Classifications

• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07K—PEPTIDES
  • C07K14/00—Peptides having more than 20 amino acids; Gastrins; Somatostatins; Melanotropins; Derivatives thereof
  • C07K14/005—Peptides having more than 20 amino acids; Gastrins; Somatostatins; Melanotropins; Derivatives thereof from viruses
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61K—PREPARATIONS FOR MEDICAL, DENTAL OR TOILETRY PURPOSES
  • A61K38/00—Medicinal preparations containing peptides
  • A61K38/16—Peptides having more than 20 amino acids; Gastrins; Somatostatins; Melanotropins; Derivatives thereof
  • A61K38/162—Peptides having more than 20 amino acids; Gastrins; Somatostatins; Melanotropins; Derivatives thereof from virus
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61P—SPECIFIC THERAPEUTIC ACTIVITY OF CHEMICAL COMPOUNDS OR MEDICINAL PREPARATIONS
  • A61P31/00—Antiinfectives, i.e. antibiotics, antiseptics, chemotherapeutics
  • A61P31/12—Antivirals
  • A61P31/14—Antivirals for RNA viruses
  • A61P31/18—Antivirals for RNA viruses for HIV
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61P—SPECIFIC THERAPEUTIC ACTIVITY OF CHEMICAL COMPOUNDS OR MEDICINAL PREPARATIONS
  • A61P37/00—Drugs for immunological or allergic disorders
  • A61P37/02—Immunomodulators
  • A61P37/04—Immunostimulants
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61K—PREPARATIONS FOR MEDICAL, DENTAL OR TOILETRY PURPOSES
  • A61K39/00—Medicinal preparations containing antigens or antibodies
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07K—PEPTIDES
  • C07K2319/00—Fusion polypeptide
• • C—CHEMISTRY; METALLURGY
  • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
  • C12N—MICROORGANISMS OR ENZYMES; COMPOSITIONS THEREOF; PROPAGATING, PRESERVING, OR MAINTAINING MICROORGANISMS; MUTATION OR GENETIC ENGINEERING; CULTURE MEDIA
  • C12N2740/00—Reverse transcribing RNA viruses
  • C12N2740/00011—Details
  • C12N2740/10011—Retroviridae
  • C12N2740/16011—Human Immunodeficiency Virus, HIV
  • C12N2740/16111—Human Immunodeficiency Virus, HIV concerning HIV env
  • C12N2740/16122—New viral proteins or individual genes, new structural or functional aspects of known viral proteins or genes

Definitions

• HIV is the virus that is responsible for the worldwide AIDS epidemic.
• the initial stages of HIV infection involve the fusion ofthe viral membrane with the target cell membrane, a process that injects the viral contents into the cellular cytoplasm.
• the molecular complex responsible for the fusion activity contains the surface protein gpl20 and the transmembrane protein gp41. It is currently believed that gpl20 interacts with the proteins CD4 and coreceptors on the target cell, resulting in a conformational change that causes gp41 to insert its amino terminus (fusion peptide region) into the target cell membrane. This structural rearrangement promotes the fusion of virus and cellular membranes tlirough a poorly understood mechanism.
• the present invention relates to a novel protein, referred to as Five (5)-Helix or Five-Helix protein, that, under the conditions described herein, folds into a stable structure, binds a peptide (referred to as C34) that corresponds to the C-peptide region of HIV gp41 protein or a portion ofthe region and inhibits HIV infection of mammalian cells, such as human cells.
• Five-Helix is made up ofthe three N-helices and at least two, but not three, ofthe three C-helices ofthe trimer of hairpin structure of HIV gp41, separated by linkers, such as amino acid residue linkers. That is, Five-Helix includes the three N-helices and at least two ofthe three C-helices of HTV gp41.
• Five-Helix can be represented as: N-linker-C-linker-N-linker-C-linker- N, wherein N represents an N-helix and C represents a C-helix or C-helix portion.
• Five-Helix or Five-Helix protein encompasses all such embodiments (those including three N-helices and two or more, but less than three complete C-helices, separated by appropriate linkers).
• the amino acid composition of Five-Helix can vary greatly, provided that Five-Helix presents a surface that is structurally complementary to the C-peptide region of HIV gp41 protein and, preferably, binds C34 or the C-peptide region of gp41, as peptides or part of gp41 as a whole. That is, the remaining (interacting) surface of Five-Helix (the C-peptide binding site, all or a portion of which is not occupied by a C-peptide) must be presented in such a manner (conformation) that it is available to bind the C-peptide region of HIV gp41.
• Five-Helix In the case of vaccine and therapeutic applications of Five- Helix, Five-Helix must bind (be capable of binding) C34 or the C-peptide region of HIV gp41. In the cases in which Five-Helix is used as a drug-screening tool or an antibody-screening tool, Five-Helix need not bind (need not be capable of binding) C34 or the C peptide region of HIV gp41.
• Five-Helix has the amino acid sequence of SEQ ID NO.: 1.
