were incubated at 4 *C for overnight in Tris-Buffered Saline TWEEN-20* (25 mM Tris-Buffered Saline, 0.1% TWEEN-20, polyoxyethylene (20) sorbitan monolaureate) containing a 1:5,000 dilution of rabbit polyclonal anti SNAP25 antiserum pAb anti-SNAP25197 #1, a polyclonal antibody which is specific for the SNAP251r cleavage product and does not cross-react with full-length SNAP25 2 0 w, (Allergan, Inc., generated under contract with Zymed Laboratories Inc., South San Francisco, CA). Primary antibody probed blots were washed three times for 15 minutes each time in Tris-Buffered Saline TWEEN-20. Washed membranes were incubated at room temperature for 2 hours in Tris-Buffered Saline TWEEN-20* containing a 1:20,000 dilution of goat polyclonal anti-rabbit Immunoglobulin G, heavy and light chains (IgG, H+L) antibody conjugated to horseradish peroxidase (HRP; Pierce Biotechnology, Inc., Rockford, IL) as a secondary antibody. Secondary antibody-probed blots were washed three times for 15 minutes each time in Tris-Buffered Saline TWEEN-20. Signal detection of the labeled BoNT/A SNAP251 9 rcleavage product was visualized using the ECL PiusTM Western Blot Detection System (Amersham Biosciences, Piscataway, NJ) and the membrane was imaged and cleavage product quantitated with a Typhoon 9410 Variable Mode Imager and Imager Analysis software (Amersham Biosciences, Piscataway, NJ). The choice of pixel size (100 to 200 pixels) and PMT voltage settings (350 to 600, normally 400) depended on the individual blot. A BoNT/A SNAP251i-cleavage product was detected in the cell lines SH-SY5Y, NG108-15, N1E-1 15, Neuro-2A and SK-N-BE(2) after at least an 8 hour incubation with at least 5 nM BoNT/A, thereby indicating the ability of BoNT/A to intoxicate these cell lines (see FIG. Sa). [0268] The mouse neuroblastoma cell line Neuro-2A was further analyzed with lower concentrations of BoNT/A to determine the concentration of neurotoxin necessary to cleave endogenously expressed SNAP-25. Cells were grown in poly-D-lysine/Laminin coated 6-well plates as described above in Example 11, la. BoNT/A (Metabiologics, Inc., Madison, WI) was added at different concentrations (0 nM, 0.05 nM, 0.1 nM, 0.2 nM, 0.5 nM, 1 nM, 5 nM and 20 nM) in the culture medium containing cells for either approximately 8 or approximately 16 hours. Toxin treated cells were harvested and lysed as described above in Example I1, la. The presence of a BoNT/A SNAP25 1 e-cleavage product was determined by Western blot analysis as described above in Example 11, 1 a. A BoNT/A SNAP25 1 97 -cleavage product was detected in the cell line Neuro-2A after at least a 8 hour incubation with at least 0.5 nM BoNT/A, thereby indicating the ability of BoNT/A to intoxicate these cell lines (see FIG. 5c). 108 of 168 WO 2008/036060 PCT/US2006/012825 1b. Assay to determine the time required by a cell to uptake BoNTIA [0269] In order to assess the amount of time needed by a cell line to uptake BoNT/A, a panel of mammalian cell lines of neuronal origin was screened to determine the length of toxin exposure necessary to cleave endogenously expressed SNAP-25. Cells from each line were grown in poly-D lysine/Laminin coated 6-well plates as described above in Example 11, 1a. Approximately I nM BoNT/A (Metabiologics, Inc., Madison, WI) was added to the culture medium for 10 min, 20 min, 30 min, 60 min 2 hours, 4 hours, 6 hours, 8 hours or 16 hours. Toxin treated cells were collected and lysed as described above in Example 11, 1a. The presence of a BoNT/A SNAP25 19 -cleavage product was determined by Western blot analysis as described above in Example lI, la. A BoNT/A SNAP25 1 97 -cleavage product was detected in the cell lines Neuro-2A, SH-SY5Y, and NG108-15 after at least an 8 hour incubation with 1 nM BoNT/A, thereby indicating the ability of these cell lines to rapidly uptake BoNT/A (see FIG. 5b). 2. Identification of cell lines with high affinity uptake for BoNT/B 2a. Assay to determine the BoNT/B concentration necessary for cell Intoxication [0270] In order to assess the amount of BoNT/B needed to intoxicate a cell line, a panel of mammalian cell lines of neuronal origin will be screened to determine the concentration of neurotoxin necessary to cleave endogenously expressed VAMP (see Table 12). Cells will be grown in poly-D-lysine/Laminin coated 6-well plates as described above in Example 1I, 1a. BoNT/B (Metabiologics, Inc., Madison, WI) will be added at different concentrations (0 nM, 1 nM, 2 nM, 5 nM, 10 nM, 20 nM and 100 nM) in the culture medium containing cells for either approximately 8 or approximately 16 hours. Cells will be harvested and lysed as described above in Example 1I, 1a. [0271] To detect for the presence of a cleaved BoNT/B substrate, western blot analysis will be conducted as described above in Example 11, I, with the exception that blocked PVDF membranes will be incubated in a primary antibody solution containing one of the following antibodies in order to detect a BoNT/B VAMP-cleavage product rather than the rabbit polyclonal anti-SNAP25 antiserum pAb anti SNAP25197 #1: 1) 1:1000 dilution of mouse monoclonal anti-VAMP-i antibody clone CI 10.1 (Synaptic Systems, Goettingen, Germany); 2) 1:20,000 dilution of mouse monoclonal anti-VAMP-2 antibody clone Cl 69.1 (Synaptic Systems, Goettingen, Germany); or 3) 1:1000 dilution of mouse monoclonal anti VAMP-3 antibody clone Cl 10.1 (Synaptic Systems, Goettingen, Germany). In addition, a secondary antibody solution containing a 1:20,000 dilution of goat polyclonal anti-mouse immunoglobulin G, heavy and light chains (igG, H+L) antibody conjugated to horseradish peroxidase (HRP; Pierce Biotechnology, Inc., Rockford, IL) will be used rather than the goat polyclonal anti-rabbit IgG-HRP antibody. Detection of a BoNT/B VAMP-cleavage product in a cell line after at least an 8 hours incubation with at least 20 nM BoNT/B will indicate the ability of BoNT/B to intoxicate these cell lines. 2b. Assay to determine the time required by a cell to uptake BoNT/B [0272] In order to assess the amount of time needed by a cell line to uptake BoNT/B, a panel of mammalian cell lines of neuronal origin will be screened to determine the length of toxin exposure necessary to cleave endogenously expressed VAMP. Cells will be grown in poly-D-lysine/Laminin coated 109 of 168 WO 2008/036060 PCT/US2006/012825 6-well plates as described above in Example 11, 2a. Approximately 1 nM BoNT/B (Metabiologics, Inc., Madison, WI) will be added to the culture medium for 10 min, 20 min, 30 min, 60 min 2 hours, 4 hours, 6 hours, 8 hours or 16 hours. Toxin treated cells will be harvested and lysed as described above in Example II, 2a. The presence of a BoNT/B VAMP-cleavage product will be determined by Western blot analysis as described above in Example 11, 2a. Detection of a BoNT/B VAMP-cleavage product in a cell line after at least an 8 hour incubation with 1 nM BoNT/B will indicate a cell line that can rapidly uptake BoNT/B. 3. Identification of cell lines with high affinity uptake for BoNT/C1 3e. Assay to determine the SoNT/CI concentration necessary for cell Intoxication [02731 In order to assess the amount of BoNT/C1 needed to intoxicate a cell line, a panel of mammalian cell lines of neuronal origin will be screened to determine the concentration of neurotoxin necessary to cleave endogenously expressed SNAP-25 or endogenously expressed Syntaxin (see Table 12). Cells will be grown in poly-D-lysine/Laminin coated 6-well plates as described above in Example 1I, la. BoNT/Ci (Metabiologics, Inc., Madison, WI) will be added at different concentrations (0 nM, 1 nM, 2 nM, 5 nM, 10 nM, 20 nM and 100 nM) in the culture medium containing cells for either approximately 8 or approximately 16 hours. Cells will be harvested and lysed as described above in Example 1I, 1a. [0274] To detect for the presence of a cleaved BoNT/C1 substrate, western blot analysis will be conducted as described above in Example 11, la, with the exception: 1) blocked PVDF membranes will be incubated in a primary antibody solution containing a 1:50,000 dilution of mouse monoclonal anti-SNAP 25 antibody (SMI-81; Sternberger Monoclonals, Lutherville, MD) rather than the rabbit polyclonal anti SNAP25 antiserum pAb anti-SNAP25197 #1 and a secondary antibody solution containing a 1:20,000 dilution of goat polyclonal anti-mouse immunoglobulin G, heavy and light chains (IgG, H+L) antibody conjugated to horseradish peroxidase (HRP; Pierce Biotechnology, Inc., Rockford, IL) rather than the goat polyclonal anti-rabbit IgG-HRP antibody in order to detect a BoNT/C1 SNAP25 1 98-cleavage product; 2) blocked PVDF membranes will be incubated in a primary antibody solution containing a 1:5000 dilution of mouse monoclonal anti-Syntaxin-1 antibody clone Cl 78.2 (Synaptic Systems, Goettingen, Germany) rather than the rabbit polyclonal anti-SNAP25 antiserum pAb anti-SNAP25197 #1 and a secondary antibody solution containing a 1:20,000 dilution of goat polyclonal anti-mouse immunoglobulin G, heavy and light chains (IgG, H+L) antibody conjugated to horseradish peroxidase (HRP; Pierce Biotechnology, Inc., Rockford, IL) rather than the goat polyclonal anti-rabbit IgG-HRP antibody in order to detect a BoNT/C1 Syntaxin-cleavage product. Detection of a SNAP25 1 9s-cleavage product in a cell line after at least an 8 hours incubation with at least 20 nM BoNT/C1 will indicate the ability of BoNT/C1 to intoxicate these cell lines. Detection of a Syntaxin-cleavage product in a cell line after at least an 8 hours incubation with at least 20 nM BoNT/C1 will indicate the ability of BoNT/C1 to intoxicate these cell lines. 3b. Assay to determine the time required by a cell to uptake BoNT/C1 [0275] In order to assess the amount of time needed by a cell line to uptake BoNT/C1, a panel of mammalian cell lines of neuronal origin will be screened to determine the length of toxin exposure 110 of 168 WO 2008/036060 PCT/US2006/012825 necessary to cleave endogenously expressed SNAP-25 or endogenously expressed Syntaxin. Cells will be grown in poly-D-lysine/Laminin coated 6-well plates as described above in Example Il, 3a. Approximately 1 nM BoNT/C1 (Metabiologics, Inc., Madison, WI) will be added to the culture medium for 10 min, 20 min, 30 min, 60 min 2 hours, 4 hours, 6 hours, 8 hours or 16 hours. Toxin treated cells will be harvested and lysed as described above in Example lI, 3a. The presence of a BoNT/C1 SNAP25 1 9 cleavage product and BoNT/C1 Syntaxin-cleavage product will be determined by Western blot analysis as described above in Example 11, 3a. Detection of a BoNT/C1 SNAP25 1 s-cleavage product in a cell line after at least an 8 hour incubation with 1 nM BoNT/C1 will indicate a cell line that can rapidly uptake BoNT/C1. Detection of a BoNT/C1 Syntaxin-cleavage product in a cell line after at least an 8 hour incubation with 1 nM BoNT/C1 will indicate a cell line that can rapidly uptake BoNT/C1. 4. Identification of cell lines with high affinity uptake for BoNT/D 4a. Assay to determine the BoNTD concentration necessary for cell intoxication [02761 In order to assess the amount of BoNT/D needed to intoxicate a cell line, a panel of mammalian cell lines of neuronal origin will be screened to determine the concentration of neurotoxin necessary to cleave endogenously expressed VAMP (see Table 12). Cells will be grown in poly-D-lysine/Laminin coated 6-well plates as described above in Example 11, 1a. BoNT/D (Metabiologics, Inc., Madison, WI) will be added at different concentrations (0 nM, 1 nM, 2 nM, 5 nM, 10 nM, 20 nM and 100 nM) in the culture medium containing cells for either approximately 8 or approximately 16 hours. Cells will be harvested and lysed as described above in Example 11, 1a. [0277] To detect for the presence of a cleaved BoNT/D substrate, westem blot analysis will be conducted as described above in Example 11, 1a, with the exception that blocked PVDF membranes will be incubated in a primary antibody solution containing one of the following antibodies in order to detect a BoNT/D VAMP-cleavage product rather than the rabbit polyclonal anti-SNAP25 antiserum pAb anti SNAP25197 #1: 1) 1:1000 dilution of mouse monoclonal anti-VAMP-i antibody clone Cl 10.1 (Synaptic Systems, Goettingen, Germany); 2) 1:20,000 dilution of mouse monoclonal anti-VAMP-2 antibody clone Cl 69.1 (Synaptic Systems, Goettingen, Germany); or 3) 1:1000 dilution of mouse monoclonal anti VAMP-3 antibody clone Cl 10.1 (Synaptic Systems, Goettingen, Germany). In addition, a secondary antibody solution containing a 1:20,000 dilution of goat polyclonal anti-mouse immunoglobulin G, heavy and light chains (IgG, H+L) antibody conjugated to horseradish peroxidase (HRP; Pierce Biotechnology, Inc., Rockford, IL) will be used rather than the goat polyclonal anti-rabbit IgG-HRP antibody. Detection of a BoNT/D VAMP-cleavage product in a cell line after at least an 8 hours incubation with at least 20 nM BoNT/D will indicate the ability of BoNT/D to intoxicate these cell lines. 4b. Assay to determine the time required by a cell to uptake BoNTID [02781 In order to assess the amount of time needed by a cell line to uptake BoNT/D, a panel of mammalian cell lines of neuronal origin will be screened to determine the length of toxin exposure necessary to cleave endogenously expressed VAMP. Cells will be grown in poly-D-lysine/Laminin coated 6-well plates as described above in Example 11, 4a. Approximately 1 nM BoNT/D (Metabiologics, Inc., 111 of 168 WO 2008/036060 PCTIUS2006/012825 Madison, WI) will be added to the culture medium for 10 min, 20 min, 30 min, 60 min 2 hours, 4 hours, 6 hours, 8 hours or 16 hours. Toxin treated cells will be harvested and lysed as described above in Example 1I. 4a. The presence of a BoNT/D VAMP-cleavage product will be determined by Western blot analysis as described above in Example 11, 4a. Detection of a BoNT/D VAMP-cleavage product in a cell line after at least an 8 hour incubation with 1 nM BoNT/D will indicate a cell line that can rapidly uptake BoNT/D. 5. Identification of cell lines with high affinity uptake for BoNT/E 5a. Assay to determine the BoNTIE concentration necessary for cell Intoxication [02791 In order to assess the amount of BoNT/E needed to intoxicate a cell line, a panel of mammalian cell lines of neuronal origin was screened to determine the concentration of neurotoxin necessary to cleave endogenously expressed SNAP-25 (see Table 12). A suitable density of cells from each line was plated into individual wells of 6-well, poly-D-lysine/Laminin coated, tissue culture plates containing 3 mL of a suitable medium (see Table 12), and grown in a 37 0C incubator under 5% carbon dioxide for approximately 24 hours. BoNT/E (Metabiologics, Inc., Madison, WI) was added at different concentrations (0 nM, 2 nM or 20 nM) in the culture medium containing cells for either approximately 6 or approximately 16 hours. Cells were collected in 15 ml tubes, washed once with 1 ml of phosphate buffered saline, pH 7.4, and then transferred to 1.5 ml microcentrifuge tubes. Cells were lysed in 0.5 ml of lysis buffer containing 50 mM N-(2-hydroxyethyl) piperazine-N'-(2-ethanesulfonic acid) (HEPES), pH 6.8, 150 mM sodium chloride, 1.5 mM magnesium chloride, 1mM ethylene glycol bis(-aminoethyl ether) N, N, N, N'tetraacetic acid (EGTA), 10% glycerol and 1% (v/v) Triton-X* 100 (4-octylphenol polyethoxylate), with rotation for 1 hour at 40C. Lysed cells were centrifuged at 5000 rpm for 10 min at 40C to eliminate debris and the supematants were transferred to fresh siliconized tubes. Protein concentrations were measured by Bradford's method and resuspended in 1 x SDS sample buffer at 1mg/mI or higher concentration. [0280] To detect for the presence of a cleaved BoNT/E substrate, western blot analysis was conducted as described above in Example 11, 1a, with the exception that blocked PVDF membranes were incubated in a primary antibody solution containing a 1:50,000 dilution of mouse monoclonal anti-SNAP-25 antibody (SMI-81; Stemberger Monoclonals, Lutherville, MD) rather than the rabbit polyclonal anti-SNAP25 antiserum pAb anti-SNAP25197 #1 and a secondary antibody solution containing a 1:20,000 dilution of goat polyclonal anti-mouse immunoglobulin G, heavy and light chains (IgG, H+L) antibody conjugated to horseradish peroxidase (HRP; Pierce Biotechnology, Inc., Rockford, IL) rather than the goat polyclonal anti-rabbit IgG-HRP antibody in order to'detect a BoNTIE SNAP25,g-cleavage product. A BoNT/E SNAP25 180 -cleavage product was detected in the cell lines Neuro-2A, SH-SY5Y, N1 E-1 15, SK-N-BE(2), NG108-15, SK-N-DZ and BE(2)-C after at least a 6 hour incubation with at least 20 nM BoNT/E, thereby indicating the ability of BoNT/E to intoxicate these cell lines (see FIG. 6a). [02811 The human neuroblastoma cell line SK-N-DZ was further analyzed with lower concentrations of BoNT/E to determine the concentration of neurotoxin necessary to cleave endogenously expressed 112 of 168 WO 2008/036060 PCT/US2006/012825 SNAP-25. Cells were grown in poly-D-lysine/Laminin coated 6-well plates as described above in Example 11, 5a. BoNT/E (Metabiologics, Inc., Madison, WI) was added at different concentrations (0 nM, 0.05 nM, 0.1 nM, 0.2 nM, 0.5 nM, 1 nM, 2 nM and 5 nM) in the culture medium containing cells for approximately 6 hours. Toxin treated cells were harvested and lysed as described above in Example 11, Sa. The presence of a BoNT/E SNAP25 1 ,o-cleavage product was determined by Western blot analysis as described above in Example 11, 5a. A BoNT/E SNAP25 180 -cleavage product was detected in the cell line SK-N-DZ after at least a 6 hour incubation with at least 0.1 nM BoNT/E, thereby indicating the ability of BoNT/E to intoxicate these cell lines (see FIG. 6c). 5b. Assay to determine the time required by a cell to uptake BoNTIE [02821 In order to assess the amount of time needed by a cell line to uptake BoNT/E, a panel of mammalian cell lines of neuronal origin was screened to determine the length of toxin exposure necessary to cleave endogenously expressed SNAP-25 (see Table 12). Cells were grown in poly-D lysine/Laminin coated 6-well plates as described above in Example 11, 5a. Approximately 1 nM BoNT/E (Metabiologics, Inc., Madison, WI) was added to the culture medium for 10 min, 20 min, 30 min, 60 min 2 hours, 4 hours, 6 hours, 8 hours or 16 hours. Toxin treated cells were harvested and lysed as described above in Example 11, 5a. The presence of a BoNT/E SNAP25 1 so-cleavage product was determined by Western blot analysis as described above In Example 11, 5a. A BoNT/E SNAP25 1 60 -cleavage product was detected in the cell lines Neuro-2A, SH-SY5Y, and NG108-15 after at least an 6 hour incubation with 1 nM BoNT/E, thereby indicating the ability of these cell lines to rapidly uptake BoNT/E (see FIG. 6b). 6. Identification of cell lines with high affinity uptake for BoNT/F 6A. Assay to determine the BoNTIF concentration necessary for cell Intoxication (0283] In order to assess the amount of BoNT/F needed to intoxicate a cell line, a panel of mammalian cell lines of neuronal origin will be screened to determine the concentration of neurotoxin necessary to cleave endogenously expressed VAMP (see Table 12). Cells will be grown In poly-D-lysine/Laminin coated 6-well plates as described above in Example 11, la. BoNT/F (Metabiologics, Inc., Madison, WI) will be added at different concentrations (0 nM, 1 nM, 2 nM, 5 nM, 10 nM, 20 nM and 100 nM) in the culture medium containing cells for either approximately 8 or approximately 16 hours. Cells will be harvested and lysed as described above in Example 11, la. [0284] To detect for the presence of a cleaved BoNT/F substrate, western blot analysis will be conducted as described above in Example lI, la, with the exception that blocked PVDF membranes will be incubated in a primary antibody solution containing one of the following antibodies in order to detect a BoNT/F VAMP-cleavage product rather than the rabbit polyclonal anti-SNAP25 antiserum pAb anti SNAP25197 #1: 1) 1:1000 dilution of mouse monoclonal anti-VAMP-1 antibody clone Cl 10.1 (Synaptic Systems, Goettingen, Germany); 2) 1:20,000 dilution of mouse monoclonal anti-VAMP-2 antibody clone CI 69.1 (Synaptic Systems, Goettingen, Germany); or 3) 1:1000 dilution of mouse monoclonal anti VAMP-3 antibody clone Cl 10.1 (Synaptic Systems, Goettingen, Germany). In addition, a secondary antibody solution containing a 1:20,000 dilution of goat polyclonal anti-mouse immunoglobulin G, heavy 113 of 168 WO 2008/036060 PCT/US2006/012825 and light chains (IgG, H+L) antibody conjugated to horseradish peroxidase (HRP; Pierce Biotechnology, Inc., Rockford, IL) will be used rather than the goat polyclonal anti-rabbit IgG-HRP antibody. Detection of a BoNT/F VAMP-cleavage product in a cell line after at least an 8 hours incubation with at least 20 nM BoNT/F will indicate the ability of BoNT/F to intoxicate these cell lines. 6b. Assay to determine the time required by a cell to uptake BoNTIF [0285] In order to assess the amount of time needed by a cell line to uptake BoNT/F, a panel of mammalian cell lines of neuronal origin will be screened to determine the length of toxin exposure necessary to cleave endogenously expressed VAMP. Cells will be grown in poly-D-lysine/Laminin coated 6-well plates as described above in Example 11, 6a. Approximately 1 nM BoNT/F (Metabiologics, Inc., Madison, WI) will be added to the culture medium for 10 min, 20 min, 30 min, 60 min 2 hours, 4 hours, 6 hours, 8 hours or 16 hours. Toxin treated cells will be harvested and lysed as described above in Example 11, 6a. The presence of a BoNT/F VAMP-cleavage product will be determined by Western blot analysis as described above in Example 11, 6a. Detection of a BoNT/F VAMP-cleavage product in a cell line after at least an 8 hour incubation with 1 nM BoNT/F will indicate a cell line that can rapidly uptake BoNT/F. 7. Identification of cell lines with high affinity uptake for BoNT/G 7a. Assay to determine the BoNTG concentration necessary for cell Intoxication [0286] In order to assess the amount of BoNT/G needed to intoxicate a cell line, a panel of mammalian cell lines of neuronal origin will be screened to determine the concentration of neurotoxin necessary to cleave endogenously expressed VAMP (see Table 12). Cells will be grown in poly-D-lysine/Laminin coated 6-well plates as described above in Example 11, la. BoNT/G (Metabiologics, Inc., Madison, WI) will be added at different concentrations (0 nM, 1 nM, 2 nM, 5 nM, 10 nM, 20 nM and 100 nM) in the culture medium containing cells for either approximately 8 or approximately 16 hours. Cells will be harvested and lysed as described above in Example 11, 1a. [02871 To detect for the presence of a cleaved BoNT/G substrate, western blot analysis will be conducted as described above in Example 11, 1a, with the exception that blocked PVDF membranes will be incubated in a primary antibody solution containing one of the following antibodies in order to detect a BoNT/G VAMP-cleavage product rather than the rabbit polyclonal anti-SNAP25 antiserum pAb anti SNAP25197 #1: 1) 1:1000 dilution of mouse monoclonal anti-VAMP-1 antibody clone Cl 10.1 (Synaptic Systems, Goettingen, Germany); 2) 1:20,000 dilution of mouse monoclonal anti-VAMP-2 antibody clone Cl 69.1 (Synaptic Systems, Goettingen, Germany); or 3) 1:1000 dilution of mouse monoclonal anti VAMP-3 antibody clone Cl 10.1 (Synaptic Systems, Goettingen, Germany). In addition, a secondary antibody solution containing a 1:20,000 dilution of goat polyclonal anti-mouse immunoglobulin G, heavy and light chains (IgG, H+L) antibody conjugated to horseradish peroxidase (HRP: Pierce Biotechnology, Inc., Rockford, IL) will be used rather than the goat polyclonal anti-rabbit igG-HRP antibody. Detection of a BoNT/G VAMP-cleavage product in a cell line after at least an 8 hours incubation with at least 20 nM BoNT/G will indicate the ability of BoNT/G to intoxicate these cell lines. 