WO2008143944A2 - Methods of glycosylation and bioconjugation - Google Patents

Methods of glycosylation and bioconjugation Download PDF

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Publication number
WO2008143944A2
WO2008143944A2 PCT/US2008/006248 US2008006248W WO2008143944A2 WO 2008143944 A2 WO2008143944 A2 WO 2008143944A2 US 2008006248 W US2008006248 W US 2008006248W WO 2008143944 A2 WO2008143944 A2 WO 2008143944A2
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galnac
gainac
acceptor
nanoparticle
catalytic domain
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PCT/US2008/006248
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French (fr)
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WO2008143944A3 (en
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Pradman K. Qasba
Boopathy Ramakrishnan
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Government Of The Usa, As Represented By The Secretary, Department Of Health And Human Services
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    • 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
    • C12N9/00—Enzymes; Proenzymes; Compositions thereof; Processes for preparing, activating, inhibiting, separating or purifying enzymes
    • C12N9/10—Transferases (2.)
    • C12N9/1048—Glycosyltransferases (2.4)
    • C12N9/1051—Hexosyltransferases (2.4.1)

Definitions

  • the present invention relates to enzymes and methods that can be used to chemically link biologically important molecules.
  • the invention relates to a method which takes advantage of the polypeptide- ⁇ -N- acetylgalactosaminyltransferase enzyme, (ppGalNAc-T), which transfers N- acetylgalactosamine sugar (GaINAc) from UDP- ⁇ -GalNAc to an acceptor polypeptide substrate.
  • ppGalNAc-T polypeptide- ⁇ -N- acetylgalactosaminyltransferase enzyme
  • GaINAc N- acetylgalactosamine sugar
  • acceptor polypeptide substrate has been engineered as a fusion peptide either at the C- terminus or N-terminus of a non-glycoprotein of interest, and this fusion peptide moiety has been used as an acceptor substrate for ppGalNAc-T.
  • the method is of particular use to promote the chemical linkage of biologically important molecules that have previously been difficult to link.
  • Eukaryotic cells express several classes of oligosaccharides attached to proteins or lipids.
  • Animal glycans can be N-linked via B-GIcNAc to Asn (N-glycans), O-linked via -GaINAc to Ser/Thr (O-glycans), or can connect the carboxyl end of a
  • Beta (l,4)-galactosyltransferase I catalyzes the transfer of galactose from the donor, UDP-galactose, to an acceptor, N-acetylglucosamine, to form a galactose- .beta.(l,4)-N-acetylglucosamine bond, and allows galactose to be linked to an N- acetylglucosamine that may itself be linked to a variety of other molecules. Examples of these molecules include other sugars and proteins.
  • the reaction can be used to make many types of molecules having great biological significance.
  • galactose-beta (l,4)-N-acetylglucosamine linkages are important for many recognition events that control how cells interact with each other in the body, and how cells interact with pathogens.
  • numerous other linkages of this type are also very important for cellular recognition and binding events as well as cellular interactions with pathogens, such as viruses. Therefore, methods to synthesize these types of bonds have many applications in research and medicine to develop pharmaceutical agents and improved vaccines that can be used to treat disease.
  • Monoclonal antibodies coupled with toxic proteins, drugs and radioisotopes are an emerging strategy in the diagnosis and treatment of disease. However, various methods are being used in conjugating antibodies with the cargo molecule with mixed success.
  • the primary amine groups present on the surface of the protein molecule are used for conjugation, however, since every lysine residue present on the protein molecule would be reactive, this method results in undesirable heterogeneous conjugation and subsequent loss of antibody activity.
  • free Cys residue either naturally present or an engineered in the protein molecule, is widely used for conjugation. Since the freely exposed Cys residue being highly reactive in basic pH, it requires special requirements in handing these protein molecules. It has long been demonstrated that the sugar moieties present on the glycoproteins, for example, IgG, can be used as a chemical handle for such conjugation. Often, to the heterogeneous nature of the glycan moiety on the recombinant glycoprotein the result is a poor coupling.
  • the instant invention provides enzymes and methods that can be used to promote the
  • ppGalNAc-T polypeptide- ⁇ -N- acetylgalactosaminyltransferase enzyme
  • GaINAc N- acetylgalactosamine sugar
  • the invention provides an isolated catalytic domain from a polypeptidyl- ⁇ -N-acetylgalactosaminyltransferase (pp-GalNAc-T) that transfers N-acetylgalactosamine (GaINAc) or a GaINAc analogue from UDP- ⁇ - GaINAc to one or more Ser or Thr residues of an acceptor polypeptide, wherein the isolated catalytic domain comprises SEQ ID NO: 1.
  • the pp-GalNAc-T transfers GaINAc or a GaINAc analogue in an ⁇ -configuration.
  • the pp-GalNAc-T is mammalian. In another embodiment, the pp-GalNAc-T is pp-GalNAc-T2.
  • the pp-GalNAc-T comprises a catalytic domain (CD) and lectin domain (LD).
  • the invention features an isolated nucleic acid segment encoding the catalytic domain of from a polypeptidyl- ⁇ -N- acetylgalactosaminyltransferase (pp-GalNAc-T) according to the above-described aspect that comprises SEQ ID NO: 2.
  • pp-GalNAc-T polypeptidyl- ⁇ -N- acetylgalactosaminyltransferase
  • a vector or expression cassette comprises the nucleic acid of the above-mentioned embodiment.
  • a cell comprises the vector or expression cassette.
  • the invention features a method for engineering a glycoprotein from a biological substrate comprising attaching to the C-terminal or N-
  • the invention features a method for glycosylating a biological substrate for use in glycoconjugation comprising attaching to the C- terminal or N-terminal end of a biological substrate an acceptor polypeptide, and using the biological substrate with the acceptor polypeptide as an acceptor substrate for a pp-GalNAc-T, and transferring one or more GaINAc residue or GaINAc analogue sugars to the acceptor polypeptide, and thereby glycoslyating the biological substrate for use in glycoconjugation.
  • the acceptor polypeptide is a nanoparticle.
  • the biological substrate is a nanoparticle.
  • the invention features a method for engineering a nanoparticle comprising attaching to the C-terminal or N-terminal end of a biological substrate a nanoparticle, and using the biological substrate with the nanoparticle as an acceptor substrate for a pp-GalNAc-T, and transferring one or more GaINAc residue or GaINAc analogue sugars to the acceptor substrate, thereby engineering a nanoparticle.
  • the nanoparticle is a multivalent nanoparticle.
  • the biological substrate is selected from the group consisting of: a non-glycoprotein, an oligopeptide and a biological matrix.
  • the GaINAc residue or GaINAc analogue sugars are transferred to one or more Ser or Thr residues of the acceptor polypeptide.
  • the non-glycoprotein or oligopeptide is a bioactive agent.
  • the bioactive agent is any bioactive agent carrying a linker sequence with a functional coupling group.
  • the bioactive agent is selected from the group consisting of: single chain antibodies, bacterial toxins, growth factors, therapeutic agents, and contrast agents.
  • the nanoparticle comprises a magnetic resonance agent.
  • the acceptor polypeptide comprises at least 10 amino acids. In a further embodiment, the acceptor polypeptide comprises at least 15 amino acids. In yet a further embodiment, the acceptor polypeptide is selected from SEQ ID NO: 3 (GAGGPIMAAATPAPAAK) or SEQ ID NO: 4 (AGGPIMAATPAPAAK).
  • the acceptor polypeptide is glycosylated at one or more sites. In a further embodiment, the acceptor polypeptide is glycosylated at a serine or threonine residue.
  • the GaINAc analogue comprises an azido group. In another embodiment, the GaINAc analogue comprises a keto group.
  • the pp-GalNAc-T transfers the GaINAc analogue to one or more Ser or Thr residues of the acceptor polypeptide.
  • the invention features a method of engineering a nanoparticle where the nanoparticle is used to treat a subject suffering from a disease or disorder.
  • the nanoparticle is used in magnetic resonance imaging.
  • the invention features a method for producing an active pp-
  • GaINAc-T comprising expressing pp-GalNAc-T in E.coli, isolating, washing and dissolving inclusion bodies from E.coli, performing S-sulfonation of the inclusion bodies in the presence of sodium sulfite, and then folding the inclusion bodies, wherein active pp-GalNAc-T is produced.
  • the step of folding the inclusion bodies comprises using oxido shuffling agents, 0.5M arginine HCl, 10% glycerol, and 1OmM lactose.
  • the active pp-GalNAc-T comprises a catalytic domain and lectin domain. In another embodiment the active pp-GalNAc-T comprises a catalytic domain. In a further embodiment, the active pp-GalNAc-T transfers GaINAc-T from
  • the active pp-GalNAc-T comprising a catalytic domain and lectin domain is more active compared to pp-GalNAc-T comprising a catalytic domain.
  • the folding occurs in vitro.
  • GaINAc-T is pp-GalNAc-T2.
  • kits comprising the isolated catalytic domain from a polypeptidyl- ⁇ -N-acetylgalactosaminyltransferase (pp- GaINAc-T) of any of the above-mentioned aspects, along with instructions for us.
  • the kits further comprise an acceptor.
  • kits further comprise a biological substrate or bioactive agent of any of the above-mentioned aspects.
  • FIG. 1 illustrates the catalytic reaction of polypeptide- ⁇ -N- acetylgalactosaminyltransferase (ppGalNAc-T).
  • ppGalNAc-T polypeptide- ⁇ -N- acetylgalactosaminyltransferase
  • Figure 2 is a protein gel showing the generation of active ppGalNAc-T2.
  • the left lane shows the insoluble inactive inclusion body of ppGalNAc-T2 produced in E. coli.
  • the middle and right lanes show in vitro folded active ppGalNAc-T2, 1 ⁇ g and 0.5 ⁇ g, respectively.
  • Nearly 2 mg active protein purified from a Ni-column is obtained from one-liter folding solution from the inclusion bodies produced from a liter of bacterial culture.
  • Figure 3 (a - c) is a panel of graphs and schematics.
  • Thrombin site shown as cutting scissors.
  • the hexagons indicate the potential O-glycosylation residues for the ppGalNAc-T2.
  • the fusion peptides are designed based on the acceptor substrates of ppGalNAc-T2.
  • the mass spectrum (MALDI- TOPS) of the Thrombin cut non-glycosylated and glycosylated peptide are shown in the left and right side of the arrow, respectively, in panels (a) (b) and (c).
  • Figure 4 illustrates the GST-tag protein with only a single Thr residue but no Ser residue in its fusion peptide is used for the transfer of (a) 2-keto-Gal and (b) GaINAz sugars from their respective UDP-derivatives.
  • the mass spectrum (MALDI- TOPS) of the non-glycopeptide and glyco-peptide released by Thrombin digestion are shown in the left and right side of the arrows, respectively.
  • the proteins in the Western Blotting were visualized using the streptavadin-horseradish peroxidase (HRP) chemiluminescence technique.
  • HRP streptavadin-horseradish peroxidase
  • Figure 5 is a schematic drawing illustrating that non-glycoproteins can be glycosylated by engineering a peptide sequence in the protein that can be glycosylated with the modified sugar, so that they can also be cross linked to the other glycoproteins such as IgG, with similar modified sugars.
  • Figure 6 is a schematic showing that the non-glycoprotein with the tag at the C- terminal end can be glycosylated with the GaINAc analogue sugars having a unique chemical handle.
  • Figure 7 is an outline of the procedure for producing an active pp-GalNAc-T.
  • Figure 8 is a schematic showing a polypeptide chain, containing uniform repeats of lysine (K) residues followed by repeat fusion peptide sequence containing Threonine (Thr) residues, can be used as a carrier molecule.
  • the instant invention provides isolated catalytic domains from polypeptidyl- ⁇ -N-acetylgalactosaminyltransferase (pp-GalNAc-T).
  • the invention provides methods for engineering a glycoprotein from a biological substrate, and methods for glycosylating a biological substrate for use in glycoconjugation. Also included in the invention are diagnostic and therapeutic uses.
  • the invention further provides in vitro folding methods to produce active enzyme.
  • a cell includes a plurality of cells, including mixtures thereof.
  • a nucleic acid molecule includes a plurality of nucleic acid molecules.
  • compositions and methods include the recited elements, but do not exclude other elements.
  • Consisting essentially of, when used to define compositions and methods, shall mean excluding other elements of any essential significance to the combination. Thus, a composition consisting essentially of the elements as defined herein would not exclude trace contaminants from the isolation and purification method and pharmaceutically acceptable carriers, such as phosphate buffered saline, preservatives, and the like.
  • Consisting of shall mean excluding more than trace elements of other ingredients and substantial method steps for administering the compositions of this invention. Embodiments defined by each of these transition terms are within the scope of this invention.
  • acceptor is meant to refer to a molecule or structure onto which a donor is actively linked through action of a catalytic domain of a galactosyltransferase, or mutant thereof.
  • acceptors include, but are not limited to, carbohydrates, glycoproteins, glycolipids.
  • the acceptor polypeptide comprises Ser and/ or Thr residues.
  • the acceptor polypeptide can comprise, in preferred embodiments repeating consensus sequences, for example, repeating Ser or Thr residues.
  • the acceptor polypeptide can be glycosylated at one or more sites.
  • the acceptor peptide is SEQ ID NO: 3 (GAGGPIMAAATPAPAAK).
  • the acceptor peptide is SEQ ID NO: 4 (AGGPIMAATPAPAAK).
  • catalytic domain is meant to refer to an amino acid segment which folds into a domain that is able to catalyze the linkage of a donor to an acceptor.
  • a catalytic domain may be from, but is not limited to, human polypeptidyl-a- N-acetylgalactosaminyltransferase II (ppGalNAc-T2) (SEQ ID NO: 1).
  • the pp- GaINAc-T enzymes comprise 17-19 family members. Each member transfers GaINAc in ⁇ -configuration. Sequences of pp-GalNAc-T family members from human and other species are known and the DNA clones available commercially.
  • a catalytic domain may have an amino acid sequence found in a wild-type enzyme, or may have an amino acid sequence that is different from a wild-type sequence.
  • donor is meant to refer to a molecule that is actively linked to an acceptor molecule through the action of a catalytic domain of a polypeptidyl-a-N- acetylgalactosaminyltransferase, or mutant thereof.
  • a donor molecule can include a sugar, or a sugar derivative.
  • donors include, but are not limited to, UDP- ⁇ -acetylgalactosamine, UDP- ⁇ -GalNAz, UDP- ⁇ -2-keto-Gal, UDP- ⁇ -galactose, UDP-mannose, UDP-N-acetylglucosamine, UDP-glucose, GDP-mannose, UDP- glucuronic acid, GDP-Fucose, and CMP-N-acetylneuraminic acid.
  • Donors include sugar derivatives that include active groups, such as cross-linking agents or labeling agents. Accordingly, oligosaccharides may be prepared according to the methods of the invention that include a sugar derivative having a desired characteristic.
  • expression cassette refers to a DNA sequence capable of directing expression of a particular nucleotide sequence in an appropriate host cell, comprising a promoter operably linked to the nucleotide sequence of interest that is operably linked to termination signals. It also typically comprises sequences required for proper translation of the nucleotide sequence.
  • the expression of the nucleotide sequence in the expression cassette may be under the control of a constitutive promoter or of an inducible promoter that initiates transcription only when the host cell is exposed to some particular external stimulus.
  • the promoter can also be specific to a particular tissue or organ or stage of development.
  • N-acetylgalactosaminyltransferase refers to enzymes substantially homologous to, and having substantially the same biological activity as, the enzyme coded for by the nucleotide sequence depicted in SEQ ID NO: 2 and the amino acid sequence depicted in SEQ ID NO: 1.
  • This definition is intended to encompass natural allelic variations in the pp-GalNAcT sequence, and all references to GaINAcT, and nucleotide and amino acid sequences thereof are intended to encompass such allelic variations, both naturally-occurring and man-made.
  • the production of proteins such as the enzyme GaINAcT from cloned genes by genetic engineering is well known and described in, for example, U.S. Pat. No. 4,761,371, incorporated by reference in its entirety herein.
  • the GaINAcT enzyme may be synthesized in host cells transformed with vectors containing DNA encoding the GaINAcT enzyme.
  • a vector is a replicable DNA construct. Vectors are used herein either to amplify DNA encoding the GaINAcT enzyme and/or to express DNA which encodes the GaINAcT enzyme.
  • An expression vector is a replicable DNA construct in which a DNA sequence encoding the GaINAcT enzyme is operably linked to suitable control sequences capable of effecting the expression of the GaINAcT enzyme in a suitable host. The need for such control sequences will vary depending upon the host selected and the transformation method chosen.
  • control sequences include a transcriptional promoter, an optional operator sequence to control transcription, a sequence encoding suitable mRNA ribosomal binding sites, and sequences which control the termination of transcription and translation.
  • Amplification vectors do not require expression control domains. All that is needed is the ability to replicate in a host, usually conferred by an origin of replication, and a selection gene to facilitate recognition of transformants.
  • oligosaccharide and “polysaccharide” are used interchangeably herein. These terms refer to saccharide chains having two or more linked sugars. Oligosaccharides and polysaccharides may be homopolymers and heteropolymers having a random sugar sequence or a preselected sugar sequence. Additionally, oligosaccharides and polysaccharides may contain sugars that are normally found in nature, derivatives of sugars, and mixed polymers thereof.
  • polypeptides and proteins are used interchangeably herein. Polypeptides and proteins can be expressed in vivo through use of prokaryotic or eukaryotic expression systems. Many such expressions systems are known in the art and are commercially available. (Clontech, Palo Alto, Calif.; Stratagene, La Jolla, Calif). Examples of such systems include, but are not limited to, the T7-expression system in prokaryotes and the bacculovirus expression system in eukaryotes. Polypeptides can also be synthesized in vitro, e.g., by the solid phase peptide synthetic method or by in vitro transcription/translation systems. Such methods are described, for example, in U.S. Pat. Nos.
  • polypeptides can be further purified by fractionation on immunoaffinity or ion-exchange columns; ethanol precipitation; reverse phase HPLC; chromatography on silica or on an anion-exchange resin such as DEAE; chromatofocusing; SDS-PAGE; ammonium sulfate precipitation; gel filtration using, for example, Sephadex G-75; or ligand affinity chromatography.
  • glycosyltransferases A large family of enzymes, called glycosyltransferases, is involved in the synthesis of complex oligosaccharides of glycoconjugates. These enzymes have been
  • Substitution of amino acid residues located in the donor binding site of beta.(l,4)- galactosyltransferase I provides greater flexibility and decreased steric hindrance, and thus allows glucose or GaINAc to be bound and chemically bonded to N- acetylglucosamine.
  • Such mutations provide for broadened donor binding, such as binding of glucose or GaINAc, while still preserving interaction with amino acid residues active during catalytic bond formation between the donor and the acceptor.
  • the instant invention demonstrates that the polypeptidyl-a-N- acetylgalactosaminyltransferase II (ppGalNAc-T2), which transfers N- acetylgalactosamine (GaINAc) from UDP- ⁇ -GalNAc to one or more Ser and/ or Thr residue of an acceptor polypeptide, can be used to glycosylate a peptide sequence engineered at the C-terminal or N-terminal end of a non-glycoprotein.
  • the pp- GaINAc-T enzymes comprise 17-19 family members.
  • ppGalNAcTs There are approximately 24 ppGalNAcTs, with othologs in higher eukaryotes that demonstrate about 90 - 98% sequence homology across species (23). Approximately 21 different ppGalNAcT isoforms have been cloned across different species (23). All of the ppGalNAc-T's show a conservation in their structure, characterized by an N-terminal cytosolic tail, a type II transmembrane domain, a variable stem region, a catalytic domain (CD) (GTl) a Gal/ GaINAc recognition domain, and a C-terminal lectin domain (LD).
  • CD catalytic domain
  • GTl catalytic domain
  • LD C-terminal lectin domain
  • the ppGalNAc-T enzymes transfer GaINAc in an ⁇ -configuration, from UDP- ⁇ -GalNAc, to a Ser and orThr residue of a peptide sequence which is variable in sequence. Some of these enzymes require GaINAc to be present on the neighboring Thr and/ or Ser residue in the polypeptide sequence.
  • the universal nucleotide sugar donor for the ppGalNAc-T's is UDP-GaINAc.
  • synthetic UDP- GaINAc analogues are useful as in vitro substrates for ppGalNAc-Ts.
  • UDP-GaINAc analogue is suitable for use in the invention; however preferred examples include UDP-GaINAc analogues with keto or azido groups, for example UDP-GaINAz, prefereably at the p 2-position, e.g. 2-keto.
  • the soluble domain of ppGalNAc-T2 was engineered in E. coli and an in vitro folding method was developed from inclusion bodies to make milligram quantities of active ppGalNAc-T2 from a liter of bacterial culture.
  • Glutathione-S-transferase was expressed in E.coli with a C-terminal 17 amino
  • the ppGalNAc-T2 enzyme not only transfers GaINAc from UDP-GaINAc to the Thr residue in the fusion peptide, but also transfers modified galactose, such as 2-keto-galactose or GaINAz, from their respective UDP- sugars. Furthermore, this modified sugar moiety is readily available for chemical modification such as biotinylation.
  • the invention described herein demonstrates a novel method to glycosylate, with ppGalNAc-T2 and C-2 modified UDP-GaINAc, important biological molecules; such as, single chain antibodies, growth factors or bacterial toxins, with engineered peptide sequences at the C-terminus of the molecule.
  • the peptide sequences at the C-terminus of the molecule can be 10, 15, 17 amino acids in length.
  • the chemical handle at the C-2 of galactose is used for conjugation and assembly of bio-nanoparticles and for the formulation of immuno-liposome for the targeted drug delivery system.