• Five-Helix presents a surface that is structurally complementary to the C-peptide region, preferably binds C34 or the C- peptide region and has an amino acid sequence that differs from that of SEQ ED NO.: 1 by addition, deletion, substitution or alteration of at least one amino acid residue.
• the order ofthe N-helices and C-helices of Five-Helix can also vary, provided that the conformation is such that the exposed protein presents a surface structurally complementary to the C-peptide region of HIV gp41.
• the linkers can be of any length or composition, provided that the Five-Helix protein conformation, described above, is retained.
• Five-Helix can be an L-amino acid protein, a D-amino acid protein or a combination of L-amino acid residues and D-amino acid residues; these residues can be modified residues.
• the present invention further relates to DNA encoding Five-Helix; methods of producing Five-Helix; methods in which Five-Helix is used, such as in methods of inhibiting entry of HIV into mammalian cells, including human cells, and methods of eliciting an immune response in an individual, such as a human; methods in which DNA encoding Five-Helix is used, such as in gene therapy methods; genetically engineered cells, such as bacteria, human and other mammalian and other eukaryotic cells, which contain and express Five-Helix protein-encoding DNA and methods of using such cells (e.g., for gene therapy or Five-Helix production); compositions, such as pharmaceutical compositions, which include Five-Helix; Five-Helix complex comprising Five-Helix and a component that binds HTV envelope protein
• Five-Helix is useful as an anti-HIV therapeutic agent, a prophylactic agent or drug to prevent HIV infection, a reagent for identifying (screening for) or designing other anti-HIV therapeutics or prophylactics, and an immunogen to elicit antibodies that prevent or reduce HIV infection.
• the invention relates to a method of identifying a compound or molecule that binds Five-Helix and inhibits HIV infection of mammalian cells, wherein the compound or molecule to be assessed is referred to as a candidate inhibitor, comprising combining a candidate inhibitor and Five-Helix, under conditions appropriate for binding of an inhibitor and Five-Helix to occur and determining if binding occurs, wherein if binding occurs, the candidate inhibitor is a compound or molecule that binds Five-Helix.
• the method optionally further comprises determining if the compound or molecule that binds Five-Helix inhibits HIV infection of mammalian (e.g., human) cells, such as in a cell-based assay. Such a compound or molecule will inhibit (totally or partially) HIV infection of cells (e.g., by preventing or interfering with formation of the trimer-of-hairpins).
• the invention in another embodiment, relates to a method of eliciting an immune response to HIV in an individual, comprising introducing, by an appropriate route, a composition comprising Five-Helix and a physiologically acceptable carrier, in a dose sufficient to elicit the immune response in the individual.
• Vaccines comprising Five-Helix (or a variant or portion thereof) in a physiologically acceptable carrier are the subject of this invention.
• the subject ofthe present invention is Six (6)-Helix protein, which comprises three N-helices and three C-helices of HIV gp41, joined by linkers, such as amino acid residue linkers.
• Six-Helix protein comprises the amino acid sequence of SEQ ID NO.: 2.
• the amino acid sequence of Six-Helix differs from that of SEQ ID NO.: 2 by addition, deletion, substitution or alteration of at least one amino acid residue.
• Six-Helix protein is useful not only for producing Five-Helix, but also as a negative control in screening for drugs that inhibit membrane fusion.
• Figures 1A and IB illustrate targeting HIV-1 membrane fusion.
• Figure 1A is a schematic of HIV-1 membrane fusion depicting events that promote formation of the gp41 trimer-of-hairpins.
• the N-terminal fusion peptide of gp41 (red), inaccessible in the native state, inserts into target cell membranes following gpl20 interaction with CD4 and coreceptors (not shown).
• Formation ofthe prehairpin intermediate exposes the N-terminal coiled coil (gray), the target of C-peptide inhibition. This transient structure collapses into the trimer-of-hairpins state that brings the membranes into close apposition for fusion.
• Figure IB shows the design ofthe 5-Helix construct.
• the ribbon diagrams depict the core structure ofthe trimer-of-hairpins (left and D.C. Chan et al., Cell 89, 263-273 (1997)) and a model of 5-Helix (right).
• the inner gray helices represent N36 peptides
• the outer blue helices represent C34 peptides.
• One C-peptide has been removed in the model of 5- Helix and orange lines have been drawn to represent connectivity between the helices.
• the N40 and C38 sequences are alternately linked by short Gly/Ser peptide sequences (gray bars in schematic at bottom (See Example 1).
• Figures 2A - 2D show properties of 5-Helix.
• Figure 2A is the circular dichroism (CD) apectrum of 5-Helix (10 ⁇ M) at 25 C. The spectrum indicates that the 5-Helix protein adopts >95% ofthe helical content expected from the design.
• Figure 2B is a graphic representation of thermal denaturation of 5-Helix monitored by ellipticity at 222 nm in TBS (filled squares) and in 3.7 M guanidine (Gu)HCl/TBS (open squares). The denaturation observed in the GuHCl solution is >90% reversible.
• Figure 2C shows results of nickel (Ni)-NTA precipitation of 5- Helix with a His-tagged C-peptide.