114 of 168 WO 2008/036060 PCTIUS2006/012825 7b. Assay to determine the time required by a cell to uptake BoNTIG [02881 In order to assess the amount of time needed by a cell line to uptake BoNT/G, a panel of mammalian cell lines of neuronal origin will be screened to determine the length of toxin exposure necessary to cleave endogenously expressed VAMP. Cells will be grown in poly-D-lysine/Laminin coated 6-well plates as described above in Example 11, 7a. Approximately 1 nM BoNT/G (Metabiologics, Inc., Madison, WI) will be added to the culture medium for 10 min, 20 min, 30 min, 60 min 2 hours, 4 hours, 6 hours, 8 hours or 16 hours. Toxin treated cells will be harvested and lysed as described above in Example 11, 7a. The presence of a BoNT/G VAMP-cleavage product will be determined by Western blot analysis as described above in Example 1I, 7a. Detection of a BoNT/G VAMP-cleavage product in a cell line after at least an 8 hour incubation with 1 nM BoNT/G will indicate a cell line that can rapidly uptake BoNT/G. 8. Identification of cell lines with high affinity uptake for TeNT 8a. Assay to determine the TeNT concentration necessary for cell Intoxication [0289] In order to assess the amount of TeNT needed to intoxicate a cell line, a panel of mammalian cell lines of neuronal origin will be screened to determine the concentration of neurotoxin necessary to cleave endogenously expressed VAMP (see Table 12). Cells will be grown in poly-D-lysine/Laminin coated 6 well plates as described above in Example 11, 1a. TeNT (Metabiologics, Inc., Madison, WI) will be added at different concentrations (0 nM, 1 nM, 2 nM, 5 nM, 10 nM, 20 nM and 100 nM) in the culture medium containing cells for either approximately 8 or approximately 16 hours. Cells will be harvested and lysed as described above in Example 1I, la. [0290] To detect for the presence of a cleaved TeNT substrate, western blot analysis will be conducted as described above in Example 1I, la, with the exception that blocked PVDF membranes will be incubated in a primary antibody solution containing one of the following antibodies in order to detect a TeNT VAMP-cleavage product rather than the rabbit polyclonal anti-SNAP25 antiserum pAb anti SNAP25197 #1: 1) 1:1000 dilution of mouse monoclonal anti-VAMP-1 antibody clone Cl 10.1 (Synaptic Systems, Goettingen, Germany); 2) 1:20,000 dilution of mouse monoclonal anti-VAMP-2 antibody clone Cl 69.1 (Synaptic Systems, Goettingen, Germany); or 3) 1:1000 dilution of mouse monoclonal anti VAMP-3 antibody clone C 10.1 (Synaptic Systems, Goettingen, Germany). In addition, a secondary antibody solution containing a 1:20,000 dilution of goat polyclonal anti-mouse immunoglobulin G, heavy and light chains (IgG, H+L) antibody conjugated to horseradish peroxidase (HRP; Pierce Biotechnology, Inc., Rockford, IL) will be used rather than the goat polyclonal anti-rabbit IgG-HRP antibody. Detection of a TeNT VAMP-cleavage product in a cell line after at least an 8 hours incubation with at least 20 nM TeNT will indicate the ability of TeNT to intoxicate these cell lines. 8b. Assay to determine the time required by a cell to uptake TeNT [0291] in order to assess the amount of time needed by a cell line to uptake TeNT, a panel of mammalian cell lines of neuronal origin will be screened to determine the length of toxin exposure 115 of 168 WO 2008/036060 PCT/US2006/012825 necessary to cleave endogenously expressed VAMP. Cells will be grown in poly-D-lysine/Laminin coaled 6-well plates as described above in Example 11, 8a. Approximately 1 nM TeNT (Metabiologics, Inc., Madison, WI) will be added to the culture medium for 10 min, 20 min, 30 min, 60 min 2 hours, 4 hours, 6 hours, 8 hours or 16 hours. Toxin treated cells will be harvested and lysed as described above in Example 11, 8a. The presence of a TeNT VAMP-cleavage product will be determined by Western blot analysis as described above in Example 1I, 8a. Detection of a TeNT VAMP-cleavage product in a cell line after at least an 8 hour incubation with 1 nM TeNT will indicate a cell line that can rapidly uptake TeNT. EXAMPLE III Treatments to Increase Uptake of a Cell for a Clostridial Toxin [0292] Cell surface gangliosides are part of the receptor system for Clostridial toxins and appear to participate in binding of a toxin to its receptor system. Although toxin binding is not strictly dependent on the presence of gangliosides, the presence of specific gangliosides appears to be required for high affinity binding. In particular, CoNTs have been observed to interact in vitro and in vivo with polysialogangliosides, especially those of the G1b series (GD1a, GD1b, GD3, GQ1b, or GT1b), see, e.g., Jane L Halpern & Elaine A. Neale, Neurospecific binding, internalization, and retrograde axonal transport, 195 Curr. Top. Microbiol. Immunol. 221-241 (1995). Likewise, the differentiated state of a cell could influence the expression, or level of expression of important components of a Clostridial toxin receptor system, such as, e.g., a cell-surface receptor. For example, Neuro-2A and SH-SY5Y cells can be differentiated to acquire a neuronal-like phenotype that may facilitate toxin uptake. To determine whether we could increase the uptake of a Clostridial toxin by a particular cell, we tested 1) whether a treatment that increased the ganglioside content of the cell membrane increased uptake of a Clostridial toxin by a cell; and 2) whether changing the state of differentiation of a cell could increase uptake of a Clostridial toxin by a cell. 1. Identification of treatments that Increased uptake of BoNT/A by a cell la. Ganglioside treatment to increase high affinity uptake of BoNTIA by a cell [0293] In order to assess the effect of ganglioside treatment on the ability of BoNT/A to intoxicate a cell, a Neuro-2A cell line was pre-treated with different gangliosides to determine whether these sugar moieties could increase the uptake of BoNT/A by these cells. Neuro-2A cells were plated at a suitable density into individual wells of 6-well, poly-D-lysine/Laminin coated, tissue culture plates containing 3 mL of a suitable medium (see Table 12), and grown in a 37 *C incubator under 5% carbon dioxide. After approximately 24 hours, the medium was replaced by a serum-free media and 25 pg/mL of one of the following gangliosides was added to individual wells: GD1a, GD1b, GD3, GQ1b, or GT1b (AXXORA, LLC, San Diego, CA). After an overnight 37 *C incubation period, the ganglioside-treated cells were washed three times with 1 ml of phosphate-buffered saline, pH 7.4 and then incubated at 37 *C with 1% serum media containing different concentrations (0 nM, 12.5 nM, 25 nM, 50nM) of BoNT/A (Metabiologics, Inc., Madison, WI) for approximately 8 or approximately 16 hours. Cells were collected in 15 ml tubes, washed once with 1 ml of phosphate-buffered saline, pH 7.4, and then transferred to 1.5 ml microcentrifuge tubes. 116 of 168 WO 2008/036060 PCT/US2006/012825 Cells were lysed in 0.5 ml of lysis buffer containing 50 mM N-(2-hydroxyethyl) piperazine-N'-(2 ethanesulfonic acid) (HEPES), pH 6.8, 150 mM sodium chloride, 1.5 mM magnesium chloride, 1mM ethylene glycol bis(p-aminoethyl ether) N, N, N, N'tetraacetic acid (EGTA), 10% glycerol and 1% (v/v) Triton-X* 100 (4-octylphenol polyethoxylate), with rotation for 1 hour at 4 0 C. Lysed cells were centrifuged at 5000 rpm for 10 min at 40C to eliminate debris and the supernatants were transferred to fresh siliconized tubes. Protein concentrations were measured by Bradford's method and resuspended in 1 x SDS sample buffer at 1mg/ml or higher concentration. The presence of a BoNT/A SNAP25 1 ercleavage product was determined by Western blot analysis as described above in Example 11, 1a. An increase in BoNT/A SNAP25 197 -cleavage product was detected in the Neuro-2A cell line treated with the ganglioside GT1b, thereby indicating that GT1 b-treatment can increase the uptake of BoNT/A by Neuro-2A cells (see FIG. 7a). 1b. Differentiation reagent treatment to Increase high affinity uptake of BoNTA by a cell [02941 In order to assess the effect of cellular differentiation on the ability of BoNT/A to intoxicate a cell, Neuro-2A and SH-SY5Y cells were treated with different growth conditions or differentiation reagents to determine whether differentiation of these cells could result in an increased uptake of BoNT/A by these cells. Cells were plated at a suitable density into individual wells of 6-well, poly-D-lysine/Laminin coated, tissue culture plates containing 3 mL of a suitable medium (see Table 12), and grown in a 37 *C incubator under 5% carbon dioxide. After approximately 24 hours, the medium was replaced with either a serum free culture media or a 10% serum media and one of the following differentiating reagents was added to individual wells: 0.2 units Neuraminidase Type V (Sigma-Aldrich, St. Louis, MO), in water containing 0.2% ALBUMAX 11 (Invitrogen, Inc., Carlsbad, CA); 20 pM All Trans-Retinoic acid (Sigma-Aldrich, St. Louis, MO) in DMSO (Sigma-Aldrich, St. Louis, MO); 1 mM N6, 2'-0-Dibutyryladenosine 3':5'-cyclic monophosphate sodium salt (db-cAMP) (Sigma-Aldrich, St. Louis, MO); 1 pM lonomycin, calcium salt (Molecular Probes, Eugene, OR) in DMSO (Sigma-Aldrich, St. Louis, MO); or 1x N-2 Supplement (Invitrogen, Inc., 17502-048, Carlsbad, CA). After a three day 37 *C incubation period, the serum-free media cells and the reagent-treated cells were washed three times with 1 ml of phosphate-buffered saline, pH 7.4 and then incubated at 37 0C with either serum-free media containing 2 nM Pure A (BTX 540) toxin (Metabiologics, Inc., Madison, WI) for approximately 18 hours (the growth condition experiments), or 10 % serum media containing 2 nM Pure A (BTX-540) toxin (Metabiologics, Inc., Madison, WI) for approximately 18 hours (the differentiation reagent experiments). Cells were harvested by trypsin treatment, collectede in 15 ml tubes, washed once with 1 ml of phosphate-buffered saline, pH 7.4, and then transferred to 1.5 ml microcentrifuge tubes. Cells were lysed in 0.5 ml of lysis buffer containing 50 mM N-(2-hydroxyethyl) piperazine-N-(2-ethanesulfonic acid) (HEPES), pH 6.8, 150 mM sodium chloride, 1.5 mM magnesium chloride, 1mM ethylene glycol bis(P-aminoethyl ether) N, N, N, N tetraacetic acid (EGTA), 10% glycerol and 1% (v/v) Triton-X 100 (4-octylphenol polyethoxylate), with rotation for 1 to 2 hours at 40C. Lysed cells were centrifuged at 5000 rpm for 10 min at 4 0 C to eliminate debris and the supernatants were transferred to fresh 1.5 mL siliconized tubes. Protein concentrations were measured by Bradford's method and resuspended in 1 x SDS sample buffer at 1mg/ml or higher concentration. The presence of a BoNT/A SNAP25ircleavage product was determined by Western blot analysis as described above in Example 11, la, with the exception that blocked PVDF membranes were 117 of 168 WO 2008/036060 PCT/US2006/012825 incubated in a primary antibody solution containing a 1:50,000 dilution of mouse monoclonal anti-SNAP 25 antibody (SMI-81; Sternberger Monoclonals, Lutherville, MD) rather than the rabbit polyclonal anti SNAP25 antiserum pAb anti-SNAP25197 #1 and a secondary antibody solution containing a 1:20,000 dilution of goat polyclonal anti-mouse immunoglobulin G, heavy and light chains (IgG, H+L) antibody conjugated to horseradish peroxidase (HRP; Pierce Biotechnology, Inc., Rockford, IL) rather than the goat polyclonal anti-rabbit IgG-HRP antibody in order to detect both the uncleaved SNAP-25 and the BoNT/A SNAP25 1 97-cleavage product. An increase in BoNT/A SNAP25 1 97 -cleavage product was detected in Neuro-2A and SH-SY5Y cells differentiated in serum-free conditions as compared to 10% serum media, thereby indicating that serum-free media conditions can increase the uptake of BoNT/A by Neuro-2A and SH-SYSY cells (see FIG. 7b). Likewise, an increase in BoNT/A SNAP251ercleavage product was detected in Neuro-2A cells treated with all trans retinoic acid, thereby indicating that retinoic induced differentiation of Neuro-2A can increase the uptake of BoNT/A by these cells (see FIG. 7b). 2. Identification of treatments that increased uptake of BoNT/B by a cell 2a. Ganglioside treatment to increase high affinity uptake of BoNTI by a cell [0295] In order to assess the effect of ganglioside treatment on the ability of BoNT/B to intoxicate a cell, suitable mammalian cells will be pre-treated with different gangliosides to determine whether these sugar moieties can increase the uptake of BoNT/B by these cells. Cells will be grown in poly-D-lysine/Laminin coated 6-well plates and treated with gangliosides as described above in Example 111, la. The ganglioside-treated cells will be incubated with BoNT/B (Metabiologics, Inc., Madison, WI) at different concentrations (0 nM, 12.5 nM, 25 nM, 5OnM) in 1% serum media for either approximately 8 or approximately 16 hours. Toxin treated cells will be harvested and lysed as described above in Example 111, la. The presence of a BoNT/B VAMP-cleavage product will be determined by Western blot analysis as described above in Example 1I, 2a. An increase in BoNT/B VAMP-cleavage product detected in the cell line treated with a ganglioside will indicate that treatment with that ganglioside can increase the uptake of BoNT/B by these cells. 2b. Differentiation reagent treatment to Increase high affinity uptake of BoNTB by a cell [0296] In order to assess the effect of cellular differentiation on the ability of BoNT/B to intoxicate a cell, suitable mammalian cells will be treated with different growth conditions or differentiation reagents to determine whether differentiation of these cells can result in an increased uptake of BoNT/B by these cells. Cells will be grown in poly-D-lysine/Laminin coated 6-well plates using either serum-free or 10% serum media treated with differentiation reagents as described above in Example III, 1b. After a three day 37 *C incubation period, the serum-free media cells and the reagent-treated cells will be washed three times with 1 ml of phosphate-buffered saline, pH 7.4 and then will be incubated at 37 "C with either serum-free media containing BoNT/B (Metabiologics, Inc., Madison, WI) for approximately 18 hours (the growth condition experiments), or 10 % serum media containing BoNT/B (Metabiologics, Inc., Madison, WI) for approximately 18 hours (the differentiation reagent experiments). Cells were harvested, collected and lysed as described above in Example Ill, la. The presence of a BoNT/B VAMP-cleavage product will be determined by Western blot analysis as described above in Example 11, 2a. An increase in a BoNT/B 118 of 168 WO 2008/036060 PCT/US2006/012825 VAMP-cleavage product detected in cells grown in serum-free media will indicate that treatment witn tnat reagent can increase the uptake of BoNT/B by these cells. An increase in a BoNT/B VAMP-cleavage product detected in cells treated with a differentiation reagent will indicate that treatment with that reagent can increase the uptake of BoNT/B by these cells. 3. Identification of treatments that increased uptake of BoNT/Ci by a cell 38. GangllosIde treatment to Increase high affinity uptake of BoNTC1 by a cell [0297] In order to assess the effect of ganglioside treatment on the ability of BoNT/C1 to intoxicate a cell, suitable mammalian cells will be pre-treated with different gangliosides to determine whether these sugar moieties can increase the uptake of BoNT/CI by these cells. Cells will be grown in poly-D lysine/Laminin coated 6-well plates and treated with gangliosides as described above in Example Ill, 1a. The ganglioside-treated cells will be incubated with BoNT/CI (Metabiologics, Inc., Madison, WI) at different concentrations (0 nM, 12.5 nM, 25 nM, 5OnM) in 1% serum media for either approximately 8 or approximately 16 hours. Toxin treated cells will be harvested and lysed as described above in Example IlIl, 1a. The presence of a BoNT/C1 SNAP25 1 80 -cleavage product will be determined by Western blot analysis as described above in Example 11, 3a. The presence of a BoNT/CI Syntaxin-cleavage product will be determined by Western blot analysis as described above in Example 11, 3a. An increase in BoNT/C1 SNAP25 1 so-cleavage product detected in the cell line treated with a ganglioside will indicate that treatment with that ganglioside can increase the uptake of BoNT/C1 by these cells. An increase in BoNT/C1 Syntaxin-cleavage product detected in the cell line treated with a ganglioside will indicate that treatment with that ganglioside can increase the uptake of BoNT/Cl by these cells. 3b. Differentiation reagent treatment to Increase high affinity uptake of BoNT/C1 by a cell [0298] In order to assess the effect of cellular differentiation on the ability of BoNT/CI to intoxicate a cell, suitable mammalian cells will be treated with different growth conditions or differentiation reagents to determine whether differentiation of these cells can result in an increased uptake of BoNT/CI by these cells. Cells will be grown in poly-D-lysine/Laminin coated 6-well plates using either serum-free or 10% serum media treated with differentiation reagents as described above in Example 1i1, 1b. After a three day 37 0C incubation period, the serum-free media cells and the reagent-treated cells will be washed three times with 1 ml of phosphate-buffered saline, pH 7.4 and then will be incubated at 37 OC with either serum-free media containing BoNT/C1 (Metabiologics, Inc., Madison, WI) for approximately 18 hours (the growth condition experiments), or 10 % serum media containing BoNT/Ci (Metabiologics, Inc., Madison, WI) for approximately 18 hours (the differentiation reagent experiments). Cells were harvested, collected and lysed as described above in Example l1l, 1a. The presence of a BoNT/C1 SNAP25 1 ao-cleavage product will be determined by Western blot analysis as described above in Example 11, 3a. The presence of a BoNT/Ci Syntaxin-cleavage product will be determined by Western blot analysis as described above in Example 11, 3a. An increase in a BoNT/CI SNAP25 1 s-cleavage product detected in cells grown in serum-free media will indicate that treatment with that reagent can increase the uptake of BoNT/Cl by these cells. An increase in a BoNT/C1 SNAP25 1 eo-cleavage product detected in cells treated with a differentiation reagent will indicate that treatment with that reagent can increase the uptake of BoNT/C1 119 of 168 WO 2008/036060 PCT/US2006/012825 by these cells. An increase in a BoNT/C1 Syntaxin-cleavage product detected in cells grown in serum free media will indicate that treatment with that reagent can increase the uptake of BoNT/C1 by these cells. An increase in a BoNT/C1 Syntaxin-cleavage product detected in cells treated with a differentiation reagent will indicate that treatment with that reagent can increase the uptake of BoNT/C1 by these cells. 4. Identification of treatments that increased uptake of BoNT/D by a cell 4a. Ganglioside treatment to increase high affinity uptake of BoNTD by a cell [0299] In order to assess the effect of ganglioside treatment on the ability of BoNT/D to intoxicate a cell, suitable mammalian cells will be pre-treated with different gangliosides to determine whether these sugar moieties can increase the uptake of BoNT/D by these cells. Cells will be grown in poly-D-lysine/Laminin coated 6-well plates and treated with gangliosides as described above in Example l1l, 1a. The ganglioside-treated cells will be incubated with BoNT/D (Metabiologics, Inc., Madison, WI) at different concentrations (0 nM, 12.5 nM, 25 nM, 5OnM) in 1% serum media for either approximately 8 or approximately 16 hours. Toxin treated cells will be harvested and lysed as described above in Example Ill, ia. The presence of a BoNT/D VAMP-cleavage product will be determined by Western blot analysis as described above in Example 11, 4a. An increase in BoNT/D VAMP-cleavage product detected in the cell line treated with a ganglioside will indicate that treatment with that ganglioside can increase the uptake of BoNT/D by these cells. 4b. Differentiation reagent treatment to increase high affinity uptake of BoNTD by a cell [0300] In order to assess the effect of cellular differentiation on the ability of BoNT/D to intoxicate a cell, suitable mammalian cells will be treated with different growth conditions or differentiation reagents to determine whether differentiation of these cells can result in an increased uptake of BoNTID by these cells. Cells will be grown in poly-D-lysine/Laminin coated 6-well plates using either serum-free or 10% serum media treated with differentiation reagents as described above in Example 1I1, 1b. After a three day 37 *C incubation period, the serum-free media cells and the reagent-treated cells will be washed three times with 1 ml of phosphate-buffered saline, pH 7.4 and then will be incubated at 37 *C with either serum-free media containing BoNT/D (Metabiologics, Inc., Madison, WI) for approximately 18 hours (the growth condition experiments), or 10 % serum media containing BoNT/D (Metabiologics, Inc., Madison, WI) for approximately 18 hours (the differentiation reagent experiments). Cells were harvested, collected and lysed as described above in Example IlIl, Ia. The presence of a BoNT/D VAMP-cleavage product will be determined by Western blot analysis as described above in Example II, 4a. An increase in a BoNT/D VAMP-cleavage product detected in cells grown in serum-free media will indicate that treatment with that reagent can increase the uptake of BoNT/D by these cells. An increase in a BoNT/D VAMP-cleavage product detected in cells treated with a differentiation reagent will indicate that treatment with that reagent can increase the uptake of BoNTD by these cells. 5. Identification of treatments that Increased uptake of BoNT/E by a cell 5a. Ganglioside treatment to increase high affinity uptake of BoNTIE by a cell 120 of 168 WO 2008/036060 PCT/US2006/012825 [0301] In order to assess the effect of ganglioside treatment on the ability of BoNT/E to intoxicate a cell, a Neuro-2A cell line was pre-treated with different gangliosides to determine whether these sugar moieties could increase the uptake of BoNT/E by these cells. Neuro-2A cells were grown in poly-D lysine/Laminin coated 6-well plates and treated with gangliosides as described above in Example ll, Ia. The ganglioside-treated cells were incubated with BoNT/E (Metabiologics, Inc., Madison, WI) at different concentrations (0 nM, 12.5 nM, 25 nM, 50nM) in 1% serum media for either approximately 6 or approximately 16 hours. Toxin treated cells were harvested and lysed as described above in Example 11, 5a. The presence of a BoNT/E SNAP25 1 so-cleavage product was determined by Western blot analysis as described above in Example 11, 5a. An increase in BoNT/E SNAP25 1 s-cleavage product was detected in the Neuro-2A cell lines treated with the gangliosides GD3, GD1b and GD1a, thereby indicating that GD3 treatment, GDlb-treatment or GD1a-treatment can increase the uptake of BoNT/E by Neuro-2A cells (see FIG. 8a). 5b. Differentiation reagent treatment to increase high affinity uptake of BoNTIE by a cell [0302] In order to assess the effect of cellular differentiation on the ability of BoNT/E to intoxicate a cell, SH-SY5Y cells were treated with different growth conditions to determine whether differentiation of these cells could result in an increased uptake of BoNT/E by these cells. SH-SY5Y cells were grown in poly-D lysine/Laminin coated 6-well plates using serum-free as described above in Example 1I1, 1b. The serum free media cells were incubated with BoNT/E (Metabiologics, Inc., Madison, WI) at concentrations of 5 nM and 20 nM for approximately 30 minutes, approximately 1 hour, approximately 2 hours, approximately 4 hours, approximately 8 hours and approximately 16 hours. Toxin treated cells were harvested, collected and lysed as described above in Example II1, 1b. The presence of a BoNT/E SNAP25 1 8o-cleavage product was determined by Western blot analysis as described above in Example 11, 5a. An increase in BoNT/E SNAP25 1 ao-cleavage product was detected in SH-SY5Y cells differentiated in serum-free conditions as early as 4 hours following exposure to toxin, with a maximal signal evident at least at 8 hours after BoNT/E-treatment, as compared to 10% serum media, thereby indicating that serum-free media conditions can increase the uptake of BoNT/E by SH-SY5Y cells (see FIG. 8b). 6. Identification of treatments that Increased uptake of BoNT/F by a cell 6a. Gangiloside treatment to increase high affinity uptake of BoNTIF by a cell [0303] In order to assess the effect of ganglioside treatment on the ability of BoNT/F to intoxicate a cell, suitable mammalian cells will be pre-treated with different gangliosides to determine whether these sugar moieties can increase the uptake of BoNT/F by these cells. Cells will be grown in poly-D-lysine/Laminin coated 6-well plates and treated with gangliosides as described above in Example l1l, Ia. The ganglioside-treated cells will be incubated with BoNT/F (Metabiologics, Inc., Madison, WI) at different concentrations (0 nM, 12.5 nM, 25 nM, 5OnM) in 1% serum media for either approximately 8 or approximately 16 hours. Toxin treated cells will be harvested and lysed as described above in Example Ill, Ia. The presence of a. BoNT/F VAMP-cleavage product will be determined by Western blot analysis as described above in Example 1I, 6a. An increase in BoNT/F VAMP-cleavage product detected in the 121 of 168 WO 2008/036060 PCT/US2006/012825 cell line treated with a ganglioside will indicate that treatment with that ganglioside can increase ne uptake of BoNT/F by these cells. 