  • ppGalNAc-T can transfer GaINAc analogue sugars with a unique chemical handle, such as GaINAz (2-azio-GalNAc), to the acceptor polypeptide (17). Therefore, it is possible to glycosylate a non- glycoprotein with ppGalNAc-T with a modified sugar carrying a unique chemical handle that can be used for conjugation. Furthermore, in the present study the soluble form of ppGalNAc-T2 was expressed in E. coli and a method of in vitro folding of the protein from inclusion bodies was set up to make large quantities of active ppGalNAc-T2.
  • Glutathione-S-transferase (GST) protein is used as a model system for engineering the fusion peptide sequence, with a single Thr residue, at its C-terminus which is the acceptor substrate for ppGalNAc-T2.
  • ppGalNAc-T2 not only transfers GaINAc or GaINAz, but also 2-keto-Gal to the single Thr residue present in the tag peptide of the GST-tag fusion protein, demonstrating that this method can be used for glycosylating non-glycoproteins, for example, but not limited to, ScFv and bacterial toxins, growth factors and other bioactive molecules.
  • the isolated catalytic domain from pp-GalNAc preferably transfers GaINAc in ⁇ configuration.
  • the isolated catalytic domain from a pp-GalNAc-T comprises a catalytic domain and lectin domain (LD), as shown in SEQ ID NO: 1, below:
  • pp-GalNAc-T The corresponding nucleic acid sequence encoding the catalytic domain from a polypeptidyl- ⁇ -N-acetylgalactosaminyltransferase (pp-GalNAc-T) comprises SEQ ID NO: 2, shown below:
  • pp-GalNAc-T family members from human and other species are known, and the DNA clones are commercially available from, for example, Open Biosources.
  • the methods of the invention are amenable to use with any pp-GalNAc- T2.
  • any pp-GalNAc is meant from any species, or pp-GalNAc-Tl or pp-GalNAc- T2.
  • Peptides of the invention include isolated catalytic domains, full length polypeptidyl-a-N-acetylgalactosaminyltransferase enzymes containing a catalytic domain of the invention, as well as recombinant polypeptides or a protein linked to additional amino acids.
  • Such polypeptides may be expressed from DNA constructs and expression cassettes that are produced through use of recombinant methods. Such methods have been described. Sambrook et al., Molecular Cloning: A Laboratory Manual, 3rd edition, Cold Spring Harbor Press, Cold Spring Harbor, N. Y. (2001).
  • polypeptidyl- ⁇ -N-acetylgalactosaminyltransferase enzymes containing a catalytic domain of the invention may be produced in soluble form. Methods that may be used to produce such soluble enzymes have been described (U.S. Pat. No. 5,032,519). Briefly, a hydrophobic transmembrane anchor region of a polypeptidyl- ⁇ - N-acetylgalactosaminyltransferase is removed to produce an enzyme that is in soluble form.
  • catalytic domain from a polypeptidyl- ⁇ -N- acetylgalactosaminyltransferase enzymes containing a catalytic domain of the invention may be produced such that they are anchored in the membrane of a cell that expresses the polypeptidyl- ⁇ -N-acetylgalactosaminyltransferase.
  • Such enzymes may be produced that are anchored in the membranes of prokaryotic and eukaryotic cells. Methods to produce such enzymes have been described (U.S. Pat. No. 6,284,493).
  • the signal and transmembrane sequences of the polypeptidyl- ⁇ -N-acetylgalactosaminyltransferase are replaced by a bacterial signal sequence, capable of effecting localization of the fusion protein to the outer membrane.
  • Suitable signal sequences include, but are not limited to those from the major E. coli lipoprotein Lpp and lam B.
  • membrane spanning regions from Omp A, Omp C, Omp F or Pho E can be used in a tripartite fusion protein to direct proper insertion of the fusion protein into the outer membrane.
  • Any prokaryotic cells can be used in accordance with the present invention including but not limited to E. coli, Bacillus sp., and Pseudomonas sp. as representative examples.
  • the present invention is also applicable for use with eukaryotic cells resulting in cell surface expression of polypeptidyl- ⁇ -N-acetylgalactosaminyltransferase in known culturable eukaryotic cells including but not limited to yeast cells, insect cells, Chinese hamster ovary cells (CHO cells), mouse L cells, mouse A9 cells, baby hamster kidney cells, C 127 cells, COS cells, Sf9 cells, and PC8 cells.
  • transmembrane domain of the polypeptidyl- ⁇ -N- acetylgalactosaminyltransferase is replaced by the transmembrane domain of a plasma membrane protein.
  • the transmembrane domain of any resident plasma membrane protein will be appropriate for this purpose.
  • P/IGF-II receptor, LDL receptor or the transferrin receptor are representative examples.
  • the pp-GalNAc-T can be pp-GalNAc- T2.
  • the present invention provides isolated nucleic acid segments that encode catalytic domains of pp-GalNAc-T.
  • Nucleic acid sequences encoding human pp- GaINAc-TII (SEQ ID NO: 2), as well as other pp-GalNAc-T from other organisms are available. These nucleic acid sequences can be modified to encode the catalytic domains and amino acid segments of the invention through use of well-known techniques (Sambrook et al., Molecular Cloning: A Laboratory Manual, 3rd edition, Cold Spring Harbor Press, Cold Spring Harbor, N. Y. (2001)).
  • nucleic acid sequence encoding human pp-GalNAc-T II (SEQ ID NO: 2) can be inserted into an expression vector such that an amino acid segment corresponding to the catalytic domain of human pp-GalNAc-TII (SEQ ID NO: 1) is expressed upon transformation of a cell with the expression vector.
  • the nucleic acid segments of the invention may be optimized for expression in select cells. Codon optimization tables are available. Harlow and Lane, Antibodies: A Laboratory Manual, Cold Spring Harbor Laboratory Press, 1988.
  • a vector may include, but is not limited to, any plasmid, phagemid, F-factor, virus, cosmid, or phage in double or single stranded linear or circular form, which may or may not be self-transmissible or mobilizable.
  • the vector can also transform a prokaryotic or eukaryotic host either by integration into the cellular genome or exist extrachromosomally (e.g. autonomous replicating plasmid with an origin of replication).
  • the nucleic acid segment in the vector is under the control of, and operably linked to, an appropriate promoter or other regulatory elements for transcription in vitro or in a host cell such as a eukaryotic cell or microbe, e.g. bacteria.
  • the vector may be a bi-functional expression vector which functions in
  • genomic DNA this may contain its own promoter or other regulatory elements and in the case of cDNA this may be under the control of a promoter or other regulatory sequences for expression in a host cell.
  • shuttle vectors by which is meant a DNA vehicle capable, naturally or by design, of replication in two different host organisms, which may be selected from bacteria and eukaryotic cells (e.g. mammalian, yeast or fungal).
  • eukaryotic cells e.g. mammalian, yeast or fungal.
  • the vector may also be a cloning vector which typically contains one or a small number of restriction endonuclease recognition sites at which nucleic acid segments can be inserted in a determinable fashion. Such insertion can occur without loss of essential biological function of the cloning vector.
  • a cloning vector may also contain a marker gene that is suitable for use in the identification and selection of cells transformed with the cloning vector. Examples of marker genes are tetracycline resistance, hygromycin resistance or ampicillin resistance. Many cloning vectors are commercially available (Stratagene, New England Biolabs, Clonetech).
  • the nucleic acid segments of the invention may also be inserted into an expression vector.
  • an expression vector typically contains (1) prokaryotic DNA elements coding for a bacterial replication origin and an antibiotic resistance gene to provide for the amplification and selection of the expression vector in a bacterial host; (2) regulatory elements that control initiation of transcription such as a promoter; and (3) DNA elements that control the processing of transcripts such as introns, transcription termination/ polyadenylation sequence.
  • a vector into which the nucleic acid segment is to be inserted is treated with one or more restriction enzymes (restriction endonuclease) to produce a linearized vector having a blunt end, a "sticky" end with a 5' or a 3' overhang, or any combination of the above.
  • restriction enzymes restriction endonuclease
  • the vector may also be treated with a restriction enzyme and subsequently treated with another modifying enzyme, such as a polymerase, an exonuclease, a phosphatase or a kinase, to create a linearized vector that has characteristics useful for ligation of a nucleic acid segment into the vector.
  • a restriction enzyme such as a polymerase, an exonuclease, a phosphatase or a kinase
  • the nucleic acid segment that is to be inserted into the vector is treated with one or more restriction enzymes to create a linearized segment having a blunt end, a
  • the nucleic acid segment may also be treated with a restriction enzyme and subsequently treated with another DNA modifying enzyme.
  • DNA modifying enzymes include, but are not limited to, polymerase, exonuclease, phosphatase or a kinase, to create a polynucleic acid segment that has characteristics useful for ligation of a nucleic acid segment into the vector.
  • the treated vector and nucleic acid segment are then ligated together to form a construct containing a nucleic acid segment according to methods known in the art (Sambrook, 2002). Briefly, the treated nucleic acid fragment and the treated vector are combined in the presence of a suitable buffer and ligase. The mixture is then incubated under appropriate conditions to allow the ligase to ligate the nucleic acid fragment into the vector. It is preferred that the nucleic acid fragment and the vector each have complimentary "sticky" ends to increase ligation efficiency, as opposed to blunt-end ligation. It is more preferred that the vector and nucleic acid fragment are each treated with two different restriction enzymes to produce two different complimentary "sticky” ends. This allows for directional ligation of the nucleic acid fragment into the vector, increases ligation efficiency and avoids ligation of the ends of the vector to reform the vector without the inserted nucleic acid fragment.
  • Suitable prokaryotic vectors include but are not limited to pBR322, pMB9, pUC, lambda bacteriophage, ml 3 bacteriophage, and Bluescript.RTM..
  • Suitable eukaryotic vectors include but are not limited to PMSG, pAV009/A+, PMTO10/A+, pMAM neo-5, bacculovirus, pDSVE, YIP5, YRPl 7, YEP. It will be clear to one of ordinary skill in the art which vector or promoter system should be used depending on which cell type is used for a host cell.
  • the invention also provides expression cassettes which contain a control sequence capable of directing expression of a particular nucleic acid segment of the invention either in vitro or in a host cell.
  • the expression cassette is an isolatable unit such that the expression cassette may be in linear form and functional in in vitro transcription and translation assays.
  • the materials and procedures to conduct these assays are commercially available from Promega Corp. (Madison, Wis.).
  • an in vitro transcript may be produced by placing a nucleic acid segment
  • the expression cassette can be incorporated into a vector allowing for replication and amplification of the expression cassette within a host cell or also in vitro transcription and translation of a nucleic acid segment.
  • Such an expression cassette may contain one or a plurality of restriction sites allowing for placement of the nucleic acid segment under the regulation of a regulatory sequence.
  • the expression cassette can also contain a termination signal operably linked to the nucleic acid segment as well as regulatory sequences required for proper translation of the nucleic acid segment. Expression of the nucleic acid segment in the expression cassette may be under the control of a constitutive promoter or an inducible promoter, which initiates transcription only when the host cell is exposed to some particular external stimulus.
  • the expression cassette may include in the 5'-3' direction of transcription, a transcriptional and translational initiation region, a nucleic acid segment and a transcriptional and translational termination region functional in vivo and/or in vitro.
  • the termination region may be native with the transcriptional initiation region, may be native with the nucleic acid segment, or may be derived from another source. Numerous termination regions are known in the art. Guerineau et al., MoI. Gen.
  • the regulatory sequence can be a nucleic acid sequence located upstream (5' non-coding sequences), within, or downstream (3' non-coding sequences) of a coding sequence, and which influences the transcription, RNA processing or stability, or translation of the associated coding sequence.
  • Regulatory sequences can include, but are not limited to, enhancers, promoter and repressor binding sites, translation leader sequences, introns, and polyadenylation signal sequences. They may include natural and synthetic sequences as well as sequences that may be a combination of synthetic and natural sequences. While regulatory sequences are not limited to promoters, some
  • useful regulatory sequences include constitutive promoters, inducible promoters, regulated promoters, tissue-specific promoters, viral promoters and synthetic promoters.
  • a promoter is a nucleotide sequence that controls expression of the coding sequence by providing the recognition for RNA polymerase and other factors required for proper transcription.
  • a promoter includes a minimal promoter, consisting only of all basal elements needed for transcription initiation, such as a TATA-box and/or initiator that is a short DNA sequence comprised of a TATA-box and other sequences that serve to specify the site of transcription initiation, to which regulatory elements are added for control of expression.
  • a promoter may be inducible. Several inducible promoters have been reported (Current Opinion in Biotechnology, 7:168 (1996)).
  • Examples include the tetracycline repressor system, Lac repressor system, copper- inducible systems, salicylate-inducible systems (such as the PRIa system). Also included are the benzene sulphonamide- (U.S. Pat. No. 5,364,780) and alcohol- (WO 97/06269 and WO 97/06268) inducible systems and glutathione S-transferase promoters. In the case of a multicellular organism, the promoter can also be specific to a particular tissue or organ or stage of development.
  • An enhancer is a DNA sequence which can stimulate promoter activity and may be an innate element of the promoter or a heterologous element inserted to enhance the level or tissue specificity of a promoter. It is capable of operating in both orientations (normal or flipped), and is capable of functioning even when moved either upstream or downstream from the promoter. Both enhancers and other upstream promoter elements bind sequence-specific DNA-binding proteins that mediate their effects.
  • the expression cassette can contain a 5' non-coding sequence which is a nucleotide sequence located 5' (upstream) to the coding sequence.
  • the expression cassette may also contain a 3' non-coding sequence, which is a nucleotide sequence, located 3' (downstream) to a coding sequence and includes
  • the invention also provides a construct containing a vector and an expression cassette.
  • the vector may be selected from, but not limited to, any vector previously described. Into this vector may be inserted an expression cassette through methods known in the art and previously described (Sambrook et al., 1989).
  • the regulatory sequences of the expression cassette may be derived from a source other than the vector into which the expression cassette is inserted.
  • a construct containing a vector and an expression cassette is formed upon insertion of a nucleic acid segment of the invention into a vector that itself contains regulatory sequences.
  • an expression cassette is formed upon insertion of the nucleic acid segment into the vector.
  • Vectors containing regulatory sequences are available commercially and methods for their use are known in the art (Clonetech, Promega, Stratagene).
  • the expression cassette, or a vector construct containing the expression cassette may be inserted into a cell.
  • the expression cassette or vector construct may be carried eposomally or integrated into the genome of the cell.
  • a variety of techniques are available and known to those skilled in the art for introduction of constructs into a cellular host. Transformation of bacteria and many eukaryotic cells may be accomplished through use of polyethylene glycol, calcium chloride, viral infection, phage infection, electroporation and other methods known in the art. Other transformation methods are available to those skilled in the art, such as direct uptake of foreign DNA constructs (see EP 295959), techniques of electroporation (Fromm et al.
  • an expression vector contains (1) prokaryotic DNA elements coding for a bacterial origin of
  • reporter genes include .beta.-galactosidase, chloramphenicol acetyl transferase, luciferase, green fluorescent protein (GFP) and the like.
  • the methods comprise attaching to the C-terminal or N-terminal end of a biological substrate an acceptor polypeptide, and using the biological substrate with the acceptor polypeptide as an acceptor substrate for a pp-GalNAc-T, and then transferring one or more GaINAc residue or GaINAc analogue sugars to the acceptor polypeptide, and thereby engineering a glycoprotein from a biological substrate.
  • Figure 7 presents a general outline of the method.
  • Figure 8 also presents a schematic detailing a method of making, for example, a multivalent nanoparticle or multiple linked nanoparticles wherein an acceptor sequence comprises, for example, multiple Ser or Thr residues for sugar transfer.
  • the methods comprise attaching to the C-terminal or N- terminal end of a biological substrate an acceptor polypeptide, and using the biological substrate with the acceptor polypeptide as an acceptor substrate for a pp- GaINAc-T, and transferring one or more GaINAc residue or GaINAc analogue sugars to the acceptor polypeptide, and thereby glycoslyating the biological substrate for use in glycoconjugation.
  • the GaINAc residue or GaINAc analogue sugars are transferred to a Ser and/ or Thr residue of the acceptor polypeptide.
  • the GST-tag protein with only a Thr and/ or Ser residue in its fusion peptide is used for the transfer of GaINAc or GaINAc analogue sugars, for example but not limited to, 2-keto-Gal and GaINAz sugars, from their respective
  • the acceptor polypeptide comprises repeating consensus sequences.
  • the acceptor polypeptide comprises repeating Ser and/ or Thr residues that can be used for the transfer of GaINAc or GaINAc analogue sugars.
  • the biological substrate can be selected from, but not limited to, a non-glycoprotein, an oligopeptide and any biological matrix. Any biological matrix that is suitable for attachment of the acceptor polypeptide is envisioned for use in the methods of the invention.
  • the non-glycoprotein or oligo-peptide is a bioactive agent.
  • the bioactive agent can be any bioactive agent carrying a linker sequence with a functional coupling group.
  • bioactive agents include, but are not limited to single chain antibodies, bacterial toxins, growth factors, therapeutic agents, and contrast agents.
  • a therapeutic agent can be a chemotherapeutic agent, an anti-inflammatory agent, an antibacterial agent, or an antifungal agent.
  • Contrast agents include MRI contrast agents such as gadolinium-based agents.
  • the method includes an acceptor peptide.
  • the acceptor peptide is attached to the C-terminal or N-terminal end of a biological substrate.
  • the biological substrate with the acceptor polypeptide is used as an acceptor substrate for a pp-GalNAc-T, and then one or more GaINAc residue or GaINAc analogue sugars is transferred to the acceptor polypeptide, and thus a glycoprotein is engineered from a biological substrate.
  • the acceptor polypeptide comprises at least 10, 1 1, 12, 13, 14, 15,16, 17, 18, 19, or 20 amino acids. In other embodiments the acceptor polypeptide is glycosylated at one or more sites, wherein the one or more sites has a Thr or Ser residue, and the pp-GalNAc-T transfers the GaINAc or GaINAc analogue to one or more Ser and/ or Thr residues of the acceptor polypeptide.
  • the acceptor polypeptide is selected from, but not limited to, SEQ ID NO: 3 (GAGGPIMAAATPAPAAK) or SEQ ID NO: 4 (AGGPIMAATPAPAAK).
  • Oligosaccharide moieties of glycoconjugates are involved in many biological processes, and as such have been used as a tool for the delivery of ligands to specific sites and tissues.
  • Glycotargeting is the use of carbohydrate ligands to target protein receptors at the site of location, and was brought about in part by the discovery of the hepatic receptor, the asialoglycoprotein receptor (ASGPR), which binds to and internalizes the circulating glycoproteins or glycopeptides that have galactose or N- acetylgalactosamine residue at the nonreducing terminus of the oligosaccharide chain (Morell AG, Gregoriadis G, Scheinberg H, Hickman J, Ashwell G.
  • Glycotargeting has use, for example, in developing a targeted drug delivery system and in developing contrast agents for MRI.
  • the guiding molecules need to be conjugated with the biologically active agents in a site-specific manner.
  • glycosyltransferases The structural information available for glycosyltransferases makes it possible to design novel glycosyltransferases with broader and requisite donor specificities. As described herein, several mutant glycosyltransferases have been generated that can transfer a sugar residue with a chemically reactive functional group (e.g., 2-keto-Gal or GaINAz) from their UDP derivatives to the N-acetylglucosamine residue of glycoconjugates, such as to the oligosaccharide chain of IgG (Qasba PK, Ramakrishnan B, Boeggeman E. Mutant glycosyltransferases assist in the development of a targeted drug delivery system and contrast agents for MRI.
  • a chemically reactive functional group e.g., 2-keto-Gal or GaINAz
  • an isolated catalytic domain from a polypeptidyl- ⁇ -N-acetylgalactosaminyltransferase (pp-GalNAc-T) that transfers N- acetylgalactosamine (GaINAc) or a GaINAc analogue from UDP- ⁇ -GalNAc to one or more Ser or Thr residues of an acceptor polypeptide, wherein the isolated catalytic domain comprises SEQ ID NO: 1, it is possible that two glycoproteins with modified sugars having unique chemical handles may be conjugated with crosslinkers with orthogonal chemical reactive groups, thus enabling the design of novel immunotoxins and MRI contrast agents .
  • Non-glycoproteins can be glycosylated by engineering a C- terminal peptide tag that can be glycosylated with a modified sugar and coupled to a biomolecule that carries an orthogonal reactive group, making the method very useful in many nanobiological applications.
  • Single-chain antibodies instead of their full- length IgG counterparts, are increasingly used for immunotherapy (27. Carter P. Improving the efficacy of antibody-based caner therapies. Nat Rev Cancer 2001 ; 1 : 118-29), and they are easily expressed in large amounts in E. coli as soluble proteins. Delivering drugs or contrast agents to a specific target site for medical imaging is highly desirable for the diagnosis and treatment of many diseases including cancer.
  • target-specific monoclonal antibodies, single-chain antibodies, affibodies, and tumor-homing or cell-penetrating peptides have emerged as important guiding molecules that can carry a cargo of therapeutic molecules to the desired site.
  • Deploying these carrier molecules for the site-specific delivery of therapeutics molecules requires site-specific conjugation of these molecules with the
  • glycosyltransferases to transfer a modified sugar residue with a chemical handle to a specific sugar moiety on a glycoconjugate or to a specific amino acid residue on a polypeptide chain, respectively, allows one to exploit these chemical handles for the bioconjugation of biomolecules.
  • the monoclonal antibodies whose N-linked glycan moieties have been modified with the mutant P-l,4-galactosyltransferase to have 2-azido- or 2-keto-Gal can be conjugated with a biomolecule having a corresponding orthogonal reactive group, such as alkynes or aminooxy.
  • a fusion peptide attached at the C- terminal end of a single-chain antibody, affibody, or a tumor-homing or cell- penetrating peptide can be glycosylated at a unique site in the fusion peptide with a modified sugar; the glycosylated fusion peptide can then be conjugated with a biomolecule carrying an orthogonal reactive group.