• Figures 3 A-3C show results of assessment of 5-Helix inhibition of HIV-1 envelope-mediated membrane fusion, as described in Example 2.
• Figure 3 A shows results of assessment of titration of viral infectivity by 5-Helix (filled squares), 6- Helix (open triangles), and 5-Helix(D4) (open circles), as described in Example 3 and 5
• the data represent the mean ⁇ SEM of two or more separate experiments.
• Figure 3B is a graphic representation of antagonistic inhibitory activities of 5-Helix and C34. The number of syncytia were measured in a cell-cell fusion assay performed in the absence or presence of 5-Helix, C34, or mixtures of 5-Helix and C34 at the indicated concentrations.
• the IC 50 values for 5-Helix and C34 in this assay are 13 ⁇ 3 nM and 0.55 ⁇ 0.03 nM , respectively (D. C. Chan et al, Proc. Natl. Acad. Sci. USA 95, 15613-15617 (1998)). Data represent the mean and range of mean of duplicate measurements, except for the control (mean ⁇ SEM of five measurements).
• Figure 3C shows results of assessment of 5-Helix inhibition of pseudotyped virus containing different HIV-1 envelope glycoproteins. The reported IC 50 values represent the mean ⁇ SEM of three independent experiments.
• Figure 4 is a helical wheel diagram depicting the interaction of 5-Helix with the C-peptide region of gp41.
• the a through g positions in each helix represent sequential positions in the 4,3-hydrophobic heptad repeat in each sequence.
• the a and d positions in the gp41 C-peptide region interact with the exposed e and g positions on the N40 coiled coil of 5-Helix.
• Residues are boxed according to their degree of conservation as determined from the alignment of 247 sequences from HIV-1, HIV-2, and SIV isolates (HIV-1 sequence database, August 2000, Los
• Figure 5 is the structural arrangement of HIV gp41. Helical regions (heptad repeats) are shown in grey, and the relative position of N- (N36) and C- (C34, DP178) peptides are indicated. In the ribbon diagram ofthe helical region, the N- peptides are in light grey, while the C-peptide are in dark grey.
• Figure 6 is the sequence of 6-Helix and 5-Helix.
• the predicted helical segments are designated by the stacked sequence.
• Figure 7 is a ribbon diagram of one ofthe possible ⁇ -helical arrangements of
• the N-helical trimer is light grey, the C-helical regions are in dark grey and the extended loop regions are in black (based on the structure of D.C. Chan, et al. (Cell 89, 263-273 (1997)).
• Figure 8 shows images of cell-cell fusion assay titration experiments.
• the syncytia (representing fused cells) are blue in the image while debris is brown.
• Figure 9 shows images of cell-cell fusion assay competition experiments. The amount of syncytia are recorded for cultures incubated in 200 nM 6-Helix or 5- Helix with increasing amounts of C34 peptide.
• Figure 10 is a schematic ofthe design ofthe Five-Helix constructs.
• the schematic diagram depicts the linkage pattern ofthe basic 5-Helix construct. Three different C-termini were added.
• 6-Helix a His-tagged C-peptide is attached to 5- Helix in order to mimic the complete six-helix bundle ofthe trimer-of hairpins.
• the N40 and C38 sequences (alternately joined using short Gly/Ser linkers) are derived from the N- and C-peptide regions of HTV HXB2 gp41.
• the red- and blue-boxed residues depict the sequences ofthe N36 (SEQ ID NO.: 11) and C34 (SEQ ED NO.: 12) peptides, respectively.)
• Figures 11A-11C show amino acid sequences of peptides (SEQ ID NOS.: 1- 10) ofthe present invention.
• trimer-of-hairpins The conformation of a major part ofthe ectodomain ofthe gp41 molecule consists of a trimer-of-hairpins structure.
• the core "trimer-of-hairpins" is comprised of a central three-stranded N-helix coiled coil surrounded by three outer C-helices, forming a bundle with a total of six helices.
• the trimer-of-hairpins is a common structural element involved in the fusion of many enveloped viruses, suggesting a critical role for this motif in promoting membrane fusion.
• the core of the trimer-of-hairpins is a bundle of six ⁇ -helices (formed by the C-terminal regions of three gp41 ectodomains) packed in an antiparallel manner against a central, three- stranded coiled coil (formed by the N-terminal regions ofthe gp41 molecules)
• the trimer-of-hairpins motif serves to bring the two membranes together. This is illustrated schematically in Figure 1 A.
• the N-helices (one from each subunit ofthe trimer) form highly conserved hydrophobic grooves into which the C-helices pack. It is generally agreed that formation of this six -helix structure is required for membrane- fusion to occur.
• trimer-of-hairpins formation for HEV-1 entry led to the hypothesis that the C-terminal region of gp41 might serve as a target for potential membrane-fusion inhibitors.
• C-peptides have been shown to inhibit HIV-1 entry into cells, with IC 50 values as low as 1 nM in vitro (C. T. Wild et al., Proc. Natl. Acad. Sci. USA 91, 9770-9774 (1994); D. C. Chan et al, Proc. Natl. Acad. Sci. USA 95, 15613-15617 (1998)).