6b. Differentiation reagent treatment to increase high affinity uptake of BoNTIF by a cell [03041 In order to assess the effect of cellular differentiation on the ability of BoNT/F to intoxicate a cell, suitable mammalian cells will be treated with different growth conditions or differentiation reagents to determine whether differentiation of these cells can result in an Increased uptake of BoNT/F by these cells. Cells will be grown in poly-D-lysine/Laminin coated 6-well plates using either serum-free or 10% serum media treated with differentiation reagents as described above in Example 1I1, 1b. After a three day 37 *C incubation period, the serum-free media cells and the reagent-treated cells will be washed three times with 1 ml of phosphate-buffered saline, pH 7.4 and then will be incubated at 37 *C with either serum-free media containing BoNT/F (Metabiologics, Inc., Madison, WI) for approximately 18 hours (the growth condition experiments), or 10 % serum media containing BoNT/F (Metabiologics, Inc., Madison, WI) for approximately 18 hours (the differentiation reagent experiments). Cells were harvested, collected and lysed as described above in Example Ill, la. The presence of a BoNT/F VAMP-cleavage product will be determined by Western blot analysis as described above in Example 11, 6a. An increase in a BoNT/F VAMP-cleavage product detected in cells grown in serum-free media will indicate that treatment with that reagent can increase the uptake of BoNT/F by these cells. An increase In a BoNT/F VAMP-cleavage product detected in cells treated with a differentiation reagent will indicate that treatment with that reagent can increase the uptake of BoNT/F by these cells. 7. Identification of treatments that Increased uptake of BoNT/G by a cell 7a. Ganglioside treatment to increase high affinity uptake of BoNTG by a cell [0305] In order to assess the effect of ganglioside treatment on the ability of BoNT/G to intoxicate a cell, suitable mammalian cells will be pre-treated with different gangliosides to determine whether these sugar moieties can increase the uptake of BoNT/G by these cells. Cells will be grown in poly-D-lysine/Laminin coated 6-well plates and treated with gangliosides as described above in Example 1i, 1a. The ganglioside-treated cells will be incubated with BoNT/G (Metabiologics, Inc., Madison, WI) at different concentrations (0 nM, 12.5 nM, 25 nM, 5OnM) in 1% serum media for either approximately 8 or approximately 16 hours. Toxin treated cells will be harvested and lysed as described above in Example IlIl, 1a. The presence of a BoNT/G VAMP-cleavage product will be determined by Western blot analysis as described above in Example 11, 7a. An increase in BoNT/G VAMP-cleavage product detected in the cell line treated with a ganglioside will indicate that treatment with that ganglioside can increase the uptake of BoNT/G by these cells. 7b. Differentiation reagent treatment to increase high affinity uptake of BoNTIG by a cell [0306] In order to assess the effect of cellular differentiation on the ability of BoNT/G to intoxicate a cell, suitable mammalian cells will be treated with different growth conditions or differentiation reagents to determine whether differentiation of these cells can result in an increased uptake of BoNT/G by these cells. Cells will be grown in poly-D-lysine/Laminin coated 6-well plates using either serum-free or 10% 122 of 168 WO 2008/036060 PCT/US2006/012825 serum media treated with differentiation reagents as described above in Example III, lb. After a three day 37 *C incubation period, the serum-free media cells and the reagent-treated cells will be washed three times with 1 ml of phosphate-buffered saline, pH 7.4 and then will be incubated at 37 *C with either serum-free media containing BoNT/G (Metabiologics, Inc., Madison, WI) for approximately 18 hours (the growth condition experiments), or 10 % serum media containing BoNT/G (Metabiologics, Inc., Madison, WI) for approximately 18 hours (the differentiation reagent experiments). Cells were harvested, collected and lysed as described above in Example Ill, 1a. The presence of a BoNT/G VAMP-cleavage product will be determined by Western blot analysis as described above in Example 1I, 7a. An increase in a BoNT/G VAMP-cleavage product detected in cells grown in serum-free media will indicate that treatment with that reagent can increase the uptake of BoNT/G by these cells. An increase in a BoNT/G VAMP-cleavage product detected in cells treated with a differentiation reagent will indicate that treatment with that reagent can increase the uptake of BoNT/G by these cells. 8. Identification of treatments that Increased uptake of TeNT by a cell 8a. Gangioside treatment to increase high affinity uptake of TeNT by a cell [03071 In order to assess the effect of ganglioside treatment on the ability of TeNT to intoxicate a cell, suitable mammalian cells will be pre-treated with different gangliosides to determine whether these sugar moieties can increase the uptake of TeNT by these cells. Cells will be grown in poly-D-lysine/Laminin coated 6-well plates and treated with gangliosides as described above in Example IlIl, la. The ganglioside-treated cells will be incubated with TeNT (Metabiologics, Inc., Madison, WI) at different concentrations (0 nM, 12.5 nM, 25 nM, 50nM) in 1% serum media for either approximately 8 or approximately 16 hours. Toxin treated cells will be harvested and lysed as described above in Example Il, 1a. The presence of a TeNT VAMP-cleavage product will be determined by Western blot analysis as described above in Example 11, 8a. An increase in TeNT VAMP-cleavage product detected in the cell line treated with a ganglioside will indicate that treatment with that ganglioside can increase the uptake of TeNT by these cells. 8b. Differentiation reagent treatment to increase high affinity uptake of TeNT by a cell [0308] In order to assess the effect of cellular differentiation on the ability of TeNT to intoxicate a cell, suitable mammalian cells will be treated with different growth conditions or differentiation reagents to determine whether differentiation of these cells can result in an increased uptake of TeNT by these cells. Cells will be grown in poly-D-lysine/Laminin coated 6-well plates using either serum-free or 10% serum media treated with differentiation reagents as described above in Example III, lb. After a three day 37 *C incubation period, the serum-free media cells and the reagent-treated cells will be washed three times with 1 ml of phosphate-buffered saline, pH 7.4 and then will be incubated at 37 "C with either serum-free media containing TeNT (Metabiologics, Inc., Madison, WI) for approximately 18 hours (the growth condition experiments), or 10 % serum media containing TeNT (Metabiologics, Inc., Madison, WI) for approximately 18 hours (the differentiation reagent experiments). Cells were harvested, collected and lysed as described above in Example ll, 1a. The presence of a TeNT VAMP-cleavage product will be determined by Western blot analysis as described above in Example 11, 8a. An increase in a TeNT 123 of 168 WO 2008/036060 PCT/US2006/012825 VAMP-cleavage product detected in cells grown in serum-free media will indicate that treatment with that reagent can increase the uptake of TeNT by these cells. An increase in a TeNT VAMP-cleavage product detected in cells treated with a differentiation reagent will indicate that treatment with that reagent can increase the uptake of TeNT by these cells. EXAMPLE IV Generation of cells transiently containing a Clostridial toxin substrate 1. Generation of cells containing a BoNT/A, BoNT/C1 or BoNT/E SNAP-25 substrate by adenorviral transduction 1s. Construction of pAd-DEST/SNAP-25x-GFP [03091 To make a pAd-DEST/SNAP-252s-GFP construct, a nucleic acid fragment encoding the amino acid region comprising SNAP-252s-GFP of is amplified from pQBI-25/SNAP252s-GFP DNA (see Example 1, la) using a polymerase chain reaction method and subcloned into a pCR2.1 vector using the TOPO* TA cloning method (Invitrogen, Inc, Carlsbad, CA). The forward and reverse oligonucleotide primers used for this reaction are designed to include unique restriction enzyme sites useful for subsequent subcloning steps. 'The resulting pCR2.1/SNAP-252m-GFP construct is digested with restriction enzymes that 1) excise the insert containing the entire open reading frame encoding the SNAP-252 6 -GFP peptide; and 2) enable this insert to be operably-linked to a pAd-DEST vector (Invitrogen, Inc., Carlsbad, CA). This insert is subcloned using a T4 DNA ligase procedure into a pAd DEST vector that is digested with appropriate restriction endonucleases to yield pAd-DEST/SNAP-252s GFP. The ligation mixture is transformed into chemically competent E. coli BL21 (DE3) cells (Invitrogen, Inc, Carlsbad, CA) using a heat shock method, plated on 1.5% Luria-Bertani agar plates (pH 7.0) containing 100 pg/mL of Ampicillin, and placed in a 37 *C incubator for overnight growth. Bacteria containing expression constructs are identified as Ampicillin resistant colonies. Candidate constructs are isolated using an alkaline lysis plasmid mini-preparation procedure and analyzed by restriction endonuclease digest mapping to determine the presence and orientation of the inset. This cloning strategy yields a mammalian expression construct encoding the SNAP-252e-GFP operably-linked to the expression elements of the pAd-DEST vector. 1b. Production of an adenoviral stock containing pAd-DEST/SNAP-25-GFP [0310] . To produce an adenoviral stock containing an expression construct encoding a BoNT/A, BoNT/C1 or BoNT/E SNAP-25-GFP substrate, such as, e.g., pAd-DEST/SNAP-25s-GFP, about 5x10 5 293A cells are plated in a 35 mm tissue culture dish containing 3 mL of complete Dulbecco's Modified Eagle Media (DMEM), supplemented with 10% fetal bovine serum (FBS), lx penicillin/streptomycin solution (Invitrogen, Inc, Carlsbad, CA) and 1x MEM non-essential amino acids solution (Invitrogen, Inc, Carlsbad, CA), and grown in a 37 *C incubator under 5% carbon dioxide until the cells reach a density of about 5x105 cells/mI (6-16 hours). One the day of transfection, replace complete, supplemented DMEM media with 2 mL of OPTI-MEM Reduced Serum Medium. A 500 pL transfection solution is prepared by adding 250 pL of OPTI-MEM Reduced Serum Medium containing 15 yL of LipofectAmine 2000 124 of 168 WO 2008/036060 PCT/US2006/012825 (Invitrogen, Carlsbad, CA) incubated at room temperature for 5 minutes to 250 pL of OPTI-MEM Reduced Serum Medium containing 5 pg of the linearized expression construct encoding a BoNT/A, BoNT/C1 or BoNT/E SNAP-25-GFP substrate, such as, e.g., pAd-DEST/SNAP-25m-GFP. To linearized a pAd DEST/SNAP-25-GFP construct, 5 pg of a pAd-DEST/SNAP-25-GFP construct is digested with Pad (New England Biolabs, Beverly, MA). The linearized plasmid is purified using QlAquick kit procedure (QIAGEN, Inc., Valencia, CA) and is resuspended in TE Buffer. This transfection is incubated at room temperature for approximately 20 minutes. The 500 pL transfection solution is then added to the 293A cells and the cells are incubated in a 37 *C incubator under 5% carbon dioxide for approximately 16 hours. Transfection media is replaced with 3 mL of fresh complete, supplemented DMEM and cells are incubated in a 37 0C incubator under 5% carbon dioxide for approximately 24 hours. The cells are trypsinized and the contents of each well are transfered to a sterile 10 cm tissue culture plate containing 10 mL of complete, supplemented DMEM. Replace the old media with fresh complete, supplemented DMEM every 2 or 3 days until visible regions of cytopathic effect are observed (typically 7-10 days). Replenish the old culture media with fresh complete, supplemented DMEM and allow the infections to proceed until approximately 80% cytopathic effect is observed (typically 10-13 days post transfection). The adenovirus-containing cells are harvested by detaching the cells using the culture media and scraping cells from the culture plate. Detached cells and media are transferred to a 15 mL tube. The harvested cells are lysed using one freeze-thaw round consisting of -80 8C for 30 minutes then 37 *C for 15 minutes. The cell lysate is centrifuged (5,000x g at 20 *C for 15 minutes) to pellet the cellular debris. The clarified supernatant containing the adenoviral particles is transferred to 2 mL cryovials in 1 mL aliquots and should contain approximately 1x10 to 108 pfu of adenoviral particles. Aliquots can be stored at -80 *C until needed. 1c. Amplification of an adenoviral stock containing pAd-DEST/SNAP-25-GFP [0311] To amplified to the adenoviral stock containing an expression construct encoding a BoNT/A, BoNT/C1 or BoNT/E SNAP-25-GFP substrate, such as, e.g., pAd-DEST/SNAP-252s-GFP, about 3x10 293A cells are plated in a 100 mm culture dish containing in 10 mL of complete Dulbecco's Modified Eagle Media (DMEM), supplemented with 10% fetal bovine serum (FBS), 1x penicillin/streptomycin solution (Invitrogen, Inc, Carlsbad, CA) and 1x MEM non-essential amino acids solution (Invitrogen, Inc, Carlsbad, CA), and grown in a 37 *C incubator under 5% carbon dioxide until the cells reach a density of about 80-90% confluency (6-16 hours). The cells are inoculated cells with 100 pL of adenoviral stock and incubated for approximately 48-72 hours in a 37 *C incubator under 5% carbon dioxide until the cells round up and are floating or lightly attached to the culture plate. The adenovirus-containing cells are harvested by detaching the cells using the culture media and scraping cells from the culture plate. Detached cells and media are transferred to a 15 mL tube. The harvested cells are lysed using three freeze-thaw round consisting of -80 *C for 30 minutes then 37 *C for 15 minutes. The cell lysate Is centrifuged (5,000x g at 20 0C for 15 minutes) to pellet the cellular debris. The clarified supernatant containing the adenoviral particles is transferred to 2 mL cryovials in 1 mL aliquots and should contain approximately 1x1 08 to 109 pfu of adenoviral particles. Aliquots can be stored at -80 *C until needed. 1d. Transduction of cells with an adenoviral stock containing pAd-DEST/SNAP-25-GFP 125 of 168 WO 2008/036060 PCT/US2006/012825 [03121 To transduce cells with the adenoviral stock containing an expression construct encoding a BoNT/A, BoNT/C1 or BoNT/E SNAP-25-GFP substrate, such as, e.g., pAd-DEST/SNAP-252W-GFP, about 1.5x10 6 SH-SY5Y cells are plated in a 6-well tissue culture dish containing 3 mL of complete 1:1 EMEM and Ham's F12 Media (EMEM:F12), supplemented with 10% fetal bovine serum (FBS), 4 mM glutamine (Invitrogen, Inc, Carlsbad, CA), 1% sodium'pyruvate (Invitrogen, Inc, Carlsbad, CA), 1.5 g/L sodium bicarbonate, lx penicillin/streptomycin solution (Invitrogen, Inc, Carlsbad, CA) and 1x MEM non essential amino acids solution (Invitrogen, Inc, Carlsbad, CA), and grown in a 37 *C incubator under 5% carbon dioxide until the cells reach a density of about 5x10 5 cells/ml (6-16 hours). Cells are inoculated with approximately 4 pL of the adenoviral stock (approximately 5x1 0o pfu/ml) and are incubated for approximately 24 hours in a 37 *C incubator under 5% carbon dioxide. The tranduction media is replaced with 3 mL of fresh complete, supplemented EMEM:F12 and cells are incubated in a 37 *C incubator under 5% carbon dioxide for approximately 24 hours. The transduced cells can be used to conduct a BoNT/A, BoNT/C1 or BoNT/E activity assay using a SNAP-25-GFP substrate. For greater details on procedures described in this example, see ViraPowertm Adenoviral Expression System Instruction Manual 25-0543 version A, Invitrogen, Inc., (Jul. 15, 2002). 2. Generation of cells containing a BoNT/A, BoNT/C1 or BoNT/E substrate by lentlvlral transduction 2a. Construction of pLent6Ubc/V5-SNAP-252e-GFP [03131 To make a pLenti6UbcN5-SNAP-25m-GFP construct, a nucleic acid fragment encoding the amino acid region comprising a BoNT/A, BoNT/C1 or BoNT/E SNAP-25-GFP substrate is amplified from, e.g., pQBI-25/SNAP252"-GFP DNA (see Example I, 1a) using a polymerase chain reaction method and subcloned into a pCR2.1 vector using the TOPO* TA cloning method (Invitrogen, Inc, Carlsbad, CA). The forward and reverse oligonucleotide primers used for this reaction are designed to include unique restriction enzyme sites useful for subsequent subcloning steps. The resulting pCR2.1/SNAP-252e-GFP construct is digested with restriction enzymes that 1) excise the insert containing the entire open reading frame encoding the SNAP-252m-GFP peptide; and 2) enable this insert to be operably-linked to a pLenti6UbcN5 vector (Invitrogen, Inc., Carlsbad, CA). This insert is subcloned using a T4 DNA ligase procedure into a pLenti6UbcV5 vector that is digested with appropriate restriction endonucleases to yield pLenti6UbcN5-SNAP-25e-GFP. The ligation mixture is transformed into chemically competent E. coli BL21 (DE3) cells (Invitrogen, Inc, Carlsbad, CA) using a heat shock method, plated on 1.5% Luria-Bertani agar plates (pH 7.0) containing 100 pg/mL of Ampicillin, and placed in a 37 *C incubator for overnight growth. Bacteria containing expression constructs are identified as Ampicillin resistant colonies. Candidate constructs are isolated using an alkaline lysis plasmid mini-preparation procedure and analyzed by restriction endonuclease digest mapping to determine the presence and orientation of the inset. This cloning strategy yields a mammalian expression construct encoding the SNAP-25zx-GFP operably-linked to the expression elements of the pLenti6UbcN5 vector an amino-terminal VS peptide. 2b. Production of a lentiviral stock containing pLent6Ubc/V5-SNAP-25-GFP 126 of 168 WO 2008/036060 PCT/US2006/012825 [0314] . To produce a lentiviral stock containing pLenti6UbcN5-SNAP-25-GFP, a 3.0 mL transfection solution is prepared by adding 1.5 mL of OPTI-MEM Reduced Serum Medium containing 36 pL of LipofectAmine 2000 (Invitrogen, Carlsbad, CA) incubated at room temperature for 5 minutes to 1.5 mL of OPTI-MEM Reduced Serum Medium containing 3 pg of an expression construct encoding a BoNT/A, BoNT/C1 or BoNT/E SNAP-25 substrate, such as, e.g., pLenti6UbcN5-SNAP-25206-GFP and 9 pg of ViraPowerTM Pacakaging Mix. After an approximately 20 minute incubation at room temperature, the DNA-lipid complexes are added to a 10 cm tissue culture plate containing 5 mL OPTI-MEM Reduced Serum Medium . A 5 mL cell suspension containing approximately 6x106 293A cells are then added to DNA-lipid complex media and grown in a 37 *C incubator under 5% carbon dioxide overnight. Transfection media is replaced with 10 mL of complete Dulbecco's Modified Eagle Media (DMEM), supplemented with 10% fetal bovine serum (FBS), 2 mM glutamine (Invitrogen, Inc, Carlsbad, CA), 1 mM sodium pyruvate (Invitrogen, Inc, Carlsbad, CA), 1x penicillin/streptomycin solution (Invitrogen, Inc, Carlsbad, CA) and 1x MEM non-essential amino acids solution (Invitrogen, Inc, Carlsbad, CA), and grown in a 37 *C incubator under 5% carbon dioxide for approximately 24-48 hours. The lentiovirus-containing cells are harvested by detaching the cells using the culture media and scraping cells from the culture plate. Detached cells and media are transferred to a 15 mL tube and centrifuged (5,000x g at 20 0C for 15 minutes) to pellet the cellular debris. The clarified supernatant containing the lentiviral particles is transferred to 2 mL cryovials in 1 mL aliquots and should contain approximately 5x10' to 2x 10 7 tulmL of lentiviral particles. Aliquots can be stored at -80 *C until needed. 2c. Transduction of cells with an lentiviral stock containing a pLent6Ubc/V5-SNAP-25-GFP [0315] To transduce cells with the lentiviral stock containing pLenti6UbcN5-SNAP-25-GFP, about 1.5x10 6 SH-SY5Y cells are plated in a 6-well tissue culture dish containing 3 mL of complete 1:1 EMEM and Ham's F12 Media (EMEM:F12), supplemented with 10% fetal bovine serum (FBS), 4 mM glutamine (Invitrogen, Inc, Carlsbad, CA), 1% sodium pyruvate (Invitrogen, Inc, Carlsbad, CA), 1.5 g/L sodium bicarbonate, 1x penicillin/streptomycin solution (Invitrogen, Inc, Carlsbad, CA) and 1x MEM non-essential amino acids solution (Invitrogen, Inc, Carlsbad, CA), and grown in a 37 *C incubator under 5% carbon dioxide until the cells reach a density of about 5x100 cells/mI (6-16 hours). Cells are inoculated with the lentiviral stock containing an expression construct encoding a BoNT/A, BoNT/Ci or BoNT/E SNAP-25 substrate, such as, e.g., pLenti6Ubc/V5-SNAP-25m-GFP (see Example I, 1), using a suitable multiplicity of infection and are incubated for approximately 16-24 hours in a 37 *C incubator under 5% carbon dioxide. The tranduction media is replaced with 3 mL of fresh complete, supplemented EMEM:F12 and cells are incubated in a 37 *C incubator under 5% carbon dioxide for approximately 24-48 hours. The transduced cells can be used to conduct a BoNT/A, BoNT/C1 or BoNT/E activity assay using a SNAP-25 GFP substrate. For greater details on procedures described in this example, see ViraPowerTM Lentiviral Expression System Instruction Manual 25-0501 version E, invitrogen, Inc., (Dec. 8, 2003). 3. Generation of cells containing a BoNT/A, BoNT/C1 or BoNT/E substrate by protein transformation 127 of 168 WO 2008/036060 PCT/US2006/012825 3a. Expression of a SNAP-25-GFP substrate using a bacterial cell line [0316] To express a BoNT/A, BoNT/C1 or BoNT/E SNAP-25-GFP substrate using bacteria, an expression construct encoding a BoNT/A, BoNT/C1 or BoNTIE SNAP-25-GFP substrate, such as, e.g., pQBI-67/SNAP-252 e-GFP as described above in Example I, Id, is introduced into chemically competent E. coli BL21 (DE3) cells (Invitrogen, Inc, Carlsbad, CA) using a heat-shock transformation protocol. The heat-shock reaction is then plated onto 1.5% Luria-Bertani agar plates (pH 7.0) containing 100 pg/mL of Ampicillin and placed in a 37 0C incubator for overnight growth. A single Ampicillin-resistant colony of transformed E. coli containing pQBI-67/SNAP-25 2 0 -GFP is used to inoculate a 15 mL test tube containing 3.0 mL Luria-Bertani media, (pH 7.0) containing 100 pg/mL of Ampicillin which is then placed in a 37 *C incubator, shaking at 250 rpm, for overnight growth. The resulting overnight starter culture is used to inoculate a 1.0 L baffled flask containing 100 mL Luria-Bertani media, (pH 7.0) containing 100 pg/mL of Ampicillin at a dilution of 1:1000. This culture is grown in a 32 *C incubator shaking at 250 rpm for approximately 6.5 hours until mid-log phase is reached (ODec of about 0.6-0.8). Protein expression is then induced by adding 1 mM isopropyl-0-D-thiogalactopyranoside (IPTG) and the culture is placed in a 32 0C incubator shaking at 250 rpm for overnight expression. Cells are harvested by centrifugation (4,000 rpm at 4 *C for 20-30 minutes) to pellet the cells. The supernatant is discarded and the cell pellet is used immediately for subsequent steps, or the pellet is stored at -80 0C until needed. 3b. Expression of a SNAP-25-GFP substrate using a mammalian cell line [0317] To express a BoNT/A, BoNT/C1 or BoNT/E SNAP-25-GFP substrate using a mammalian cell line, about 1.5x1 05 SH-SY5Y cells are plated in a 35 mm tissue culture dish containing 3 mL of complete 1:1 EMEM and Ham's F12 Media (EMEM:F12), supplemented with 10% fetal bovine serum (FBS), 4 mM glutamine (Invitrogen, Inc, Carlsbad, CA), 1% sodium pyruvate (Invitrogen, Inc, Carlsbad, CA), 1.5 g/L sodium bicarbonate, 1x penicillin/streptomycin solution (Invitrogen, Inc, Carlsbad, CA) and 1x MEM non essential amino acids solution (Invitrogen, Inc, Carlsbad, CA), and grown in a 37 *C incubator under 5% carbon dioxide until the cells reach a density of about 5x10 5 cells/mI (6-16 hours). A 500 pL transfection solution is prepared by adding 250 pL of OPTI-MEM Reduced Serum Medium containing 15 pL of LipofectAmine 2000 (Invitrogen, Carlsbad, CA) incubated at room temperature for 5 minutes to 250 pL of OPTI-MEM Reduced Serum Medium containing 5 pg of an expression construct encoding a BoNT/A, BoNT/C1 or BoNT/E SNAP-25-GFP substrate, such as, e.g., pQBI-25/SNAP25 2 os-GFP (see Example I, 1a). This transfection is incubated at room temperature for approximately 20 minutes. The complete, supplemented EMEM:F12 media is replaced with 2 mL of OPTI-MEM Reduced Serum Medium and the 500 pL transfection solution is added to the SH-SY5Y cells and the cells are incubated in a 37 0C incubator under 5% carbon dioxide for approximately 16 hours. Transfection media is replaced with 3 mL of fresh complete, supplemented EMEM:F12 and cells are incubated in a 37 0C incubator under 5% carbon dioxide for approximately 48 hours. Cells are harvest by rinsing cells once with 3.0 mL of 100 mM phosphate-buffered saline, pH 7.4 and detaching rinsed cells by adding 500 pi of 100 mM phosphate buffered saline, pH 7.4 and scraping cells from the culture plate. Detached cells are transferred to a 1.5 mL test tube and are pelleted by microcentrifugation (10,000x g at 4 *C for 5 minutes). The supernatant is discarded and the cell pellet is used immediately for subsequent steps, or the pellet is stored at -80 0C until needed. 