  • a cargo molecule having multiple conjugation sites at its C-terminal end can be used to conjugate many scFv or affibodies, introducing multimeric antibody interactions at the target site.
  • a bifunctional crosslinker is used to crosslink two proteins at random sites to a protein residue distributed at several places on the protein surface.
  • This method of crosslinking often blocks the functional sites on the protein and, thus, reduces the bioefficacy of the protein.
  • the method of linking through glycan residues introduced at a specific site in the guiding molecules, such as mAb, scFv molecules, homing peptides or cell-penetrating peptides makes it possible to conjugate cytokines, cytotoxic drugs, toxins for antibody-based cancer therapy (Park, JW et al. Future directions of liposome and immunoliposome based cancer therapeutics. Semin Oncol 2004.31 :196-205), lipids for the assembly of immunoliposomes for developing a targeted drug delivery system (Carter, P. Improving the efficacy of antibody based cancer therapies. Nat Rev Cancer. 2001 : 1,118 - 29), fluorophores for ELIS A-based assays, and radionudides for imaging and immunotherapy applications.
  • the invention features methods for glycosylating a biological substrate for use in glycoconjugation comprising attaching to the C- terminal or N-terminal end of a biological substrate an acceptor polypeptide, and then using the biological substrate with the acceptor polypeptide as an acceptor substrate
  • the present invention can provide, in certain embodiments, therapeutic agents in the form of nanoparticle complexes that supply affected cells with therapeutics or diagnostics, thereby reducing or eliminating the disease state needing treatment.
  • a modified Gal sugar for example in exemplary embodiments a 2-modified- Gal sugar, having a unique chemical handle, is enzymatically transferred by ppGalNAc T to the Thr or Ser present in the fused acceptor polypeptide sequence.
  • this chemical handle can be used for selective conjugation with biologically important molecules, hi certain preferred embodiments, the acceptor sequence comprises repetitive consensus sequences, for example repetitive Thr and/ or Ser residues.
  • the chemical handle of the C-2 modified sugar is used, for example, for conjugation and assembly of bio-nanoparticles and for the formulation of immuno-liposome for the targeted drug delivery system.
  • N-glycan for example as disclosed by the present inventors in US application 20060084162, incorporated by reference herein in its entirety, can be used as a substrate for the coupling of two biomolecules, as shown in Figure 5, for example.
  • the IgG molecule can be used as the substrate for the transfer of the modified sugar by the pp- GaINAcT.
  • the acceptor polypeptide is attached to the C- terminal or N-terminal end.
  • the target agent is linked in a site-directed manner, only where the carbohydrate is attached by the method described herein, to the protein. For example, as in the single chain antibodies at the C-terminus end which is away from the antigen binding site.
  • a nanoparticle in certain embodiments, comprises a glycoprotein that is engineered from a biological substrate where an acceptor polypeptide is attached to the C-terminal or N-terminal end of a
  • Figure 8 shows a polypeptide chain, containing uniform repeats of lysine (K) residues followed by repeat fusion peptide sequence containing Threonine residues, can be used as a carrier molecule.
  • the side chain amino groups of the lysine can be conjugated to the cargo molecules, such as chromophores that carry contrast agents, such as Gadolinium (Gd) or radioisotopes etc.
  • the Threonine can be glycosylated with the modified sugars using ppGalN Ac-Ts then conjugated to single chain monoclonal antibody (scFv) for targeting.
  • scFv single chain monoclonal antibody
  • Any single chain monoclonal antibody is suitable for use in the invention.
  • the designer polypeptide itself can be used for the targeting and drug delivery.
  • a biological substrate such as a bioactive agent, for example a therapeutic agent, is used to engineer the nanoparticle.
  • a second, third, fourth or more bioactive polypeptide is used in association with the nanoparticle to engineer multivalent nanoparticles.
  • the bioactive agents do not have to be the same, for example a nanoparticle comprising three bioactive agents may comprise a chemotherapeutic, a tracking agent and a targeted delivery agent, such as an antibody.
  • Nanoparticles of the invention have use in methods of treating diseases.
  • the methods of the invention are used to engineer a glycoprotein from a magnetic resonance agent for use in diagnostic therapies.
  • nanoparticles are engineered as described herein, where the nanoparticles are superparamagnetic nanoparticle.
  • the methods of the invention are useful for engineering of nanoparticles, including multivalent nanoparticles, carrying any number of therapeutic agents.
  • the nanoparticles can be used to treat cancer, inflammatory disease, cardiovascular disease, obesity, ageing, bacterial infection, or any other disease amenable to therapy.
  • An active pp-GalNAc-T in the presence of Mn2+ transfers GaINAc sugar from its UDP- ⁇ -GalNAc donor substrate to the side chain hydroxyl group of the Thr/Ser residue present in a polypeptide acceptor substrate.
  • the folding methods occur in vitro.
  • the catalytic domain of pp-GalNAc-T When the catalytic domain of pp-GalNAc-T is expressed in E. CoIi, it forms insoluble inclusion bodies. These inclusion bodies can be collected and then solubilized and folded in vitro to produce catalytically active domains. Thus, the in vitro folding efficiency is directly related to the quantity of active enzyme that is produced after in vitro folding of the isolated inclusion bodies. Accordingly, methods to increase the in vitro folding efficiency would provide increased production of the enzymatically active catalytic domains that can be used to create useful products.
  • General method for isolating and folding of the inclusion bodies is similar to the one previously described for galactosyltransferase catalytic domains have been previously described (Ramakrishnan et al., J. Biol. Chem., 276:37665 (2001)).
  • the method generally comprises first expressing pp-GalNAc-T in E.coli, and isolating, washing and dissolving inclusion bodies from E.coli.
  • Inclusion bodies can be collected and then solubilized and folded in vitro to produce catalytically active domains. Following the isolating, washing and dissolving inclusion bodies from E.coli.
  • the method comprises performing S-sulfonation of the inclusion bodies in the presence of sodium sulfite, and folding the inclusion bodies, thus producing active pp-GalNAc-T.
  • the active pp-GalNAc-T of the invention can comprise a catalytic domain (CD) together with lectin domain or the catalytic domain alone. Shown in SEQ ID NO: 1 is the protein sequence of the CD-LD portion of the family member, pp-
  • GalNAc-T2 Described herein is an in vitro folding method for CD-LD portion of pp-
  • the pp-GalNAc-T2 is the human pp-GalNAc- T2 member of the family. Further, using the methods as described herein the CD domain alone also folds.
  • the active pp-GalNAc-T comprising a CD-LD portion is more active compared to pp-GalNAc-T comprising a catalytic domain.
  • more active is meant that the folded CD-LD portion, compared to the folded CD alone, gives more transfer of GaINAc from the donor substrate UDP- ⁇ -GalNAc, and less hydrolysis of the donor substrate.
  • More active can be determined as a percent, for example exhibiting 5%, 10%, 15%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100%, or greater activity.
  • the folding method is applicable to pp-GalNAc-T2 family members. In examples described herein for the design and transfer to the peptide sequence that is fused at the C-terminal end of the GST protein, the folded CD-LD of the human pp-GalNAc-T2 was used.
  • kits comprise the isolated catalytic domain (CD) or the isolated CD-LD from a polypeptidyl- ⁇ -N- acetylgalactosaminyltransferase (pp-GalNAc-T) as described herein and instructions for use. Kits can further comprise a biological substrate or bioactive agent as described herein.
  • CD isolated catalytic domain
  • pp-GalNAc-T polypeptidyl- ⁇ -N- acetylgalactosaminyltransferase
  • Kits can further comprise a biological substrate or bioactive agent as described herein.
  • Example 1 Engineering of a C-terminal fusion peptide sequence
  • a C-terminal fusion peptide sequence was engineered that contained a Thr/Ser residue in the non-glycoprotein , shown in Figure Ia.
  • the fusion peptide can
  • FIG 1 illustrates the catalytic reaction of polypeptide-a-N-acetylgalactosaminyltransferase (ppGalNAc-T).
  • the enzyme in the presence of Mn2+, transfers GaINAc sugar from its UDP- ⁇ -GalNAc donor substrate to the side chain hydroxyl group of the Thr/Ser residue present in a polypeptide acceptor substrate.
  • the ppGalNAc-T can transfer GaINAc analogues sugars such as, GaINAz, shown in Figure Ib, from UDP-GaINAz to the same acceptor substrate (17). It has been shown previously, that the mutant b4Gal-Tl, Y289L-Gal-Tl, can transfer GaINAc sugar from UDP-GaINAc as efficiently as its natural donor sugar galactose (Gal) from UDP-GaI (13). In addition to GaINAc, the mutant also transfers as well a 2-keto-Gal, shown in Figure Ic (14,15).
  • the ppGalNAc-T2 can also transfer 2-keto-Gal from UDP-2-keto-Gal.
  • ppGalNAc-T is known to transfer GaINAc analogues having a unique chemical handle such as, 2-azido-acetyl group.
  • the glycosylated glycoprotein with the modified sugar can then be conjugated through this unique chemical handle to a bioactive molecule, such as immunoglobulin or toxin etc. This is shown in Figure Ib & c.
  • a bioactive molecule such as immunoglobulin or toxin etc.
  • Glutathione-S-transferase has been used as a model for a non-glycoprotein, since it has previously been used for the expression of a number of fusion recombinant proteins at its C-terminal end.
  • GST-tag protein was expressed with a 17 amino acid fusion peptide having one or many Thr residues at the C-terminal end.
  • Example 2 Expression of soluble active ppGalNAc-T2 in E. coli
  • ppGalNAc-T2 enzyme has been previously expressed in various expression systems producing an active soluble protein (18), the expression in E. coli has produced inactive inclusion bodies.
  • the ppGalNAc-T2 expressed in yeast showed no N-glycosylation in the crystal structure, and was considered as a perfect candidate for expression in E. coli that could be folded from inclusion bodies. Therefore, an in vitro folding method was developed to generate active protein.
  • b4Gal-Tl S-sulfonation method has been used to produce large quantities of b-l,4-galactosy ⁇ transferase (b4Gal-Tl) from inclusion bodies (19).
  • ppGalN Ac-Tl has been used for glycosylation of the non-glycoform of mucl protein expressed in E. coli (20).
  • ppGalNAc-T2 has been also used to construct the 0-mucin structure on the non-glycoform of the interferon-alpha2b (IFN- alpha2b) expressed in E. coli (21).
  • IFN- alpha2b interferon-alpha2b
  • glycosyltransferases can be generated from E. coli that can be used for such application as well.
  • Example 3 GIy cosylation of GST-tag protein
  • Glutathione-S-transferase (GST) protein with a 17 amino acid tag at its C- terminal, following a Thrombin cleavage site has been successfully expressed as a soluble protein from E. coli and purified on a glutathione column.
  • the tag was expressed with an oligopeptide sequence, SGGPIMDSTTP APTTK, used in the previous enzyme kinetic studies of ppGalNAc-T2 (18).
  • the 17-amino acid tag was released by Thrombin digestion and analyzed by mass spectrometry (MALDI-TOP), shown in Figure 3a.
  • glycosylated tag Analysis of the glycosylated tag showed that the glycosylated peptide exists as a mixture of three to four glycosylated peptides, suggesting that the four Thr residues present in the tag peptide may have been the sites for the glycosylation.
  • the redesigned tag peptide, SGGPIMAAATPAPAAK, with one Thr and one Ser residues, is found to have glycosylated with two sugars, suggesting that in addition to the glycosylation of the Thr residue, the less preferred Ser residue is also glycosylated (Figure 3b).
  • ppGalNAc-T enzymes in the live cell can incorporate GaINAz (2-azido-acetyl-galactosamine), a modified sugar resembling GaINAc, to the glycan chains.
  • GaINAz 2-azido-acetyl-galactosamine
  • a modified sugar resembling GaINAc to the glycan chains.
  • the incorporation of such unnatural monosaccharide that bears uniquely reactive chemical handle such as azides has enabled the selective labeling of glycoconjugates with a variety of reagents (17). Since these studies were carried out in vivo, it was not possible to identify the specific ppGalNAc-T that is responsible for the transfer of GaINAz among the 17 the ppGalNAc-Ts present in humans.
  • ppGalNAc-T2 is used to transfer the modified galactose which resembles GaINAc, such as 2-keto-galactose and GaINAz, to the fusion peptide in the GST-Tag protein.
  • GaINAc such as 2-keto-galactose and GaINAz
  • the GST-Tag protein with only one Thr residue present in its fusion tag peptide is used. Use of others can be envisioned.
  • TOPS TOPS of the non-glycopeptide and glyco-peptide released by Thrombin digestion are shown in the left and right side of the arrows, respectively.
  • the glycosylated protein is biotinylated using the biotin carrying appropriate chemical group to react with the 2-keto or azido moiety of the modified sugars.
  • the proteins in the Western Blotting were visualized using the sterptavadine-HRP chemiluminescence technique. A strong luminance is only observed for the biotinylated proteins with the fusion peptide (- Thrombin), while the proteins without the fusion peptide (+Thrombin) no trace of chemiluminescence has been observed.
  • mutant b4Gal-Tl eri2yme Y289L-Gal- Tl
  • GaINAc GaINAc from UDP-GaINAc as efficiently as galactose (Gal) from UDP-GaI to the N-acetylglucosamine (GIcNAc) residue present at the non-reducing end (13).
  • the mutant b4Gal-Tl enzyme can also transfer modified sugars such a 2-keto-galactose from its UDP-derivative and this catalytic activity was successfully applied in the detection of O-GlcN Ac modification in the proteins (14).
  • glyco-proteins such as ovalbumin and immunoglobulin IgG with free GIcNAc at the non- reducing end of their N-glycans.
  • two glyco-proteins with modified sugars, such as 2-keto-Gal, with unique chemical handle can be conjugated with chemical cross linkers, thus enabling the design of novel immuno-toxins and MIR image enhancers (15).
  • non-glycoproteins have been shown to be glycosylated by engineering a peptide sequence in the protein that can be glycosylated with the
  • modified sugar so that they can also be cross linked to the other glyco-proteins such as IgG, with similar modified sugars.
  • the modified sugar 2-keto-Gal can be transferred to the free GIcNAc residue present in the non-reducing end of a glycopeptide such as IgG (15).
  • this sugar can be subjected to further chemical modification such as biotinylation.
  • this IgG with the modified Gal can be cross linked to the non-glycoprotein, such as GST with a fusion peptide carrying a modified sugar at its C-terminal end.
  • the two molecules can be conjugated through their glycan moieties, thus synthesizing novel immuno-conjugates through their glycan moieties.
  • ScFv single chain antibodies
  • these ScFv molecules can be easily expressed in E. coli as soluble proteins in large amounts, and they have been found to have similar affinity towards their antigens as their full length IgG counterpart molecules. Therefore, the ScFv molecules have been used for synthesizing the immuno-liposome by attaching a lipid moiety to the ScFv molecules through chemical modification.
  • the methods described herein can be used more efficiently by simply glycosylating the ScFv molecule with a fusion peptide at its C-terminal end similar to GST-Tag protein.
  • this glycan moiety with the modified sugar can be conjugated with a lipid molecule with corresponding reactive group such as immunoxy or alkynes.
  • a ScFV molecule with lipid attached at its C-terminal end through a modified sugar moiety mimics the GPI, glycosyl- phosphatidylinositol, anchoring protein, and thus can be used for the formulation of the immuno-liposomes.
  • Such C-terminal modification in most SvFv proteins seems to be feasible since the C- terminal end is away from the antigen binding site (Fab).
  • conjugated protein with lipid at their C-terminal end through a sugar moiety mimics GPI, glycosylphosphatidylinositol, anchored protein and they can be used to formulate liposomes. Particularly this technique is important for the single chain antibodies, which are often expressed in E. coli as an active protein.
  • These proteins with a C- terminal tag, such as the present one in GST carrying the modified sugar can be conjugated to lipid molecules, thus synthesizing the immuno-liposomes. Often the antigen binding regions in these ScFv molecules are well away from their C-terminal end, thus this scheme is expected to work well.
  • the full chain IgG can be engineered to have the heavy chain C-terminal to have the fusion peptide which can be glycosylated and conjugated to lipid in vitro, thus enabling one to synthesize immuno-liposome using the whole IgG molecule itself.
  • Oligosaccharides are attached at unique sites in proteins and glycolipids. They bring about specific geometries of interactions between the two glycoconjugates, resulting in the correct and efficient molecular interplay between various molecular structures (Ramakrishnan B, Qasba PK. Structure-based design ofl 31 ,4-
  • galactosyltransferase I (34GaI-Tl) with equally efficient N- acetylgalactosaminyltransferase activity. J Biol Chem 2002;277:20833-40). Glycosyltransferases assemble the oligosaccharide structures on glycoco ⁇ jugates. Recently, the structural information of several of these glycosyltransferases has become available (Khidekel N, et al. A chemoenzymatic approach toward the rapid and sensitive detection of 0-G IcNAc posttranslational modifications.
  • the 3-1,4- galactosyltransferase mutant enzyme Tyr289Leu-Gal-Tl (Y289L-Gal-Tl) was developed that transfers 2-acetonyl-2-deoxygalactose (2-keto-Gal) or 2-N-acetyl- azide (GaINAz) from their UDP derivatives to the N-acetylglucosamine residue (GIcNAc), which is present at the non-reducing end of the glycans of glycoproteins (Qasba PK, Ramakrishnan B, Boeggeman E.
  • GIcNAc N-acetylglucosamine residue
  • Mutant glycosyltransferases assist in the development of a targeted drug delivery system and contrast agents for MRJ. Am Ass Pharm Soc J 2006;8: 190-5). After the transfer of the modified sugar residue, the chemical handle is used for selective conjugation with various molecules (Ramakrishnan B, Bioconjug Chem 2007; 18: 1912-8). Using this method, it has been shown that even the N-glycan moiety of the IgG molecule can be used as the substrate for the transfer of 2-keto-Gal sugar by the mutant Y289L-Gal-Tl .
  • this method requires the presence of a free GIcNAc moiety at the non-reducing end of the glycan chain of the glycoprotein and cannot be used for non-glycoproteins, such as single-chain antibodies or bacterial toxins expressed in Escherichia coli.
  • the polypeptide a-N- acetylgalactosaminyltransferase enzyme (ppGalNAc-T) has been used, which transfers N-acetylgalactosamine sugar (GaINAc) from UDP-GaINAc to the Thr/Ser residues on an acceptor polypeptide that is at least 11 amino acids long [25].
  • GST glutathione S-transferase
  • the ppGalNAc-T2 not only transfers GaINAc but also GaINAz or 2-keto-Gal from its UDP derivative to the single Thr residue present in the fusion peptide tag of GST. Furthermore, we have expressed the soluble form of ppGalNAc-T2 in E. coli as inclusion bodies and developed an in vitro folding method to make large quantities of active ppGalNAc-T2 (Hollinger P, Hudson PJ. Engineered antibody fragments and the rise of single domains. Nat Biotechnol 2005;23:l 126-36). Therefore, using ppGalNAc-T it is possible to glycosylate non- glycoproteins, such as single-chain antibodies (scFv), bacterial toxins, with a modified sugar carrying a unique chemical handle that can be used for conjugation.
  • scFv single-chain antibodies
  • T2 T2 clone (BC041120) was obtained from Open Biosystems.
  • the PCR amplified product was digested with Bam I and Eco RI restriction enzyme and ligated with the pET23a vector predigested with the same enzymes.
  • the ligated vector was transfected into XL2 super competent cells and plated.
  • the ampicillin resistant clones were screened for the presence of the ppGalNAc-T2 gene in their plasmid DNA between their Bam I and Eco RI restriction sites.
  • the positive clones were sequenced and transfected into Rosetta (DE3) LysS competence cell for the expression of the protein.
  • ppGalANc-T2 The expression and purification of the recombinant ppGalANc-T2 protein was done as described previously (18). Nearly 60 to 70 mgs of protein were obtained as inclusion bodies from one liter bacterial culture.
  • the in vitro folding of ppGalNAc-T2 was carried out similar to b4Gal-Tl (19) with few modifications. Typically, 100 mg of sulfonated protein is folded in one liter folding solution for 48 hours. Inclusion of 10% glycerol and 10 mM lactose in the folding solution enhances the folding efficiency of ppGalNAc-T2. After refolding the protein, the folding solution is extensively dialyzed against water. During dialysis the miss folded protein precipitates out, while the folded protein remains soluble.
  • the soluble protein is first concentrated and then purified on a Ni-column. Nearly 2 mg of folded ppGalNAc-T2 protein is obtained form 1 liter of folding solution. The purified protein was tested for its catalytic activity using a 13 amino acid peptide, PTTDSTTP APTTK, as an acceptor using the methods described previously (18). The specific activity of the refolded ppGalNAc-T2 is 20 pmoles/min/ng protein.
  • the GST gene from pGEX-2T vector was amplified first with the 5'- primer and 3' -primer 1 and purified on a low melt agarose gel.
  • the purified GST gene was further amplified with the 5 '-primer and 3'-primer2 which coded for a 17 amino
  • GAGGPIMAAATPAPAAK as a C-terminal extension of GST following a Thrombin cleavage site.
  • the final PCR amplified DNA fragment was digested with Bam HI and Eco RI enzymes and ligated with predigested pET23a vector with the same enzymes.
  • the ligated vector was transfected into XL2 competent cells.
  • the ampicilin resistant clones were screened for the presence of the full GST gene between the Bam HI and Eco RI sites in their plasmid DNA.
  • the positive plasmid DNA was transfected into Rosetta (DE3) LysS cells.
  • the GST-tag protein was expressed as a soluble protein in E. coli and purified on a glutathione affinity column (GE). A total of 50 to 60 mg purified protein was obtained from one liter bacterial culture.
  • the C-terminal glycosylation tag was released from a 5 mg protein by thrombin cleavage and analyzed by mass spectrometry.