• Evidence suggests that C-peptides work in a dominant-negative fashion by binding to the N-peptide region and disrupting trimer- of-hairpins formation.
• N-peptides peptides derived from the gp41 N-terminal region (referred to as N-peptides) are modest inhibitors of HIV-1 membrane fusion. The inhibitory mechanism of N-peptides has not been determined, in part because these peptides have a strong tendency to aggregate.
• Described herein are results that show that a protein that binds to the C- peptide region of gp41 inhibits HIV entry into cells.
• Such proteins are inhibitors of HIV and serve as the basis for development of additional anti-HTV agents. They might also be used for generating a neutralizing antibody response that targets the N- terminal region ofthe gp41 ectodomain.
• Five-Helix takes advantage ofthe binding properties ofthe N-helix peptide coiled coil while minimizing the tendency ofthe N- peptides to aggregate.
• Five-Helix five ofthe six helices that make up the core ofthe gp41 trimer-of-hairpins structure are connected with (joined by) short peptide linkers. (See Figure 1 A.)
• Five-Helix lacks a third C-peptide helix, thus creating a vacancy in order to create a high-affinity binding site for the C-terminal region of gp41.
• the three N-peptide helices and more than two (but less than three complete) C-peptide helices are connected with short peptide linkers.
• the three N-peptide helices, two complete C-peptide helices and a portion ofthe third C-peptide helix are connected with peptide linkers.
• the portion ofthe third C- helix can be as few as one amino acid residue ofthe third C-helix or any number of additional amino acid residues ofthe helix up to, but not including, all of he amino acid residues ofthe helix.
• Five-Helix protein ofthe present invention is soluble under physiological conditions.
• the core ofthe trimer-of-hairpins, as formed by individual N- and C- peptides, is already quite stable, with a melting temperature of 65 °C.
• Applicants have shown that if 5 of the 6 helices are covalently joined to form a 5-Helix protein, the stability ofthe core is further increased (the stability is greater than the stability ofthe 6-Helix core).
• Five-Helix is folded, soluble, and stable. It has an ⁇ -helical content in close agreement with the value predicted from the design.
• Five- Helix interacts strongly and specifically with epitope-tagged C-peptides.
• This interaction induces a helical conformation in the bound C-peptide as judged by the difference in circular dichroism before and after mixing.
• See Figure 2D. These properties are consistent with the intended design of Five-Helix.
• Three-Helix potently inhibits HEV-1 membrane fusion (nanomolar IC 50 ) as measured by viral infectivity and cell-cell fusion assays.
• a control protein denoted Six-Helix, in which the C-peptide binding site is occupied by an attached C-peptide (i.e., all six helices that constitute the gp41 trimer-of-hairpins have been linked into a single polypeptide, as described in Example 1) , does not have appreciable inhibitory activity. (See Figure 3 A and Figures 8 and 9).
• Five-Helix(D4) in which the C-peptide binding site is disrupted by mutation of four interface residues (V549, L556, Q563 and V570) to Asp, does not block the membrane fusion event even at 1 ⁇ M. (See Example 3 and Figure 3A.)
• the inhibitory activities of 5-Helix and C-peptides are expected to be antagonistic: when 5-Helix binds C-peptide, the amino acid residues thought to be responsible for the antiviral activities of each inhibitor are buried in the binding interface. Indeed, mixtures of 5-Helix and C34 [a well characterized and potent peptide inhibitor with an IC 50 of approximately 1 nM] display a dose-dependent antagonistic effect (Figure 3B). In the presence of 5-Helix, high-potency inhibition by C34 is only observed when the peptide is in stoichiometric excess (Figure 3B). Five-Helix inhibits infection by viruses pseudotyped with a variety of HIV-1 envelope proteins (from clades A, B, and D) with similar potency (Figure 3D).
• Five-Helix could be expressed endogenously (e.g., via gene therapy) with secretion into the bloodstream. If Five-Helix were expressed endogenously in HTV- infected cells, it could inhibit intracellular folding and transport of gpl60. Five-Helix, Five- Helix (D4), and Six-Helix are also potential reagents for small-molecule drug- screening purposes. Five-Helix offers a great deal of flexibility in the design of variants with better therapeutic characteristics. In principle, Five-Helix can be modified extensively, except at its C-peptide binding site, to alter its immunogenic, antigenic, bioavailability, or inhibitory properties.
• the C-peptide binding site might be lengthened, shortened, or shifted in the gp41 sequence in order to optimize inhibitory potency by targeting different regions ofthe gp41 ectodomain. It would be desirable to generate neutralizing antibodies that mimic the binding properties of Five-Helix.
• the broadly neutralizing ability of Five-Helix most likely stems from its interaction with the highly conserved residues in the C- peptide region of gp41 ( Figure 4).
• Unstructured C-peptide immunogens may not elicit broadly neutralizing antibodies because the linear sequence of the gp41 C- peptide region is variable among different HIV-1 strains. Such unstructured C- peptides do not have a long region of conserved amino acids residues.