128 of 168 WO 2008/036060 PCT/US2006/012825 3c. Purification of a SNAP-25-GFP substrate [0318] To purify a SNAP-25-GFP substrate, a cell pellet expressing an expression construct encoding a BoNT/A, BoNT/C1 or BoNT/E SNAP-25 substrate, such as, e.g., either a pQBI-67/SNAP-252N-GFP or a pQBI-25/SNAP-25 2 oo-GFP construct, is resuspended in 10 mL of Tris-EDTA Buffer (10 mM Tris-HCI, pH 8.0; 1 mM EDTA, pH 8.0), containing 1 mg/mL of lysozyme and the cells are lysed using three freeze thaw rounds consisting of -80 *C for 5 minutes then 37 *C for 5 minutes. The cell lysate is centrifuged (5,000x g at 4 *C for 15 minutes) to pellet the cellular debris and the supernatant is transferred to a new tube containing an equal volume of Column Binding Buffer (4 M ammonium sulfate). A hydrophobic interaction chromatography (HIC) column is prepared using a 20 mL Econo-Pac column support (Bio-Rad Laboratories, Hercules, CA) that is packed with 2.5-5.0 mL of methyl HIC resin (Bio-Rad Laboratories, Hercules, CA), which is then equilibrated by rinsing with 5 column volumes of Column Equilibration Buffer (2 M ammonium sulfate). The clarified lysate is applied slowly to the equilibrated column by gravity flow (approximately 0.25-0.3 mI/minute). The column is then washed with 5 column volumes of Column Wash Buffer (1.3 M ammonium sulfate). The SNAP-252N-GFP substrate is eluted with 20-30 mL of Column Elution Buffer (10 mM TE Buffer) and is collected in approximately twelve 1 mL fractions. The progress of the SNAP-252N-GFP substrate sample through the column as well as which elution fractions contain the sample is monitored using an ultraviolet light from a hand-held transilluminator. The amount of SNAP-25206-GFP substrate contained in each elution fraction is determined by a Bradford dye assay. In this procedure, 20 pL aliquot from each 1.0 mL fraction is combined with 200 pl of Bio-Rad Protein Reagent (Bio-Rad Laboratories, Hercules, CA), diluted I to 4 with deionized, distilled water, and then the intensity of the colorimetric signal is measured using a spectrophotometer. The five fractions with the strongest signal are considered to comprise the elution peak and are pooled. Total protein yield are determined by estimating the total protein concentration of the pooled peak elution fractions using bovine gamma globulin as a standard (Bio-Rad Laboratories, Hercules, CA). The amount of SNAP-252M-GFP substrate is adjusted to a protein concentration of approximately 100 ng/mL.. 3d. Protein transformation of a SNAP-25-GFP substrate [0319] To transform a SNAP-25-GFP substrate into a mammalian cell line, about 1.5x10 6 SH-SY5Y cells are plated in a 35 mm tissue culture dish containing 3 mL of complete 1:1 EMEM and Ham's F12 Media (EMEM:F12), supplemented with 10% fetal bovine serum (FBS), 4 mM glutamine (Invitrogen, Inc, Carlsbad, CA), 1% sodium pyruvate (Invitrogen, Inc, Carlsbad, CA), 1.5 g/L sodium bicarbonate, 1x penicillin/streptomycin solution (Invitrogen, Inc, Carlsbad, CA) and 1x MEM non-essential amino acids solution (Invitrogen, Inc, Carlsbad, CA), and grown in a 37 *C incubator under 5% carbon dioxide until the cells reach a density of about 5x10 5 cells/mI (6-16 hours). A 200 pL protein transfection solution is prepared by adding 100 pL of distilled water containing 6 pl of Chariotm protein delivery agent (Active Motif, Carlsbad, CA) to 100 pL of 100 mM phosphate-buffered saline, pH 7.4 containing 1 pg of a SNAP25-GFP substrate, such as, e.g., SNAP252o 6 -GFP, and this solution is incubated at room temperature for approximately 30 minutes. After incubation, the cells are washed once by rinsing cells with 3.0 mL of 100 mM phosphate-buffered saline, pH 7.4. The 200 pL protein transfection solution is added to the washed cells, followed by 400 pL of OPTI-MEM Reduced Serum Medium and the cells are 129 of 168 WO 2008/036060 PCTIUS2006/012825 incubated in a 37 *C incubator under 5% carbon dioxide for approximately 1 hour. Add 1 mL of fresh complete, supplemented EMEM:F12 to the cells and incubate in a 37 *C incubator under 5% carbon dioxide. After 1-2 hours, the transformed cells can be used to conduct a BoNT/A, BoNT/C1 or BoNT/E activity assay. 4. Generation of cells containing a BoNT/B, BoNT/D, BoNT/F, BoNT/G or TeNT VAMP substrate by adenorviral transduction 4a. Construction of pAd-DEST/VAMP-GFP [0320] To make a pAd-DESTNAMP-GFP construct encoding a BoNT/B, BoNT/D, BoNT/F, BoNT/G or TeNT VAMP-GFP substrate, a nucleic acid fragment encoding the amino acid region comprising VAMP GFP of is amplified from, e.g., pQBl-25NAMP-1-GFP DNA, pQBI-25NAMP-2-GFP DNA or pQBI 25NAMP-3-GFP DNA (see Examples I, 2a; I, 2b; or 1, 2c) using a polymerase chain reaction method and subcloned into a pCR2.1 vector using the TOPO* TA cloning method (Invitrogen, Inc, Carlsbad, CA). The forward and reverse oligonucleotide primers used for this reaction are designed to include unique restriction enzyme sites useful for subsequent suboloning steps. The resulting pCR2.1NAMP-GFP construct is digested with restriction enzymes that 1) excise the insert containing the entire open reading frame encoding the VAMP-GFP peptide; and 2) enable this insert to be operably-linked to a pAd-DEST vector (Invitrogen, Inc., Carlsbad, CA). This insert is subcloned using a T4 DNA ligase procedure into a pAd-DEST vector that is digested with appropriate restriction endonucleases to yield pAd-DESTNAMP GFP. The ligation mixture is transformed into chemically competent E. coliBL21 (DE3) cells (Invitrogen, Inc, Carlsbad, CA) using a heat shock method, plated on 1.5% Luria-Bertani agar plates (pH 7.0) containing 100 pg/mL of Ampicillin, and placed in a 37 00 incubator for overnight growth. Bacteria containing expression constructs are identified as Ampicillin resistant colonies. Candidate constructs are isolated using an alkaline lysis plasmid mini-preparation procedure and analyzed by restriction endonuclease digest mapping to determine the presence and orientation of the inset. This cloning strategy yields a mammalian expression construct encoding the VAMP-GFP operably-linked to the expression elements of the pAd-DEST vector. 4b. Production of an adenoviral stock containing pAd-DEST/VAMP-GFP [0321] . To produce an adenoviral stock containing an expression construct encoding a BoNT/B, BoNT/D, BoNT/F, BoNT/G or TeNT VAMP-GFP substrate, such as, e.g., pAd-DESTNAMP-GFP, about 5x10 5 293A cells are plated in a 35 mm tissue culture dish containing 3 mL of complete Dulbecco's Modified Eagle Media (DMEM), supplemented with 10% fetal bovine serum (FBS), 1x penicillin/streptomycin solution (Invitrogen, Inc, Carlsbad, CA) and 1x MEM non-essential amino acids solution (Invitrogen, Inc, Carlsbad, CA), and grown in a 37 *C incubator under 5% carbon dioxide until the cells reach a density of about 5x10 5 cells/mI (6-16 hours). One the day of transfection, replace complete, supplemented DMEM media with 2 mL of OPTI-MEM Reduced Serum Medium. A 500 pL transfection solution is prepared by adding 250 pL of OPTI-MEM Reduced Serum Medium containing 15 pL of LipofectAmine 2000 (Invitrogen, Carlsbad, CA) incubated at room temperature for 5 minutes to 250 pL of OPTI-MEM Reduced Serum Medium containing 5 pg of the linearized expression construct encoding a 130 of 168 WO 2008/036060 PCTIUS2006/012825 BoNT/B, BoNT/D, BoNT/F, BoNT/G or TeNT VAMP-GFP substrate, such as, e.g., pAd-DESTNAMP GFP. To linearized a pAd-DESTNAMP-GFP construct, 5 pg of a pAd-DESTNAMP-GFP construct is digested with Pact (New England Biolabs, Beverly, MA). The linearized plasmid is purified using OlAquick kit procedure (QIAGEN, Inc., Valencia, CA) and is resuspended in TE Buffer. This transfection is incubated at room temperature for approximately 20 minutes. The 500 pL transfection solution is then added to the 293A cells and the cells are incubated in a 37 *C incubator under 5% carbon dioxide for approximately 16 hours. Transfection media is replaced with 3 mL of fresh complete, supplemented DMEM and cells are incubated in a 37 *C incubator under 5% carbon dioxide for approximately 24 hours. Trypsinize the cells and transfer the contains of each well to a sterile 10 cm tissue culture plate containing 10 mL of complete, supplemented DMEM. Replace the old media with fresh complete, supplemented DMEM every 2 or 3 days until visible regions of cytopathic effect are observed (typically 7-10 days). Replenish the old culture media with fresh complete, supplemented DMEM and allow the infections to proceed until approximately 80% cytopathic effect is observed (typically 10-13 days post transfection). The adenovirus-containing cells are harvested by detaching the cells using the culture media and scraping cells from the culture plate. Detached cells and media are transferred to a 15 mL tube. The harvested cells are lysed using one freeze-thaw round consisting of -80 *C for 30 minutes then 37 *C for 15 minutes. The cell lysate is centrifuged (5,000x g at 20 *C for 15 minutes) to pellet the cellular debris. The clarified supernatant containing the adenoviral particles is transferred to 2 mL cryovials in 1 mL aliquots and should contain approximately 1x107 to 108 pfu of adenoviral particles. Aliquots can be stored at -80 *C until needed. 4c. Amplification of an adenoviral stock containing pAd-DEST/VAMP-GFP [0322] To amplified to the adenoviral stock containing an expression construct encoding a BoNT/B, BoNT/D, BoNT/F, BoNT/G or TeNT VAMP-GFP substrate, such as, e.g., pAd-DESTNAMP-GFP, about 3x10 6 293A cells are plated in a 100 mm culture dish containing in 10 mL of complete Dulbecco's Modified Eagle Media (DMEM), supplemented with 10% fetal bovine serum (FBS), 1x penicillin/streptomycin solution (Invitrogen, Inc, Carlsbad, CA) and 1x MEM non-essential amino acids solution (Invitrogen, Inc, Carlsbad, CA), and grown in a 37 *C incubator under 5% carbon dioxide until the cells reach a density of about 80-90/a confluency (6-16 hours). The cells are inoculated cells with 100 pL of adenoviral stock and incubated for approximately 48-72 hours in a 37 *C incubator under 5% carbon dioxide until the cells round up and are floating or lightly attached to the culture plate. The adenovirus containing cells are harvested by detaching the cells using the culture media and scraping cells from the culture plate. Detached cells and media are transferred to a 15 mL tube. The harvested cells are lysed using three freeze-thaw round consisting of -80 *C for 30 minutes then 37 *C for 15 minutes. The cell lysate is centrifuged (5,000x g at 20 *C for 15 minutes) to pellet the cellular debris. The clarified supernatant containing the adenoviral particles is transferred to 2 mL cryovials in 1 mL aliquots and should contain approximately 1x10 8 to 10 9 pfu of adenoviral particles. Aliquots can be stored at -80 @C until needed. 4d. Transduction of cells with an adenoviral stock containing pAd-DESTIVAMP-GFP [0323] To transduce cells with the adenoviral stock containing an expression construct encoding a 131 of 168 WO 2008/036060 PCTIUS2006/012825 BoNT/B, BoNT/D, BoNT/F, BoNT/G or TeNT VAMP-GFP substrate, such as, e.g., pAd-DESTNAMP GFP, a suitable density (1x10 5 to 1x10 ) of appropriate cells are plated in a 6-well tissue culture dish containing 3 mL of complete, supplemented culture media and are grown in a 37 0C incubator under 5% carbon dioxide until the cells reach a density appropriate for transduction. Cells are inoculated with approximately 4 pL of the adenoviral stock (approximately 5x10 8 pfu/ml) and are incubated for approximately 24 hours in a 37 0C incubator under 5% carbon dioxide. The tranduction media is replaced with 3 mL of fresh complete, supplemented media and cells are incubated in a 37 *C incubator under 5% carbon dioxide for approximately 24 hours. The transduced cells can be used to conduct a BoNT/B, BoNT/D, BoNT/F, BoNT/G or TeNT activity assay using a VAMP-GFP substrate. For greater details on procedures described in this example, see ViraPowerTM Adenoviral Expression System Instruction Manual 25-0543 version A, Invitrogen, Inc., (Jul. 15, 2002). 5. Generation of cells containing a BoNT/B, BoNT/D, BoNT/F, BoNT/G or TeNT substrate by lentiviral transduction 5a. Construction of pLenti6Ubc/V5-VAMP-GFP (0324] To make a pLenti6UbcN5-VAMP-GFP construct encoding a BoNT/B, BoNT/D, BoNT/F, BoNT/G or TeNT VAMP-GFP substrate, a nucleic acid fragment encoding the amino acid region comprising a BoNT/B, BoNT/D, BoNT/F, BoNT/G or TeNT VAMP-GFP substrate is amplified from, e.g., e.g., pQBI 25NAMP-1-GFP DNA, pQBI-25NAMP-2-GFP DNA or pQBI-25NAMP-3-GFP DNA (see Examples I, 2a; 1, 2b; or I, 2c), using a polymerase chain reaction method and subcloned into a pCR2.1 vector using the TOPO TA cloning method (Invitrogen, Inc, Carlsbad, CA). The forward and reverse oligonucleotide primers used for this reaction are designed to include unique restriction enzyme sites useful for subsequent subcloning steps. The resulting pCR2.1NAMP-GFP construct is digested with restriction enzymes that 1) excise the insert containing the entire open reading frame encoding the VAMP-GFP peptide; and 2) enable this insert to be operably-linked to a pLenti6UbcV5 vector (Invitrogen, Inc., Carlsbad, CA). This Insert is subcloned using a T4 DNA ligase procedure into a pLenti6UbcN5 vector that is digested with appropriate restriction endonucleases to yield pLenti6UbcN5-VAMP-GFP. The ligation mixture is transformed into chemically competent E. coli BL21 (DE3) cells (Invitrogen, Inc, Carlsbad, CA) using a heat shock method, plated on 1.5% Luria-Bertani agar plates (pH 7.0) containing 100 pg/mL of Ampicillin, and placed in a 37 *C incubator for overnight growth. Bacteria containing expression constructs are identified as Ampicillin resistant colonies. Candidate constructs are isolated using an alkaline lysis plasmid mini-preparation procedure and analyzed by restriction endonuclease digest mapping to determine the presence and orientation of the inset. This cloning strategy yields a mammalian expression construct encoding the VAMP-GFP operably-linked to the expression elements of the pLenti6UbcN5 vector an amino-terminal V5 peptide. 5b. Production of a lentiviral stock containing pLent6Ubc/V5-VAMP-GFP [0325] . To produce a lentiviral stock containing an expression construct encoding a BoNT/B, BoNT/D, BoNT/F, BoNT/G or TeNT VAMP-GFP substrate, a 3.0 mL transfection solution Is prepared by adding 1.5 mL of OPTI-MEM Reduced Serum Medium containing 36 pL of LipofectAmine 2000 (Invitrogen, 132 of 168 WO 2008/036060 PCT/US2006/012825 Carlsbad, CA) incubated at room temperature for 5 minutes to 1.5 mL of OPTI-MEM Reduced Serum Medium containing 3 pg of an expression construct encoding a BoNT/B, BoNT/D, BoNT/F, BoNT/G or TeNT VAMP-GFP substrate, such as, e.g., pLenti6Ubc/V5-VAMP-GFP and 9 pg of ViraPowerTm Pacakaging Mix. After an approximately 20 minute incubation at room temperature, the DNA-lipid complexes are added to a 10 cm tissue culture plate containing 5 mL OPTI-MEM Reduced Serum Medium . A 5 mL cell suspension containing approximately 6x10 6 293A cells are then added to DNA-lipid complex media and grown in a 37 *C incubator under 5% carbon dioxide overnight. Transfection media is replaced with 10 mL of complete Dulbecco's Modified Eagle Media (DMEM), supplemented with 10% fetal bovine serum (FBS), 2 mM glutamine (Invitrogen, Inc, Carlsbad, CA), 1 mM sodium pyruvate (Invitrogen, Inc, Carlsbad, CA), 1x penicillin/streptomycin solution (Invitrogen, Inc, Carlsbad, CA) and 1x MEM non-essential amino acids solution (Invitrogen, Inc, Carlsbad, CA), and grown in a 37 *C incubator under 5% carbon dioxide for approximately 24-48 hours. The lentiovirus-containing cells are harvested by detaching the cells using the culture media and scraping cells from the culture plate. Detached cells and media are transferred to a 15 mL tube and centrifuged (5,000x g at 20 *C for 15 minutes) to pellet the cellular debris. The clarified supernatant containing the lentiviral particles is transferred to 2 mL cryovials in 1 mL aliquots and should contain approximately 5x10 6 to 2x 10 7 tu/mL of lentiviral particles. Aliquots can be stored at -80 *C until needed. 5c. Transduction of cells with an lentiviral stock containing a pLent6Ubc/V5-VAMP-GFP [0326] To transduce cells with the lentiviral stock containing an expression construct encoding a BoNT/B, BoNT/D, BoNT/F, BoNT/G or TeNT VAMP-GFP substrate, a suitable density (11.5x10 5 to 1.5x10) of appropriate cells is plated in a 6-well tissue culture dish containing 3 mL of complete, supplemented culture media and the cells are grown in a 37 *C incubator under 5% carbon dioxide until the cells reach a density of about 5x10 5 cells/mi (6-16 hours). Cells are inoculated with the lentiviral stock containing an expression construct encoding a BoNT/B, BoNT/D, BoNT/F, BoNT/G or TeNT VAMP-GFP substrate, such as, e.g., pLenti6UbcN5-VAMP-GFP, using a suitable multiplicity of infection and are incubated for approximately 16-24 hours in a 37 "C incubator under 5% carbon dioxide. The tranduction media is replaced with 3 mL of fresh complete, supplemented media and cells are incubated in a 37 "C incubator under 5% carbon dioxide for approximately 24-48 hours. The transduced cells can be used to conduct a BoNT/B, BoNT/D, BoNT/F, BoNT/G or TeNT activity assay using a VAMP-GFP substrate. For greater details on procedures described in this example, see ViraPowerTM Lentiviral Expression System Instruction Manual 25-0501 version E, Invitrogen, Inc., (Dec. 8, 2003). 6. Generation of cells containing a BoNT/B, BoNT/D, BoNT/F, BoNT/G or TeNT substrate by protein transformation 6a. Expression of a VAMP-GFP substrate using a bacterial cell line [03271 To express a BoNT/B, BoNT/D, BoNT/F, BoNT/G or TeNT VAMP-GFP substrate using bacteria, an expression construct encoding a BoNT/B, BoNT/D, BoNT/F, BoNT/G or TeNT VAMP-GFP substrate, such as, e.g., pQBI-67NAMP-1-GFP, pQBI-67/VAMP-2-GFP or pQBI-67NAMP-3-GFP as described above In Examples I, 2d; I, 2e; or I, 2f, is introduced into chemically competent E. coli BL21 (DE3) cells 133 of 168 WO 2008/036060 PCT/US2006/012825 (Invitrogen, Inc, Carlsbad, CA) using a heat-shock transformation protocol. The heat-shock reaction is then plated onto 1.5% Luria-Bertani agar plates (pH 7.0) containing 100 pg/mL of Ampicillin and placed in a 37 *C incubator for overnight growth. A single Ampicillin-resistant colony of transformed E. coli containing pQBI-67NAMP-GFP is used to inoculate a 15 mL test tube containing 3.0 mL Luria-Bertani media, (pH 7.0) containing 100 pg/mL of Ampicillin which is then placed in a 37 *C incubator, shaking at 250 rpm, for overnight growth. The resulting overnight starter culture is used to inoculate a 1.0 L baffled flask containing 100 mL Luria-Bertani media, (pH 7.0) containing 100 pg/mL of Ampicillin at a dilution of 1:1000. This culture is grown in a 32 *C incubator shaking at 250 rpm for approximately 6.5 hours until mid-log phase is reached (ODew of about 0.6-0.8). Protein expression is then induced by adding 1 mM isopropyl-p-D-thiogalactopyranoside (IPTG) and the culture is placed in a 32 *C incubator shaking at 250 rpm for overnight expression. Cells are harvested by centrifugation (4,000 rpm at 4 *C for 20-30 minutes) to pellet the cells. The supernatant is discarded and the cell pellet is used immediately for subsequent steps, or the pellet is stored at -80 *C until needed. 6b. Expression of a VAMP-GFP substrate using a mammalian cell line [0328] To express a BoNT/B, BoNT/D, BoNT/F, BoNTIG or TeNT VAMP-GFP substrate using a mammalian cell line, a suitable density (1.0x10 5 to 1.0x10 6 ) of appropriate cells is plated in a 35 mm tissue culture dish containing 3 mL of complete, supplemented culture media and the cells are grown in a 37 *C incubator under 5% carbon dioxide until the cells reach a density of about 5x10 6 cells/mI (6-16 hours). A 500 pL transfection solution is prepared by adding 250 pL of OPTI-MEM Reduced Serum Medium containing 15 pL of LipofectAmine 2000 (Invitrogen, Carlsbad, CA) incubated at room temperature for 5 minutes to 250 pL of OPTI-MEM Reduced Serum Medium containing 5 pg of an expression construct encoding a BoNT/B, BoNT/D, BoNT/F, BoNT/G or TeNT VAMP-GFP substrate, such as, e.g., pQBI-25NAMP-1-GFP, pQBI-25NAMP-2-GFP or pQBI-25NAMP-3-GFP (see Examples I, 2a; I, 2b; or I, 2c). This transfection is incubated at room temperature for approximately 20 minutes. The complete, supplemented culture media is replaced with 2 mL of OPTI-MEM Reduced Serum Medium and the 500 pL transfection solution is added to the cells and the cells are incubated in a 37 *C incubator under 5% carbon dioxide for approximately 16 hours. Transfection media is replaced with 3 mL of fresh complete, supplemented EMEM:F12 and cells are incubated in a 37 *C incubator under 5% carbon dioxide for approximately 48 hours. Cells are harvest by rinsing cells once with 3.0 mL of 100 mM phosphate-buffered saline, pH 7.4 and detaching rinsed cells by adding 500 pl of 100 mM phosphate buffered saline, pH 7.4 and scraping cells from the culture plate. Detached cells are transferred to a 1.5 mL test tube and are pelleted by microcentrifugation (10,000x g at 4 *C for 5 minutes). The supernatant is discarded and the cell pellet is used immediately for subsequent steps, or the pellet is stored at -80 *C until needed. 6c. Purification of a VAMP-GFP substrate [0329] To purify a VAMP-GFP substrate, a cell pellet expressing an expression construct encoding a BoNT/B, BoNT/D, BoNT/F, BoNT/G or TeNT VAMP-GFP substrate, such as, e.g., either a pQ8I 67NAMP-1-GFP or a pQBI-25NAMP-1-GFP construct, is resuspended in 10 mL of Tris-EDTA Buffer (10 mM Tris-HCI, pH 8.0; 1 mM EDTA, pH 8.0), containing 1 mg/mL of lysozyme and the cells are lysed using 134 of 168 WO 2008/036060 PCT/US2006/012825 three freeze-thaw rounds consisting of -80 "C for 5 minutes then 37 *C for 5 minutes. The cell lysate is centrifuged (5,000x g at 4 *C for 15 minutes) to pellet the cellular debris and the supernatant is transferred to a new tube containing an equal volume of Column Binding Buffer (4 M ammonium sulfate). A hydrophobic interaction chromatography (HIC) column is prepared using a 20 mL Econo-Pac column support (Bio-Rad Laboratories, Hercules, CA) that is packed with 2.5-5.0 mL of methyl HIC resin (Bio-Rad Laboratories, Hercules, CA), which is then equilibrated by rinsing with 5 column volumes of Column Equilibration Buffer (2 M ammonium sulfate). The clarified lysate is applied slowly to the equilibrated column by gravity flow (approximately 0.25-0.3 mL/minute). The column is then washed with 5 column volumes of Column Wash Buffer (1.3 M ammonium sulfate). The VAMP-GFP substrate is eluted with 20 30 mL of Column Elution Buffer (10 mM TE Buffer) and is collected in approximately twelve I mL fractions. The progress of the VAMP-GFP substrate sample through the column as well as which elution fractions contain the sample is monitored using an ultraviolet light from a hand-held transilluminator. The amount of VAMP-GFP substrate contained in each elution fraction is determined by a Bradford dye assay. In this procedure, 20 pL aliquot from each 1.0 mL fraction is combined with 200 pL of Bio-Rad Protein Reagent (Bio-Rad Laboratories, Hercules, CA), diluted 1 to 4 with deionized, distilled water, and then the intensity of the colorimetric signal is measured using a spectrophotometer. The five fractions with the strongest signal are considered to comprise the elution peak and are pooled. Total protein yield are determined by estimating the total protein concentration of the pooled peak elution fractions using bovine gamma globulin as a standard (Bio-Rad Laboratories, Hercules, CA). The amount of VAMP-GFP substrate is adjusted to a protein concentration of approximately 100 ng/mL.. 6d. Protein transformation of a VA MP-GFP substrate [0330] To transform a VAMP-GFP substrate into a mammalian cell line, a suitable density (1.0x10 6 to 1.Ox10) of appropriate cells is plated in a 35 mm tissue culture dish containing 3 mL of complete, supplemented culture media and the cells are grown in a 37 *C incubator under 5% carbon dioxide until the cells reach a density of about 5x10 5 cells/mI (6-16 hours). A 200 pL protein transfection solution is prepared by adding 100 pL of distilled water containing 6 pl of ChariotTm protein delivery agent (Active Motif, Carlsbad, CA) to 100 pL of 100 mM phosphate-buffered saline, pH 7.4 containing 1 pg of a VAMP GFP substrate and this solution is incubated at room temperature for approximately 30 minutes. After incubation, the cells are washed once by rinsing cells with 3.0 mL of 100 mM phosphate-buffered saline, pH 7.4. The 200 pL protein transfection solution is added to the washed cells, followed by 400 pL of OPTI-MEM Reduced Serum Medium and the cells are incubated in a 37 *C incubator under 5% carbon dioxide for approximately 1 hour. Add 1 mL of fresh complete, supplemented culture media to the cells and incubate in a 37 *C incubator under 5% carbon dioxide. After 1-2 hours, the transformed cells can be used to conduct a BoNT/B, BoNTID, BoNT/F, BoNT/G or TeNT activity assay using a VAMP-GFP substrate. 