  • the other GST-Tag fusion proteins containing the multiple glycosylation sites were also made similar to the above methods. All the oligonucleotides were synthesized by the Molecular technology branch, NCI, Frederick.
  • a 5 mg of GST-tag protein was incubated over night at 37°C with 50 ng of ppGalNAc-T2, in the presence of 20 mM mes-NaOH buffer (pH6.5), 10 mM MnC12 and 0.5 mM UDP-sugar (UDP-GaINAc or UDP-2-keto-Gal or UDP-GaINAz) in a
  • glycosylated GST-tag protein was centrifuged on a centricon (10 K molecular cutoff) filter to remove all the reaction buffer and washing with pure water twice.
  • the salt free glycosylated GST-tag was recovered in a 20 ml water. An aliquot of it (4 ml) was cut with human Thrombin and analyzed by mass spectrometry (MALI-TOP).
  • the desalted glycosylate GST-tag protein with 2-keto-Gal was biotinylated in 60 ml volume containing 75 mM sodium acetate buffer pH 5.0, and 30 mM aminoxymethylcarbonyhydrazino-D-biotin (ARP, Dojindo laboratories). The reaction was carried out overnight at room temperature.
  • the biotinylated sample was desalted using centricon (10 K) filter and recovered in 20 ml of water. An aliquot of the sample was cut with thrombin and analyzed using mass spectrometry.
  • the biotinylated proteins uncut and cut with Thrombin were analyzed by Western Blotting and they were detected by chemiluminescence technique using streptavadin- horseradish peroxidase (HRP) as described previously (15).
  • Boeggeman E., Ramakrishnan, B., Kilgore, C, Khidekel, N., Hsieh- Wilson, L. C, Simpson, J.T., and Qasba, P. K. Direct Identification of Nonreducing GIcNAc Residues on N-Glycans of Glycoproteins Using a Novel Chemoenzymatic Method. Bioconjug Chem. (2007) Mar 20; [Epub ahead of print]
  • the N-terminal stem region of bovine and human betal,4-galactosyltransferase I increases the in vitro folding efficiency of their catalytic domain from inclusion bodies.

Abstract

The instant invention provides isolated catalytic domains from a polypeptidyl-α- N-acetylgalactosaminyltransferase (pp-GalNAc-T). The invention provides methods for engineering a glycoprotein from a biological substrate, and methods for glycosylating a biological substrate for use in glycoconjugation. Also included in the invention are diagnostic and therapeutic uses. The invention further provides in vitro folding methods for pp-GalNAc-T.

Description

METHODS OF GLYCOSYLATION AND BIOCONJUGATION
RELATED APPLICATIONS
This application claims the benefit of US Provisional Application No. 60/930,294, filed May 14, 2007. The entire contents of the aforementioned application are hereby incorporated herein by reference.
GOVERNMENT SUPPORT
Research supporting this application was carried out by the United States of America as represented by the Secretary, Department of Health and Human Services. This research was supported [in part] by the Intramural Research Program of the NIH, National Cancer Institute, Center for Cancer Research. This research has been funded in part with Federal funds from the NCI, NIH, under contract No. NOl -CO- 12400. The Government may have certain rights in this invention.
FIELD OF THE INVENTION The present invention relates to enzymes and methods that can be used to chemically link biologically important molecules. In particular, the invention relates to a method which takes advantage of the polypeptide-α-N- acetylgalactosaminyltransferase enzyme, (ppGalNAc-T), which transfers N- acetylgalactosamine sugar (GaINAc) from UDP-α-GalNAc to an acceptor polypeptide substrate. An acceptor polypeptide substrate has been engineered as a fusion peptide either at the C- terminus or N-terminus of a non-glycoprotein of interest, and this fusion peptide moiety has been used as an acceptor substrate for ppGalNAc-T. The method is of particular use to promote the chemical linkage of biologically important molecules that have previously been difficult to link.
BACKGROUND OF THE INVENTION
Eukaryotic cells express several classes of oligosaccharides attached to proteins or lipids. Animal glycans can be N-linked via B-GIcNAc to Asn (N-glycans), O-linked via -GaINAc to Ser/Thr (O-glycans), or can connect the carboxyl end of a
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protein to a phosphatidylinositol unit (GPI-anchors) via a common core glycan structure. Beta (l,4)-galactosyltransferase I catalyzes the transfer of galactose from the donor, UDP-galactose, to an acceptor, N-acetylglucosamine, to form a galactose- .beta.(l,4)-N-acetylglucosamine bond, and allows galactose to be linked to an N- acetylglucosamine that may itself be linked to a variety of other molecules. Examples of these molecules include other sugars and proteins. The reaction can be used to make many types of molecules having great biological significance. For example, galactose-beta (l,4)-N-acetylglucosamine linkages are important for many recognition events that control how cells interact with each other in the body, and how cells interact with pathogens. In addition, numerous other linkages of this type are also very important for cellular recognition and binding events as well as cellular interactions with pathogens, such as viruses. Therefore, methods to synthesize these types of bonds have many applications in research and medicine to develop pharmaceutical agents and improved vaccines that can be used to treat disease. Monoclonal antibodies coupled with toxic proteins, drugs and radioisotopes are an emerging strategy in the diagnosis and treatment of disease. However, various methods are being used in conjugating antibodies with the cargo molecule with mixed success. Often, the primary amine groups present on the surface of the protein molecule are used for conjugation, however, since every lysine residue present on the protein molecule would be reactive, this method results in undesirable heterogeneous conjugation and subsequent loss of antibody activity. Alternatively, free Cys residue, either naturally present or an engineered in the protein molecule, is widely used for conjugation. Since the freely exposed Cys residue being highly reactive in basic pH, it requires special requirements in handing these protein molecules. It has long been demonstrated that the sugar moieties present on the glycoproteins, for example, IgG, can be used as a chemical handle for such conjugation. Often, to the heterogeneous nature of the glycan moiety on the recombinant glycoprotein the result is a poor coupling.
There is a need in the field for improved conjugation methods. Accordingly, the instant invention provides enzymes and methods that can be used to promote the
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chemical linkage of biologically important molecules that have previously been difficult to link.
SUMMARY OF THE INVENTION Described herein is a method which takes advantage of the polypeptide-α-N- acetylgalactosaminyltransferase enzyme, (ppGalNAc-T), which transfers N- acetylgalactosamine sugar (GaINAc) from UDP-α-GalNAc to an acceptor polypeptide substrate. An acceptor polypeptide substrate has been engineered as a fusion peptide either at the C- terminus or N-terminus of a non-glycoprotein of interest, and this fusion peptide moiety has been used as an acceptor substrate for ppGalNAc-T.
Accordingly, in one aspect, the invention provides an isolated catalytic domain from a polypeptidyl-α-N-acetylgalactosaminyltransferase (pp-GalNAc-T) that transfers N-acetylgalactosamine (GaINAc) or a GaINAc analogue from UDP-α- GaINAc to one or more Ser or Thr residues of an acceptor polypeptide, wherein the isolated catalytic domain comprises SEQ ID NO: 1.
In one embodiment, the pp-GalNAc-T transfers GaINAc or a GaINAc analogue in an α-configuration.
In a further embodiment, the pp-GalNAc-T is mammalian. In another embodiment, the pp-GalNAc-T is pp-GalNAc-T2.
In another embodiment of the invention, the pp-GalNAc-T comprises a catalytic domain (CD) and lectin domain (LD).
In one embodiment, the invention features an isolated nucleic acid segment encoding the catalytic domain of from a polypeptidyl-α-N- acetylgalactosaminyltransferase (pp-GalNAc-T) according to the above-described aspect that comprises SEQ ID NO: 2.
In a further embodiment, a vector or expression cassette comprises the nucleic acid of the above-mentioned embodiment. In a related embodiment, a cell comprises the vector or expression cassette. In another aspect, the invention features a method for engineering a glycoprotein from a biological substrate comprising attaching to the C-terminal or N-
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terminal end of a biological substrate an acceptor polypeptide, and using the biological substrate with the acceptor polypeptide as an acceptor substrate for a pp- GaINAc-T, and transferring one or more GaINAc residue or GaINAc analogue sugars to the acceptor polypeptide, thereby engineering a glycoprotein from a biological substrate.
In another aspect, the invention features a method for glycosylating a biological substrate for use in glycoconjugation comprising attaching to the C- terminal or N-terminal end of a biological substrate an acceptor polypeptide, and using the biological substrate with the acceptor polypeptide as an acceptor substrate for a pp-GalNAc-T, and transferring one or more GaINAc residue or GaINAc analogue sugars to the acceptor polypeptide, and thereby glycoslyating the biological substrate for use in glycoconjugation.
In one embodiment, the acceptor polypeptide is a nanoparticle. In another embodiment, the biological substrate is a nanoparticle. In another aspect, the invention features a method for engineering a nanoparticle comprising attaching to the C-terminal or N-terminal end of a biological substrate a nanoparticle, and using the biological substrate with the nanoparticle as an acceptor substrate for a pp-GalNAc-T, and transferring one or more GaINAc residue or GaINAc analogue sugars to the acceptor substrate, thereby engineering a nanoparticle.
In one embodiment , the nanoparticle is a multivalent nanoparticle. In another embodiment, the biological substrate is selected from the group consisting of: a non-glycoprotein, an oligopeptide and a biological matrix.
In a further embodiment, the GaINAc residue or GaINAc analogue sugars are transferred to one or more Ser or Thr residues of the acceptor polypeptide. In another embodiment, the non-glycoprotein or oligopeptide is a bioactive agent. In yet a further embodiment, the bioactive agent is any bioactive agent carrying a linker sequence with a functional coupling group. In still a further embodiment, the bioactive agent is selected from the group consisting of: single chain antibodies, bacterial toxins, growth factors, therapeutic agents, and contrast agents.
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In another embodiment of the invention, the nanoparticle comprises a magnetic resonance agent.
In still another embodiment of the invention, the acceptor polypeptide comprises at least 10 amino acids. In a further embodiment, the acceptor polypeptide comprises at least 15 amino acids. In yet a further embodiment, the acceptor polypeptide is selected from SEQ ID NO: 3 (GAGGPIMAAATPAPAAK) or SEQ ID NO: 4 (AGGPIMAATPAPAAK).
In another embodiment, the acceptor polypeptide is glycosylated at one or more sites. In a further embodiment, the acceptor polypeptide is glycosylated at a serine or threonine residue.
In one embodiment, the GaINAc analogue comprises an azido group. In another embodiment, the GaINAc analogue comprises a keto group.
In another embodiment, the pp-GalNAc-T transfers the GaINAc analogue to one or more Ser or Thr residues of the acceptor polypeptide. In another embodiment, the invention features a method of engineering a nanoparticle where the nanoparticle is used to treat a subject suffering from a disease or disorder.
In a particular embodiment, the nanoparticle is used in magnetic resonance imaging. In another aspect, the invention features a method for producing an active pp-
GaINAc-T comprising expressing pp-GalNAc-T in E.coli, isolating, washing and dissolving inclusion bodies from E.coli, performing S-sulfonation of the inclusion bodies in the presence of sodium sulfite, and then folding the inclusion bodies, wherein active pp-GalNAc-T is produced. In one embodiment, the step of folding the inclusion bodies comprises using oxido shuffling agents, 0.5M arginine HCl, 10% glycerol, and 1OmM lactose.
In another embodiment, the active pp-GalNAc-T comprises a catalytic domain and lectin domain. In another embodiment the active pp-GalNAc-T comprises a catalytic domain. In a further embodiment, the active pp-GalNAc-T transfers GaINAc-T from
UDP-α-GalNAc and less hydrolysis of the donor substrate.
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In still a further embodiment, the active pp-GalNAc-T comprising a catalytic domain and lectin domain is more active compared to pp-GalNAc-T comprising a catalytic domain.
In certain preferred embodiments, the folding occurs in vitro. In other preferred embodiments according to any of the above aspects, the pp-
GaINAc-T is pp-GalNAc-T2.
The invention also features in other aspects kits comprising the isolated catalytic domain from a polypeptidyl-α-N-acetylgalactosaminyltransferase (pp- GaINAc-T) of any of the above-mentioned aspects, along with instructions for us. In certain embodiments, the kits further comprise an acceptor.
In other certain embodiments, the kits further comprise a biological substrate or bioactive agent of any of the above-mentioned aspects.
DESCRIPTION OF THE DRAWINGS Figure 1 (a - c) illustrates the catalytic reaction of polypeptide-α-N- acetylgalactosaminyltransferase (ppGalNAc-T). (a) shows that the enzyme, in the presence of Mn2+ transfers GaINAc sugar from its UDP-α-GalNAc donor substrate to the side chain hydroxyl group of the Thr/Ser residue present in a polypeptide acceptor substrate, (b) shows GaINAz and (c) shows a 2-keto-Gal, which can be also transferred by ppGalNAc-T.
Figure 2 is a protein gel showing the generation of active ppGalNAc-T2. The left lane shows the insoluble inactive inclusion body of ppGalNAc-T2 produced in E. coli. The middle and right lanes show in vitro folded active ppGalNAc-T2, 1 μg and 0.5 μg, respectively. Nearly 2 mg active protein purified from a Ni-column is obtained from one-liter folding solution from the inclusion bodies produced from a liter of bacterial culture.
Figure 3 (a - c) is a panel of graphs and schematics. The Glutathione-S-transferase (GST) protein (shown in cartoon diagram insert) is expressed with a 17 amino acid sequence (in single letter code) as a fusion peptide at its C-terminus following the
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Thrombin site (RG), shown as cutting scissors. The hexagons indicate the potential O-glycosylation residues for the ppGalNAc-T2. The fusion peptides are designed based on the acceptor substrates of ppGalNAc-T2. The mass spectrum (MALDI- TOPS) of the Thrombin cut non-glycosylated and glycosylated peptide are shown in the left and right side of the arrow, respectively, in panels (a) (b) and (c).
Figure 4 (a and b) illustrates the GST-tag protein with only a single Thr residue but no Ser residue in its fusion peptide is used for the transfer of (a) 2-keto-Gal and (b) GaINAz sugars from their respective UDP-derivatives. The mass spectrum (MALDI- TOPS) of the non-glycopeptide and glyco-peptide released by Thrombin digestion are shown in the left and right side of the arrows, respectively. The proteins in the Western Blotting were visualized using the streptavadin-horseradish peroxidase (HRP) chemiluminescence technique.
Figure 5 is a schematic drawing illustrating that non-glycoproteins can be glycosylated by engineering a peptide sequence in the protein that can be glycosylated with the modified sugar, so that they can also be cross linked to the other glycoproteins such as IgG, with similar modified sugars.
Figure 6 is a schematic showing that the non-glycoprotein with the tag at the C- terminal end can be glycosylated with the GaINAc analogue sugars having a unique chemical handle.
Figure 7 is an outline of the procedure for producing an active pp-GalNAc-T.
Figure 8 is a schematic showing a polypeptide chain, containing uniform repeats of lysine (K) residues followed by repeat fusion peptide sequence containing Threonine (Thr) residues, can be used as a carrier molecule.
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DETAILED DESCRIPTION OF THE INVENTION
The instant invention provides isolated catalytic domains from polypeptidyl- α-N-acetylgalactosaminyltransferase (pp-GalNAc-T). The invention provides methods for engineering a glycoprotein from a biological substrate, and methods for glycosylating a biological substrate for use in glycoconjugation. Also included in the invention are diagnostic and therapeutic uses. The invention further provides in vitro folding methods to produce active enzyme.
Definitions The following definitions are provided for specific terms which are used in the following written description.
As used in the specification and claims, the singular form "a", "an" and "the" include plural references unless the context clearly dictates otherwise. For example, the term "a cell" includes a plurality of cells, including mixtures thereof. The term "a nucleic acid molecule" includes a plurality of nucleic acid molecules.
As used herein, the term "comprising" is intended to mean that the compositions and methods include the recited elements, but do not exclude other elements. "Consisting essentially of, when used to define compositions and methods, shall mean excluding other elements of any essential significance to the combination. Thus, a composition consisting essentially of the elements as defined herein would not exclude trace contaminants from the isolation and purification method and pharmaceutically acceptable carriers, such as phosphate buffered saline, preservatives, and the like. "Consisting of shall mean excluding more than trace elements of other ingredients and substantial method steps for administering the compositions of this invention. Embodiments defined by each of these transition terms are within the scope of this invention.
The term "acceptor" is meant to refer to a molecule or structure onto which a donor is actively linked through action of a catalytic domain of a galactosyltransferase, or mutant thereof. Examples of acceptors include, but are not limited to, carbohydrates, glycoproteins, glycolipids. In preferred embodiments, the acceptor polypeptide comprises Ser and/ or Thr residues. The acceptor polypeptide
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can comprise, in preferred embodiments repeating consensus sequences, for example, repeating Ser or Thr residues. The acceptor polypeptide can be glycosylated at one or more sites. In certain embodiments, the acceptor peptide is SEQ ID NO: 3 (GAGGPIMAAATPAPAAK). In other embodiments, the acceptor peptide is SEQ ID NO: 4 (AGGPIMAATPAPAAK).
The term "catalytic domain" is meant to refer to an amino acid segment which folds into a domain that is able to catalyze the linkage of a donor to an acceptor. For example, a catalytic domain may be from, but is not limited to, human polypeptidyl-a- N-acetylgalactosaminyltransferase II (ppGalNAc-T2) (SEQ ID NO: 1). The pp- GaINAc-T enzymes comprise 17-19 family members. Each member transfers GaINAc in α-configuration. Sequences of pp-GalNAc-T family members from human and other species are known and the DNA clones available commercially. Any pp-GalNAc-T from any species and in combination with a peptide acceptor can be used in the invention described herein. A catalytic domain may have an amino acid sequence found in a wild-type enzyme, or may have an amino acid sequence that is different from a wild-type sequence.
The term "donor" is meant to refer to a molecule that is actively linked to an acceptor molecule through the action of a catalytic domain of a polypeptidyl-a-N- acetylgalactosaminyltransferase, or mutant thereof. A donor molecule can include a sugar, or a sugar derivative. Examples of donors include, but are not limited to, UDP- α-acetylgalactosamine, UDP-α-GalNAz, UDP-α-2-keto-Gal, UDP-α-galactose, UDP-mannose, UDP-N-acetylglucosamine, UDP-glucose, GDP-mannose, UDP- glucuronic acid, GDP-Fucose, and CMP-N-acetylneuraminic acid. Donors include sugar derivatives that include active groups, such as cross-linking agents or labeling agents. Accordingly, oligosaccharides may be prepared according to the methods of the invention that include a sugar derivative having a desired characteristic.
The term "expression cassette" as used herein refers to a DNA sequence capable of directing expression of a particular nucleotide sequence in an appropriate host cell, comprising a promoter operably linked to the nucleotide sequence of interest that is operably linked to termination signals. It also typically comprises sequences required for proper translation of the nucleotide sequence. The expression cassette
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may be one that is naturally occurring but has been obtained in a recombinant form useful for heterologous expression. The expression of the nucleotide sequence in the expression cassette may be under the control of a constitutive promoter or of an inducible promoter that initiates transcription only when the host cell is exposed to some particular external stimulus. In the case of a multicellular organism, the promoter can also be specific to a particular tissue or organ or stage of development.
The term "N-acetylgalactosaminyltransferase (GaINAcT)" as used herein refers to enzymes substantially homologous to, and having substantially the same biological activity as, the enzyme coded for by the nucleotide sequence depicted in SEQ ID NO: 2 and the amino acid sequence depicted in SEQ ID NO: 1. This definition is intended to encompass natural allelic variations in the pp-GalNAcT sequence, and all references to GaINAcT, and nucleotide and amino acid sequences thereof are intended to encompass such allelic variations, both naturally-occurring and man-made. The production of proteins such as the enzyme GaINAcT from cloned genes by genetic engineering is well known and described in, for example, U.S. Pat. No. 4,761,371, incorporated by reference in its entirety herein.
The GaINAcT enzyme may be synthesized in host cells transformed with vectors containing DNA encoding the GaINAcT enzyme. A vector is a replicable DNA construct. Vectors are used herein either to amplify DNA encoding the GaINAcT enzyme and/or to express DNA which encodes the GaINAcT enzyme. An expression vector is a replicable DNA construct in which a DNA sequence encoding the GaINAcT enzyme is operably linked to suitable control sequences capable of effecting the expression of the GaINAcT enzyme in a suitable host. The need for such control sequences will vary depending upon the host selected and the transformation method chosen. Generally, control sequences include a transcriptional promoter, an optional operator sequence to control transcription, a sequence encoding suitable mRNA ribosomal binding sites, and sequences which control the termination of transcription and translation. Amplification vectors do not require expression control domains. All that is needed is the ability to replicate in a host, usually conferred by an origin of replication, and a selection gene to facilitate recognition of transformants.
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The terms "oligosaccharide" and "polysaccharide" are used interchangeably herein. These terms refer to saccharide chains having two or more linked sugars. Oligosaccharides and polysaccharides may be homopolymers and heteropolymers having a random sugar sequence or a preselected sugar sequence. Additionally, oligosaccharides and polysaccharides may contain sugars that are normally found in nature, derivatives of sugars, and mixed polymers thereof.