• FIG. 4 is a helical wheel diagram depicting the interaction of Five-Helix with the C-peptide region of gp 41. As shown, on the helical wheel, the whole "face" is comprised of conserved or identical amino acid residues. As also shown, there is a high degree of conservation in the a and d positions ofthe C-peptide region of HIV gp41.
• Peptides from the C-terminal region ofthe gp41 ectodomain constrained in such a manner that they present highly conserved amino acid residues on a single face ofthe molecule (such as in positions a, d and e in Figure 4) can be produced. They can be used as immunogens to produce antibodies that will presumably bind those amino acid residues in the corresponding unconstrained peptide (C-peptide region of HIV gp41) and, thus, mimic the binding characteristics of Five-Helix. For example, antibodies that bind some or all ofthe highly conserved (identical and/or conserved) amino acid residues in C38 (see Figure 4) can be produced.
• Such antibodies which mimic the binding of Five-Helix, will work, in effect, as a preventive or vaccine by reducing or preventing the activity (binding) of Five-Helix.
• Such antibodies to constrained peptides from the C-terminal region of HTV gp41 ectodomain are a subject of this invention.
• the epitope for 2F5 the only known human monoclonal antibody directed against gp41 with broad neutralizing activity, is located immediately C-terminal to the C-peptide region targeted by Five-Helix (T. Muster, et al, J. Virol. 67, 6642-6647 (1993); M. Purtscher, et al., AIDS 10, 587-593 (1996)).
• the core ofthe 2F5 epitope (Leu-Asp-Lys-Trp; residues 663-666 in the HIV HXB2 gp 160 sequence) is highly conserved (81% identity) across the same set of HIV-1, HIV-2, and SIV isolates used to generate Figure 4.
• HEV-1 escape variants to 2F5 neutralization do not contain mutations in the epitope sequence, suggesting that inhibition by 2F5 may involve recognition of additional determinants.
• the conformation ofthe 2F5-bound epitope remains unknown, but antibodies elicited with fragments of gp41 containing this sequence do not possess significant virus-neutralizing activity (T. Muster, et al., J. Virol. 68, 4031-4034 (1994); L. Eckhart, et al, J. Gen. Virol. 77, 2001-2008 (1996)). It remains to be seen if 2F5 inhibits infection by interfering with trimer-of-hairpins formation.
• Five-Helix itself is a vaccine candidate.
• the possibility of eliciting an antibody response against transiently exposed conformations of proteins involved in HEV-1 fusion has been suggested (R. A. LaCasse, et al, Science 283, 357-362 (1999)).
• One possible well-defined target is the N-terminal coiled coil that is exposed in the prehairpin intermediate (D. M. Eckert, et al., Cell 99, 103-1 15 (1999)).
• a 5-Helix-like intermediate may be exposed during the fusion process, and, in this case, antibodies directed against 5-Helix may inhibit viral entry.
• Results described herein point to the C-peptide region of HEV-1 gp41 as a viable target to inhibit the formation ofthe trimer-of-hairpins.
• Structural and computational methods predict similar trimer-of-hairpins motifs for viruses in many diverse families, including orthomyxoviridae, paramyxoviridae, filoviridae, retro viridae, and others.
• inhibition of viral entry by peptides analogous to the C-peptides of gp41 has been demonstrated.
• the Five-helix design approach may offer a widely applicable strategy for inhibiting viral infections.
• Five-Helix provides a means to study a formed C-peptide binding site in detail, which cannot be done with aggregable N-peptides.
• the exposed C-peptide binding site in this Five-Helix molecule is useful to identify or design molecules that bind to the N-helical core of gp41 and can be further assessed, using known methods, for their ability to inhibit fusion ofthe HEV membrane with the membrane of a mammalian cell, such as a human cell, thus inhibiting (reducing or preventing) infection ofthe cell.
• Five-Helix can be assessed for its ability to bind to the C-helical region of gp41 and inhibit its function.
• the N-helical core of gp41 is highly conserved (in terms of amino acid composition) and, thus, it is likely that 5-Helix and variants thereof will be broadly neutralizing against a variety of clinical HEV strains and, thus, useful therapeutically.
• the Five-Helix protein which is based upon the known structure ofthe gp41 ectodomain, consists, in one embodiment, of three N-peptides and two C-peptides covalently linked and arranged to fold into a substantial part ofthe N-helical core with two ofthe three C-helix binding sites occupied by C-peptide. The remaining C-peptide binding site ofthe N-peptide is exposed. The site exposes an epitope that is 40 amino acids in length.
• the backbone atoms ofthe site are rigidly held in a structured conformation, as the N-peptide core is locked into place by the outer two C-peptides.
• the amino acid sequence of one embodiment of Five-Helix is the following: MQLLSGIVQQQQNNLLRAIEAQQHLLQLTVWGIKQLQARILAGGSGGHTTWM EWDREINNYTSLmSLffiESQNQQEKNEQELLEGSSGGQLLSGIVQQQNNLLR AIEAQQHLLQLTVWGIKQLQARILAGGSGGHTTWMEWDREINNYTSLIHSLI EESQNQQEKNEQELLEGSSGGQLLSGIVQQQQNNLLRAIEAQQHLLQLTVWGI KQLQARILAGGR (SEQ ID NO. : 1 ).