7. Generation of cells containing a BoNT/C1 Syntaxin substrate by adenorvIral transduction 7a. Construction of pAd-DEST/Syntaxln-GFP [0331] To make a pAd-DEST/Syntaxin-GFP construct encoding a BoNT/C1 Syntaxin-GFP substrate, a 135 of 168 WO 2008/036060 PCT/US2006/012825 nucleic acid fragment encoding the amino acid region comprising Syntaxin-GFP of is amplified an expression construct encoding a BoNT/C1-GFP substrate, such as, e.g., pQBI-25/Syntaxin-1-GFP DNA (see Example I, 3a) using a polymerase chain reaction method and subcloned into a pCR2.1 vector using the TOPO TA cloning method (Invitrogen, Inc, Carlsbad, CA). The forward and reverse oligonucleotide primers used for this reaction are designed to include unique restriction enzyme sites useful for subsequent subcloning steps. The resulting pCR2.1/Syntaxin-GFP construct is digested with restriction enzymes that 1) excise the insert containing the entire open reading frame encoding the Syntaxin-GFP peptide; and 2) enable this insert to be operably-linked to a pAd-DEST vector (Invitrogen, Inc., Carlsbad, CA). This insert is subcloned using a T4 DNA ligase procedure into a pAd-DEST vector that is digested with appropriate restriction endonucleases to yield pAd-DEST/Syntaxin-GFP. The ligation mixture is transformed into chemically competent E. coli BL21 (DE3) cells (Invitrogen, Inc, Carlsbad, CA) using a heat shock method, plated on 1.5% Luria-Bertani agar plates (pH 7.0) containing 100 pg/mL of Ampicillin, and placed in a 37 *C incubator for overnight growth. Bacteria containing expression constructs are identified as Ampicillin resistant colonies. Candidate constructs are isolated using an alkaline lysis plasmid mini-preparation procedure and analyzed by restriction endonuclease digest mapping to determine the presence and orientation of the inset. This cloning strategy yields a mammalian expression construct encoding the Syntaxin-GFP operably-linked to the expression elements of the pAd DEST vector. 7b. Production of an adenoviral stock containing pAd-DEST/Syntaxln-GFP [0332] . To produce an adenoviral stock containing an expression construct encoding a BoNT/Cl Syntaxin-GFP substrate, about 5x105 293A cells are plated in a 35 mm tissue culture dish containing 3 mL of complete Dulbecco's Modified Eagle Media (DMEM),'supplemented with 10% fetal bovine serum (FBS), 1x penicillin/streptomycin solution (Invitrogen, Inc, Carlsbad, CA) and 1x MEM non-essential amino acids solution (Invitrogen, Inc, Carlsbad, CA), and grown in a 37 *C incubator under 5% carbon dioxide until the cells reach a density of about 5x10 5 cells/mI (6-16 hours). One the day of transfection, replace complete, supplemented DMEM media with 2 mL of OPTI-MEM Reduced Serum Medium. A 500 pL transfection solution is prepared by adding 250 pL of OPTI-MEM Reduced Serum Medium containing 15 pL of LipofectAmine 2000 (Invitrogen, Carlsbad, CA) incubated at room temperature for 5 minutes to 250 pL of OPTI-MEM Reduced Serum Medium containing 5 pg of the linearized expression construct encoding a BoNT/C1 Syntaxin-GFP substrate, such as, e.g., pAd-DEST/Syntaxin-GFP. To linearized a pAd-DEST/Syntaxin-GFP construct, 5 pg of a pAd-DEST/Syntaxin-GFP construct is digested with Pad (New England Biolabs, Beverly, MA). The linearized plasmid is purified using QlAquick kit procedure (QIAGEN, Inc., Valencia, CA) and is resuspended in TE Buffer. This transfection is incubated at room temperature for approximately 20 minutes. The 500 pL transfection solution is then added to the 293A cells and the cells are incubated in a 37 *C incubator under 5% carbon dioxide for approximately 16 hours. Transfection media is replaced with 3 mL of fresh complete, supplemented DMEM and cells are incubated in a 37 *C incubator under 5% carbon dioxide for approximately 24 hours. Trypsinize the cells and transfer the contains of each well to a sterile 10 cm tissue culture plate containing 10 mL of complete, supplemented DMEM. Replace the old media with fresh complete, supplemented DMEM every 2 or 3 days until visible regions of cytopathic effect are observed (typically 7-10 days). Replenish the old culture 136 of 168 WO 2008/036060 PCT/US2006/012825 media with fresh complete, supplemented DMEM and allow the infections to proceed until approximately 80% cytopathic effect is observed (typically 10-13 days post transfection). The adenovirus-containing cells are harvested by detaching the cells using the culture media and scraping cells from the culture plate. Detached cells and media are transferred to a 15 mL tube. The harvested cells are lysed using one freeze-thaw round consisting of -80 0C for 30 minutes then 37 *C for 15 minutes. The cell lysate is centrifuged (5,000x g at 20 *C for 15 minutes) to pellet the cellular debris. The clarified supernatant containing the adenoviral particles is transferred to 2 mL cryovials in 1 mL aliquots and should contain approximately 1x107 to 108 pfu of adenoviral particles. Aliquots can be stored at -80 *C until needed. 7c. Amplification of an adenoviral stock containing pAd-DEST/Syntaxin-GFP [0333] To amplified to the adenoviral stock containing an expression construct encoding a BoNT/C1 Syntaxin-GFP substrate, such as, e.g., pAd-DEST/Syntaxin-GFP, about 3x10r 293A cells are plated in a 100 mm culture dish containing in 10 mL of complete Dulbecco's Modified Eagle Media (DMEM), supplemented with 10% fetal bovine serum (FBS), lx penicillin/streptomycin solution (Invitrogen, Inc, Carlsbad, CA) and 1x MEM non-essential amino acids solution (Invitrogen, Inc, Carlsbad, CA), and grown in a 37 *C incubator under 5% carbon dioxide until the cells reach a density of about 80-90% confluency (6-16 hours). The cells are inoculated cells with 100 pL of adenoviral stock and incubated for approximately 48-72 hours in a 37 *C incubator under 5% carbon dioxide until the cells round up and are floating or lightly attached to the culture plate. The adenovirus-containing cells are harvested by detaching the cells using the culture media and scraping cells from the culture plate. Detached cells and media are transferred to a 15 mL tube. The harvested cells are lysed using three freeze-thaw round consisting of -80 *C for 30 minutes then 37 *C for 15 minutes. The cell lysate is centrifuged (5,000x g at 20 *C for 15 minutes) to pellet the cellular debris. The clarified supernatant containing the adenoviral particles is transferred to 2 mL cryovials in 1 mL aliquots and should contain approximately 1x10 to 10 9 pfu of adenoviral particles. Aliquots can be stored at -80 *C until needed. 7d. Transduction of cells with an adenoviral stock containing pAd-DEST/Syntaxin-GFP [03341 To transduce cells with the adenoviral stock containing an expression construct encoding a BoNT/C1 Syntaxin-GFP substrate, such as, e.g., pAd-DEST/Syntaxin-GFP, a suitable density (1x105 to 1x106) of appropriate cells are plated in a 6-well tissue culture dish containing 3 mL of complete, supplemented culture media and are grown in a 37 *C incubator under 5% carbon dioxide until the cells reach a density appropriate for transduction. Cells are inoculated with approximately 4 pL of the adenoviral stock (approximately 5x1O plu/ml) and are incubated for approximately 24 hours in a 37 *C incubator under 5% carbon dioxide. The tranduction media is replaced with 3 mL of fresh complete, supplemented media and cells are incubated in a 37 *C incubator under 5% carbon dioxide for approximately 24 hours. The transduced cells can be used to conduct a BoNT/C1 activity assay using a Syntaxin-GFP substrate. For greater details on procedures described in this example, see ViraPowerTM Adenoviral Expression System Instruction Manual 25-0543 version A, Invitrogen, Inc., (Jul. 15, 2002). 8. Generation of cells containing a BoNT/C1 substrate by lentiviral transduction 137 of 168 WO 2008/036060 PCT/US2006/012825 Ba. Construction of pLentl6Ubc/V5-Syntaxin-GFP [0335} To make a pLenti6UbcN5-Syntaxin-GFP construct encoding a BoNT/C1 Syntaxin-GFP substrate, a nucleic acid fragment encoding the amino acid region comprising a BoNT/Ci Syntaxin-GFP substrate is amplified from, e.g., pQBI-25/Syntaxin-1-GFP DNA (see Example I, 3a) using a polymerase chain reaction method and subcloned into a pCR2.1 vector using the TOPO* TA cloning method (Invitrogen, Inc, Carlsbad, CA). The forward and reverse oligonucleotide primers used for this reaction are designed to include unique restriction enzyme sites useful for subsequent subcloning steps. The resulting pCR2.1/Syntaxin-GFP construct is digested with restriction enzymes that 1) excise the insert containing the entire open reading frame encoding the Syntaxin-GFP peptide; and 2) enable this insert to be operably-linked to a pLenti6UbcNS vector (Invitrogen, Inc., Carlsbad, CA). This insert is subcloned using a T4 DNA ligase procedure into a pLenti6UbcN5 vector that is digested with appropriate restriction endonucleases to yield pLenti6UbcN5-Syntaxin-GFP. The ligation mixture is transformed into chemically competent E. coli BL21 (DE3) cells (Invitrogen, Inc, Carlsbad, CA) using a heat shock method, plated on 1.5% Luria-Bertani agar plates (pH 7.0) containing 100 pg/mL of Ampicillin, and placed in a 37 *C incubator for overnight growth. Bacteria containing expression constructs are identified as Ampicillin resistant colonies. Candidate constructs are isolated using an alkaline lysis plasmid mini-preparation procedure and analyzed by restriction endonuclease digest mapping to determine the presence and orientation of the inset. This cloning strategy yields a mammalian expression construct encoding the Syntaxin-GFP operably-linked to the expression elements of the pLenti6UbcN5 vector an amino-terminal V5 peptide. Ob. Production of a lentiviral stock containing pLent6Ubc/V5-Syntaxn-GFP [0336] . To produce a lentiviral stock containing an expression construct encoding a BoNT/C1 Syntaxin GFP substrate, a 3.0 mL transfection solution is prepared by adding 1.5 mL of OPTI-MEM Reduced Serum Medium containing 36 pL of LipofectAmine 2000 (Invitrogen, Carlsbad, CA) incubated at room temperature for 5 minutes to 1.5 mL of OPTI-MEM Reduced Serum Medium containing 3 pg of an expression construct encoding a BoNT/C1 Syntaxin-GFP substrate, such as, e.g., pLenti6UbcV5 Syntaxin-GFP and 9 pg of ViraPowerTM Pacakaging Mix. After an approximately 20 minute incubation at room temperature, the DNA-lipid complexes are added to a 10 cm tissue culture plate containing 5 mL OPTI-MEM Reduced Serum Medium . A 5 mL cell suspension containing approximately 6x106 293A cells are then added to DNA-lipid complex media and grown in a 37 *C incubator under 5% carbon dioxide overnight. Transfection media is replaced with 10 mL of complete Dulbecco's Modified Eagle Media (DMEM), supplemented with 10% fetal bovine serum (FBS), 2 mM glutamine (Invitrogen, Inc, Carlsbad, CA), 1 mM sodium pyruvate (Invitrogen, Inc, Carlsbad, CA), 1x penicillin/streptomycin solution (Invitrogen, Inc, Carlsbad, CA) and 1x MEM non-essential amino acids solution (Invitrogen, Inc, Carlsbad, CA), and grown in a 37 *C incubator under 5% carbon dioxide for approximately 24-48 hours. The lentiovirus-containing cells are harvested by detaching the cells using the culture media and scraping cells from the culture plate. Detached cells and media are transferred to a 15 mL tube and centrifuged (5,000x g at 20 *C for 15 minutes) to pellet the cellular debris. The clarified supernatant containing the lentiviral particles is transferred to 2 mL cryovials in 1 mL aliquots and should contain approximately 5x1 0 to 2x 107 tu/mL of lentiviral particles. Aliquots can be stored at -80 *C until needed. 138 of 168 WO 2008/036060 PCT/US2006/012825 8c. Transduction of cells with an lentiviral stock containing a pLent6Ubc/V5-Syntaxln-GFP [0337] To transduce cells with the lentiviral stock containing an expression construct encoding a BoNT/C1 Syntaxin-GFP substrate, a suitable density (1.5x10 6 to 1.5x10 6 ) of appropriate cells is plated in a 6-well tissue culture dish containing 3 mL of complete, supplemented culture media and the cells are grown in a 37 *C incubator under 5% carbon dioxide until the cells reach a density of about 5x1 05 cells/mi (6-16 hours). Cells are inoculated with the lentiviral stock containing an expression construct encoding a BoNT/C1 Syntaxin-GFP substrate, such as, e.g., pLenti6UbcN5-Syntaxin-GFP, using a suitable multiplicity of infection and are incubated for approximately 16-24 hours in a 37 0C incubator under 5% carbon dioxide. The tranduction media is replaced with 3 mL of fresh complete, supplemented media and cells are incubated in a 37 *C incubator under 5% carbon dioxide for approximately 24-48 hours. The transduced cells can be used to conduct a BoNT/C1 activity assay using a Syntaxin-GFP substrate. For greater details on procedures described in this example, see ViraPowerTM Lentiviral Expression System Instruction Manual 25-0501 version E, Invitrogen, Inc., (Dec. 8, 2003). 9. Generation of cells containing a BoNT/C1 substrate by protein transformation 9a. Expression of a Syntaxin-GFP substrate using a bacterial cell line [0338] To express a BoNT/C1 Syntaxin-GFP substrate using bacteria, an expression construct encoding a BoNT/C1 Syntaxin-GFP substrate, such as, e.g., pQBI-67/Syntaxin-1-GFP as described above in Example I, 3b, is introduced into chemically competent E. coli BL21 (DE3) cells (Invitrogen, Inc, Carlsbad, CA) using a heat-shock transformation protocol. The heat-shock reaction is then plated onto 1.5% Luria Bertani agar plates (pH 7.0) containing 100 pg/mL of Ampicillin and placed in a 37 0C incubator for overnight growth. A single Arnpicilin-resistant colony of transformed E. coli containing pQBI-67/Syntaxin GFP is used to inoculate a 15 mL test tube containing 3.0 mL Luria-Bertani media, (pH 7.0) containing 100 pg/mL of Ampicillin which is then placed in a 37 0C incubator, shaking at 250 rpm, for overnight growth. The resulting overnight starter culture is used to inoculate a 1.0 L baffled flask containing 100 mL Luria-Bertani media, (pH 7.0) containing 100 pg/mL of Ampicillin at a dilution of 1:1000. This culture is grown in a 32 *C incubator shaking at 250 rpm for approximately 6.5 hours until mid-log phase is reached (ODwo of about 0.6-0.8). Protein expression is then induced by adding 1 mM isopropyl-o-D thiogalactopyranoside (IPTG) and the culture is placed in a 32 *C incubator shaking at 250 rpm for ovemight expression. Cells are harvested by centrifugation (4,000 rpm at 4 0C for 20-30 minutes) to pellet the cells. The supernatant is discarded and the cell pellet is used immediately for subsequent steps, or the pellet is stored at -80 *C until needed. 9b. Expression of a Syntaxin-GFP substrate using a mammalian cell line [0339] To express a BoNT/C1 Syntaxin-GFP substrate using a mammalian cell line, a suitable density (1 .0x10 5 to 1.0x10 6 ) of appropriate cells is plated in a 35 mm tissue culture dish containing 3 mL of complete, supplemented culture media and the cells are grown in a 37 *C incubator under 5% carbon dioxide until the cells reach a density of about 5x105 cells/mI (6-16 hours). A 500 pL transfection solution is prepared by adding 250 pL of OPTI-MEM Reduced Serum Medium containing 15 pL of LipofectAmine 139 of 168 WO 2008/036060 PCTIUS2006/012825 2000 (Invitrogen, Carlsbad, CA) incubated at room temperature for 5 minutes to 250 pL of OPTI-MEM Reduced Serum Medium containing 5 pg of an expression construct encoding a BoNT/C1 Syntaxin-GFP substrate, such as, e.g., pOBl-25/Syntaxin-1-GFP (see Example I, 3a). This transfection is incubated at room temperature for approximately 20 minutes. The complete, supplemented culture media is replaced with 2 mL of OPTI-MEM Reduced Serum Medium and the 500 pL transfection solution is added to the cells and the cells are incubated in a 37 *C incubator under 5% carbon dioxide for approximately 16 hours. Transfection media is replaced with 3 mL of fresh complete, supplemented culture media and cells are incubated in a 37 *C incubator under 5% carbon dioxide for approximately 48 hours. Cells are harvest by rinsing cells once with 3.0 mL of 100 mM phosphate-buffered saline, pH 7.4 and detaching rinsed cells by adding 500 pl of 100 mM phosphate-buffered saline, pH 7.4 and scraping cells from the culture plate. Detached cells are transferred to a 1.5 mL test tube and are pelleted by microcentrifugation (10,000x g at 4 *C for 5 minutes). The supernatant is discarded and the cell pellet is used immediately for subsequent steps, or the pellet is stored at -80 *C until needed. 9c. Purification of a Syntaxin-GFP substrate [0340] To purify a Syntaxin-GFP substrate, a cell pellet expressing an expression construct encoding a BoNT/C1 Syntaxin-GFP substrate, such as, e.g., either a pQBI-67/Syntaxin-1-GFP or a pQBI 25/Syntaxin-1-GFP construct, is resuspended in 10 mL of Tris-EDTA Buffer (10 mM Tris-HCI, pH 8.0; 1 mM EDTA, pH 8.0), containing 1 mg/mL of lysozyme and the cells are lysed using three freeze-thaw rounds consisting of -80 *C for 5 minutes then 37 *C for 5 minutes. The cell lysate is centrifuged (5,000x g at 4 *C for 15 minutes) to pellet the cellular debris and the supernatant is transferred to a new tube containing an equal volume of Column Binding Buffer (4 M ammonium sulfate). A hydrophobic interaction chromatography (HIC) column is prepared using a 20 'mL Econo-Pac column support (Bio-Rad Laboratories, Hercules, CA) that Is packed with 2.5-5.0 mL of methyl HIC resin (Bio-Rad Laboratories, Hercules, CA), which is then equilibrated by rinsing with 5 column volumes of Column Equilibration Buffer (2 M ammonium sulfate). The clarified lysate is applied slowly to the equilibrated column by gravity flow (approximately 0.25-0.3 mL/minute). The column is then washed with 5 column volumes of Column Wash Buffer (1.3 M ammonium sulfate). The Syntaxin-GFP substrate is eluted with 20-30 mL of Column Elution Buffer (10 mM TE Buffer) and is collected in approximately twelve 1 mL fractions. The progress of the Syntaxin-GFP substrate sample through the column as well as which elution fractions contain the sample is monitored using an ultraviolet light from a hand-held transilluminator. The amount of Syntaxin GFP substrate contained in each elution fraction is determined by a Bradford dye assay. In this procedure, 20 pL aliquot from each 1.0 mL fraction is combined with 200 pL of Bio-Rad Protein Reagent (Bio-Rad Laboratories, Hercules, CA), diluted 1 to 4 with deionized, distilled water, and then the intensity of the colorimetric signal is measured using a spectrophotometer. The five fractions with the strongest signal are considered to comprise the elution peak and are pooled. Total protein yield are determined by estimating the total protein concentration of the pooled peak elution fractions using bovine gamma globulin as a standard (Bio-Rad Laboratories, Hercules, CA). The amount of Syntaxin-GFP substrate is adjusted to a protein concentration of approximately 100 ng/mL.. 9d. Protein transformation of a Syntaxin-GFP substrate 140 of 168 WO 2008/036060 PCT/US2006/012825 [03411 To transform a Syntaxin-GFP substrate into a mammalian cell line, a suitable density (1.0x10 5 to 1.0x10o) of appropriate cells is plated in a 35 mm tissue culture dish containing 3 mL of complete, supplemented culture media and the cells are grown in a 37 0C incubator under 5% carbon dioxide until the cells reach a density of about 5x10 5 cells/ml (6-16 hours). A 200 pL protein transfection solution is prepared by adding 100 pL of distilled water containing 6 pL of Chariotm protein delivery agent (Active Motif, Carlsbad, CA) to 100 pL of 100 mM phosphate-buffered saline, pH 7.4 containing 1 pg of a Syntaxin-GFP substrate and this solution is incubated at room temperature for approximately 30 minutes. After incubation, the cells are washed once by rinsing cells with 3.0 mL of 100 mM phosphate-buffered saline, pH 7.4. The 200 pL protein transfection solution is added to the washed cells, followed by 400 pL of OPTI-MEM Reduced Serum Medium and the cells are incubated in a 37 *C incubator under 5% carbon dioxide for approximately 1 hour. Add 1 mL of fresh complete, supplemented culture media to the cells and incubate in a 37 *C incubator under 5% carbon dioxide. After 1-2 hours, the transformed cells can be used to conduct a BoNT/C1 activity assay using a Syntaxin-GFP substrate. EXAMPLEV Generation of cells stably containing a Clostridial toxin substrate 1. Generation of cells stably containing a BoNT/A, BoNT/C1 or BoNT/E substrate Ia. Stably transformed Neuro-2A cells using a recombinant crossing-over procedure [0342] To generate a stably-integrated cell line expressing a BoNT/A, BoNT/C1 or BoNT/E SNAP-25 substrate using a crossing over procedure, approximately 1.5x10 5 Neuro-2A cells were plated in a 35 mm tissue culture dish containing 3 mL of complete EMEM, supplemented with 10% FBS, 2 mM glutamine (Invitrogen, Inc, Carlsbad, CA), 1 mM sodium pyruvate (Invitrogen, Inc, Carlsbad, CA), 1.5 g/L sodium bicarbonate and 1x MEM non-essential amino acids solution (Invitrogen, Inc, Carlsbad, CA), and grown in a 37 0C incubator under 5% carbon dioxide until the cells reached a density of about 5xlOs cells/mi. A 500 pL transfection solution was prepared by adding 250 pL of OPTI-MEM Reduced Serum Medium containing 15 pL of LipofectAmine 2000 (Invitrogen, Carlsbad, CA) incubated at room temperature for 5 minutes to 250 pL of OPTI-MEM Reduced Serum Medium containing 5 pg of an expression construct encoding a BoNT/A, BoNT/C1 or BoNT/E, substrate, such as, e.g., pQBI-25/SNAP25m-GFP (see EXAMPLE 1, 1). This transfection was incubated at room temperature for approximately 20 minutes. The complete, supplemented EMEM media was replaced with 2 mL of OPTI-MEM Reduced Serum Medium and the 500 pL transfection solution was added to the Neuro-2A cells and the cells incubated in a 37 *C incubator under 5% carbon dioxide for approximately 16 hours. Transfection media was replaced with 3 mL of fresh complete, supplemented EMEM and cells were incubated in a 37 *C incubator under 5% carbon dioxide for approximately 48 hours. Media was replaced with 3 mL of fresh complete EMEM, containing approximately 5 pg/mL of G418, 10% FBS, 2 mM glutamine (Invitrogen, Inc, Carlsbad, CA), 1 mM sodium pyruvate (Invitrogen, Inc, Carlsbad, CA). 1.5 g/L sodium bicarbonate and 1x MEM non essential amino acids solution (Invitrogen, Inc, Carlsbad, CA). Cells were incubated in a 37 *C incubator under 5% carbon dioxide for approximately 4 weeks, with old media being replaced with fresh G418 141 of 168 WO 2008/036060 PCTIUS2006/012825 selective, complete, supplemented EMEM every 4 to 5 days. Once G418-resistant Neuro-2A colonies were established, resistant clones were replated to new 35 mm culture plates containing fresh G418 selective, complete, supplemented EMEM, until these cells reached a density of 6 to 20x10 6 cells/mL. [0343] To test for expression of SNAP-252N-GFP from isolated Neuro-2A cell lines that stably-integrated expression construct encoding a BoNT/A, BoNT/C1 or BoNT/E, substrate, such as, e.g., pQBI 25/SNAP252m-GFP (see Example 1, 1a), approximately 1.5x100 Neuro-2A cells from each cell line were plated in a 35 mm tissue culture dish containing 3 mL of G418-selective, complete, supplemented EMEM and grown in a 37 "C incubator under 5% carbon dioxide until cells reached a density of about 5x106 cells/ml (6-16 hours). Media was replaced with 3 mL of fresh G418-selective, complete, supplemented EMEM and cells were incubated in a 37 *C incubator under 5% carbon dioxide. After 48 hours, the cells were harvested by rinsing the cells once with 3.0 mL of 100 mM phosphate-buffered saline, pH 7.4 and lysed with a buffer containing 62.6 mM 2-amino-2-hydroxymethyl-1,3-propanediol hydrochloric acid (Tris HCI), pH 6.8 and 2% sodium lauryl sulfate (SDS). Lysed cells were centrifuged at 5000 rpm for 10 min at 4*C to eliminate debris and the supematants were transferred to fresh siliconized tubes. Protein concentrations were measured by Bradford's method and resuspended in 1 x SDS sample buffer at 1 mg/ml or higher concentration. [0344] To detect for the presence of the SNAP-25-GFP substrate, samples were boiled for 5 min, and 40 i aliquots were separated by MOPS polyacrylamide gel electrophoresis using NuPAGE* Novex 4-12% Bis-Tris precast polyacrylamide gels (Invitrogen, Inc, Carlsbad, CA) under denaturing, reducing conditions. Separated peptides were transferred from the gel onto polyvinylidene fluoride (PVDF) membranes (Invitrogen, Inc, Carlsbad, CA) by Western blotting using a Trans-Blot* SD semi-dry electrophoretic transfer cell apparatus (Bio-Rad Laboratories, Hercules, CA). PVDF membranes were blocked by incubating at room temperature for 2 hours in a solution containing 25 mM Tris-Buffered Saline (25 mM 2-amino-2-hydroxymethyl-1,3-propanediol hydrochloric acid (Tris-HCI)(pH 7.4), 137 mM sodium chloride, 2.7 mM potassium chloride), 0.1% TWEEN-20*, polyoxyethylene (20) sorbitan monolaureate, 2% bovine serum albumin, 5% nonfat dry milk. Blocked membranes were incubated at 4 *C for overnight in Tris-Buffered Saline TWEEN-20* (25 mM Tris-Buffered Saline, 0.1% TWEEN-20, polyoxyethylene (20) sorbitan monolaureate) containing a 1:50,000 dilution of mouse monoclonal anti SNAP-25 antibody (SMI-81; Sternberger Monoclonals, Lutherville, MD). Primary antibody probed blots were washed three times for 15 minutes each time in Tris-Buffered Saline TWEEN-20*. Washed membranes were incubated at room temperature for 2 hours in Tris-Buffered Saline TWEEN-20* containing a 1:20,000 dilution of goat polyclonal anti-mouse immunoglobulin G, heavy and light chains (IgG, H+L) antibody conjugated to horseradish peroxidase (HRP; Pierce Biotechnology, Inc., Rockford, IL) as a secondary antibody. Secondary antibody-probed blots were washed three times for 15 minutes each time in Tris-Buffered Saline TWEEN-20*. Signal detection of the labeled SNAP-252-GFP substrate was visualized using the ECL PlusTM Western Blot Detection System (Amersharn Biosciences, Piscataway, NJ) and the membrane was imaged and substrate quantitated with a Typhoon 9410 Variable Mode Imager and Imager Analysis software (Amersham Biosciences, Piscataway, NJ). The choice of pixel size (100 to 200 pixels) and PMT voltage settings (350 to 600, normally 400) depended on the 142 of 168 WO 2008/036060 PCT/US2006/012825 individual blot. X isolated Neuro-2A cell lines were identified that stably integrated and expressed the SNAP-25 2 o-GFP substrate of SEQ ID NO: 1. [0345] To determine the subcellular localization of the SNAP-25-GFP substrate from isolated Neuro-2A cell lines that stably-integrated an expression construct encoding a BoNT/A, BoNT/C1 or BoNT/E, substrate, such as, e.g., pOBI-25/SNAP252s-GFP (see Example 1, 1a), approximately 1.5x106 Neuro-2A cells from each cell line were plated in a 35 mm tissue culture dish containing 3 mL of G418-selective, complete, supplemented EMEM and grown in a 37 *C incubator under 5% carbon dioxide until cells reached a density of about 5x106 celIs/mI (6-16 hours). Media was replaced with 3 mL of fresh G418 selective, complete, supplemented EMEM and cells were incubated in a 37 *C incubator under 5% carbon dioxide. After 24-48 hours, living cells were observation using a fluorescence inverted microscope. X isolated Neuro-2A cell lines were detected to have the localization of the GFP fluorescence in the cell membrane indicating that the expressed SNAP252N-GFP in these isolated Neuro 2A cell lines was correctly targeted to the cell membrane. Stably transduced cells can be used to conduct a BoNT/A, BoNT/C1 or BoNT/E activity assay. 