The terms "polypeptides" and "proteins" are used interchangeably herein. Polypeptides and proteins can be expressed in vivo through use of prokaryotic or eukaryotic expression systems. Many such expressions systems are known in the art and are commercially available. (Clontech, Palo Alto, Calif.; Stratagene, La Jolla, Calif). Examples of such systems include, but are not limited to, the T7-expression system in prokaryotes and the bacculovirus expression system in eukaryotes. Polypeptides can also be synthesized in vitro, e.g., by the solid phase peptide synthetic method or by in vitro transcription/translation systems. Such methods are described, for example, in U.S. Pat. Nos. 5,595,887; 5,116,750; 5,168,049 and 5,053,133; Olson et al., Peptides, 9, 301, 307 (1988). The solid phase peptide synthetic method is an established and widely used method, which is described in the following references: Stewart et al., Solid Phase Peptide Synthesis, W. H. Freeman Co., San Francisco (1969); Merrifield, J. Am. Chem. Soc, 85 2149 (1963); Meienhofer in "Hormonal Proteins and Peptides," ed.; C. H. Li, Vol. 2 (Academic
Press, 1973), pp. 48-267; Bavaay and Merrifield, "The Peptides," eds. E. Gross and F. Meienhofer, Vol. 2 (Academic Press, 1980) pp. 3-285; and Clark-Lewis et al., Meth. Enzymol., 287, 233 (1997). These polypeptides can be further purified by fractionation on immunoaffinity or ion-exchange columns; ethanol precipitation; reverse phase HPLC; chromatography on silica or on an anion-exchange resin such as DEAE; chromatofocusing; SDS-PAGE; ammonium sulfate precipitation; gel filtration using, for example, Sephadex G-75; or ligand affinity chromatography.
Polypeptidyl-α-N-acetylgalactosaminyltransferase (pp-GalNAc-T) A large family of enzymes, called glycosyltransferases, is involved in the synthesis of complex oligosaccharides of glycoconjugates. These enzymes have been
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assembled in a CAZy database (available on the world wide web at www.cazy.org). They transfer a sugar moiety, primarily from an activated sugar nucleotide donor to a sugar acceptor or to a protein, lipid, or aglycon, with either retention or inversion of the stereochemistry at the Cl position of the donor sugar. Recently the structural information of several of these glycosyltransferases has become available (Qasba, P. K.; Ramakrishnan, B.; Boeggeman, E. Substrate-induced conformational changes in glycosyltransferases. Trends Biochem. Sci. 2005, 30, 53-62), making it possible to engineer these enzymes so that they can transfer a non-preferred sugar residue (Ramakrishnan, B.; Qasba, P. K. Structure-based design of /3-1,4- galactosyl- transferase-I (/3 4GaI-Tl) with equally efficient N^acetylgalactosaminyltransferase activity. J. Biol. Chem. 2002, 277, 20833-20840; Ramakrishnan, B.; Boeggeman, E.; Qasba, P. K. Mutation of Arg 228 to lysine enhances the glucosyltransf erase activity of bovine /3-1,4-galactosyltransferase I. Biochemistry 2005, 44, 3202-3210; Marcus, S. L.; Polakowski, R.; Seto, N. O.; Leinala, E.; Borisova, S.; Blancher. A.; Roubinet, F.; Evans, S. V.; Palcic, M. M. A single point mutation reverses the donor specificity of human blood group B-synthesizing galactosyltransferase. J. Biol. Chem. 2003, 278, 12403-12405; Ouzzine, M.; Gulberti, S.; Levoin, N.; Netter, P.; Magdalou, J.; Fournel-Gigleux, S. The donor substrate specificity of the human beta 1 ,3-glucuronosyltransferase I toward UDP-glucuronic acid is determined by two crucial histidine and arginine residues. J. Biol. Chem. 2002, 277, 25439-25445.) or sugar residue with a chemically reactive unique functional group (Khidekel, N.; Arndt, S.; Lamarre-Vincent, N.; Lippert, A.; Poulin-'Kerstien, K.G.; Ramakrishnan, B.; Qasba, P. K.; Hsieh- Wilson, L. C. A Chemoenzymatic approach toward the rapid and sensitive detection of O-GlcNAc posttranslational modifications. J. Am. Chem. Soc. 2003, 125, 16162-16163). The presence of a modified sugar moiety with a chemical handle on a glycoconjugate makes it possible to link bioactive molecules via a modified glycan chain.
A chemo-enzymatic method to detect free N-acetylglucosamine (GIcNAc) at the non-reducing end of the glycan chain of glycoproteins using a mutant beta 1,4 galactosyltransferase has been described by the present inventors in US Patent Application 20060084162, incorporated by reference in its entirety herein.
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Substitution of amino acid residues located in the donor binding site of beta.(l,4)- galactosyltransferase I provides greater flexibility and decreased steric hindrance, and thus allows glucose or GaINAc to be bound and chemically bonded to N- acetylglucosamine. Such mutations provide for broadened donor binding, such as binding of glucose or GaINAc, while still preserving interaction with amino acid residues active during catalytic bond formation between the donor and the acceptor.
The instant invention demonstrates that the polypeptidyl-a-N- acetylgalactosaminyltransferase II (ppGalNAc-T2), which transfers N- acetylgalactosamine (GaINAc) from UDP-α-GalNAc to one or more Ser and/ or Thr residue of an acceptor polypeptide, can be used to glycosylate a peptide sequence engineered at the C-terminal or N-terminal end of a non-glycoprotein. The pp- GaINAc-T enzymes comprise 17-19 family members. There are approximately 24 ppGalNAcTs, with othologs in higher eukaryotes that demonstrate about 90 - 98% sequence homology across species (23). Approximately 21 different ppGalNAcT isoforms have been cloned across different species (23). All of the ppGalNAc-T's show a conservation in their structure, characterized by an N-terminal cytosolic tail, a type II transmembrane domain, a variable stem region, a catalytic domain (CD) (GTl) a Gal/ GaINAc recognition domain, and a C-terminal lectin domain (LD).
The ppGalNAc-T enzymes transfer GaINAc in an α-configuration, from UDP- α-GalNAc, to a Ser and orThr residue of a peptide sequence which is variable in sequence. Some of these enzymes require GaINAc to be present on the neighboring Thr and/ or Ser residue in the polypeptide sequence. The universal nucleotide sugar donor for the ppGalNAc-T's is UDP-GaINAc. However, in addition, synthetic UDP- GaINAc analogues are useful as in vitro substrates for ppGalNAc-Ts. Virtually any UDP-GaINAc analogue is suitable for use in the invention; however preferred examples include UDP-GaINAc analogues with keto or azido groups, for example UDP-GaINAz, prefereably at the p 2-position, e.g. 2-keto.
As described herein, the soluble domain of ppGalNAc-T2 was engineered in E. coli and an in vitro folding method was developed from inclusion bodies to make milligram quantities of active ppGalNAc-T2 from a liter of bacterial culture.
Glutathione-S-transferase (GST) was expressed in E.coli with a C-terminal 17 amino
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acid long fusion peptide sequence with one Thr residue, acting as an acceptor sequence for the ppGalNAc-T2. The ppGalNAc-T2 enzyme not only transfers GaINAc from UDP-GaINAc to the Thr residue in the fusion peptide, but also transfers modified galactose, such as 2-keto-galactose or GaINAz, from their respective UDP- sugars. Furthermore, this modified sugar moiety is readily available for chemical modification such as biotinylation. The invention described herein demonstrates a novel method to glycosylate, with ppGalNAc-T2 and C-2 modified UDP-GaINAc, important biological molecules; such as, single chain antibodies, growth factors or bacterial toxins, with engineered peptide sequences at the C-terminus of the molecule. The peptide sequences at the C-terminus of the molecule can be 10, 15, 17 amino acids in length. In certain preferred embodiments, the chemical handle at the C-2 of galactose is used for conjugation and assembly of bio-nanoparticles and for the formulation of immuno-liposome for the targeted drug delivery system.
Previous in vivo studies have shown that ppGalNAc-T can transfer GaINAc analogue sugars with a unique chemical handle, such as GaINAz (2-azio-GalNAc), to the acceptor polypeptide (17). Therefore, it is possible to glycosylate a non- glycoprotein with ppGalNAc-T with a modified sugar carrying a unique chemical handle that can be used for conjugation. Furthermore, in the present study the soluble form of ppGalNAc-T2 was expressed in E. coli and a method of in vitro folding of the protein from inclusion bodies was set up to make large quantities of active ppGalNAc-T2.
In certain embodiments, Glutathione-S-transferase (GST) protein is used as a model system for engineering the fusion peptide sequence, with a single Thr residue, at its C-terminus which is the acceptor substrate for ppGalNAc-T2. ppGalNAc-T2 not only transfers GaINAc or GaINAz, but also 2-keto-Gal to the single Thr residue present in the tag peptide of the GST-tag fusion protein, demonstrating that this method can be used for glycosylating non-glycoproteins, for example, but not limited to, ScFv and bacterial toxins, growth factors and other bioactive molecules.
In certain embodiments, the invention features an isolated catalytic domain from a polypeptidyl-α-N-acetylgalactosaminyltransferase (pp-GalNAc-T) that transfers N-acetylgalactosamine from UDP-α-GalNAc to a Ser/Thr residue of an
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acceptor polypeptide. The isolated catalytic domain from pp-GalNAc preferably transfers GaINAc in α configuration.
In preferred embodiments of the invention, the isolated catalytic domain from a pp-GalNAc-T comprises a catalytic domain and lectin domain (LD), as shown in SEQ ID NO: 1, below:
(SEQ ID NO: 1)
AQSMETLPPGKVRWPDFNQEAYVGGTMVRSGQDPYARNKFN QVESDKLRMDRAIPDTRHDQCQRKQWRVDLPATSVVITFHNE ARSALLRTVVSVLKKSPPHLIKEIILVDDYSNDPEDGALLGKIEK
VRVLRNDRREGLMRSRVRGADAAQAKVLTFLDSHCECNEHW LEPLLERVAEDRTRVVSPIIDVINMDNFQYVGASADLKGGFDW NLVFKWDYMTPEQRRSRQGNPVAPIKTPMIAGGLFVMDKFYF EELGKYDMMMDVWGGENLEISFRVWQCGGSLEIIPCSRVGHV FRKQHPYTFPGGSGTVFARNTRRAAEVWMDEYKNFYYAAVPS
ARNVPYGNIQSRLELRKKLSCKPFKWYLENVYPELRVPDHQDI AFGALQQGTNCLDTLGHFADGVVGVYECHNAGGNQEWALTK EKSVKHMDLCLTVVDRAPGSLIKLQGCRENDSRQKWEQIEGN SKLRHVGSNLCLDSRTAKSGGLSVEVCGPALSQQWKFTLNLQ Q
The corresponding nucleic acid sequence encoding the catalytic domain from a polypeptidyl-α-N-acetylgalactosaminyltransferase (pp-GalNAc-T) comprises SEQ ID NO: 2, shown below:
(SEQ ID NO: 2)
GCACAAAGCATGGAGACCCTCCCTCCAGGGAAAGTACGGTG GCCAGACTTTAACCAGG AAGCTTATGT TGGAGGGACG ATGGTCCGCT CCGGGCAGGA CCCTTACGCCCGCAACAAGT TCAACCAGGT GGAGAGTGAT AAGCTTCGAA TGGACAGAGC
CATCCCTGACACCCGGCATG ACCAGTGTCA GCGGAAGCAG TGGCGGGTGG ATCTGCCGGC CACCAGCGTGGTGATCACGT TTCACAATGA AGCCAGGTCG GCCCTACTCA GGACCGTGGT CAGCGTGCTTAAGAAAAGCCCGCCCCATCTCATAAAAGAAA TCATCTTGGTGGATGACTACAGCAATGATCCTGAGGACG
GGGCTCTCTT GGGGAAAATT GAGAAAGTGC GAGTTCTTAG AAATGATCGACGAGAAGGCC TCATGCGCTC ACGGGTTCGG GGGGCCGATG CTGCCCAAGC CAAGGTCCTGACCTTCCTGG ACAGTCACTG CGAGTGTAAT GAGCACTGGC TGGAGCCCCT CCTGGAAAGGGTGGCGGAGGACAGGACTCG GGTTGTGTCA
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CCCATCATCG ATGTCATTAA TATGGACAACTTTCAGTATG TGGGGGCATCTGCTGACTTGAAGGGCGGTTTTGATTGGAAC TTGGTATTCAAGTGGGATT ACATGACGCC TGAGCAGAGA AGGTCCCGGC AGGGGAACCC AGTCGCCCCTATAAAAACCC CCATGATTGC TGGTGGGCTG TTTGTGATGG ATAAGTTCTA
TTTTGAAGAACTGGGGAAGT ACGACATGAT GATGGATGTG TGGGGAGGAG AGAACCTAGA GATCTCGTTCCGCGTGTGGC AGTGTGGTGGCAGCCTGGAGATCATCCCGTGCAGCCGTGTG GGACACGTGTTCCGGAAGCAGCACCCCTACACGTTCCCGGG TGGCAGTGGCACTGTCTTTGCCCGAAACACCCGCCGGGCAG
CAGAGGTCTGGATGGATGAATACAAAAATTTCTATTATGCA GCAGTGCCTTCTGCTAGAAACGTTCCTTATGGAAATATTCAG AGCAGATTGGAGCTTAGGAAGAAACTCAGCTGCAAGCCTTT CAAATGGTACCTTGAAAATGTCT ATCCAGAGTT AAGGGTTCCAGACCATCAGG
ATATAGCTTTTGGGGCCTTGCAGCAGGGAACTAACTGCCTC GACACTTTGGGACACTTTGCTGATGGTGTGGTTGGAGTTTAT GAATGTCACAATGCTGGGGGAAACCAGGAATGGGCCTTGAC GAAGGAGAAGTCAGTGAAGCACATGGATTTGTGCCTTACTG TGGTGGACCGGGCACCGGGCTCTCTTATAAAGCTGCAGGGC
TGCCGAGAAAATGACAGCAGACAGAAATGGGAACAGATCG AGGGCAACTCCAAGCTGAGGCACGTGGGCAGCAACCTGTGC CTGGACAGTCGCACGGCCAAGAGCGGGGGCCTAAGCGTGG AGGTGTGTGGCCCGGCCCTTTCGCAGCAGTGGAAGTTCACG CTCAACCTGCAGCAGTAG
Sequences of pp-GalNAc-T family members from human and other species are known, and the DNA clones are commercially available from, for example, Open Biosources. The methods of the invention are amenable to use with any pp-GalNAc- T2. By any pp-GalNAc is meant from any species, or pp-GalNAc-Tl or pp-GalNAc- T2.
Peptides of the invention include isolated catalytic domains, full length polypeptidyl-a-N-acetylgalactosaminyltransferase enzymes containing a catalytic domain of the invention, as well as recombinant polypeptides or a protein linked to additional amino acids. Such polypeptides may be expressed from DNA constructs and expression cassettes that are produced through use of recombinant methods. Such methods have been described. Sambrook et al., Molecular Cloning: A Laboratory Manual, 3rd edition, Cold Spring Harbor Press, Cold Spring Harbor, N. Y. (2001).
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polypeptidyl-α-N-acetylgalactosaminyltransferase enzymes containing a catalytic domain of the invention may be produced in soluble form. Methods that may be used to produce such soluble enzymes have been described (U.S. Pat. No. 5,032,519). Briefly, a hydrophobic transmembrane anchor region of a polypeptidyl-α- N-acetylgalactosaminyltransferase is removed to produce an enzyme that is in soluble form.
Alternatively, catalytic domain from a polypeptidyl-α-N- acetylgalactosaminyltransferase enzymes containing a catalytic domain of the invention may be produced such that they are anchored in the membrane of a cell that expresses the polypeptidyl-α-N-acetylgalactosaminyltransferase. Such enzymes may be produced that are anchored in the membranes of prokaryotic and eukaryotic cells. Methods to produce such enzymes have been described (U.S. Pat. No. 6,284,493).
Briefly, in the case of prokaryotes, the signal and transmembrane sequences of the polypeptidyl-α-N-acetylgalactosaminyltransferase are replaced by a bacterial signal sequence, capable of effecting localization of the fusion protein to the outer membrane. Suitable signal sequences include, but are not limited to those from the major E. coli lipoprotein Lpp and lam B. In addition, membrane spanning regions from Omp A, Omp C, Omp F or Pho E can be used in a tripartite fusion protein to direct proper insertion of the fusion protein into the outer membrane. Any prokaryotic cells can be used in accordance with the present invention including but not limited to E. coli, Bacillus sp., and Pseudomonas sp. as representative examples.
The present invention is also applicable for use with eukaryotic cells resulting in cell surface expression of polypeptidyl-α-N-acetylgalactosaminyltransferase in known culturable eukaryotic cells including but not limited to yeast cells, insect cells, Chinese hamster ovary cells (CHO cells), mouse L cells, mouse A9 cells, baby hamster kidney cells, C 127 cells, COS cells, Sf9 cells, and PC8 cells.
For example, the transmembrane domain of the polypeptidyl-α-N- acetylgalactosaminyltransferase is replaced by the transmembrane domain of a plasma membrane protein. The transmembrane domain of any resident plasma membrane protein will be appropriate for this purpose. The transmembrane portions of the M6
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P/IGF-II receptor, LDL receptor or the transferrin receptor are representative examples.
In any of the methods described herein the pp-GalNAc-T can be pp-GalNAc- T2.
Nucleic Acids and Vectors
The present invention provides isolated nucleic acid segments that encode catalytic domains of pp-GalNAc-T. Nucleic acid sequences encoding human pp- GaINAc-TII (SEQ ID NO: 2), as well as other pp-GalNAc-T from other organisms are available. These nucleic acid sequences can be modified to encode the catalytic domains and amino acid segments of the invention through use of well-known techniques (Sambrook et al., Molecular Cloning: A Laboratory Manual, 3rd edition, Cold Spring Harbor Press, Cold Spring Harbor, N. Y. (2001)). For example, a portion of the nucleic acid sequence encoding human pp-GalNAc-T II (SEQ ID NO: 2) can be inserted into an expression vector such that an amino acid segment corresponding to the catalytic domain of human pp-GalNAc-TII (SEQ ID NO: 1) is expressed upon transformation of a cell with the expression vector. [0072] The nucleic acid segments of the invention may be optimized for expression in select cells. Codon optimization tables are available. Harlow and Lane, Antibodies: A Laboratory Manual, Cold Spring Harbor Laboratory Press, 1988.
The nucleic acid segments can be inserted into numerous types of vectors. A vector may include, but is not limited to, any plasmid, phagemid, F-factor, virus, cosmid, or phage in double or single stranded linear or circular form, which may or may not be self-transmissible or mobilizable. The vector can also transform a prokaryotic or eukaryotic host either by integration into the cellular genome or exist extrachromosomally (e.g. autonomous replicating plasmid with an origin of replication).
Preferably the nucleic acid segment in the vector is under the control of, and operably linked to, an appropriate promoter or other regulatory elements for transcription in vitro or in a host cell such as a eukaryotic cell or microbe, e.g. bacteria. The vector may be a bi-functional expression vector which functions in
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multiple hosts. In the case of genomic DNA, this may contain its own promoter or other regulatory elements and in the case of cDNA this may be under the control of a promoter or other regulatory sequences for expression in a host cell.
Specifically included are shuttle vectors by which is meant a DNA vehicle capable, naturally or by design, of replication in two different host organisms, which may be selected from bacteria and eukaryotic cells (e.g. mammalian, yeast or fungal).
The vector may also be a cloning vector which typically contains one or a small number of restriction endonuclease recognition sites at which nucleic acid segments can be inserted in a determinable fashion. Such insertion can occur without loss of essential biological function of the cloning vector. A cloning vector may also contain a marker gene that is suitable for use in the identification and selection of cells transformed with the cloning vector. Examples of marker genes are tetracycline resistance, hygromycin resistance or ampicillin resistance. Many cloning vectors are commercially available (Stratagene, New England Biolabs, Clonetech). The nucleic acid segments of the invention may also be inserted into an expression vector. Typically an expression vector contains (1) prokaryotic DNA elements coding for a bacterial replication origin and an antibiotic resistance gene to provide for the amplification and selection of the expression vector in a bacterial host; (2) regulatory elements that control initiation of transcription such as a promoter; and (3) DNA elements that control the processing of transcripts such as introns, transcription termination/ polyadenylation sequence.
Methods to introduce a nucleic acid segment into a vector are well known in the art (Sambrook et al., 1989). Briefly, a vector into which the nucleic acid segment is to be inserted is treated with one or more restriction enzymes (restriction endonuclease) to produce a linearized vector having a blunt end, a "sticky" end with a 5' or a 3' overhang, or any combination of the above. The vector may also be treated with a restriction enzyme and subsequently treated with another modifying enzyme, such as a polymerase, an exonuclease, a phosphatase or a kinase, to create a linearized vector that has characteristics useful for ligation of a nucleic acid segment into the vector. The nucleic acid segment that is to be inserted into the vector is treated with one or more restriction enzymes to create a linearized segment having a blunt end, a
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"sticky" end with a 5' or a 3' overhang, or any combination of the above. The nucleic acid segment may also be treated with a restriction enzyme and subsequently treated with another DNA modifying enzyme. Such DNA modifying enzymes include, but are not limited to, polymerase, exonuclease, phosphatase or a kinase, to create a polynucleic acid segment that has characteristics useful for ligation of a nucleic acid segment into the vector.
The treated vector and nucleic acid segment are then ligated together to form a construct containing a nucleic acid segment according to methods known in the art (Sambrook, 2002). Briefly, the treated nucleic acid fragment and the treated vector are combined in the presence of a suitable buffer and ligase. The mixture is then incubated under appropriate conditions to allow the ligase to ligate the nucleic acid fragment into the vector. It is preferred that the nucleic acid fragment and the vector each have complimentary "sticky" ends to increase ligation efficiency, as opposed to blunt-end ligation. It is more preferred that the vector and nucleic acid fragment are each treated with two different restriction enzymes to produce two different complimentary "sticky" ends. This allows for directional ligation of the nucleic acid fragment into the vector, increases ligation efficiency and avoids ligation of the ends of the vector to reform the vector without the inserted nucleic acid fragment.