• amino acid sequence of 6-Helix is the following:
• Five-Helix protein can be produced by a variety of methods. For example, it can be produced, as described in Example 1 , from a larger protein, such as 6-Helix, by enzymatic (trypsin) digestion. Alternatively, it can be produced, using known methods and expression systems, by expressing Five-Helix protein-encoding DNA, which can be a single DNA that encodes the entire Five-Helix protein or two or more DNA "units", each of which encodes a portion (e.g., one or more N helices, one or more C helices) of N-Helix protein. The yield of expression and purification of Five-Helix can be significantly improved by direct expression ofthe Five-Helix gene in an appropriate host cell, such as E. coli.
• an appropriate host cell such as E. coli.
• the Five-Helix gene encodes the residues present in the final Five-Helix protein.
• a C-terminal His- tag can be attached to facilitate purification (with or without a protease cleavage site to later remove the tag).
• the protein can then be used directly without the proteolytic cleavage and unfolding steps required for producing Five-Helix starting from Six-Helix.
• This Five-Helix molecule may be expressed as a folded active molecule, allowing its use in biological selections or screens for optimizing its properties.
• protein synthetic methods can be used to produce Five- Helix protein.
• the five helices of Five-Helix can be joined covalently (such as by means of a linker of at least one (one or more) amino acid residues) or by other means which results in formation of a protein which is stable under physiological conditions and is correctly folded such that the remaining surface of Five Helix is presented so that it is available to bind C34 peptide.
• the helices can be similarly joined.
• Five-Helix can have a wide variety of sequences, both in the N- and C-helix regions and in the linker components, and can be comprised of L-amino acid residues, D-amino acid residues or a combination of both L- and D-amino acid residues.
• the amino acids residues can be modified.
• Five-Helix can include amino acid residues in addition to those ofthe helices and linkers (e.g., to stabilize the molecule). It is likely that the Five-Helix described here can be altered to enhance stability and activity. Minor changes in the design ofthe loops connecting the N- and C-helices (both in length and composition) and the exact borders ofthe N- and C-helices are likely to have significant effects on the stability, yield, and activity of Five-Helix.
• Five-Helix exposes a C-peptide binding site encompassing 40 amino acids along the N-helical core.
• a strategy for exposing shorter segments ofthe C-peptide binding site on 5-helix (or related molecules) involves attaching a short C-peptide sequence onto the longer exposed epitope.
• a molecule of this type might aid in the development of drugs targeted specifically to a shorter epitope along the N-helical core.
• a single pocket region (similar to that found in IQN17; D. M. Eckert, et al., Cell 99, 103-115 (1999)) could be exposed in Five-Helix by binding a C-peptide that lacks the residues that bind there (the first 10 or so residues of C34).
• These short C-peptide sequences could be attached to Five-Helix through a variety of means, including covalent crosslinking or merely extending the sequence of Five-Helix to cover part ofthe exposed epitope.
• Five-Helix is useful in a variety of contexts. As described herein, Five-Helix is a potent inhibitor of viral membrane fusion, and, thus, acts on the virus before it enters the cell (unlike current practical therapy) which acts on HlV-infected cells. Five-Helix is soluble and has been shown to be stable under the conditions described herein. It should also be possible to generate 5-Helix variants with an increased molecular weight (by oligomerization or tethering to a large protein) to reduce the rate of kidney clearance. In addition, Five-Helix dimers can be made by disulfide crosslinking, to produce a molecule filtered to a lesser extent than the Five-Helix "monomer". Thus, it is reasonable to expect that dimers might have an enhanced bioavailability when compared to that ofthe C-peptides.
• Five-Helix prevents virus from entering cells, unlike standard therapy that targets viral proteins after viral entry, and thus, Five-Helix can be used prophylactically to prevent infection or reduce the extent to which infection occurs.
• One use for such a therapeutic is in the event of a needlestick injury, such as might occur in a hospital or in settings in which needles contaminated with HTV are shared.
• an individual who is stuck with a needle and is or might be infected with HTV can receive a sufficient quantity of Five-Helix (therapeutically effective quantity) in one or more dose(s) in order to prevent or reduce HEV entry into cells.
• Five-Helix can be administered, for example, by intravenous or intramuscular injection.
• Five-Helix is used to reduce HEV infection in an individual.
• Five-Helix is administered, either as Five-Helix itself or via expression of Five-Helix-encoding DNA in appropriate host cells or vectors, to an individual in sufficient quantity to reduce (totally or partially) HEV infection ofthe individual's cells. That is, a dose of Five- Helix sufficient to reduce HEV infection (an effective dose) is administered in such a manner (e.g., by injection, topical administration, intravenous route) that it inhibits (totally or partially) HEV entry into cells.