1b. Stably transduced SH-SY5Y cells using a lentiviral procedure [03461 To generate a stably-integrated cell line expressing a BoNT/A, BoNT/C1 or BoNT/E SNAP-25 substrate using a lentioviral procedure, about 1.5x1 0' SH-SY5Y cells are plated in a 6-well tissue culture dish containing 3 mL of complete 1:1 EMEM and Ham's F12 Media (EMEM:F12), supplemented with 10% fetal bovine serum (FBS), 4 mM glutamine (Invitrogen, Inc, Carlsbad, CA), 1% sodium pyruvate (Invitrogen, Inc, Carlsbad, CA), 1.5 g/L sodium bicarbonate, 1x penicillin/streptomycin solution (Invitrogen, Inc, Carlsbad, CA) and 1x MEM non-essential amino acids solution (Invitrogen, Inc, Carlsbad, CA), and grown in a 37 *C incubator under 5% carbon dioxide until the cells reach a density of about 5x1 05 cells/m (6-16 hours). Cells are inoculated with the lentioviral stock containing an expression construct encoding a BoNT/A, BoNT/C1 or BoNT/E, substrate, such as, e.g., pLenti6UbcN5-SNAP-25 2 s-GFP, as described above in Example IV, 2b, using a suitable multiplicity of infection and are incubated for approximately 16 24 hours in a 37 *C incubator under 5% carbon dioxide. The tranduction media is replaced with 3 mL of fresh complete, supplemented EMEM:F12 containing an appropriate amount of Blasticidin. Cells are incubated in a 37 *C incubator under 5% carbon dioxide for approximately 2 weeks, with old media being replaced with fresh Blasticidin-selective, complete, supplemented EMEM:F12 every 3 to 4 days. Once Blasticidin-resistant SH-SY5Y colonies are established, resistant clones are replated to new 35 mm culture plates containing fresh Blasticidin-selective, complete, supplemented EMEM:F12, until these cells reached a density of 6 to 20x10 5 cells/mL. For greater details on procedures described in this example, see ViraPowerTM Lentiviral Expression System Instruction Manual 25-0501 version E, Invitrogen, Inc., (Dec. 8, 2003). [03471 The presence of the SNAP-25-GFP substrate in isolated cell lines will be determined by Western blot analysis as describes above in Example V. la. The subcellular localization of the SNAP-252os-GFP substrate in isolated cell lines will be determined by fluorescence microscopy as describes above in Example V, 1a. Stably transduced cells can be used to conduct a BoNT/A, BoNT/C1 or BoNT/E activity 143 of 168 WO 2008/036060 PCT/US2006/012825 assay. 1c. Stably transduced SK-N-DZ cells using a recombinant crossing-over procedure [0348] To generate a stably-integrated cell line expressing a BoNT/A, BoNT/C1 or BoNT/E SNAP-25 substrate using a crossing over procedure, approximately 1.5x1 05 SK-N-DZ cells were plated in a 35 mm tissue culture dish containing 3 mL of complete DMEM, supplemented with 10% FBS, 4 mM glutamine (Invitrogen, Inc, Carlsbad, CA) and lx MEM non-essential amino acids solution (Invitrogen, Inc, Carlsbad, CA), and grown in a 37 *C incubator under 5% carbon dioxide until the cells reached a density of about 5x10 5 cells/ml. A 500 pL transfection solution was prepared by adding 250 pL of OPTI-MEM Reduced Serum Medium containing 15 pL of LipofectAmine 2000 (Invitrogen, Carlsbad, CA) incubated at room temperature for 5 minutes to 250 pL of OPTI-MEM Reduced Serum Medium containing 5 pg of an expression construct encoding a BoNT/A, BoNT/Cl or BoNT/E, substrate, such as, e.g., pQBI 25/SNAP252N-GFP (see Example I, 1a). This transfection was incubated at room temperature for approximately 20 minutes. The complete, supplemented DMEM media was replaced with 2 mL of OPTI MEM Reduced Serum Medium and the 500 pL transfection solution was added to the SK-N-DZ cells and the cells incubated in a 37 *C incubator under 5% carbon dioxide for approximately 16 hours. Transfection media was replaced with 3 mL of fresh complete, supplemented DMEM and cells were incubated in a 37 *C incubator under 5% carbon dioxide for approximately 48 hours. Media was replaced with 3 mL of fresh complete DMEM, containing approximately 5 pg/mL of G418, 10% FBS, 1x penicillin/streptomycin solution (Invitrogen, Inc, Carlsbad, CA) and 1x MEM non-essential amino acids solution (Invitrogen, Inc, Carlsbad, CA). Cells were incubated in a 37 *C incubator under 5% carbon dioxide for approximately 4 weeks, with old media being replaced with fresh G418 selective, complete, supplemented DMEM every 4 to 5 days. Once G418-resistant SK-N-DZ colonies were established, resistant clones were replated to new 35 mm culture plates containing fresh complete DMEM, supplemented with approximately 5 pg/mL of G418, 10% FBS, lx penicillin/streptomycin solution (Invitrogen, Inc, Carlsbad, CA) and lx MEM non-essential amino acids solution (Invitrogen, Inc, Carlsbad, CA), until these cells reached a density of 6 to 20x10 cells/mL. [0349] To test for expression of SNAP-25-GFP from isolated SK-N-DZ cell lines that stably-integrated an expression construct encoding a BoNT/A, BoNT/C1 or BoNT/E, substrate, such as, e.g., pQBI 25/SNAP252e-GFP (see Example 1, 1a), approximately 1.5x105 SK-N-DZ cells from each cell line were plated in a 35 mm tissue culture dish containing 3 mL of G418-selective, complete, supplemented DMEM and grown in a 37 "C incubator under 5% carbon dioxide until cells reached a density of about 5x10 5 cells/mi (6-16 hours). Media was replaced with 3 mL of fresh G418-selective, complete, supplemented DMEM and cells were incubated in a 37 *C incubator under 5% carbon dioxide. After 48 hours, the cells were harvested by rinsing the cells once with 3.0 mL of 100 mM phosphate-buffered saline, pH 7.4 and lysed with a buffer containing 62.6 mM 2-amino-2-hydroxymethyl-1,3-propanedlol hydrochloric acid (Tris HCI), pH 6.8 and 2% sodium lauryl sulfate (SDS). Lysed cells were centrifuged at 5000 rpm for 10 min at 4 0 C to eliminate debris and the supematants were transferred to fresh siliconized tubes. Protein concentrations were measured by Bradford's method and resuspended in 1 x SDS sample buffer at 1mg/mI or higher concentration. 144 of 168 WO 2008/036060 PCT/US2006/012825 [0350] To detect for the presence of the SNAP-25 2 6-GFP substrate, samples were boiled for 5 min, and 40 I aliquots were separated by MOPS polyacrylamide gel electrophoresis using NuPAGE* Novex 4 12% Bis-Tris precast polyacrylamide gels (Invitrogen, Inc, Carlsbad, CA) under denaturing, reducing conditions. Separated peptides were transferred from the gel onto polyvinylidene fluoride (PVDF) membranes (Invitrogen, Inc, Carlsbad, CA) by Western blotting using a Trans-Blot* SD semi-dry electrophoretic transfer cell apparatus (Bio-Rad Laboratories, Hercules, CA). PVDF membranes were blocked by Incubating at room temperature for 2 hours in a solution containing 25 mM Tris-Buffered Saline (25 mM 2-amino-2-hydroxymethyl-1,3-propanedio hydrochloric acid (Tris-HCI)(pH 7.4), 137 mM sodium chloride, 2.7 mM potassium chloride), 0.1% TWEEN-20*, polyoxyethylene (20) sorbitan monolaureate, 2% bovine serum albumin, 5% nonfat dry milk. Blocked membranes were incubated at 4 *C for overnight In Tris-Buffered Saline TWEEN-20* (25 mM Tris-Buffered Saline, 0.1% TWEEN-20*, polyoxyethylene (20) sorbitan monolaureate) containing a 1:50,000 dilution of mouse monoclonal anti SNAP-25 antibody (SMI-81; Stemberger Monoclonals, Lutherville, MD). Primary antibody probed blots were washed three times for 15 minutes each time in Tris-Buffered Saline TWEEN-20. Washed membranes were Incubated at room temperature for 2 hours in Tris-Buffered Saline TWEEN-20 containing a 1:20,000 dilution of goat polyclonal anti-mouse immunoglobulin G, heavy and light chains (IgG, H+L) antibody conjugated to horseradish peroxidase (HRP; Pierce Biotechnology, Inc., Rockford, IL) as a secondary antibody. Secondary antibody-probed blots were washed three times for 15 minutes each time in Tris-Buffered Saline TWEEN-20*. Signal detection of the labeled SNAP-252-GFP substrate was visualized using the ECL PIusTM Western Blot Detection System (Amersham Biosciences, Piscataway, NJ) and the membrane was imaged and substrate quantitated with a Typhoon 9410 Variable Mode Imager and Imager Analysis software (Amersham Biosciences, Piscataway, NJ). The choice of pixel size (100 to 200 pixels) and PMT voltage settings (350 to 600, normally 400) depended on the individual blot. X isolated SK-N-DZ cell lines were identified that stably integrated and expressed the SNAP-252-GFP substrate of SEQ ID NO: 1. [0351] To determine the subcellular localization of the SNAP-25N-GFP substrate from isolated SK-N DZ cell lines that stably-integrated an expression construct encoding a BoNT/A, BoNT/C1 or BoNT/E, substrate, such as, e.g., pQBI-25/SNAP252-GFP (see Example 1, 1a), approximately 1.5x105 SK-N-DZ cells from each cell line were plated in a 35 mm tissue culture dish containing 3 mL of G418-selective, complete, supplemented DMEM and grown in a 37 *C incubator under 5% carbon dioxide until cells reached a density of about 5x100 5 cells/ml (6-16 hours). Media was replaced with 3 mL of fresh G418 selective, complete, supplemented DMEM and cells were incubated in a 37 *C incubator under 5% carbon dioxide. After 24-48 hours, living cells were observation using a fluorescence inverted microscope. X isolated SK-N-DZ cell lines were detected to have the localization of the GFP fluorescence in the cell membrane indicating that the expressed SNAP25 2 N-GFP in these isolated SK-N DZ cell lines was correctly targeted to the cell membrane. Stably transduced cells can be used to conduct a BoNT/A, BoNT/Ci or BoNT/E activity assay using a SNAP-25-GFP substrate. 1d. Stably transduced SK-N-DZ cells using a lentiviral procedure 145 of 168 WO 2008/036060 PCT/US2006/012825 [0352] To generate a stably-integrated cell line expressing a BoNT/A, BoNT/Ci or BoNT/E SNAP-25 substrate using a lentioviral procedure, approximately 1.5x10 6 SK-N-DZ cells are plated in a 6-well tissue culture dish containing 3 mL of complete DMEM, supplemented with 10% FBS, 4 mM glutamine (Invitrogen, Inc, Carlsbad, CA) and 1x MEM non-essential amino acids solution (Invitrogen, Inc, Carlsbad, CA), and grown in a 37 *C incubator under 5% carbon dioxide until the cells reach a density of about 5x10 5 cells/ml (6-16 hours). Cells are inoculated with the lentiviral stock containing an expression construct encoding a BoNT/A, BoNT/CI or BoNT/E substrate, such as, e.g., pLenti6Ubc/V5-SNAP-25ve GFP, as described above in Example IV, 2b, using a suitable multiplicity of infection and are incubated for approximately 16-24 hours in a 37 *C incubator under 5% carbon dioxide. The tranduction media is replaced with 3 mL of fresh complete, supplemented EMEM:F12 containing an appropriate amount of Blasticidin. Cells are incubated in a 37 *C incubator under 5% carbon dioxide for approximately 2 weeks, with old media being replaced with fresh Blasticidin-selective, complete, supplemented EMEM:F12 every 3 to 4 days. Once Blasticidin-resistant SH-SY5Y colonies are established, resistant clones are replated to new 35 mm culture plates containing fresh Blasticidin-selective, complete, supplemented EMEM:F12, until these cells reached a density of 6 to 20x10l cells/mL. For greater details on procedures described in this example, see ViraPowerTM Lentiviral Expression System Instruction Manual 25-0501 version E, Invitrogen, Inc., (Dec. 8, 2003). [0353] The presence of the SNAP-252e-GFP substrate in isolated cell lines will be determined by Western blot analysis as describes above in Example V, 1a. The subcellular localization of the SNAP 252e-GFP substrate in isolated cell lines will be determined by fluorescence microscopy as describes above in Example V, 1a. Stably transduced cells can be used to conduct a BoNT/A, BoNT/C1 or BoNT/E activity assay using a SNAP-25-GFP substrate. 2. Generation of cells stably containing a BoNTIB, BoNT/D, BoNT/F, BoNTIG or TeNT substrate 2a. Stably transformed cells using a recombinant crossing-over procedure [0354] To generate a stably-integrated cell line expressing a BoNT/B, BoNT/D, BoNT/F, BoNT/G or TeNT VAMP substrate using a crossing over procedure, a suitable density (1 x105 to 1 x106 6 cells)of appropriate cells are plated in a 35 mm tissue culture dish containing 3 mL of complete, supplemented culture media and grown in a 37 *C incubator under 5% carbon dioxide until the cells reached a density appropriate for transfection. A 500 pL transfection solution is prepared by adding 250 pL of OPTI-MEM Reduced Serum Medium containing 15 pL of LipofectAmine 2000 (Invitrogen, Carlsbad, CA) incubated at room temperature for 5 minutes to 250 pt of OPTI-MEM Reduced Serum Medium containing 5 pg of expression construct encoding a BoNT/B, BoNT/D, BoNT/F, BoNT/G or TeNT VAMP substrate, such as, e.g., pQBI-25NAMP-1-GFP, pOBI-25NAMP-2-GFP or pQBI-25NAMP-3-GFP (see Examples I, 2a; I, 2b; or I, 2c). This transfection was incubated at room temperature for approximately 20 minutes. The complete, supplemented media is replaced with 2 mL of OPTI-MEM Reduced Serum Medium and the 500 pL transfection solution is added to the cells and the cells are incubated in a 37 *C incubator under 5% carbon dioxide for approximately 16 hours. Transfection media is replaced with 3 mL of fresh 146 of 168 WO 2008/036060 PCT/US2006/012825 complete, supplemented culture media and the cells are incubated in a 37 *C incubator under 5% carbon dioxide for approximately 48 hours. Media is replaced with 3 mL of fresh complete, supplemented culture media, containing approximately 5 pg/mL of G418. Cells are incubated in a 37 *C incubator under 5% carbon dioxide for approximately 4 weeks, with old media being replaced with fresh G418 selective, complete, supplemented media every 4 to 5 days. Once G418-resistant colonies are established, resistant clones are replated to new 35 mm culture plates containing fresh complete culture media, supplemented with approximately 5 pg/mL of G418 until these cells reached a density of 6 to 20x10 5 cells/mL. [03551 To test for expression of a BoNT/B, BoNT/D, BoNT/F, BoNT/G or TeNT VAMP-GFP from isolated cell lines that stably-integrated an expression construct encoding a BoNT/B, BoNT/D, BoNT/F, BoNT/G or TeNT VAMP-GFP substrate, such as, e.g., pQBI-25NAMP-1-GFP, pQBI-25NAMP-2-GFP or pQBI 25NAMP-3-GFP (see Examples I, 2a; I, 2b; or I, 2c), approximately 1.5x10 5 cells from each cell line are plated in a 35 mm tissue culture dish containing 3 mL of G418-selective, complete, supplemented DMEM and are grown in a 37 0C incubator under 5% carbon dioxide until cells reached a density of about 5x10 5 cells/ml (6-16 hours). Media is replaced with 3 mL of fresh G418-selective, complete, supplemented culture media and cells are Incubated in a 37 *C incubator under 5% carbon dioxide. After 48 hours, the cells are harvested by rinsing the cells once with 3.0 mL of 100 mM phosphate-buffered saline, pH 7.4 and are lysed with a buffer containing 62.6 mM 2-amino-2-hydroxymethyl-1,3-propanediol hydrochloric acid (Tris-HCI), pH 6.8 and 2% sodium lauryl sulfate (SDS). Lysed cells are centrifuged at 5000 rpm for 10 min at 40C to eliminate debris and the supematants are transferred to fresh siliconized tubes. Protein concentrations are measured by Bradford's method and are resuspended in 1 x SDS sample buffer at 1mg/ml or higher concentration. [0356] To detect for the presence of the VAMP-GFP substrate, samples are separated by MOPS polyacrylamide gel electrophoresis and analyzed by Western blotting procedures as described above in Examples 11, 2a; Il, 4a; 1I, 6a; 11, 7a; and II, 8a, in order to identify cell lines that have stably integrated and express the VAMP-GFP substrate. [0357] To determine the subcellular localization of the VAMP-GFP substrate from isolated cell lines that stably-integrated an expression construct encoding a BoNT/B, BoNT/D, BoNT/F, BoNT/G or TeNT VAMP-GFP substrate, such as, e.g., pOBI-25NAMP-1 -GFP, pQBI-25NAMP-2-GFP or pQBI-25NAMP-3 GFP (see Examples I, 2a; I, 2b; or 1, 2c), approximately 1.5x1 0' cells from each cell line are plated in a 35 mm tissue culture dish containing 3 mL of G418-selective, complete, supplemented culture media and are grown in a 37 0C incubator under 5% carbon dioxide until cells reached a density of about 5x1 05 cells/mi (6-16 hours). Media is replaced with 3 mL of fresh G418-selective, complete, supplemented culture media and cells are incubated in a 37 *C incubator under 5% carbon dioxide. After 24-48 hours, living cells are observation using a fluorescence inverted microscope in order to identify isolated cell lines that exhibit GFP fluorescence localized to the cell membrane, thereby indicating that the expressed VAMP GFP in these isolated cell lines is correctly targeted to the cell membrane. Stably transduced cells can be used to conduct a BoNT/B, BoNT/D, BoNT/F, BoNT/G or TeNT activity assay using a VAMP-GFP 147 of 168 WO 2008/036060 PCTIUS2006/012825 substrate. 2b. Stably transduced cells using a lentiviral procedure [0358] To generate a stably-integrated cell line expressing a BoNT/B, BoNT/D, BoNT/F, BoNT/G or TeNT VAMP substrate using a lentiviral procedure, a suitable density (1 x10 6 to 1 x106 6 cells)of appropriate cells are plated in a 6-well tissue culture dish containing 3 mL of complete, supplemented culture media and are grown in a 37 *C incubator under 5% carbon dioxide until the cells reach a density appropriate for transduction. Cells are inoculated with the lentiviral stock, as described above in Example IV, 5b, using a suitable multiplicity of infection and are incubated for approximately 16-24 hours in a 37 *C incubator under 5% carbon dioxide. The tranduction media is replaced with 3 mL of fresh complete, supplemented media containing an appropriate amount of Blasticidin. Cells are incubated in a 37 *C incubator under 5% carbon dioxide for approximately 2 weeks, with old media being replaced with fresh Blasticidin-selective, complete, supplemented media every 3 to 4 days. Once Blasticidin-resistant colonies are established, resistant clones are replated to new 35 mm culture plates containing fresh Blasticidin-selective, complete, supplemented media, until these cells reached a density of 6 to 20x10 5 cells/mL. For greater details on procedures described in this example, see ViraPowerm Lentiviral Expression System Instruction Manual 25-0501 version E, Invitrogen, Inc., (Dec. 8, 2003). [0359] The presence of the VAMP-GFP substrate in isolated cell lines will be determined by Westem blot analysis as describes above in Example V. 2a. The subcellular localization of the VAMP-GFP substrate in isolated cell lines will be determined by fluorescence microscopy as describes above in Example V, 2a. Stably transduced cells can be used to conduct a BoNT/B, BoNT/D, BoNT/F, BoNTIG or TeNT activity assay using a VAMP-GFP substrate. 3. Generation of cells stably containing a BoNT/C1 Syntaxin substrate 3a. Stably transformed cells using a recombinant crossing-over procedure [0360] To generate a stably-integrated cell line expressing a BoNT/C1 Syntaxin substrate using a crossing over procedure, a suitable density (1 x10 5 to 1 x106 cells)of appropriate cells are plated in a 35 mm tissue culture dish containing 3 mL of complete, supplemented culture media and grown in a 37 *C incubator under 5% carbon dioxide until the cells reached a density appropriate for transfection. A 500 pl transfection solution is prepared by adding 250 pL of OPTI-MEM Reduced Serum Medium containing 15 pL of LipofectAmine 2000 (Invitrogen, CarlsbAd, CA) incubated at room temperature for 5 minutes to 250 pL of OPTI-MEM Reduced Serum Medium containing 5 pg of expression construct encoding a BoNT/C1 Syntaxin substrate, such as, e.g., pQBI-25/Syntaxin-1-GFP (see Example I, 3a). This transfection was incubated at room temperature for approximately 20 minutes. The complete, supplemented media is replaced with 2 mL of OPTI-MEM Reduced Serum Medium and the 500 pL transfection solution is added to the cells and the cells are incubated in a 37 *C incubator under 5% carbon dioxide for approximately 16 hours. Transfection media is replaced with 3 mL of fresh complete, supplemented culture media and the cells are incubated in a 37 *C incubator under 5% carbon dioxide for approximately 48 hours. Media is replaced with 3 mL of fresh complete, supplemented culture media, containing approximately 5 pg/mL of 148 of 168 WO 2008/036060 PCT/US2006/012825 G418. Cells are incubated in a 37 "C incubator under 5% carbon dioxide for approximately 4 weeks, with old media being replaced with fresh G418 selective, complete, supplemented media every 4 to 5 days. Once G418-resistant colonies are established, resistant clones are replated to new 35 mm culture plates containing fresh complete culture media, supplemented with approximately 5 pg/mL of G418 until these cells reached a density of 6 to 20x106 cells/mL. [0361] To test for expression of a BoNT/C1 Synataxin-GFP from isolated cell lines that stably-integrated an expression construct encoding a BoNT/C1 Syntaxin-GFP substrate, such as, e.g., pQBI-25/Syntaxin 1-GFP (see Example 1, 3a), approximately 1.5x10 5 cells from each cell line are plated in a 35 mm tissue culture dish containing 3 mL of G418-selective, complete, supplemented culture media and are grown in a 37 *C incubator under 5% carbon dioxide until cells reached a density of about 5x10 cells/ml (6-16 hours). Media is replaced with 3 mL of fresh G418-selective, complete, supplemented culture media and cells are incubated in a 37 *C incubator under 5% carbon dioxide. After 48 hours, the cells are harvested by rinsing the cells once with 3.0 mL of 100 mM phosphate-buffered saline, pH 7.4 and are lysed with a buffer containing 62.6 mM 2-amino-2-hydroxymethyl-1,3-propanediol hydrochloric acid (Tris-HCI), pH 6.8 and 2% sodium lauryl sulfate (SDS). Lysed cells are centrifuged at 5000 rpm for 10 min at 4"C to eliminate debris and the supematants are transferred to fresh siliconized tubes. Protein concentrations are measured by Bradford's method and are resuspended in I x SDS sample buffer at 1mg/ml or higher concentration. [0362] To detect for the presence of the Syntaxin-GFP substrate, samples are separated by MOPS polyacrylamide gel electrophoresis and analyzed by Western blotting procedures as described above in Examples 11, 3a, in order to identity cell lines that have stably integrated and express the Syntaxin-GFP substrate. [0363] To determine the subcellular localization of the Syntaxin-GFP substrate from isolated cell lines that stably-integrated an expression construct encoding a BoNT/C1 Syntaxin-GFP substrate, such as, e.g., pQBI-25/Syntaxin-1-GFP (see Example I, 3a), approximately 1.5x10 5 cells from each cell line are plated in a 35 mm tissue culture dish containing 3 mL of G418-selective, complete, supplemented culture media and are grown in a 37 *C incubator under 5% carbon dioxide until cells reached a density of about 5x106 cells/ml (6-16 hours). Media is replaced with 3 mL of fresh G418-selective, complete, supplemented culture media and cells are incubated in a 37 *C incubator under 5% carbon dioxide. After 24-48 hours, living cells are observation using a fluorescence inverted microscope in order to identify isolated cell lines that exhibit GFP fluorescence localized to the cell membrane, thereby indicating that the expressed Syntaxin-GFP in these isolated cell lines is correctly targeted to the cell membrane. Stably transduced cells can be used to conduct a BoNT/C1 activity assay using a Syntaxin-GFP substrate. 