Suitable prokaryotic vectors include but are not limited to pBR322, pMB9, pUC, lambda bacteriophage, ml 3 bacteriophage, and Bluescript.RTM.. Suitable eukaryotic vectors include but are not limited to PMSG, pAV009/A+, PMTO10/A+, pMAM neo-5, bacculovirus, pDSVE, YIP5, YRPl 7, YEP. It will be clear to one of ordinary skill in the art which vector or promoter system should be used depending on which cell type is used for a host cell. The invention also provides expression cassettes which contain a control sequence capable of directing expression of a particular nucleic acid segment of the invention either in vitro or in a host cell. The expression cassette is an isolatable unit such that the expression cassette may be in linear form and functional in in vitro transcription and translation assays. The materials and procedures to conduct these assays are commercially available from Promega Corp. (Madison, Wis.). For example, an in vitro transcript may be produced by placing a nucleic acid segment
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under the control of a T7 promoter and then using T7 RNA polymerase to produce an in vitro transcript. This transcript may then be translated in vitro through use of a rabbit reticulocyte lysate. Alternatively, the expression cassette can be incorporated into a vector allowing for replication and amplification of the expression cassette within a host cell or also in vitro transcription and translation of a nucleic acid segment.
Such an expression cassette may contain one or a plurality of restriction sites allowing for placement of the nucleic acid segment under the regulation of a regulatory sequence. The expression cassette can also contain a termination signal operably linked to the nucleic acid segment as well as regulatory sequences required for proper translation of the nucleic acid segment. Expression of the nucleic acid segment in the expression cassette may be under the control of a constitutive promoter or an inducible promoter, which initiates transcription only when the host cell is exposed to some particular external stimulus. The expression cassette may include in the 5'-3' direction of transcription, a transcriptional and translational initiation region, a nucleic acid segment and a transcriptional and translational termination region functional in vivo and/or in vitro. The termination region may be native with the transcriptional initiation region, may be native with the nucleic acid segment, or may be derived from another source. Numerous termination regions are known in the art. Guerineau et al., MoI. Gen.
Genet., 262:141 (1991); Proudfoot, Cell, 64:671 (1991); Sanfacon et al., Genes Dev., 5:141 (1991); Munroe et al., Gene, 91 :151 (1990); Ballas et al., Nucleic Acids Res., 17:7891 (1989); Joshi et al., Nucleic Acid Res., 15:9627 (1987).
The regulatory sequence can be a nucleic acid sequence located upstream (5' non-coding sequences), within, or downstream (3' non-coding sequences) of a coding sequence, and which influences the transcription, RNA processing or stability, or translation of the associated coding sequence. Regulatory sequences can include, but are not limited to, enhancers, promoter and repressor binding sites, translation leader sequences, introns, and polyadenylation signal sequences. They may include natural and synthetic sequences as well as sequences that may be a combination of synthetic and natural sequences. While regulatory sequences are not limited to promoters, some
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useful regulatory sequences include constitutive promoters, inducible promoters, regulated promoters, tissue-specific promoters, viral promoters and synthetic promoters.
A promoter is a nucleotide sequence that controls expression of the coding sequence by providing the recognition for RNA polymerase and other factors required for proper transcription. A promoter includes a minimal promoter, consisting only of all basal elements needed for transcription initiation, such as a TATA-box and/or initiator that is a short DNA sequence comprised of a TATA-box and other sequences that serve to specify the site of transcription initiation, to which regulatory elements are added for control of expression. A promoter may be inducible. Several inducible promoters have been reported (Current Opinion in Biotechnology, 7:168 (1996)). Examples include the tetracycline repressor system, Lac repressor system, copper- inducible systems, salicylate-inducible systems (such as the PRIa system). Also included are the benzene sulphonamide- (U.S. Pat. No. 5,364,780) and alcohol- (WO 97/06269 and WO 97/06268) inducible systems and glutathione S-transferase promoters. In the case of a multicellular organism, the promoter can also be specific to a particular tissue or organ or stage of development.
An enhancer is a DNA sequence which can stimulate promoter activity and may be an innate element of the promoter or a heterologous element inserted to enhance the level or tissue specificity of a promoter. It is capable of operating in both orientations (normal or flipped), and is capable of functioning even when moved either upstream or downstream from the promoter. Both enhancers and other upstream promoter elements bind sequence-specific DNA-binding proteins that mediate their effects. The expression cassette can contain a 5' non-coding sequence which is a nucleotide sequence located 5' (upstream) to the coding sequence. It is present in the fully processed mRNA upstream of the initiation codon and may affect processing of the primary transcript to mRNA, stability of the mRNA, or translation efficiency (Turner et al., Molecular Biotechnology, 3:225 (1995)). The expression cassette may also contain a 3' non-coding sequence, which is a nucleotide sequence, located 3' (downstream) to a coding sequence and includes
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polyadenylation signal sequences and other sequences encoding regulatory signals capable of affecting mRNA processing or gene expression. The polyadenylation signal is usually characterized by affecting the addition of polyadenylic acid tracts to the 3' end of the mRNA precursor. The invention also provides a construct containing a vector and an expression cassette. The vector may be selected from, but not limited to, any vector previously described. Into this vector may be inserted an expression cassette through methods known in the art and previously described (Sambrook et al., 1989). In one embodiment, the regulatory sequences of the expression cassette may be derived from a source other than the vector into which the expression cassette is inserted. In another embodiment, a construct containing a vector and an expression cassette is formed upon insertion of a nucleic acid segment of the invention into a vector that itself contains regulatory sequences. Thus, an expression cassette is formed upon insertion of the nucleic acid segment into the vector. Vectors containing regulatory sequences are available commercially and methods for their use are known in the art (Clonetech, Promega, Stratagene).
The expression cassette, or a vector construct containing the expression cassette may be inserted into a cell. The expression cassette or vector construct may be carried eposomally or integrated into the genome of the cell. A variety of techniques are available and known to those skilled in the art for introduction of constructs into a cellular host. Transformation of bacteria and many eukaryotic cells may be accomplished through use of polyethylene glycol, calcium chloride, viral infection, phage infection, electroporation and other methods known in the art. Other transformation methods are available to those skilled in the art, such as direct uptake of foreign DNA constructs (see EP 295959), techniques of electroporation (Fromm et al. Nature (London), 319:791 (1986) or high velocity ballistic bombardment with metal particles coated with the nucleic acid constructs (Kline et al. Nature (London) 327:70 (1987), and U.S. Pat. No. 4,945,050).
The selection of an appropriate expression vector will depend upon the method of introducing the expression vector into host cells. Typically an expression vector contains (1) prokaryotic DNA elements coding for a bacterial origin of
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replication and an antibiotic resistance gene to provide for the amplification and selection of the expression vector in a bacterial host; (2) DNA elements that control initiation of transcription, such as a promoter; (3) DNA elements that control the processing of transcripts, such as introns, transcription termination/polyadenylation sequence; and (4) a reporter gene that is operatively linked to the DNA elements to control transcription initiation. Useful reporter genes include .beta.-galactosidase, chloramphenicol acetyl transferase, luciferase, green fluorescent protein (GFP) and the like.
Methods of Making
Included in the invention are methods for engineering a glycoprotein from a biological substrate. The methods comprise attaching to the C-terminal or N-terminal end of a biological substrate an acceptor polypeptide, and using the biological substrate with the acceptor polypeptide as an acceptor substrate for a pp-GalNAc-T, and then transferring one or more GaINAc residue or GaINAc analogue sugars to the acceptor polypeptide, and thereby engineering a glycoprotein from a biological substrate. Figure 7 presents a general outline of the method. Figure 8 also presents a schematic detailing a method of making, for example, a multivalent nanoparticle or multiple linked nanoparticles wherein an acceptor sequence comprises, for example, multiple Ser or Thr residues for sugar transfer.
Included in the invention are methods for glycosylating a biological substrate for use in glycoconjugation. The methods comprise attaching to the C-terminal or N- terminal end of a biological substrate an acceptor polypeptide, and using the biological substrate with the acceptor polypeptide as an acceptor substrate for a pp- GaINAc-T, and transferring one or more GaINAc residue or GaINAc analogue sugars to the acceptor polypeptide, and thereby glycoslyating the biological substrate for use in glycoconjugation. The GaINAc residue or GaINAc analogue sugars are transferred to a Ser and/ or Thr residue of the acceptor polypeptide. It is preferred, in certain embodiments, that the GST-tag protein with only a Thr and/ or Ser residue in its fusion peptide is used for the transfer of GaINAc or GaINAc analogue sugars, for example but not limited to, 2-keto-Gal and GaINAz sugars, from their respective
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UDP-derivatives. In other certain examples, it is preferred that the acceptor polypeptide comprises repeating consensus sequences. For example, the acceptor polypeptide comprises repeating Ser and/ or Thr residues that can be used for the transfer of GaINAc or GaINAc analogue sugars. In the methods as described herein, the biological substrate can be selected from, but not limited to, a non-glycoprotein, an oligopeptide and any biological matrix. Any biological matrix that is suitable for attachment of the acceptor polypeptide is envisioned for use in the methods of the invention. In certain preferred embodiments, the non-glycoprotein or oligo-peptide is a bioactive agent. Preferably, the bioactive agent can be any bioactive agent carrying a linker sequence with a functional coupling group. Examples of bioactive agents include, but are not limited to single chain antibodies, bacterial toxins, growth factors, therapeutic agents, and contrast agents. For example, a therapeutic agent can be a chemotherapeutic agent, an anti-inflammatory agent, an antibacterial agent, or an antifungal agent. Contrast agents include MRI contrast agents such as gadolinium-based agents.
The method includes an acceptor peptide. The acceptor peptide is attached to the C-terminal or N-terminal end of a biological substrate. The biological substrate with the acceptor polypeptide is used as an acceptor substrate for a pp-GalNAc-T, and then one or more GaINAc residue or GaINAc analogue sugars is transferred to the acceptor polypeptide, and thus a glycoprotein is engineered from a biological substrate.
Unlike N-linked glycosylation, which occurs at a defined consensus sequence, there does not appear to be a defined peptide substrate specificity of the ppGalNAcTs. Some studies have indicated that there is a preference for Proline at the P3' position with respect to the site of modification, that charged residues at Pl and P3' were not favorable and that glycosylation of Thr over Ser was preferred (24).
In certain embodiments, the acceptor polypeptide comprises at least 10, 1 1, 12, 13, 14, 15,16, 17, 18, 19, or 20 amino acids. In other embodiments the acceptor polypeptide is glycosylated at one or more sites, wherein the one or more sites has a Thr or Ser residue, and the pp-GalNAc-T transfers the GaINAc or GaINAc analogue to one or more Ser and/ or Thr residues of the acceptor polypeptide.
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In other certain embodiments, the acceptor polypeptide is selected from, but not limited to, SEQ ID NO: 3 (GAGGPIMAAATPAPAAK) or SEQ ID NO: 4 (AGGPIMAATPAPAAK).
Therapeutics and Diagnostics
Oligosaccharide moieties of glycoconjugates are involved in many biological processes, and as such have been used as a tool for the delivery of ligands to specific sites and tissues. Glycotargeting is the use of carbohydrate ligands to target protein receptors at the site of location, and was brought about in part by the discovery of the hepatic receptor, the asialoglycoprotein receptor (ASGPR), which binds to and internalizes the circulating glycoproteins or glycopeptides that have galactose or N- acetylgalactosamine residue at the nonreducing terminus of the oligosaccharide chain (Morell AG, Gregoriadis G, Scheinberg H, Hickman J, Ashwell G. The role of sialic acid in determining the survival of glycoproteins in the circulation. J Biol Chem. 1971 ;246: 1461 - 1467). Glycotargeting has use, for example, in developing a targeted drug delivery system and in developing contrast agents for MRI.
Bioconjugates
Targeting biologically active molecules to the site where they need to act presents a challenging task (Jain R.K. The next frontier of molecular medicine: delivery of therapeutics. Nat Med 1998;4:655-7). Monoclonal or single-chain antibodies against ligands or receptors (Hale G. Therapeutic antibodies -delivering the promise? Adv Drug Deliv Rev 2006;58:633-9; Schrama D, Reisfeld RA, Becker JC. Antibody targeted drugs as cancer therapeutics. Nat Rev Drug Discov 2006;5: 147-59; Hollinger P, Hudson PJ. Engineered antibody fragments and the rise of single domains. Nat Biotechnol 2005;23:l 126-36) and tumor-homing (Laakkonen P, Porkka K, Hoffman JA, Ruoslahti E. A tumor-homing peptide with a targeting specificity related to lymphatic vessels. Nat Med 2002;8:751), or cell-penetrating peptides (Jarver P, Langel U. Cell-penetrating peptides - a brief introduction. Biochim Biophys Acta 2006; 1758:260) are being developed, which act as tissue and cell-specific guiding molecules that have potential
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to carry biologically active molecules, however, the guiding molecules need to be conjugated with the biologically active agents in a site-specific manner.
Various methods are being used with mixed success in conjugating peptides or antibodies with the cargo molecule. Often, the primary amine groups present on the surface of the protein molecule are used for conjugation; however, as every lysine residue present on the protein molecule would be reactive, this method results in undesirable heterogeneous conjugation and even loss of antibody activity. Recently, methods have been introduced for the site-specific coupling of biomolecules that indude site-directed introduction and chemoselective ligation of Cys residues to convert non-glycoproteins to glycoproteins (Carrico IS, Carlson BL, Bertozzi CR. Introducing genetically encoded aldehydes into proteins. Nat Chem Biol 2007;3:321- 2), and site-directed introduction of azido/alkynyl-tagged Met analogues into proteins (O'Shanessy DJ, Quarles RH. Labeling of the oligosaccharide moieties immunogloblins. J Immunol Methods 1987;99: 153-61). In the former method, either engineered or naturally present Cys residue, which is highly reactive in basic pH, requires special handling of the protein to prevent its free Cys residue from undergoing undesired oxidation. In the latter method, all the Met residues present in the protein are modified. Carrico et al. have described a method for introducing genetically encoded aldehydes at either terminal end of proteins, which can then be used for conjugation (Sato H, Hayashi E, Yamada N, et al. Further studies on the site- specific protein modification by microbial transglutaminase. Biocoηjug Chem 2001 ;12:701-10). The sugar moieties present on the glycoproteins, such as IgG, upon periodate oxidation provide aldehyde groups that have been used for coupling (Zhou Z, Cironi P, Lin AJ, et al. Genetically encoded short peptide tags for orthogonal protein labeling by Sfp and Acps phosphopantetheinyl transferases. ACS Chem Biol 2007;2:337-46). However, the heterogeneous nature of the glycan moiety on the recombinant glycoprotein causes poor coupling. Various investigators are developing chemoenzymatic methods for the site-specific conjugation of biomolecules (Qasba PK. Involvement of sugars in protein-protein interactions. Carbohydr Polym 2000;41 :293-309; Qasba PK, Ramakrishnan B, Boeggeman E. Substrate-induced conformational changes in glycosyltransferases. Trends Biochem Sci 2005;30:53-62).
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The structural information available for glycosyltransferases makes it possible to design novel glycosyltransferases with broader and requisite donor specificities. As described herein, several mutant glycosyltransferases have been generated that can transfer a sugar residue with a chemically reactive functional group (e.g., 2-keto-Gal or GaINAz) from their UDP derivatives to the N-acetylglucosamine residue of glycoconjugates, such as to the oligosaccharide chain of IgG (Qasba PK, Ramakrishnan B, Boeggeman E. Mutant glycosyltransferases assist in the development of a targeted drug delivery system and contrast agents for MRI. Am Ass Pharm Soc J 2006;8: 190-5). Based on this technique, and using the novel catalytic domains as described herein, for example an isolated catalytic domain from a polypeptidyl-α-N-acetylgalactosaminyltransferase (pp-GalNAc-T) that transfers N- acetylgalactosamine (GaINAc) or a GaINAc analogue from UDP-α-GalNAc to one or more Ser or Thr residues of an acceptor polypeptide, wherein the isolated catalytic domain comprises SEQ ID NO: 1, it is possible that two glycoproteins with modified sugars having unique chemical handles may be conjugated with crosslinkers with orthogonal chemical reactive groups, thus enabling the design of novel immunotoxins and MRI contrast agents . Non-glycoproteins can be glycosylated by engineering a C- terminal peptide tag that can be glycosylated with a modified sugar and coupled to a biomolecule that carries an orthogonal reactive group, making the method very useful in many nanobiological applications. Single-chain antibodies, instead of their full- length IgG counterparts, are increasingly used for immunotherapy (27. Carter P. Improving the efficacy of antibody-based caner therapies. Nat Rev Cancer 2001 ; 1 : 118-29), and they are easily expressed in large amounts in E. coli as soluble proteins. Delivering drugs or contrast agents to a specific target site for medical imaging is highly desirable for the diagnosis and treatment of many diseases including cancer. For this purpose, target-specific monoclonal antibodies, single-chain antibodies, affibodies, and tumor-homing or cell-penetrating peptides have emerged as important guiding molecules that can carry a cargo of therapeutic molecules to the desired site. Deploying these carrier molecules for the site-specific delivery of therapeutics molecules requires site-specific conjugation of these molecules with the
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cargo molecules. Using wild-type or mutant glycosyltransferases to transfer a modified sugar residue with a chemical handle to a specific sugar moiety on a glycoconjugate or to a specific amino acid residue on a polypeptide chain, respectively, allows one to exploit these chemical handles for the bioconjugation of biomolecules. The monoclonal antibodies whose N-linked glycan moieties have been modified with the mutant P-l,4-galactosyltransferase to have 2-azido- or 2-keto-Gal can be conjugated with a biomolecule having a corresponding orthogonal reactive group, such as alkynes or aminooxy. Similarly, a fusion peptide attached at the C- terminal end of a single-chain antibody, affibody, or a tumor-homing or cell- penetrating peptide can be glycosylated at a unique site in the fusion peptide with a modified sugar; the glycosylated fusion peptide can then be conjugated with a biomolecule carrying an orthogonal reactive group. In addition, a cargo molecule having multiple conjugation sites at its C-terminal end can be used to conjugate many scFv or affibodies, introducing multimeric antibody interactions at the target site. In the currently prevailing methods, generally a bifunctional crosslinker is used to crosslink two proteins at random sites to a protein residue distributed at several places on the protein surface. This method of crosslinking often blocks the functional sites on the protein and, thus, reduces the bioefficacy of the protein. The method of linking through glycan residues introduced at a specific site in the guiding molecules, such as mAb, scFv molecules, homing peptides or cell-penetrating peptides, makes it possible to conjugate cytokines, cytotoxic drugs, toxins for antibody-based cancer therapy (Park, JW et al. Future directions of liposome and immunoliposome based cancer therapeutics. Semin Oncol 2004.31 :196-205), lipids for the assembly of immunoliposomes for developing a targeted drug delivery system (Carter, P. Improving the efficacy of antibody based cancer therapies. Nat Rev Cancer. 2001 : 1,118 - 29), fluorophores for ELIS A-based assays, and radionudides for imaging and immunotherapy applications.
In certain examples the invention features methods for glycosylating a biological substrate for use in glycoconjugation comprising attaching to the C- terminal or N-terminal end of a biological substrate an acceptor polypeptide, and then using the biological substrate with the acceptor polypeptide as an acceptor substrate
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for a pp-GalNAc-T; and transferring one or more GaINAc residue or GaINAc analogue sugars to the acceptor polypeptide, thereby glycoslyating the biological substrate for use in glycoconjugation. The acceptor polypeptide may be a nanoparticle. The present invention can provide, in certain embodiments, therapeutic agents in the form of nanoparticle complexes that supply affected cells with therapeutics or diagnostics, thereby reducing or eliminating the disease state needing treatment.
Included in the invention are therapeutic methods. In the methods described herein, a modified Gal sugar, for example in exemplary embodiments a 2-modified- Gal sugar, having a unique chemical handle, is enzymatically transferred by ppGalNAc T to the Thr or Ser present in the fused acceptor polypeptide sequence. After the transfer of the sugar residue, this chemical handle can be used for selective conjugation with biologically important molecules, hi certain preferred embodiments, the acceptor sequence comprises repetitive consensus sequences, for example repetitive Thr and/ or Ser residues. In other certain preferred embodiments, the chemical handle of the C-2 modified sugar is used, for example, for conjugation and assembly of bio-nanoparticles and for the formulation of immuno-liposome for the targeted drug delivery system. With this method, even N-glycan for example as disclosed by the present inventors in US application 20060084162, incorporated by reference herein in its entirety, can be used as a substrate for the coupling of two biomolecules, as shown in Figure 5, for example. In the instant application, the IgG molecule can be used as the substrate for the transfer of the modified sugar by the pp- GaINAcT.
In preferred embodiments, the acceptor polypeptide is attached to the C- terminal or N-terminal end. The target agent is linked in a site-directed manner, only where the carbohydrate is attached by the method described herein, to the protein. For example, as in the single chain antibodies at the C-terminus end which is away from the antigen binding site.
The method can be used to engineer nanoparticles. A nanoparticle, in certain embodiments, comprises a glycoprotein that is engineered from a biological substrate where an acceptor polypeptide is attached to the C-terminal or N-terminal end of a
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biological substrate, and the biological substrate with the acceptor polypeptide is used as an acceptor substrate for a pp-GalNAc-T, where one or more GaINAc residues or GaINAc analogue sugars are transferred to the acceptor polypeptide, as shown in Figure 8. Figure 8 shows a polypeptide chain, containing uniform repeats of lysine (K) residues followed by repeat fusion peptide sequence containing Threonine residues, can be used as a carrier molecule. The side chain amino groups of the lysine can be conjugated to the cargo molecules, such as chromophores that carry contrast agents, such as Gadolinium (Gd) or radioisotopes etc. The Threonine can be glycosylated with the modified sugars using ppGalN Ac-Ts then conjugated to single chain monoclonal antibody (scFv) for targeting. Any single chain monoclonal antibody is suitable for use in the invention. Thus the designer polypeptide itself can be used for the targeting and drug delivery. In certain examples, a biological substrate, such as a bioactive agent, for example a therapeutic agent, is used to engineer the nanoparticle. In other examples a second, third, fourth or more bioactive polypeptide is used in association with the nanoparticle to engineer multivalent nanoparticles. The bioactive agents do not have to be the same, for example a nanoparticle comprising three bioactive agents may comprise a chemotherapeutic, a tracking agent and a targeted delivery agent, such as an antibody.