• a gene therapy approach is used to provide the effective dose, by introducing cells that express Five-Helix protein into an individual. Five-Helix can be administered to an individual who is HEV infected to reduce further infection, or to an uninfected individual to prevent infection or reduce the extent to which infection occurs.
• compositions which comprise Five-Helix in an appropriate carrier are a subject of this invention. They are useful for preventive and therapeutic purposes and can be administered via a variety of routes (e.g., injection, topical administration, intravenous route). Five-Helix appears to present a single, intact C-helix binding site and, thus, is useful for screening for drugs that inhibit membrane fusion. Five-Helix exposes a larger, more rigid target for potential drug screens than does IQN17. The molecules 6-Helix and 5-Helix(D4) are a useful negative control in these studies. The Five-Helix exposed epitope can also be used as an antigen for producing antibodies, particularly neutralizing antibodies using known methods. The antibodies can be monoclonal or polyclonal.
• the serum stability of Five-Helix can be tested, using known methods, to ascertain its therapeutic potential. If Five-Helix is degraded, the most likely point of attack/degradation is the glycine/serine linker regions. In this case, different linker regions can be generated and tested (see below). The inhibitory ability of these anti- Five-Helix sera and ascites can be tested using standard fusion assays.
• the outside surface of Five-Helix can be varied, for example, to enhance bioavailability, decrease toxicity and avoid immune clearance. Since Five-Helix exhibits potent inhibitory activity, whereas the 6-Helix bundle does not, it is the exposed groove, including the pocket region, that is responsible for inhibition. The rest ofthe molecule simply provides a scaffold for displaying the exposed groove. Therefore, this scaffold can be modified without adversely affecting the inhibitory activity of Five-Helix. Modification ofthe scaffold may provide several advantages. First, it would facilitate procedures in which multiple administrations of Five-Helix are required. For example, when Five-Helix is used as an anti-HEV therapeutic agent, multiple doses might be required. After extended administration, individuals might develop antibodies to Five-Helix that are likely to increase its clearance from the body.
• C-peptide inhibitors function by binding to the N-peptide region of this intermediate
• Five-Helix likely functions by binding to the C-peptide region.
• trimer-of-hairpins is a common feature of many viral membrane fusion proteins. It has been observed in crystal structures of Influenza, Ebola, SV5 (simian parainfluenza virus 5), and RSV (human respiratory syncitial virus). In addition, many other members of the retrovirus, paramyxovirus, and filovirus families are predicted to contain this motif. A similar structure has been observed in the associated vertebrate vesicle fusion proteins. The basic strategy described herein can be applied to any of these systems in order to inhibit fusion.
• One subject of this invention is a method of inhibiting formation ofthe trimer-of-hairpins of an enveloped virus (a virus that comprises a viral envelope protein) by contacting the virus with a drug that binds a viral envelope protein (e.g., the C peptide region of a viral envelope protein) and inhibits formation ofthe trimer-of-hairpins ofthe enveloped protein.
• a drug that binds a viral envelope protein e.g., the C peptide region of a viral envelope protein
• 5-Helix was based on the N36/C34 six-helix bundle crystal structure (D. C. Chan, et al, Cell 89, 263-273 (1997)).
• each peptide region was extended (compared with N36 and C34) by three residues on its N-terminus and one residue on its C-terminus, generating the final N40 and C38 segments (representing residues 543-582 and 625-662 of HEV-1 HXB2 gpl60, respectively).
• Three N40 and two C38 segments were joined using a -GGSGG- linker after N40 and a -GSSGG- linker after C38. All constructs include an N- terminal Met for translation initiation.
• 5-Helix proteins Two distinct 5-Helix proteins that differ only at their C-termini were generated for this study: (i) His-tagged 5-Helix, which ends in -GG(H)6, and (ii) untagged 5-Helix, which ends in -GGR.
• 6-Helix a third construct, denoted 6-Helix, was generated in which the 5-Helix backbone was connected to the His-tagged C-peptide, C37-H6 (see Example 4), through a trypsin- cleavable linker (-GGR-) (see Figures 10 and 11 A-l 1C). All DNA constructs were assembled from PCR cassettes sequentially cloned into the pAED4 vector [D. S. Doering, P.
• E. coli XLl-Blue recA- strain, Stratagene
• All proteins were recombinantly expressed in E. coli strain RP3098 grown in 2xYT to an OD (590 nm) between 0.5-0.7 before induction with ⁇ PTG (0.4 mM) for 3 hours.
• Bacterial pellets were resuspended in Tris NaCl buffers (Qiaexpressionist booklet, March 1999, Qiagen) supplemented with Complete ⁇ DTA-free protease inhibitor tablets (Roche), and subsequently frozen at -20°C until the day of purification.
• His-tagged 5-Helix (generated from plasmid p-5HelixH6) was purified directly from the inclusion bodies resuspended in 8 M urea in TBS (50 mM Tris, pH 8.0, 100 mM NaCl) and 10 mM imidazole. The mixture was clarified by centrifugation (35,000 x g for 30 minutes) before binding to a Ni-NTA agarose (Qiagen) column at room temperature.