3b. Stably transduced cells using a lentiviral procedure [0364] To generate a stably-integrated cell line expressing a BoNT/Ci Syntaxin substrate using a lentiviral procedure, a suitable density (1 x106 to 1 x106 6 cells)of appropriate cells are plated in a 6-well tissue culture dish containing 3 mL of complete, supplemented culture media and are grown in a 37 *C 149 of 168 WO 2008/036060 PCTIUS2006/012825 incubator under 5% carbon dioxide until the cells reach a density appropriate for transduction. Cells are inoculated with the lentiviral stock, as described above in Example IV, 8b, using a suitable multiplicity of infection and are incubated for approximately 16-24 hours in a 37 *C incubator under 5% carbon dioxide. The tranduction media is replaced with 3 mL of fresh complete, supplemented media containing an appropriate amount of Blasticidin. Cells are incubated in a 37 *C incubator under 5% carbon dioxide for approximately 2 weeks, with old media being replaced with fresh Blasticidin-selective, complete, supplemented media every 3 to 4 days. Once Blasticidin-resistant colonies are established, resistant clones are replated to new 35 mm culture plates containing fresh Blasticidin-selective, complete, supplemented media, until these cells reached a density of 6 to 20x105 cells/mL. For greater details on procedures described in this example, see ViraPowerTM Lentiviral Expression System Instruction Manual 25-0501 version E, Invitrogen, Inc., (Dec. 8, 2003). [0365] The presence of the Syntaxin-GFP substrate in isolated cell lines will be determined by Western blot analysis as describes above in Example V, 3a. The subcellular localization of the Syntaxin-GFP substrate in isolated cell lines will be determined by fluorescence microscopy as describes above in Example V, 3a. Stably transduced cells can be used to conduct a BoNT/C1 activity assay using a Syntaxin-GFP substrate. EXAMPLE VI Clostridial Toxin Activity Assays 1. BoNT/A activity assays Ia. Assay of BoNTA activity In a BOTOX* product [0366] To conduct a BoNT/A activity assay using a formulated botulinum neurotoxin product such as, e.g., a BOTOX8 product, differentiated Neuro-2A cells expressing a BoNT/A SNAP252N-GFP substrate will be prepared, for example, using one of the methods as described above in Examples IV, 1 and V, 1. A standard curve will be obtained by treating Neuro-2A cells with 0.001 nM, 0.002 nM, 0.005 nM, 0.01 nM, 0.02 nM or 0.05 nM of Pure A (BTX-540; Metabiologics, Inc., Madison, WI), with each of the concentrations run in triplicates in a 24 well plate. Simultaneously, separate wells in the same plate will be treated with BOTOX* dissolved in 1 ml of complete EMEM media to a final concentration of approximately 0.0055 nM. Cells in three replicate wells will be treated with the contents of each resuspended BOTOX* vial. After six hours, cells will be analyzed using the Typhoon 9140 Imager with excitation at 484 nm and emission at 510 nm. The emissions at each concentration of Pure A and each BOTOX* sample will be calculated as a percentage of the untreated control (fluorescence measured at 510 nm of non-toxin treated cells). The experimentally-derived concentration of BOTOX* for each vial will be extrapolated from the Pure A concentration curve using the value calculated from an average of three replicate wells. 1b. Assay of BoNTA activity In a food sample [0367] To conduct a BoNT/A activity assay using a food sample such as, e.g., a processed food sample, 150 of 168 WO 2008/036060 PCT/US2006/012825 differentiated Neuro-2A cells expressing a BoNT/A SNAP252e-GFP substrate will be prepared, for example, using one of the methods as described above in Examples IV, 1 and V, 1. A standard curve will be obtained by treating Neuro-2A cells with 0.001, 0.002, 0.005, 0.01, 0.02 or 0.05 nM of Pure A (BTX 540; Metabiologics, Inc., Madison, WI), with each of the concentrations run in triplicates in a 24 well plate. Simultaneously, separate wells in the same plate will be treated with a processed food sample from vials of BOTOX* diluted In 1 ml of complete EMEM media. Cells in three replicate wells will be treated with the contents of each diluted sample. After six hours, cells will be analyzed using the Typhoon 9140 Imager with excitation at 484 nm and emission at 510 nm. The emissions at each concentration of Pure A and each processed food sample will be calculated as a percentage of the untreated control (fluorescence measured at 510 nm of non-toxin treated cells). The experimentally derived concentration of BoNT/A present in the processed food sample will be extrapolated from the Pure A concentration curve using the value calculated from an average of three replicate wells. 2. BoNT/B activity assays 2&. Assay of BoNT/B activity In a formulated BoNTIB product (0368] To conduct a BoNT/B activity assay using a formulated botulinum neurotoxin product such as, e.g., a formulated BoNT/B product, cells expressing a BoNT/B VAMP-GFP substrate will be prepared, for example, using one of the methods as described above in Examples IV, 2 and V, 2. A standard curve will be obtained by treating cells with 0.001 nM, 0.002 nM, 0.005 nM, 0.01 nM, 0.02 nM or 0.05 nM of BoNT/B (Metabiologics, Inc., Madison, WI), with each of the concentrations run in triplicates in a 24 well plate. Simultaneously, separate wells in the same plate will be treated with formulated BoNT/B dissolved in 1 ml of complete culture media to a final concentration of approximately 0.0055 nM. Cells in three replicate wells will be treated with the contents of each resuspended formulated BoNT/B vial. After six hours, cells will be analyzed using the Typhoon 9140 Imager with excitation at 484 nm and emission at 510 nm. The emissions at each concentration of BoNT/B and each formulated BoNT/B sample will be calculated as a percentage of the untreated control (fluorescence measured at 510 nm of non-toxin treated cells). The experimentally-derived concentration of formulated BoNT/B for each vial will be extrapolated from the BoNT/B concentration curve using the value calculated from an average of three replicate wells. 2b. Assay of BoNT/B activity In a food sample (0369] To conduct a BoNT/B activity assay using a food sample such as, e.g., a processed food sample, cells expressing a BoNT/B VAMP-GFP substrate will be prepared, for example, using one of the methods as described above in Examples IV, 2 and V, 2. A standard curve will be obtained by treating cells with 0.001, 0.002, 0.005, 0.01, 0.02 or 0.05 nM of BoNT/B (Metabiologics, Inc., Madison, WI), with each of the concentrations run in triplicates in a 24 well plate. Simultaneously, separate wells in the same plate will be treated with a processed food sample from vials of formulated BoNT/B diluted in 1 ml of complete culture media. Cells in three replicate wells will be treated with the contents of each diluted sample. After six hours, cells will be analyzed using the Typhoon 9140 Imager with excitation at 484 nm and emission at 510 nm. The emissions at each concentration of BoNT/B and each processed food sample will be calculated as a percentage of the untreated control (fluorescence measured at 510 nm of non-toxin 151 of 168 WO 2008/036060 PCT/US2006/012825 treated cells). The experimentally derived concentration of BoNT/B present in the processed food sample will be extrapolated from the BoNT/B concentration curve using the value calculated from an average of three replicate wells. 3. BoNT/C1 activity assays 3a. Assay of BoNT/C1 activity in a formulated BoNT/Ci product [0370] To conduct a BoNT/Cl activity assay using a formulated botulinum neurotoxin product such as, e.g., a formulated BoNT/CI product, cells expressing a BoNT/Ci SNAP-252N-GFP substrate or a BoNT/C1 Syntaxin-GFP substrate will be prepared, for example, using one of the methods as described above in Examples IV, 3 and V, 3. A standard curve will be obtained by treating cells with 0.001 nM, 0.002 nM, 0.005 nM, 0.01 nM, 0.02 nM or 0.05 nM of BoNT/B (Metabiologics, Inc., Madison, WI), with each of the concentrations run in triplicates in a 24 well plate. Simultaneously, separate wells In the same plate will be treated with formulated BoNT/B dissolved in 1 ml of complete culture media to a final concentration of approximately 0.0055 nM. Cells in three replicate wells will be treated with the contents of each resuspended formulated BoNT/C1 vial. After six hours, cells will be analyzed using the Typhoon 9140 Imager with excitation at 484 nm and emission at 510 nm. The emissions at each concentration of BoNT/C1 and each formulated BoNT/Cl sample will be calculated as a percentage of the untreated control (fluorescence measured at 510 nm of non-toxin treated cells). The experimentally-derived concentration of formulated BoNT/C1 for each vial will be extrapolated from the BoNT/C1 concentration curve using the value calculated from an average of three replicate wells. 3b. Assay of BoNT/CI activity In a food sample [03711 To conduct a BoNT/C1 activity assay using a food sample such as, e.g., a processed food sample, cells expressing a BoNT/C1 Syntaxin-GFP substrate will be prepared, for example, using one of the methods as described above in Examples IV, 3 and V, 3. A standard curve will be obtained by treating cells with 0.001, 0.002, 0.005, 0.01, 0.02 or 0.05 nM of BoNT/C1 (Metabiologics, Inc., Madison, WI), with each of the concentrations run in triplicates in a 24 well plate. Simultaneously, separate wells in the same plate will be treated with a processed food sample from vials of formulated BoNT/Cl diluted in 1 ml of complete culture media. Cells in three replicate wells will be treated with the contents of each diluted sample. After six hours, cells will be analyzed using the Typhoon 9140 Imager with excitation at 484 nm and emission at 510 nm. The emissions at each concentration of BoNT/C1 and each processed food sample will be calculated as a percentage of the untreated control (fluorescence measured at 510 nm of non-toxin treated cells). The experimentally derived concentration of BoNT/C1 present in the processed food sample will be extrapolated from the BoNT/C1 concentration curve using the value calculated from an average of three replicate wells. 4. BoNT/B activity assays 4a. Assay of BoNTID activity in a formulated BoNTID product [0372] To conduct a BoNT/D activity assay using a formulated botulinum neurotoxin product such as, 152 of 168 WO 2008/036060 PCTIUS2006/012825 e.g., a formulated BoNT/D product, cells expressing a BoNT/D VAMP-GFP substrate will be prepared, for example, using one of the methods as described above in Examples IV, 4 and V, 4. A standard curve will be obtained by treating cells with 0.001 nM, 0.002 nM, 0.005 nM, 0.01 nM, 0.02 nM or 0.05 nM of BoNT/D (Metabiologics, Inc., Madison, WI), with each of the concentrations run in triplicates In a 24 well plate. Simultaneously, separate wells in the same plate will be treated with formulated BoNT/D dissolved in 1 ml of complete culture media to a final concentration of approximately 0.0055 nM. Cells in three replicate wells will be treated with the contents of each resuspended formulated BoNT/D vial. After six hours, cells will be analyzed using the Typhoon 9140 Imager with excitation at 484 nm and emission at 510 nm. The emissions at each concentration of BoNT/D and each formulated BoNT/D sample will be calculated as a percentage of the untreated control (fluorescence measured at 510 nm of non-toxin treated cells). The experimentally-derived concentration of formulated BoNT/D for each vial will be extrapolated from the BoNT/D concentration curve using the value calculated from an average of three replicate wells. 4b. Assay of BoNT/D activity In a food sample [0373] To conduct a BoNT/D activity assay using a food sample such as, e.g., a processed food sample, cells expressing a BoNT/D VAMP-GFP substrate will be prepared, for example, using one of the methods as described above in Examples IV, 4 and V, 4. A standard curve will be obtained by treating cells with 0.001, 0.002, 0.005, 0.01, 0.02 or 0.05 nM of BoNT/D (Metabiologics, Inc., Madison, WI), with each of the concentrations run in triplicates in a 24 well plate. Simultaneously, separate wells in the same plate will be treated with a processed food sample from vials of formulated BoNT/D diluted in 1 ml of complete culture media. Cells in three replicate wells will be treated with the contents of each diluted sample. After six hours, cells will be analyzed using the Typhoon 9140 Imager with excitation at 484 nm and emission at 510 nm. The emissions at each concentration of BoNT/D and each processed food sample will be calculated as a percentage of the untreated control (fluorescence measured at 510 nm of non-toxin treated cells). The experimentally derived concentration of BoNTID present in the processed food sample will be extrapolated from the BoNT/D concentration curve using the value calculated from an average of three replicate wells. 5. BoNT/E activity assays 5a. Assay of BoNTIE activity in a formulated BoNTE product [03741 To conduct a BoNT/E activity assay using a formulated botulinum neurotoxin product such as, e.g., a formulated BoNT/E product, differentiated SK-N-DZ cells expressing a BoNT/E SNAP252m-GFP substrate will be prepared, for example, using one of the methods as described above in Examples IV, 5 and V, 5. A standard curve will be obtained by treating SK-N-DZ cells with 0.001 nM, 0.002 nM, 0.005 nM, 0.01 nM, 0.02 nM or 0.05 nM of BoNT/E (Metabiologics, Inc., Madison, WI), with each of the concentrations run in triplicates in a 24 well plate. Simultaneously, separate wells in the same plate wIll be treated with formulated BoNT/E dissolved in 1 ml of complete DMEM media to a final concentration of approximately 0.0055 nM. Cells in three replicate wells will be treated with the contents of each resuspended formulated BoNT/E vial. After six hours, cells will be analyzed using the Typhoon 9140 Imagery with excitation at 484 nm and emission at 510 nm. The emissions at each concentration of 153 of 168 WO 2008/036060 PCT/US2006/012825 BoNT/E and each formulated BoNT/E sample will be calculated as a percentage of the untreated control (fluorescence measured at 510 nm of non-toxin treated cells). The experimentally-derived concentration of formulated BoNT/E for each vial will be extrapolated from the BoNT/E concentration curve using the value calculated from an average of three replicate wells. 5b. Assay of BoNTIE activity In a food sample [0375] To conduct a BoNT/E activity assay using a food sample such as, e.g., a processed food sample, differentiated SK-N-DZ cells expressing a BoNT/E SNAP25 2 0 r-GFP substrate will be prepared, for example, using one of the methods as described above in Examples IV, 5 and V, 5. A standard curve will be obtained by treating SK-N-DZ cells with 0.001, 0.002, 0.005, 0.01, 0.02 or 0.05 nM of BoNT/E (Metabiologics, Inc., Madison, WI), with each of the concentrations run in triplicates in a 24 well plate. Simultaneously, separate wells in the same plate will be treated with a processed food sample from vials of formulated BoNT/E diluted in 1 ml of complete DMEM media. Cells in three replicate wells will be treated with the contents of each diluted sample. After six hours, cells will be analyzed using the Typhoon 9140 Imager with excitation at 484 nm and emission at 510 nm. The emissions at each concentration of BoNT/E and each processed food sample will be calculated as a percentage of the untreated control (fluorescence measured at 510 nm of non-toxin treated cells). The experimentally derived concentration of BoNT/E present in the processed food sample will be extrapolated from the BoNT/E concentration curve using the value calculated from an average of three replicate wells. 6. BoNT/F activity assays 6A. Assay of BoNTIF activity In a formulated BoNTIF product [0376] To conduct a BoNT/F activity assay using a formulated botulinum neurotoxin product such as, e.g., a formulated BoNT/F product, cells expressing a BoNT/F VAMP-GFP substrate will be prepared, for example, using one of the methods as described above in Examples IV, 6 and V, 6. A standard curve will be obtained by treating cells with 0.001 nM, 0.002 nM, 0.005 nM, 0.01 nM, 0.02 nM or 0.05 nM of BoNT/F (Metabiologics, Inc., Madison, WI), with each of the concentrations run In triplicates in a 24 well plate. Simultaneously, separate wells in the same plate will be treated with formulated BoNT/F dissolved in 1 ml of complete culture media to a final concentration of approximately 0.0055 nM. Cells in three replicate wells will be treated with the contents of each resuspended formulated BoNT/F vial. After six hours, cells will be analyzed using the Typhoon 9140 Imager with excitation at 484 nm and emission at 510 nm. The emissions at each concentration of BoNT/F and each formulated BoNT/F sample will be calculated as a percentage of the untreated control (fluorescence measured at 510 nm of non-toxin treated cells). The experimentally-derived concentration of formulated BoNT/F for each vial will be extrapolated from the BoNT/F concentration curve using the value calculated from an average of three replicate wells. 6b. Assay of BoNT/F activity In a food sample [0377] To conduct a BoNT/F activity assay using a food sample such as, e.g., a processed food sample, cells expressing a BoNT/F VAMP-GFP substrate will be prepared, for example, using one of the methods as described above in Examples IV, 6 and V, 6. A standard curve will be obtained by treating cells with 154 of 168 WO 2008/036060 PCT/US2006/012825 0.001, 0.002, 0.005, 0.01, 0.02 or 0.05 nM of BoNT/F (Metabiologics, Inc., Madison, WI), witn eacn of the concentrations run in triplicates in a 24 well plate. Simultaneously, separate wells in the same plate will be treated with a processed food sample from vials of formulated BoNT/F diluted in I ml of complete culture media. Cells in three replicate wells will be treated with the contents of each diluted sample. After six hours, cells will be analyzed using the Typhoon 9140 Imager with excitation at 484 nm and emission at 510 nm. The emissions at each concentration of BoNT/F and each processed food sample will be calculated as a percentage of the untreated control (fluorescence measured at 510 nm of non-toxin treated cells). The experimentally derived concentration of BoNT/F present in the processed food sample will be extrapolated from the BoNT/F concentration curve using the value calculated from an average of three replicate wells. 7. BoNT/G activity assays 7a. Assay of BoNTIG activity In a formulated BoNT/G product [03781 To conduct a BoNT/G activity assay using a formulated botulinum neurotoxin product such as, e.g., a formulated BoNT/G product, cells expressing a BoNT/G VAMP-GFP substrate will be prepared, for example, using one of the methods as described above in Examples IV, 7 and V, 7. A standard curve will be obtained by treating cells with 0.001 nM, 0.002 nM, 0.005 nM, 0.01 nM, 0.02 nM or 0.05 nM of BoNT/B (Metabiologics, Inc., Madison, WI), with each of the concentrations run in triplicates in a 24 well plate. Simultaneously, separate wells in the same plate will be treated with formulated BoNT/G dissolved in 1 ml of complete culture media to a final concentration of approximately 0.0055 nM. Cells in three replicate wells will be treated with the contents of each resuspended formulated BoNT/G vial. After six hours, cells will be analyzed using the Typhoon 9140 Imager with excitation at 484 nm and emission at 510 nm. The emissions at each concentration of BoNT/G and each formulated BoNT/G sample will be calculated as a percentage of the untreated control (fluorescence measured at 510 nm of non-toxin treated cells). The experimentally-derived concentration of formulated BoNT/G for each vial will be extrapolated from the BoNT/G concentration curve using the value calculated from an average of three replicate wells. 7b. Assay of BoNT/G activity in a food sample [0379] To conduct a BoNT/G activity assay using a food sample such as, e.g., a processed food sample, cells expressing a BoNT/G VAMP-GFP substrate will be prepared, for example, using one of the methods as described above in Examples IV, 7 and V, 7. A standard curve will be obtained by treating cells with 0.001, 0.002, 0.005, 0.01, 0.02 or 0.05 nM of BoNT/G (Metabiologics, Inc., Madison, WI), with each of the concentrations run in triplicates in a 24 well plate. Simultaneously, separate wells in the same plate will be treated with a processed food sample from vials of formulated BoNTIG diluted in 1 ml of complete culture media. Cells in three replicate wells will be treated with the contents of each diluted sample. After six hours, cells will be analyzed using the Typhoon 9140 Imager with excitation at 484 nm and emission at 510 nm. The emissions at each concentration of BoNT/G and each processed food sample will be calculated as a percentage of the untreated control (fluorescence measured at 510 nm of non-toxin treated cells). The experimentally derived concentration of BoNT/G present in the processed food sample will be extrapolated from the BoNT/G concentration curve using the value calculated from an 155 of 168 WO 2008/036060 PCT/US2006/012825 average of three replicate wells. 8. TeNT activity assays ea. Assay of TeNT activity In a formulated TeNT product [03801 To conduct a TeNT activity assay using a formulated botulinum neurotoxin product such as, e.g., a formulated TeNT product, cells expressing a TeNT VAMP-GFP substrate will be prepared, for example, using one of the methods as described above in Examples IV, 8 and V, 8. A standard curve will be obtained by treating cells with 0.001 nM, 0.002 nM, 0.005 nM, 0.01 nM, 0.02 nM or 0.05 nM of TeNT (Metabiologics, Inc., Madison, WI), with each of the concentrations run in triplicates in a 24 well plate. Simultaneously, separate wells in the same plate will be treated with formulated TeNT dissolved in 1 ml of complete culture media to a final concentration of approximately 0.0055 nM. Cells in three replicate wells will be treated with the contents of each resuspended formulated TeNT vial. After six hours, cells will be analyzed using the Typhoon 9140 Imager with excitation at 484 nm and emission at 510 nm. The emissions at each concentration of TeNT and each formulated TeNT sample will be calculated as a percentage of the untreated control (fluorescence measured at 510 nm of non-toxin treated cells). The experimentally-derived concentration of formulated TeNT for each vial will be extrapolated from the TeNT concentration curve using the value calculated from an average of three replicate wells. 8b. Assay of TeNT activity In a food sample [0381] To conduct a TeNT activity assay using a food sample such as, e.g., a processed food sample, cells expressing a TeNT VAMP-GFP substrate will be prepared, for example, using one of the methods as described above in Examples IV, 8 and V, 8. A standard curve will be obtained by treating cells with 0.001, 0.002, 0.005, 0.01, 0.02 or 0.05 nM of TeNT (Metabiologics, Inc., Madison, WI), with each of the concentrations run in triplicates in a 24 well plate. Simultaneously, separate wells in the same plate will be treated with a processed food sample from vials of formulated TeNT diluted in 1 ml of complete culture media. Cells in three replicate wells will be treated with the contents of each diluted sample. After six hours, cells will be analyzed using the Typhoon 9140 Imager with excitation at 484 nm and emission at 510 nm. The emissions at each concentration of TeNT and each processed food sample will be calculated as a percentage of the untreated control (fluorescence measured at 510 nm of non-toxin treated cells). The experimentally derived concentration of TeNT present in the processed food sample will be extrapolated from the TeNT concentration curve using the value calculated from an average of three replicate wells. [0382] Although the invention has been described with reference to the examples provided above, it should be understood that various modifications can be made without departing from the spirit of the invention. Accordingly, the invention is limited only by the following claims. 156 of 168