Nanoparticles of the invention have use in methods of treating diseases. In other examples, the methods of the invention are used to engineer a glycoprotein from a magnetic resonance agent for use in diagnostic therapies. In these preferred examples, nanoparticles are engineered as described herein, where the nanoparticles are superparamagnetic nanoparticle.
Disease states needing treatment are only limited by current available therapeutics. As described herein, the methods of the invention are useful for engineering of nanoparticles, including multivalent nanoparticles, carrying any number of therapeutic agents. For example, the nanoparticles can be used to treat cancer, inflammatory disease, cardiovascular disease, obesity, ageing, bacterial infection, or any other disease amenable to therapy.
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Methods of making active pp-GalNAc-T
Also included in the invention are in vitro folding methods for producing an active pp-GalNAc-T. An active pp-GalNAc-T, in the presence of Mn2+ transfers GaINAc sugar from its UDP-α-GalNAc donor substrate to the side chain hydroxyl group of the Thr/Ser residue present in a polypeptide acceptor substrate. In exemplary embodiments, the folding methods occur in vitro.
When the catalytic domain of pp-GalNAc-T is expressed in E. CoIi, it forms insoluble inclusion bodies. These inclusion bodies can be collected and then solubilized and folded in vitro to produce catalytically active domains. Thus, the in vitro folding efficiency is directly related to the quantity of active enzyme that is produced after in vitro folding of the isolated inclusion bodies. Accordingly, methods to increase the in vitro folding efficiency would provide increased production of the enzymatically active catalytic domains that can be used to create useful products. General method for isolating and folding of the inclusion bodies is similar to the one previously described for galactosyltransferase catalytic domains have been previously described (Ramakrishnan et al., J. Biol. Chem., 276:37665 (2001)).
The method generally comprises first expressing pp-GalNAc-T in E.coli, and isolating, washing and dissolving inclusion bodies from E.coli. Inclusion bodies can be collected and then solubilized and folded in vitro to produce catalytically active domains. Following the isolating, washing and dissolving inclusion bodies from
E.coli, the method comprises performing S-sulfonation of the inclusion bodies in the presence of sodium sulfite, and folding the inclusion bodies, thus producing active pp-GalNAc-T.
It has been found that using oxido shuffling agents, 0.5M arginine HCl, 10% glycerol, and 1OmM lactose in the step of folding the inclusion bodies increases the amount of active pp-GalNAc-T produced by 2-fold, 3-fold, 4-fold or more active protein.
The active pp-GalNAc-T of the invention can comprise a catalytic domain (CD) together with lectin domain or the catalytic domain alone. Shown in SEQ ID NO: 1 is the protein sequence of the CD-LD portion of the family member, pp-
GalNAc-T2. Described herein is an in vitro folding method for CD-LD portion of pp-
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GalNAc-T2. In preferred embodiments, the pp-GalNAc-T2 is the human pp-GalNAc- T2 member of the family. Further, using the methods as described herein the CD domain alone also folds.
The active pp-GalNAc-T comprising a CD-LD portion is more active compared to pp-GalNAc-T comprising a catalytic domain. By more active is meant that the folded CD-LD portion, compared to the folded CD alone, gives more transfer of GaINAc from the donor substrate UDP-α-GalNAc, and less hydrolysis of the donor substrate. More active can be determined as a percent, for example exhibiting 5%, 10%, 15%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100%, or greater activity. As described above, the folding method is applicable to pp-GalNAc-T2 family members. In examples described herein for the design and transfer to the peptide sequence that is fused at the C-terminal end of the GST protein, the folded CD-LD of the human pp-GalNAc-T2 was used.
Kits
Also included in the invention are kits. Preferably, kits comprise the isolated catalytic domain (CD) or the isolated CD-LD from a polypeptidyl-α-N- acetylgalactosaminyltransferase (pp-GalNAc-T) as described herein and instructions for use. Kits can further comprise a biological substrate or bioactive agent as described herein.
EXAMPLES
It should be appreciated that the invention should not be construed to be limited to the examples that are now described; rather, the invention should be construed to include any and all applications provided herein and all equivalent variations within the skill of the ordinary artisan.
Example 1: Engineering of a C-terminal fusion peptide sequence
In order to glycosylate a non-glycoprotein for the purpose of glyco- conjugation, a C-terminal fusion peptide sequence was engineered that contained a Thr/Ser residue in the non-glycoprotein , shown in Figure Ia. The fusion peptide can
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then be glycosylated with ppGalNAc-T, which transfers GaINAc from its UDP derivative to the Thr/Ser residue in the fusion peptide. Figure 1 illustrates the catalytic reaction of polypeptide-a-N-acetylgalactosaminyltransferase (ppGalNAc-T). As shown in Figure Ia, the enzyme, in the presence of Mn2+, transfers GaINAc sugar from its UDP-α-GalNAc donor substrate to the side chain hydroxyl group of the Thr/Ser residue present in a polypeptide acceptor substrate. In vivo studies have shown that the ppGalNAc-T can transfer GaINAc analogues sugars such as, GaINAz, shown in Figure Ib, from UDP-GaINAz to the same acceptor substrate (17). It has been shown previously, that the mutant b4Gal-Tl, Y289L-Gal-Tl, can transfer GaINAc sugar from UDP-GaINAc as efficiently as its natural donor sugar galactose (Gal) from UDP-GaI (13). In addition to GaINAc, the mutant also transfers as well a 2-keto-Gal, shown in Figure Ic (14,15). Here we find that in addition to transferring GaINAc and GaINAz sugars, the ppGalNAc-T2 can also transfer 2-keto-Gal from UDP-2-keto-Gal. Additionally, ppGalNAc-T is known to transfer GaINAc analogues having a unique chemical handle such as, 2-azido-acetyl group. The glycosylated glycoprotein with the modified sugar can then be conjugated through this unique chemical handle to a bioactive molecule, such as immunoglobulin or toxin etc. This is shown in Figure Ib & c. Although there are 17 homologs in the ppGalNAc-T enzyme family in humans, any one of them with its preferred acceptor substrate can be used. Here we have used ppGalNAc-T2 since its three dimensional crystal structure and enzymology is well known from the previous studies (18). Glutathione-S-transferase (GST) has been used as a model for a non-glycoprotein, since it has previously been used for the expression of a number of fusion recombinant proteins at its C-terminal end. Here, GST-tag protein was expressed with a 17 amino acid fusion peptide having one or many Thr residues at the C-terminal end. These peptides were designed based on enzymology and crystallographic studies done with ppGalNAc-T2 and ppGalNAc- TlO (18).
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Example 2: Expression of soluble active ppGalNAc-T2 in E. coli
Although, ppGalNAc-T2 enzyme, with a stem region, catalytic domain and lectin domain, has been previously expressed in various expression systems producing an active soluble protein (18), the expression in E. coli has produced inactive inclusion bodies. The ppGalNAc-T2 expressed in yeast, showed no N-glycosylation in the crystal structure, and was considered as a perfect candidate for expression in E. coli that could be folded from inclusion bodies. Therefore, an in vitro folding method was developed to generate active protein. Previously a S-sulfonation method has been used to produce large quantities of b-l,4-galactosy ^transferase (b4Gal-Tl) from inclusion bodies (19). Using this method, an active ppGalNAc-T2 can be obtained, albeit at low efficiencies. However, it was found that inclusion of 10% glycerol and 10 mM lactose increases the in vitro folding efficiency of ppGalNAc-T2 to nearly 2 mg of purified protein from one liter of folding solution containing 100 mg of sulfonated protein that was obtained from one and a half liter bacterial culture. This is shown in Figure 2. In Figure 2, the soluble domain of ppGalNAc-T2, that contains a stem region, catalytic domain and the lectin domain, is expressed as an inclusion bodies in E. coli (shown in the left lane). An in vitro folding method was used, which was previously used for folding the β4Gal-Tl (19). It was found that active ppGalNAc-T2 can be generated. Inclusion of glycerol and lactose in the refolding solution during the in vitro folding enhances the refolding efficiency of the enzyme. Nearly 2 mg active protein purified from a Ni-column was obtained from one liter folding solution (1 μg and 0,5 μg, middle and right lanes, respectively). The specific activity of the in vitro folded enzyme (20 pmoles/min/ng ) is comparable to that of the same protein expressed in other systems (18). The in vitro folded ppGalNAc-T2 has been used in the experiments described herein. ppGalN Ac-Tl has been used for glycosylation of the non-glycoform of mucl protein expressed in E. coli (20). Similarly ppGalNAc-T2 has been also used to construct the 0-mucin structure on the non-glycoform of the interferon-alpha2b (IFN- alpha2b) expressed in E. coli (21). Thus in vitro glycosylation of non-glycoform of glycoproteins is becoming increasingly important. The in vitro folding method for ppGalNAc-T2 from inclusion bodies described here shows that large quantities of
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these glycosyltransferases can be generated from E. coli that can be used for such application as well.
Example 3: GIy cosy lation of GST-tag protein The Glutathione-S-transferase (GST) protein with a 17 amino acid tag at its C- terminal, following a Thrombin cleavage site, has been successfully expressed as a soluble protein from E. coli and purified on a glutathione column. As a first step the tag was expressed with an oligopeptide sequence, SGGPIMDSTTP APTTK, used in the previous enzyme kinetic studies of ppGalNAc-T2 (18). After the enzyme reaction, the 17-amino acid tag was released by Thrombin digestion and analyzed by mass spectrometry (MALDI-TOP), shown in Figure 3a. In Figure 3, the mass spectrum (MALDI-TOPS) of the thrombin cut non-glycosylated and glycosylated peptide are shown in the left and right side of the arrow, respectively, in (a), (b) and (c). (a) Although the fusion tag peptide contains four Thr residues and two Ser residues, the over night incubation of the GST-tag protein with the ppGalNAc-T2 seems to glycosylate maximum of four glycosylation sites. This may be due to the fact that ppGalNAc-T2 may not efficiently glycosylate two adjacent Thr residues, where as ppGal ANc-T 10 is known to glycosylate two adjacent Thr residues more efficiently than other family members (22). (b) When one Thr and Ser residues are present, both these amino acids have been found to be glycosylated, (c) Presence of one Thr residue results in a single glycosylation of the tag peptide thus, this tag is used for following studies.
Analysis of the glycosylated tag showed that the glycosylated peptide exists as a mixture of three to four glycosylated peptides, suggesting that the four Thr residues present in the tag peptide may have been the sites for the glycosylation. On the contrary, the redesigned tag peptide, SGGPIMAAATPAPAAK, with one Thr and one Ser residues, is found to have glycosylated with two sugars, suggesting that in addition to the glycosylation of the Thr residue, the less preferred Ser residue is also glycosylated (Figure 3b). By mutating the Ser residue to Ala in the tag peptide, the tagged peptide sequence with only one Thr residue, AGGPIM AATP AP AAK, was produces that undergoes glycosylation at only one site (Figure 3c). When this Thr is
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mutated to Leu residue, no glycosylation was observed, confirming that the glycosylation takes place at the unique Thr residue (not shown). In the past, although a number of peptides have been tested as the acceptor substrates for the ppGalNAc- T2, none of them are presented as a fusion peptide. Thus, these glycosylation studies described herein confirm that the fusion tag peptide can be glycosylated either at one or more sites having a Thr or even Ser residue present in the fusion tag peptide.
It has been previously shown that ppGalNAc-T enzymes in the live cell can incorporate GaINAz (2-azido-acetyl-galactosamine), a modified sugar resembling GaINAc, to the glycan chains. The incorporation of such unnatural monosaccharide that bears uniquely reactive chemical handle such as azides has enabled the selective labeling of glycoconjugates with a variety of reagents (17). Since these studies were carried out in vivo, it was not possible to identify the specific ppGalNAc-T that is responsible for the transfer of GaINAz among the 17 the ppGalNAc-Ts present in humans. Here ppGalNAc-T2 is used to transfer the modified galactose which resembles GaINAc, such as 2-keto-galactose and GaINAz, to the fusion peptide in the GST-Tag protein. Here, the GST-Tag protein with only one Thr residue present in its fusion tag peptide is used. Use of others can be envisioned.
The catalytic reactions using UDP-2-keto-Gal or UDP-GaINAz as donor substrates were carried out under the same conditions as the one used for UDP-
GaINAz. After catalysis, the Thrombin digestion released glycopeptide that showed the presence of one sugar moiety in the fusion peptide as indicated by mass spectrometry (Figure 3 a). This suggested that the Thr residue is glycosylated by the ppGalNAc-T2 by the modified sugars as well. In order to detect the presence of the unique chemical handle such as the 2-keto or azido on the tag peptide of the GST-tag protein, the samples were biotinylated by appropriate chemical reactions. The biotinylated samples with and without the tag peptides were subjected to the Western Blotting and the proteins were detected by chemiluminescence technique, as shown in Figure 4. Figure 4 shows the GST-tag protein with only a single Thr residue but no Ser residue in its fusion peptide is used for the transfer of (a) 2-keto-Gal and (b)
GaINAz sugars from their respective UDP-derivatives. The mass spectrum (MALDI-
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TOPS) of the non-glycopeptide and glyco-peptide released by Thrombin digestion are shown in the left and right side of the arrows, respectively. The glycosylated protein is biotinylated using the biotin carrying appropriate chemical group to react with the 2-keto or azido moiety of the modified sugars. The proteins in the Western Blotting were visualized using the sterptavadine-HRP chemiluminescence technique. A strong luminance is only observed for the biotinylated proteins with the fusion peptide (- Thrombin), while the proteins without the fusion peptide (+Thrombin) no trace of chemiluminescence has been observed. This indicates that he biotinylation specifically takes place only at the sugar moiety present in the fusion tag peptide. The observation of chemiluminescence from the protein with the tag attached alone clearly indicated that the biotinylation was done on the modified sugars of the tag peptide not on the peptide. Thus these studies further suggest that ppGalNAc-T2 can also transfer the modified galactose from their UDP-derivatives efficiently to the fusion peptide and the chemical handle present in the glycan moiety is readily available for further modification such as biotinylation.
Example S: Applications in glyco-conjugation
It has previously been shown that the mutant b4Gal-Tl eri2yme, Y289L-Gal- Tl, can transfer GaINAc from UDP-GaINAc as efficiently as galactose (Gal) from UDP-GaI to the N-acetylglucosamine (GIcNAc) residue present at the non-reducing end (13). In addition to this it has also been found that the mutant b4Gal-Tl enzyme can also transfer modified sugars such a 2-keto-galactose from its UDP-derivative and this catalytic activity was successfully applied in the detection of O-GlcN Ac modification in the proteins (14). The same technique was expanded to other glyco- proteins such as ovalbumin and immunoglobulin IgG with free GIcNAc at the non- reducing end of their N-glycans. Based on these techniques, it has been previously proposed that two glyco-proteins with modified sugars, such as 2-keto-Gal, with unique chemical handle can be conjugated with chemical cross linkers, thus enabling the design of novel immuno-toxins and MIR image enhancers (15). In the examples described herein non-glycoproteins have been shown to be glycosylated by engineering a peptide sequence in the protein that can be glycosylated with the
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modified sugar, so that they can also be cross linked to the other glyco-proteins such as IgG, with similar modified sugars. We have previously shown that using the Y289L-Gal-Tl mutant the modified sugar 2-keto-Gal can be transferred to the free GIcNAc residue present in the non-reducing end of a glycopeptide such as IgG (15). Upon transferring the 2-keto-gal, this sugar can be subjected to further chemical modification such as biotinylation. Here we propose that this IgG with the modified Gal can be cross linked to the non-glycoprotein, such as GST with a fusion peptide carrying a modified sugar at its C-terminal end. The two molecules can be conjugated through their glycan moieties, thus synthesizing novel immuno-conjugates through their glycan moieties.
This is shown in Figure 5. Thus the present study extends the previously described technique where biologically important molecules can be conjugated through their glycan moiety.
In recent years, single chain antibodies (ScFv) are increasingly used as compared to the full length IgG molecules. Often, these ScFv molecules can be easily expressed in E. coli as soluble proteins in large amounts, and they have been found to have similar affinity towards their antigens as their full length IgG counterpart molecules. Therefore, the ScFv molecules have been used for synthesizing the immuno-liposome by attaching a lipid moiety to the ScFv molecules through chemical modification. The methods described herein can be used more efficiently by simply glycosylating the ScFv molecule with a fusion peptide at its C-terminal end similar to GST-Tag protein. Then, this glycan moiety with the modified sugar can be conjugated with a lipid molecule with corresponding reactive group such as immunoxy or alkynes. Thus, a ScFV molecule with lipid attached at its C-terminal end through a modified sugar moiety mimics the GPI, glycosyl- phosphatidylinositol, anchoring protein, and thus can be used for the formulation of the immuno-liposomes. Such C-terminal modification in most SvFv proteins seems to be feasible since the C- terminal end is away from the antigen binding site (Fab). This configuration is shown in Figure 6, a schematic showing that the non-glycoprotein with the tag at the C- terminal end can be glycosylated with the GaINAc analogue sugars having a unique chemical handle. Instead of conjugation to an another glycoprotein these proteins can
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be conjugated to lipid molecules with a proper reactive polar groups. Such conjugated protein with lipid at their C-terminal end through a sugar moiety mimics GPI, glycosylphosphatidylinositol, anchored protein and they can be used to formulate liposomes. Particularly this technique is important for the single chain antibodies, which are often expressed in E. coli as an active protein. These proteins with a C- terminal tag, such as the present one in GST carrying the modified sugar, can be conjugated to lipid molecules, thus synthesizing the immuno-liposomes. Often the antigen binding regions in these ScFv molecules are well away from their C-terminal end, thus this scheme is expected to work well. In fact even the full chain IgG can be engineered to have the heavy chain C-terminal to have the fusion peptide which can be glycosylated and conjugated to lipid in vitro, thus enabling one to synthesize immuno-liposome using the whole IgG molecule itself.
Structural insight of IgG molecule shows that even the full length IgG molecule can also tag at the heavy chain C-terminal end by the same method and used for either conjugation to other glycoproteins or lipids (Figure 6). Thus this method will be useful in many nonobiological applications. Although the glycosylation of a surface Thr/Ser residue on the protein by the ppGalNAc-T is possible, the crystal structure of the ppGalNAc-T2 suggest that such Thr/Ser residue has to be present not only in at least 11 amino acid long peptide in the extended conformation but also it has to be well exposed to the solvent region. Proteins with long flexible loop region having Thr/Ser residue may be the candidate acceptors for such undesired glycosylation. The present technique demonstrates the possibility of linking various bio-molecules and lipids via sugar moieties for the design of novel nano-particles which can be used for targeted drug delivery.
Example 6. Site-specific conjugation of biomolecules: application to targeted drug delivery and contrast agents for MRI
Oligosaccharides are attached at unique sites in proteins and glycolipids. They bring about specific geometries of interactions between the two glycoconjugates, resulting in the correct and efficient molecular interplay between various molecular structures (Ramakrishnan B, Qasba PK. Structure-based design ofl 31 ,4-
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galactosyltransferase I ((34GaI-Tl) with equally efficient N- acetylgalactosaminyltransferase activity. J Biol Chem 2002;277:20833-40). Glycosyltransferases assemble the oligosaccharide structures on glycocoηjugates. Recently, the structural information of several of these glycosyltransferases has become available (Khidekel N, et al. A chemoenzymatic approach toward the rapid and sensitive detection of 0-G IcNAc posttranslational modifications. J Am Chem Soc 2003; 125: 16162-3), making it possible to engineer these enzymes so that they can transfer a non-preferred sugar residue (Boeggeman E, et al. Direct identification of nonreducing GIcNAc residues on N-glycans of glycoproteins using a novel chemoenzymatic method. Bioconjug Chem 2007;l 8:806-14) or a sugar residue with a chemically reactive unique functional group (Ramakrishnan B, Boeggeman E, Qasba PK. Novel method for in vitro O-glycosylation of proteins: application for bioconjugation. Bioconjug Chem 2007;18:1912-8). The presence of a modified sugar moiety with a chemical handle on a glycoconjugate makes it possible to link biologically active molecules through a modified glycan chain.
As described previously, based on structural information, the 3-1,4- galactosyltransferase mutant enzyme Tyr289Leu-Gal-Tl (Y289L-Gal-Tl) was developed that transfers 2-acetonyl-2-deoxygalactose (2-keto-Gal) or 2-N-acetyl- azide (GaINAz) from their UDP derivatives to the N-acetylglucosamine residue (GIcNAc), which is present at the non-reducing end of the glycans of glycoproteins (Qasba PK, Ramakrishnan B, Boeggeman E. Mutant glycosyltransferases assist in the development of a targeted drug delivery system and contrast agents for MRJ. Am Ass Pharm Soc J 2006;8: 190-5). After the transfer of the modified sugar residue, the chemical handle is used for selective conjugation with various molecules (Ramakrishnan B, Bioconjug Chem 2007; 18: 1912-8). Using this method, it has been shown that even the N-glycan moiety of the IgG molecule can be used as the substrate for the transfer of 2-keto-Gal sugar by the mutant Y289L-Gal-Tl . However, this method requires the presence of a free GIcNAc moiety at the non-reducing end of the glycan chain of the glycoprotein and cannot be used for non-glycoproteins, such as single-chain antibodies or bacterial toxins expressed in Escherichia coli.