• Protein was eluted in 6 M urea/TBS/100 mM imidazole in 40 ml ( ⁇ 5 column volumes). The protein was refolded by slow dripping into a one liter, stirred solution of 20 mM Tris (pH 8.0) at room temperature. Refolded protem was then reconcentrated by passage over a Ni-NTA agarose column and eluted with 20 ml ( ⁇ 2 column volumes) of 100 mM imidazole in TBS.
• Untagged 5-Helix was produced via proteolysis of 6-Helix (see below) to generate a 5-Helix/C37-H6 complex. Following digestion with trypsin (1 :200 weight ratio in TBS at room temperature for 1 hour, Sigma), the 5-Helix/C37-H6 complex was bound to Ni-NTA agarose and washed extensively to remove excess trypsin. The beads were resuspended in 8 M GuHCl/TBS and heated (70°C) in order to denature the complex.
• the nonbinding fraction containing denatured 5-Helix, was sequentially dialyzed into 8 M urea/20 mM Tris, pH 8.0 (4 hours at room temperature) and 4 M urea/20 mM Tris, pH 8.0 (overnight at 4°C).
• the protein was loaded onto a DEAE column (Fastflow, Pharmacia) and a reverse urea gradient (4 M to 0 M urea in 20 mM Tris, pH 8.0) was run over 20 column volumes in 4 hours at room temperature.
• the protein was eluted from the DEAE resin using a NaCl gradient (0 to 300 mM) in 20 mM Tris, pH 8.0 (10 column volumes).
• 6-Helix (generated from plasmid p-6Helix) was purified directly from the soluble fraction ofthe bacterial lysate. The solution was passed over Ni-NTA agarose column and eluted with an imidazole gradient (10-250 mM) in TBS over 10 column volumes. For all proteins, monomers were separated from aggregates by gel filtration
• the 400 ⁇ l miniculture is incubated at 37 °C for 8 to 24 hours; fused cells (syncytia) will transcribe and translate ⁇ -galactosidase.
• the cells are fixed in gluteraldehyde and exposed to X-gal/Fe solution for one hour.
• Syncytia that contain ⁇ -galactosidase turn blue-green.
• 5-Helix demonstrates a potent inhibition of syncytia formation, with an IC 50 of 10-20 nM; in one assay the IC 50 was 13 nM. 6-Helix does not block fusion appreciably even at 1 ⁇ M concentrations.
• HEV human osteosarcoma
• HOS human osteosarcoma
• 5-Helix(D4) four highly conserved residues in the C-peptide binding site of His-tagged 5-Helix (Val549, Leu556, Gln563, and Val570) were mutated to Asp in the final (third) N40 segment.
• the construct [p-5Helix(D4)] was recombinantly expressed and purified in the same manner as the His-tagged 5-Helix.
• the slightly decreased stability of 5- Helix(D4) likely reflects the low helical propensity and charge ofthe Asp residues which, in this context, are placed within a predominantly hydrophobic groove on the surface of 5-Helix.
• His-tagged C-peptide C37-H6 is a His-tagged C-peptide ofthe following sequence:
• the peptide is derived from HIV-1 HXB2 residues 625-661 (underlined) and contains the entire C34 sequence (W628 to L661).
• C37-H6 is produced from the tryptic digestion of a recombinantly expressed construct, p4- NC 1.1, consisting of one N40 segment joined to C37-H6 through a -GGR- linker. Following expression, NCl.l is purified from the soluble fraction of bacterial lysates in the same manner as 6-Helix.
• C37-H6 Trypsin digestion (same conditions as for untagged 5-Helix) generates C37-H6, which is then purified to homogeneity by reverse phase HPLC using a Vydac C-18 column and a linear gradient of acetonitrile in water containing 0.1% trifluoroacetic acid. The identity of C37-H6 was confirmed by mass spectrometry (MALDI-TOF, PerSeptive). Like C34, C37-H6 is a potent inhibitor of HEV-1 membrane fusion, with an IC 50 ⁇ 1 nM in the cell-cell fusion assay. The data in Figures 2A-2D were generated using the untagged version of 5-
• the 5-Helix precipitation experiment (Fig. 2C) was performed in 20 ml TBS with 16 mM untagged 5-Helix, 30 mM His-tagged C37-H6, and/or 150 mM C34.
• the solution was added to 10 ml of Ni-NTA agarose and incubated at room temperature for 10 minutes. After the unbound supernatant was removed, the beads were washed twice with 1 ml TBS and then eluted with 500 mM imidazole.
• the Ni- bound and unbound samples were run on a 16.5% Tris-Tricine polyacrylamide gel (Biorad) and stained with Gel-code Blue (Pierce).
• HOS-CD4 cells HXB2 and UG024.2
• HOS-CD4-CCR5 cells JRFL and RW020.5
• Cells were obtained from the NIH AIDS Reagent Program (N. Landau).
• Figure 3A viral infectivity assays were performed in the standard 24-well format (D. C. Chan et al., Proc. Natl. Acad. Sci.

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