Claims (103)

1. A composition comprising a cell population, said population comprising cells containing an exogenous Clostridial toxin substrate capable of being localized to the plasma membrane of said cells; wherein said cells are capable of Clostridial toxin intoxication; wherein said exogenous Clostridial toxin substrate comprises a fluorescent member, a membrane targeting domain and a Clostridial toxin recognition sequence comprising a cleavage site, where the cleavage site intervenes between said fluorescent member and said membrane localization domain; and wherein greater than 50% of said cell population comprises said cells containing said exogenous Clostridial toxin substrate.

2. The composition according to Claim 1, wherein said cells transiently contains said exogenous Clostridial toxin substrate.

3. The composition according to Claim 1, wherein said cells stably contains said exogenous Clostridial toxin substrate.

4. The composition according to Claim 1, wherein said substrate is expressed from a nucleic acid molecule.

5. The composition according to Claim 4, wherein said nucleic acid molecule comprises a viral expression construct encoding a Clostridial toxin substrate.

6. The composition according to Claim 1, wherein said toxin substrate is introduced into said cell using a protein delivery method.

7. The composition according to Claim 1, wherein said cell is a neuronal cell.

8. The composition according to Claim 7, wherein said neuronal cell is selected from the group consisting of a primary neuronal cell, an immortalized neuronal cell and a transformed neuronal cell.

9. The composition according to Claim 7, wherein said neuronal cell is selected from the group consisting of a neuroblastoma cell, a neuronal hybrid cell, a spinal cord cell, a central nervous system cell, a cerebral cortex cell, a dorsal root ganglion cell, a hippocampal cell and a pheochromocytoma cell. 157 of 168 WO 2008/036060 PCT/US2006/012825

10. The composition according to Claim 7, wherein said neuronal cell is selected from the group consisting of Neuro-2a, SH-SY5Y, NG108-C15, N1E-1 15, ND8/34 and SK-N-DZ..

11. The composition according to Claim 1, wherein said cell is a non-neuronal cell.

12. The composition according to Claim 11, wherein said non-neuronal cell is selected from the group consisting of a primary non-neuronal cell, an immortalized non-neuronal cell and a transformed non neuronal cell.

13. The composition according to Claim 11, wherein said non-neuronal cell is selected from the group consisting of an anterior pituitary cell, an adrenal cell, a pancreatic cell, an ovarian cell, a kidney cell, a stomach cell, a blood cell, an epithelial cell, a fibroblast, a thyroid cell, a chondrocyte, a muscle cell, a hepatocyte, a glandular cell.

14. The composition according to Claim 11, wherein said kidney cell is HEK-293.

15. The composition according to Claim 1, wherein said cell is sensitive to said intoxication at Clostridial toxin concentrations of 2 nM and below.

16. The composition according to Claim 1, wherein said cell is sensitive to said intoxication at Clostridial toxin concentrations of 0.1 nM and below.

17. The composition according to Claim 1, wherein said cell'is sensitive to said intoxication at Clostridial toxin concentrations of 0.02 nM and below.

18. The composition according to Claim 1, wherein said fluorescent member is a fluorescent protein.

19. The composition according to Claim 18, wherein said fluorescent protein is selected from the group consisting of a green fluorescent protein, a blue fluorescent protein, a cyan fluorescent protein, a yellow fluorescent protein and a red fluorescent protein.

20. The composition according to Claim 1, wherein said fluorescent protein is a fluorophore binding protein.

21. The composition according to Claim 20, wherein said fluorophore binding protein is selected from the group consisting of a tetracysteine peptide, an AGT and a dehalogenase.

22. The composition according to Claim 21, wherein said tetracysteine peptide binds to a fluorophore selected from the group consisting of a nonfluorescent biarsenical derivitive of fluorescein and a nonfluorescent biarsenical derivitive of resorufin. 158 of 168 WO 2008/036060 PCT/US2006/012825

23. The composition according to Claim 21, wherein said AGT binds to a fluorophore selected Trom ine group consisting of a para-benzyl guanine diethylaminocoumarin, a para-benzyl guanine diacetytfluorescein, a para-benzyl guanine dyomic DY-505-05, a para-benzyl guanine ATTO 488, a para-benzyl guanine ATTO 532, a para-benzyl guanine dyomic DY-547, a para-benzyl guanine tetramethyrhodamine, a para-benzyl guanine ATTO 600, a para-benzy guanine dyomic DY-632, a para-benzy guanine dyomic DY-647, a para-benzyl guanine dyomic DY-732 and a para-benzyl guanine dyomic DY-747.

24. The composition according to Claim 21, wherein said dehalogenase binds to a fluorophore selected from the group consisting of a HaloTag Coumarian, a HaloTag diAcFAM and a HaloTag TMR.

25. The composition according to Claim 1, wherein said membrane targeting domain comprises a interhelical loop region of SNAP-25.

26. The composition according to Claim 25, wherein said Interhelical loop region of SNAP-25 comprises at least 5 residues from amino acids 85-120 of SEQ ID NO: 1.

27. The composition according to Claim 25, wherein said interhelical loop region of SNAP-25 comprises at most 35 residues from amino acids 85-120 of SEQ ID NO: 1.

28. The composition according to Claim 25, wherein said interhelical loop region of SNAP-25 comprises an amino acid sequence selected from the group consisting SEQ ID NO: 128, SEQ ID NO: 129, SEQ ID NO: 130, SEQ ID NO: 131, SEQ ID NO: 132, SEQ ID NO: 133 and SEQ ID NO: 134.

29. The composition according to Claim 1, wherein said membrane targeting domain comprises the amino acid motif QPXRV, where X is any amino acid.

30. The composition according to Claim 29, wherein said motif comprises an amino acid sequence selected from the group consisting SEQ ID NO: 135, SEQ ID NO: 136, SEQ ID NO: 137, SEQ ID NO: 138, SEQ ID NO: 139, SEQ ID NO: 140, SEQ ID NO: 141 and SEQ ID NO: 142.

31. The composition according to Claim 1, wherein said membrane targeting domain comprises the amino-terminal a-helix region of SNAP-25.

32. The composition according to Claim 31, wherein said amino-terminal a-helix region of SNAP-25 comprises at least 5 residues from amino acids 1-84 of SEQ ID NO: 1

33. The composition according to Claim 31, wherein said amino-terminal a-helix region of SNAP-25 comprises at most 80 residues from amino acids 1-84 of SEQ ID NO: 1 159 of 168 WO 2008/036060 PCT/US2006/012825

34. The composition according to Glaim 1, wherein said membrane targeting domain comprises me carboxy-terminal a-helix region of SNAP-25.

35. The composition according to Claim 34, wherein said carboxy-terminal a-helix region of SNAP-25 comprises at least 5 residues from amino acids 121-206 of SEQ ID NO: 1.

36. The composition according to Claim 34, wherein said carboxy-terminal a-helix region of SNAP-25 comprises at most 85 residues from amino acids 121-206 of SEQ ID NO: 1.

37. The composition according to Claim 1, wherein said substrate comprises a Clostridial toxin recognition sequence selected from the group consisting of a BoNT/A recognition sequence including a cleavage site, a BoNT/B recognition sequence including a cleavage site, a BoNT/Ci recognition sequence including a cleavage site, a BoNT/D recognition sequence including a cleavage site, a BoNT/E recognition sequence including a cleavage site, a BoNT/F recognition sequence including a cleavage site, a BoNT/G recognition sequence including a cleavage site and a TeNT recognition sequence including a cleavage site.

38. The composition according to Claim 1, wherein said Clostridial toxin recognition sequence comprises at least six consecutive residues of SNAP-25, said six consecutive residues comprising Gln-Arg.

39. The composition according to Claim 1, wherein said Clostridial toxin recognition sequence comprises at least six consecutive residues of VAMP, said six consecutive residues comprising Gln-Phe.

40. The composition according to Claim 1, wherein said Clostridial toxin recognition sequence comprises at least six consecutive residues of SNAP-25, said six consecutive residues comprising Arg-Ala.

41. The composition according to Claim 1, wherein said Clostridial toxin recognition sequence comprises at least six consecutive residues of Syntaxin, said six consecutive residues comprising Lys-Ala.

42. The composition according to Claim 1, wherein said Clostridial toxin recognition sequence comprises at least six consecutive residues of VAMP, said six consecutive residues comprising Lys-Leu.

43. The composition according to Claim 1, wherein said Clostridial toxin recognition sequence comprises at least six consecutive residues of SNAP-25, said six consecutive residues comprising Arg-lie.

44. The composition according to Claim 1, wherein said Clostridial toxin recognition sequence comprises at least six consecutive residues of VAMP, said six consecutive residues comprising Gln-Lys.

45. The composition according to Claim 1, wherein said Clostridial toxin recognition sequence comprises at least six consecutive residues of VAMP, said six consecutive residues comprising Ala-Ala. 160 of 168 WO 2008/036060 PCT/US2006/012825

46. A composition comprising a cell population, said population comprising cells containing an exogenous BoNT/A substrate capable of being localized to the plasma membrane of said cells; wherein said cells are capable of BoNT/A intoxication; wherein said exogenous BoNT/A substrate is comprised of a fluorescent member, a membrane targeting domain and a BoNT/A recognition sequence comprising a cleavage site, where the cleavage site Intervenes between said fluorescent member and said membrane localization domain; and wherein greater than 50% of said cell population comprises said cells containing said exogenous BoNT/A substrate.

47. A composition comprising a cell population, said population comprising cells containing an exogenous BoNT/E substrate capable of being localized to the plasma membrane of said cells; wherein said cells are capable of BoNT/E intoxication; wherein said exogenous BoNT/E substrate is comprised of a fluorescent member, a membrane targeting domain and a BoNT/E recognition sequence comprising a cleavage site, where the cleavage site intervenes between said fluorescent member and said membrane localization domain; and wherein greater than 50% of said cell population comprises said cells containing said exogenous BoNT/A substrate.

48. A method of determining Clostridial toxin activity, said method comprising the steps of: a. contacting with a sample a cell population, said population comprising cells containing an exogenous Clostridial toxin substrate capable of being localized to the plasma membrane of said cells wherein said cells are capable of Clostridial toxin intoxication; wherein said exogenous Clostridial toxin substrate comprises a fluorescent member, a membrane targeting domain and a Clostridial toxin recognition sequence comprising a cleavage site, where the cleavage site intervenes between said fluorescent member and said membrane localization domain; and wherein greater than 50% of said cell population comprises said cells containing said exogenous Clostridial toxin substrate; 161 of 168 WO 2008/036060 PCT/US2006/012825 b. exciting said fluorescent member; and c. determining the fluorescence of said contacted cell population relative to a control cell population, where a difference in fluorescence of said contacted cell population as compared to said control cell population is indicative of Clostridial toxin activity.

49. The method according to Claim 48, wherein said sample is selected from the group consisting of a purified Clostridial toxin, a partially purified Clostridial toxin or unpurified Clostridial toxin.

50. The method according to Claim 48, wherein said sample is selected from the group consisting of a purified Clostridial toxin light chain, a partially purified Clostridial toxin light chain or unpurified Clostridial toxin light chain.

51. The method according to Claim 48, wherein said sample is selected from the group consisting of a bulk Clostridial toxin, a formulated Clostridial toxin, a cosmetics Clostridial toxin formulation or a clinical Clostridial toxin formulation.

52. The method according to Claim 48, wherein said sample Is selected from the group consisting of a recombinant Clostridial toxin and a recombinant Clostridial toxin light chain.

53. The method according to Claim 48, wherein said sample is selected from the group consisting of a raw food, a cooked food, a partially cooked food or a processed food.

54. The method according to Claim 48, wherein said sample is a sample taken from a mammal.

55. The method according to Claim 54, wherein said mammalian sample Is selected from the group consisting of a tissue, a saliva, an excretion or a feces.

56. The method according to Claim 48, wherein said cell transiently contains said exogenous Clostridial toxin substrate.

57. The method according to Claim 48, wherein said cell stably contains said exogenous Clostridial toxin substrate.

58. The method according to Claim 48, wherein said substrate is expressed from a nucleic acid molecule.

59. The method according to Claim 58, wherein said nucleic acid molecule comprises a viral expression construct encoding a Clostridial toxin substrate. 162 of 168 WO 2008/036060 PCT/US2006/012825

60. The method according to Claim 48, wherein said toxin substrate is introduced into said cell using a protein delivery method.

61. The method according to Claim 48, wherein said cell is a neuronal cell.

62. The method according to Claim 61, wherein said neuronal cell is selected from the group consisting of a primary neuronal cell, an immortalized neuronal cell and a transformed neuronal cell.

63. The method according to Claim 61, wherein said neuronal cell Is selected from the group consisting of a neuroblastoma cell, a neuronal hybrid cell, a spinal cord cell, a central nervous system cell, a cerebral cortex cell, a dorsal root ganglion cell, a hippocampal cell and a pheochromocytoma cell.

64. The method according to Claim 48, wherein said cell is a non-neuronal cell.

65. The method according to Claim 64, wherein said non-neuronal cell is selected from the group consisting of a primary neuronal cell, an immortalized neuronal cell and a transformed neuronal cell.

66. The method according to Claim 64, wherein said non-neuronal cell is selected from the group consisting of an anterior pituitary cell, an adrenal cell, a pancreatic cell, an ovarian cell, a kidney cell, a stomach cell, a blood cell, an epithelial cell, a fibroblast, a thyroid cell, a chondrocyte, a muscle cell, a hepatocyte, a glandular cell.

67. The method according to Claim 48, wherein said cell is sensitive to said intoxication at Clostridial toxin concentrations of 2 nM and below.

68. The method according to Claim 48, wherein said cell is sensitive to said intoxication at Clostridial toxin concentrations of 0.1 nM and below.

69. The method according to Claim 48, wherein said cell is sensitive to said Intoxication at Clostridial toxin concentrations of 0.02 nM and below.

70. The composition according to Claim 48, wherein said fluorescent member is a fluorescent protein.

71. The composition according to Claim 70, wherein said fluorescent protein is selected from the group consisting of a green fluorescent protein, a blue fluorescent protein, a cyan fluorescent protein, a yellow fluorescent protein and a red fluorescent protein.

72. The composition according to Claim 48, wherein said fluorescent protein is a fluorophore binding protein. 163 of 168 WO 2008/036060 PCT/US2006/012825

73. I ne composition according to uam 72, wherein saia fluoropnore ninaing protein is seiecteO Trom ne group consisting of a tetracysteine peptide, an AGT and a dehalogenase.

74. The composition according to Claim 73, wherein said tetracysteine peptide binds to a fluorophore selected from the group consisting of a nonfluorescent biarsenical derivitive of fluorescein and a nonfluorescent biarsenical derivitive of resoruf in.

75. The composition according to Claim 73, wherein said AGT binds to a fluorophore selected from the group consisting of a para-benzyl guanine diethylaminocoumarin, a para-benzyl guanine diacetytfluorescein, a para-benzyl guanine dyomic DY-505-05, a para-benzyl guanine ATTO 488, a para-benzyl guanine ATTO 532, a para-benzyl guanine dyomic DY-547, a para-benzyl guanine tetramethylrhodamine, a para-benzyl guanine ATTO 600, a para-benzyl guanine dyomic DY-632, a para-benzyl guanine dyomic DY-647, a para-benzyl guanine dyomic DY-732 and a para-benzyl guanine dyomic DY-747.

76. The composition according to Claim 73, wherein said dehalogenase binds to a fluorophore selected from the group consisting of a HaloTag Coumarian, a HaloTag diAcFAM and a HaloTag TMR.

77. The composition according to Claim 48, wherein said membrane targeting domain comprises a interhelical loop region of SNAP-25.

78. The composition according to Claim 77, wherein said interhelical loop region of SNAP-25 comprises at least 5 residues from amino acids 85-120 of SEQ ID NO: 1.

79. The composition according to Claim 77, wherein said interhelical loop region of SNAP-25 comprises at most 35 residues from amino acids 85-120 of SEQ ID NO: 1.

80. The composition according to Claim 77, wherein said interhelical loop region of SNAP-25 comprises an amino acid sequence selected from the group consisting SEQ ID NO: 128, SEQ ID NO: 129, SEQ ID NO: 130, SEQ ID NO: 131, SEQ ID NO: 132, SEQ ID NO: 133 and SEQ ID NO: 134.

81. The composition according to Claim 48, wherein said membrane targeting domain comprises the amino acid motif QPXRV, where X is any amino acid.

82. The composition according to Claim 81, wherein said motif comprises an amino acid sequence selected from the group consisting SEQ ID NO: 135, SEQ ID NO: 136, SEQ ID NO: 137, SEQ ID NO: 138, SEQ ID NO: 139, SEQ ID NO: 140, SEQ ID NO: 141 and SEQ ID NO: 142.

83. The composition according to Claim 48, wherein said membrane targeting domain comprises the amino-terminal a-helix region of SNAP-25. 164 of 168 WO 2008/036060 PCT/US2006/012825

84. Tne composition according to Claim 83, wherein said amino-terminal a-nelix region 01 bNAV-Ib comprises at least 5 residues from amino acids 1-84 of SEQ ID NO: 1

85. The composition according to Claim 83, wherein said amino-terminal a-helix region of SNAP-25 comprises at most 80 residues from amino acids 1-84 of SEQ ID NO: 1

86. The composition according to Claim 48, wherein said membrane targeting domain comprises the carboxy-terminal a-helix region of SNAP-25.

87. The composition according to Claim 86, wherein said carboxy-terminal a-helix region of SNAP-25 comprises at least 5 residues from amino acids 121-206 of SEQ ID NO: 1.

88. The composition according to Claim 86, wherein said carboxy-terminal a-helix region of SNAP-25 comprises at most 85 residues from amino acids 121-206 of SEQ ID NO: 1.

89. The composition according to Claim 48, wherein said substrate comprises a Clostridial toxin recognition sequence selected from the group consisting of a BoNT/A recognition sequence including a cleavage site, a BoNT/B recognition sequence including a cleavage site, a BoNT/Ci recognition sequence including a cleavage site, a BoNT/D recognition sequence including a cleavage site, a BoNT/E recognition sequence including a cleavage site, a BoNT/F recognition sequence including a cleavage site, a BoNT/G recognition sequence including a cleavage site and a TeNT recognition sequence Including a cleavage site.

90. The composition according to Claim 48, wherein said Clostridial toxin recognition sequence comprises at least six consecutive residues of SNAP-25, said six consecutive residues comprising Gin-Arg.

91. The composition according to Claim 48, wherein said Clostridial toxin recognition sequence comprises at least six consecutive residues of VAMP, said six consecutive residues comprising Gin Phe.

92. The composition according to Claim 48, wherein said Clostridial toxin recognition sequence comprises at least six consecutive residues of SNAP-25, said six consecutive residues comprising Arg-Ala.

93. The composition according to Claim 48, wherein said Clostridial toxin recognition sequence comprises at least six consecutive residues of Syntaxin, said six consecutive residues comprising Lys-Ala. 165 of 168 WO 2008/036060 PCT/US2006/012825

94. The composition according to Claim 48, wherein said Clostridial toxin recognition sequence comprises at least six consecutive residues of VAMP, said six consecutive residues comprising Lys Leu.

95. The composition according to Claim 48, wherein said Clostridial toxin recognition sequence comprises at least six consecutive residues of SNAP-25, said six consecutive residues comprising Arg-Ile.

96. The composition according to Claim 48, wherein said Clostridial toxin recognition sequence comprises at least six consecutive residues of VAMP, said six consecutive residues comprising GIn Lys.

97. The composition according to Claim 48, wherein said Clostridial toxin recognition sequence comprises at least six consecutive residues of VAMP, said six consecutive residues comprising Ala Ala.

98. The method according to Claim 48, wherein determining the fluorescence of said contacted cell relative to a control cell comprises detecting an increased fluorescence of the cytoplasmic substrate from the contacted cell as indicative of Clostridial toxin activity.

99. The method according to Claim 48, wherein determining the fluorescence of said contacted cell relative to a control cell comprises detecting a decrease fluorescence of the membrane-localized substrate from the contacted cell as indicative of Clostridial toxin activity.

100. The method according to Claim 48, wherein determining the fluorescence of said contacted cell relative to a control cell comprises detecting a shift in fluorescence intensity of the membrane localized substrate to the cytoplasmic substrate of said contact cell as indicative of Clostridial toxin activity.

101. The method according to Claim 48, wherein determining the fluorescence of said contacted cell relative to a control cell comprises detecting a shift in fluorescence intensity of the membrane localized substrate to the cytoplasmic substrate of said contact cell as indicative of Clostridial toxin activity.

102. A method of determining BoNT/A activity, said method comprising the steps of: a. contacting with a sample a cell population, said population comprising cells containing an exogenous BoNT/A substrate capable of being localized to the plasma membrane of said cells; wherein said cels are capable of BoNT/A intoxication; 166 of 168 WO 2008/036060 PCT/US2006/012825 wherein said exogenous BoNT/A substrate comprises a fluorescent member, a membrane targeting domain and a BoNT/A recognition sequence comprising a cleavage site, where the cleavage site intervenes between said fluorescent member and said membrane localization domain; and wherein greater than 50% of said cell population comprises said cells containing said exogenous BoNT/A substrate; b. exciting said fluorescent member; and c. determining the fluorescence of said contacted cell population relative to a control cell population, where a difference in fluorescence of said contacted cell population as compared to said control cell population is indicative of BoNT/E activity.

103. A method of determining BoNT/E activity, said method comprising the steps of: a. contacting with a sample a cell population, said population comprising cells containing an exogenous BoNT/E substrate capable of being localized to the plasma membrane of said cells; wherein said cels are capable of BoNT/E intoxication; wherein said exogenous BoNT/E substrate comprises a fluorescent member, a membrane targeting domain and a BoNT/E recognition sequence comprising a cleavage site, where the cleavage site intervenes between said fluorescent member and said membrane localization domain; and wherein greater than 50% of said cell population comprises said cells containing said exogenous BoNT/E substrate; b. exciting said fluorescent member; and c. determining the fluorescence of said contacted cell population relative to a control cell population, where a difference in fluorescence of said contacted cell population as compared to said control cell population is indicative of BoNT/E activity. 167 of 168