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To conjugate non-glycoproteins through glycan residues, the polypeptide a-N- acetylgalactosaminyltransferase enzyme (ppGalNAc-T) has been used, which transfers N-acetylgalactosamine sugar (GaINAc) from UDP-GaINAc to the Thr/Ser residues on an acceptor polypeptide that is at least 11 amino acids long [25]. Using glutathione S-transferase (GST) protein as a model system, the fusion peptide sequence has been engineered at its C terminus, with a single Thr residue, which is the acceptor substrate for ppGalNAc-T2. The ppGalNAc-T2 not only transfers GaINAc but also GaINAz or 2-keto-Gal from its UDP derivative to the single Thr residue present in the fusion peptide tag of GST. Furthermore, we have expressed the soluble form of ppGalNAc-T2 in E. coli as inclusion bodies and developed an in vitro folding method to make large quantities of active ppGalNAc-T2 (Hollinger P, Hudson PJ. Engineered antibody fragments and the rise of single domains. Nat Biotechnol 2005;23:l 126-36). Therefore, using ppGalNAc-T it is possible to glycosylate non- glycoproteins, such as single-chain antibodies (scFv), bacterial toxins, with a modified sugar carrying a unique chemical handle that can be used for conjugation.
Materials and Methods of the Invention
The results reported herein were obtained using the following Materials and
Methods.
Polypeptidyl-a-N-acetylglactosaminyltransferase II gene construction, expression and folding in E. coli
The human polypeptidyl-a-N-acetylglactosaminyltransferase II (ppGalNAc-
T2) clone (BC041120) was obtained from Open Biosystems. The C-terminal His tag carrying soluble domain of ppGalNAc-T2, coding residues 60 to 583 of the protein, was PCR amplified using the following primers having Bam HI and Eco RI restriction enzyme sites (shown in italics) at their 5' terminal.
(1) CGCGGATCCGCG GCACAAAGCATGGAGACCCTCCCTCCAGGGAAA
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(2)
GCGCGCCGAATTCGGTCCCTGCTGCAGGTTGAGCGTGAACTTTCCA
CTGCTG
The PCR amplified product was digested with Bam I and Eco RI restriction enzyme and ligated with the pET23a vector predigested with the same enzymes. The ligated vector was transfected into XL2 super competent cells and plated. The ampicillin resistant clones were screened for the presence of the ppGalNAc-T2 gene in their plasmid DNA between their Bam I and Eco RI restriction sites. The positive clones were sequenced and transfected into Rosetta (DE3) LysS competence cell for the expression of the protein.
The expression and purification of the recombinant ppGalANc-T2 protein was done as described previously (18). Nearly 60 to 70 mgs of protein were obtained as inclusion bodies from one liter bacterial culture. The in vitro folding of ppGalNAc-T2 was carried out similar to b4Gal-Tl (19) with few modifications. Typically, 100 mg of sulfonated protein is folded in one liter folding solution for 48 hours. Inclusion of 10% glycerol and 10 mM lactose in the folding solution enhances the folding efficiency of ppGalNAc-T2. After refolding the protein, the folding solution is extensively dialyzed against water. During dialysis the miss folded protein precipitates out, while the folded protein remains soluble. The soluble protein is first concentrated and then purified on a Ni-column. Nearly 2 mg of folded ppGalNAc-T2 protein is obtained form 1 liter of folding solution. The purified protein was tested for its catalytic activity using a 13 amino acid peptide, PTTDSTTP APTTK, as an acceptor using the methods described previously (18). The specific activity of the refolded ppGalNAc-T2 is 20 pmoles/min/ng protein.
Construction and expression of GST protein with the C-terminal 17 amino acid glycosylation tag
The GST gene from pGEX-2T vector (GE) was amplified first with the 5'- primer and 3' -primer 1 and purified on a low melt agarose gel. The purified GST gene was further amplified with the 5 '-primer and 3'-primer2 which coded for a 17 amino
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acid peptide, GAGGPIMAAATPAPAAK, as a C-terminal extension of GST following a Thrombin cleavage site.
5 '-Primer: CGCGGATCCGCGTCCCCTATACTAGGTTATTGGAAAATTAA GGGCCTTGTG 3'- Primerl :CGCCGGCGTAGCAGCGGCCATGATGGGTCCGCCGGCTCCAC
GCGGAACCAGATCCGA 3'-Primer2:
CCGGAATTCCGGCTACTTCGCCGCCGGCGCCGGCGTAGCAGCG GCCATGATGGG
The final PCR amplified DNA fragment was digested with Bam HI and Eco RI enzymes and ligated with predigested pET23a vector with the same enzymes. The ligated vector was transfected into XL2 competent cells. The ampicilin resistant clones were screened for the presence of the full GST gene between the Bam HI and Eco RI sites in their plasmid DNA. The positive plasmid DNA was transfected into Rosetta (DE3) LysS cells. The GST-tag protein was expressed as a soluble protein in E. coli and purified on a glutathione affinity column (GE). A total of 50 to 60 mg purified protein was obtained from one liter bacterial culture. The C-terminal glycosylation tag was released from a 5 mg protein by thrombin cleavage and analyzed by mass spectrometry. The other GST-Tag fusion proteins containing the multiple glycosylation sites were also made similar to the above methods. All the oligonucleotides were synthesized by the Molecular technology branch, NCI, Frederick.
Glycosylation of GST- tag with ppGalNAc-T2
A 5 mg of GST-tag protein was incubated over night at 37°C with 50 ng of ppGalNAc-T2, in the presence of 20 mM mes-NaOH buffer (pH6.5), 10 mM MnC12 and 0.5 mM UDP-sugar (UDP-GaINAc or UDP-2-keto-Gal or UDP-GaINAz) in a
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total volume of 25 ml. The glycosylated GST-tag protein was centrifuged on a centricon (10 K molecular cutoff) filter to remove all the reaction buffer and washing with pure water twice. The salt free glycosylated GST-tag was recovered in a 20 ml water. An aliquot of it (4 ml) was cut with human Thrombin and analyzed by mass spectrometry (MALI-TOP).
Biotinylation of the glycosylated GST-tag and gel electrophoresis
The desalted glycosylate GST-tag protein with 2-keto-Gal was biotinylated in 60 ml volume containing 75 mM sodium acetate buffer pH 5.0, and 30 mM aminoxymethylcarbonyhydrazino-D-biotin (ARP, Dojindo laboratories). The reaction was carried out overnight at room temperature. The biotinylated sample was desalted using centricon (10 K) filter and recovered in 20 ml of water. An aliquot of the sample was cut with thrombin and analyzed using mass spectrometry. The biotinylated proteins uncut and cut with Thrombin were analyzed by Western Blotting and they were detected by chemiluminescence technique using streptavadin- horseradish peroxidase (HRP) as described previously (15).
An equal amount of thrombin cleaved and uncleaved GaINAz glycosylated GST-tag was biotinylated using "click-it Biotin Glycoprotein Detection Kit" from Invitrogen, as suggested by the manufacture. The reaction was carried out for one hour at room temperature. Since the biotinylation was carried out using the unknown components supplied by the manufacture, it was not possible to simply desalt the protein using centricon filters. Therefore, the mass spectrometry analysis could not be carried out. However, the click it reaction buffer did not interfere with the protein gel electrophoresis, therefore Western Blotting can be carried out and the biotinylated protein was detected by chemiluminescence by streptavadin-horseradish peroxidase (HRP) as described earlier (15). Incorporation by Reference
The contents of all references, patents, pending patent applications and published patents, cited throughout this application are hereby expressly incorporated by reference.
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Equivalents
Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments of the invention described herein. Such equivalents are intended to be encompassed by the following claims.
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References
(1) Wu, A.M., Senter, P.D. Arming antibodies: prospects and challenges for immunoconjugates. Nat Biotechnol. (2005) 23, 1 137-46. Review.
(2) Garnett, M.C. Targeted drug conjugates: principles and progress. Adv. Drug Deliv. Rev. (2001) 53, 171-216.
(3) Firestone, R.A., Willner, D., Hofstead, S.J., King, H.D., Kaneko, T., Braslawsky, G.R., Greenfield, R.S., Trail, P.A., Lasch, S.J., Henderson, A.J., Casazza, A.M., Hellstrδm, K.E. and Hellstrόm, I. Synthesis and antitumour activity of the immunoconjugate BR96-Dox. J. Control. Release (1996) 39, 251-259.
(4) Dhawan S. Design and construction of novel molecular conjugates for signal amplification (I): conjugation of multiple horseradish peroxidase molecules to immunoglobulin via primary amines on lysine peptide chains. Peptides (2002) 23, 2091-8
(5)Stimmel, J.B., Merrill, B.M., Kuyper, L.F., Moxham, CP. and Hutchins, J.T. Site- specific conjugation of serine → cysteine variant monoclonal antibodies. J Biol Chem (2000) 275, 30445-50.
(6) Albrecht, H., Burke, P.A., Natarajan, A., Xiong, CY. and Kalicinsky, M. Production of soluble ScF vs with C-terminal-free thiol for sitespecific conjugation or stable dimeric ScFvs on demand. Bioconjug Chem (2004) 15, 16-26.
(7) Saito, G., Swanson, J.A. and Lee, K.D. Drug delivery strategy utilizing conjugation via reversible disulfide linkages: role and site of cellular reducing activities.
Adv Drug Deliv Rev. (2003) 55, 199-215. Review.
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(8) O'Shanessy, D. J., Dobersen, M.J. and Quarles, R.H., A novel procedure for labeling immunoglobulins by conjugation to oligosaccharide moieties. Immunol. Lett. (1984) 8, 273-277.
(9) O'Shanessy, DJ. and Quarles, R.H. Labeling of the oligosaccharide moieties of immunoglobulins. J. Immunol. Methods (1987) 99, 153-161.
(10) Rodwell, D., Alvarez, V.L., Lee, C, Lopes, A.D., Goers, J.W.F., King, H.D. Powsner, HJ. and McKearn, TJ. Site-specific covalent modification of monoclonal antibodies: in vitro and in vivo evaluations. Proc. Natl. Acad. Sci. USA (1986) 83, 2632-2636.
(11) Stan, A.C., Radu, D. L., Casares, S., Bona, CA. and Brumeanu, T-D. Antineoplastic efficacy of doxorubicin enzymatically assembled on galactose residues of a monoclonal antibody specific for the carcinoembryonic antigen. Cancer Res. (1999) 59, 115-121.
(12) Qu, Z., Sharkey, R.M., Hansen, HJ., Shih, L.B., Govindan, S.V., Shen, J., Goldenberg, D.M. and Leung, S. -O. Carbohydrates engineered at antibody constant domains can be used for site-specific conjugation of drugs and chelates. J. Immunol. Methods (1998) 213, 131-144
(13) Ramakrishnan, B. and Qasba, P. K. Structure-based design of beta 1,4- galactosyltransferase I (beta 4GaI-Tl) with equally efficient N- acetylgalactosaminyltransferase activity: point mutation broadens beta 4GaI-Tl donor specificity. J Biol Chem. (2002) 277, 20833-9.
(14) Khidekel, N., Arndt, S., Lamarre-Vincent, N., Lippert, A., Poulin-Kerstien, K.G., Ramakrishnan, B., Qasba, P.K. and Hsieh- Wilson, L.C. A chemoenzymatic approach toward the rapid and sensitive detection of O-GlcNAc posttranslational modifications. J Am Chem Soc. (2003) 125, 16162-3.
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(15) Boeggeman, E., Ramakrishnan, B., Kilgore, C, Khidekel, N., Hsieh- Wilson, L. C, Simpson, J.T., and Qasba, P. K. Direct Identification of Nonreducing GIcNAc Residues on N-Glycans of Glycoproteins Using a Novel Chemoenzymatic Method. Bioconjug Chem. (2007) Mar 20; [Epub ahead of print]
(16) Ten Hagen, K.G., Fritz, T.A. and Tabak, L.A. All in the family: the UDP- GalNAcipolypeptide N-acetylgalactosaminyltransferases. Glycobiology. (2003) 13, 1R-16R.
(17) Dube, D. H., Prescher, J. A., Quang, CN. , and Bertozzi, CR. Probing mucin-type O-linked glycosylation in living animals. Proc Natl Acad Sci U S A. (2006) 103, 4819-24.
(18) Fritz. T.A., Raman, J., and Tabak, L.A. Dynamic association between the catalytic and lectin domains of human UDP-GaINAc :polypeptide alpha-N- acetylgalactosaminyltransferase-2. J Biol Chem. (2006) 281, 8613-9.
(19) Boeggeman, E.E., Ramakrishnan, B. and Qasba, P.K. The N-terminal stem region of bovine and human betal,4-galactosyltransferase I increases the in vitro folding efficiency of their catalytic domain from inclusion bodies. Protein Expr Purif. (2003) 30, 219-29.
(20) Freire, T., Lo-Man, R., Piller, F., Piller, V., Leclerc, C. and Bay, S. Enzymatic large-scale synthesis of MUC6-Tn glycoconjugates for antitumor vaccination. Glycobiology. (2006) 16, 390-401.
(21) DeFrees, S., Wang, Z.G., Xing, R., Scott, A.E., Wang, bJ., Zopf, D., Gouty, D.L., Sjoberg, E. R., Panneerselvam, K., Brinkman-Van der Linden, E.C., Bayer, R.J., Tarp, M. A., and Clausen, H. GlycoPEGylation of recombinant therapeutic proteins produced in Escherichia coli. Glycobiology. (2006) 16, 833-43.
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(22) Kubota, T., Shiba, T., Sugioka, S., Furukawa, S., Sawaki, H., Kato, R., Wakatsuki, S., and Narimatsu, H. Structural basis of carbohydrate transfer activity by human UDP-GaINAc: polypeptide alpha-N-acetylgalactosaminyltransferase (pp- GaINAc-TlO). J MoI Biol. (2006) 359, 708-27.
(23) Hang H. C. and Bertozzi CR. The chemistry and biology of mucin-typr O-linked glycosylation. Bioorganic and Medicinal Chemistry (13): 5021 - 5034. 2005.
(24) Wandall H.H., Hassan H, Mirgorodskaya E., Kristensen A.K., Roepstorff O, Bennett E.P., Nielsen P. A., Hollingsworkth M. A., Burchell J., Taylor-Papadimitrou J., Clausen H. J Biol Chem (272):23503 - 23514. 1997.
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Claims

Express Mail Label No. EM006542883USWhat is claimed is:
1. An isolated catalytic domain from a polypeptidyl-α-N- acetylgalactosaminyltransferase (pp-GalNAc-T) that transfers N-acetylgalactosamine (GaINAc) or a GaINAc analogue from UDP-α-GalNAc to one or more Ser or Thr residues of an acceptor polypeptide, wherein the isolated catalytic domain comprises SEQ ID NO: 1.
2. The isolated catalytic domain from a pp-GalNAc-T of claim 1, wherein the pp-GalNAc-T transfers GaINAc or a GaINAc analogue in an α configuration.
3. The isolated catalytic domain from a pp-GalNAc-T of claim 1, wherein the pp-GalNAc-T is mammalian.
4. The isolated catalytic domain from a pp-GalNAc-T of claim 1, wherein the pp-GalNAc-T is pp-GalNAc-T2.
5. The isolated catalytic domain from a pp-GalNAc-T of claim 1 , wherein the pp-GalNAc-T comprises a catalytic domain (CD) and lectin domain (LD).
6. An isolated nucleic acid segment encoding the catalytic domain of claim 1 comprising SEQ ID NO: 2.
7. A vector or expression cassette comprising the nucleic acid of claim 6.
8. A cell comprising the vector or expression cassette of claim 7.
9. A method for engineering a glycoprotein from a biological substrate comprising: attaching to the C-terminal or N-terminal end of a biological substrate an acceptor polypeptide; and
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using the biological substrate with the acceptor polypeptide as an acceptor substrate for a pp-GalNAc-T; and transferring one or more GaINAc residue or GaINAc analogue sugars to the acceptor polypeptide; thereby engineering a glycoprotein from a biological substrate.
10. A method for glycosylating a biological substrate for use in glycoconjugation comprising: attaching to the C-terminal or N-terminal end of a biological substrate an acceptor polypeptide; and using the biological substrate with the acceptor polypeptide as an acceptor substrate for a pp-GalNAc-T; and transferring one or more GaINAc residue or GaINAc analogue sugars to the acceptor polypeptide; thereby glycoslyating the biological substrate for use in glycoconjugation.
11. The method of claim 9 or 10, wherein the acceptor polypeptide is a nanoparticle.
12. The method of claim 9 or 10, wherein the biological substrate is a nanoparticle.
13. A method for engineering a nanoparticle comprising: attaching to the C-terminal or N-terminal end of a biological substrate a nanoparticle; and using the biological substrate with the nanoparticle as an acceptor substrate for a pp-GalNAc-T; and transferring one or more GaINAc residue or GaINAc analogue sugars to the acceptor substrate; thereby engineering a nanoparticle.
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14. The method of claim 13, wherein the nanoparticle is a multivalent nanoparticle.
15. The method of claim 9, 10 or 13, wherein the biological substrate is selected from the group consisting of: a non-glycoprotein, an oligopeptide and a biological matrix.
16. The method of claim 9, 10 or 13, wherein the GaINAc residue or GaINAc analogue sugars are transferred to one or more Ser or Thr residues of the acceptor polypeptide.
17. The method of claim 15, wherein the non-glycoprotein or oligopeptide is a bioactive agent.
18. The method of claim 17, wherein the bioactive agent is any bioactive agent carrying a linker sequence with a functional coupling group
19. The method of claim 18, wherein the bioactive agent is selected from the group consisting of: single chain antibodies, bacterial toxins, growth factors, therapeutic agents, and contrast agents.
20. The method of claim 12 or 13, wherein the nanoparticle comprises a magnetic resonance agent.
21. The method of claim 9 10, or 12, wherein the acceptor polypeptide comprises at least 10 amino acids.
22. The method of claim 9, 10 or 12, wherein the acceptor polypeptide comprises at least 15 amino acids.
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23. The method of claim 9, 10 or 13, wherein the acceptor polypeptide is selected from SEQ ID NO: 3 (GAGGPIMAAATPAPAAK) or SEQ ID NO: 4 (AGGPIMAATPAPAAK).
24. The method of claim 23, wherein the acceptor polypeptide is glycosylated at one or more sites.
25. The method of claim 24, wherein the acceptor polypeptide is glycosylated at a ser or thr residue.
25. The method of claim 9, 10 or 13, wherein the GaINAc analogue comprises an azido group.
26. The method of claim 9, 10 or 13, wherein the GaINAc analogue comprises a keto group.
27. The method of claim 9, 10 or 13, wherein the pp-GalNAc-T transfers the GaINAc analogue to one or more Ser or Thr residues of the acceptor polypeptide.
28. A method of engineering a nanoparticle according to claim 13, wherein the nanoparticle is used to treat a subject suffering from a disease or disorder.
29. A method of engineering a nanoparticle according to claim 13, wherein nanoparticle is used in magnetic resonance imaging.
30. A method for producing an active pp-GalNAc-T comprising: expressing pp-GalNAc-T in E. coli; isolating, washing and dissolving inclusion bodies from E.coli; performing S-sulfonation of the inclusion bodies in the presence of sodium sulfite; and folding the inclusion bodies;
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wherein active pp-GalNAc-T is produced.
31. The method of claim 30, wherein the step of folding the inclusion bodies comprises using oxido shuffling agents, 0.5M arginine HCl, 10% glycerol, and 1OmM lactose.
32. The method of claim 30, wherein the active pp-GalNAc-T comprises a catalytic domain and lectin domain.
33. The method of claim 30, wherein the active pp-GalNAc-T comprises a catalytic domain.
34. The method of claim 30, wherein active pp-GalNAc-T transfers GaINAc-T from UDP-α-GalNAc and less hydrolysis of the donor substrate.
35. The method of claim 30, wherein the active pp-GalNAc-T comprising a catalytic domain and lectin domain is more active compared to pp-GalNAc-T comprising a catalytic domain.
36. The method of claim 30, wherein the folding occurs in vitro.
37. The method of any of the above claims 6-36, wherein the pp-GalNAc-T is pp- GalNAc-T2.
38. A kit comprising the isolated catalytic domain from a polypeptidyl-α-N- acetylgalactosaminyltransferase (pp-GalN Ac-T) of any of claims 1 - 37 and instructions for us.
39. The kit of claim 38, further comprising an acceptor.
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40. The kit of claim 38, further comprising a biological substrate or bioactive agent of any of claims 1—37.
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WO2009102820A2 (en) * 2008-02-11 2009-08-20 Government Of The U.S A., As Represented By The Secretary, Department Of Health And Human Services Modified sugar substrates and methods of use
WO2009102820A3 (en) * 2008-02-11 2009-10-22 Government Of The U.S A., As Represented By The Secretary, Department Of Health And Human Services Modified sugar substrates and methods of use
WO2014065661A1 (en) * 2012-10-23 2014-05-01 Synaffix B.V. Modified antibody, antibody-conjugate and process for the preparation thereof
US9504758B2 (en) 2012-10-23 2016-11-29 Synaffix B.V. Modified antibody, antibody-conjugate and process for the preparation thereof
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US10745488B2 (en) 2012-10-23 2020-08-18 Synaffix B.V. Modified antibody, antibody-conjugate and process for the preparation thereof
EP3912642A1 (en) * 2012-10-23 2021-11-24 Synaffix B.V. Modified antibody, antibody-conjugate and process for the preparation thereof
US10973922B2 (en) 2013-05-02 2021-04-13 Glykos Finland Oy Glycoprotein-toxic payload conjugates
US10905783B2 (en) 2015-11-27 2021-02-02 Michal RIVLIN Glucosamine and derivatives thereof in imaging
CN114981293A (en) * 2021-01-29 2022-08-30 Cj第一制糖株式会社 Novel initiator assembly protein variants and method for producing L-lysine using the same
WO2023178422A1 (en) * 2022-03-21 2023-09-28 National Research Council Of Canada Lipid based nanoparticles for targeted gene delivery to the brain
WO2023178421A1 (en) * 2022-03-21 2023-09-28 National Research Council Of Canada Antibodies with engineered o-glycosylation sequons for site-specific conjugation

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