TRANS-SIALIDASE AND METHODS OF USE AND MAKING THEREOF

Abstract: Polypeptides are provided having trans-sialidase enzymatic activity in substantially pure form, nucleic acids coding therefor, antibodies specific for such polypeptides, processes for producing the enzyme and methods of use of the enzyme, in particular for the synthesis of sialyl alpha (2->3)-linked saccharides, glycoproteins and glycolipids. Such enzymes are isolatable as nucleic acid or amino acid sequences from parasites of the genus Trypanosoma.

Description: TRANS-SIALIDASE AND METHODS OF USE AND MAKING THEREOF i This application is a continuation of U.S. serial number /fe» 07/857,519, filed March 25, 1992, the entire contents of which above-referenced application are incorporated herein by 5 reference. BACKGROUND OF THE INVENTION This invention, in the field of carbohydrate biochemistry, parasitology and medicine, relates to a newly discovered polypeptide having trans-sialidase enzymatic activity, in 10 substantially pure form, nucleic acids coding therefor, antibodies specific for the polypeptide, processes for producing the enzyme and methods of use of the enzyme, in particular for the synthesis of sialyl o.(2→3) -linked saccharides, glycoproteins and glycolipids. 15 Description of the Background Art About 80 different kinds of glycosidic linkages are known in the glycoconjugates of higher animals. Each is formed by two of the ten monosaccharides found in glycoconjugates, or by one monosaccharide in glycosidic linkage to a protein or a lipid. 20 The formation of glycosidic linkages are catalyzed by enzymes known as glycosyltransferases, which utilize nucleotide sugars as donors, and glycosides as acceptors. Each distinctive glycosidic bond in an oligosaccharide is formed by a specific transferase enzyme. Enzymes known as glycosidases remove 25 terminal sugars from oligosaccharide portions of glycoconjugates '1 * ' in a sugar- and linkage-specific manner. Sialic acids are a class of important saccharides that are fr widely distributed in bacteria and animal tissues, and in most mammals, as either N-acetyl or N-glycolyl derivatives. As 30 referred to herein, "sialic acid" refers to N-acetylneuraminic acid, abbreviated as NeuNAc. Sialic acids donated by CMP-NeuNAc are generally linked to oligosaccharides by enzymes termed sialyl transferases, and are removed by enzymes termed sialidases or neuraminidases. Sialic acid plays a role in a number of cell-cell and cell-substrate interactions (Runyan, D. et al.. J. Cell Biol. 102 . :432-441 (1986) ; Wassarman, P.M. Annu. Rev. Cell Biol. 3:109-142 (1987)). In addition, various organisms, such as influenza virus (Crowell, R.L. et al. American Society of ■ Microbiology. Washington, DC (1986)), mycoplasma (Roberts, D.D. et al. J. Biol. Chem. 264:9289-9293 (1989)), and Plasmodium falciparum (Hadley, J.H. et al. Annu. Rev. Microbiol. 40:415-477 (1987) ) , recognize sialic acid during attachment and/or invasion of their targets. Although a hypothesis was presented over twenty years ago that glycosyltransferases themselves might function as recognition molecules, specifically mediating intercellular interactions via binding and specific transglycosylation reactions (Roseman, S. Chem. Phys. Lipids 5:270-297 (1970); Roth, S. et al. J. Cell Biol. 51:536-547 (1971)), this hypothesis was not accepted or demonstrated because all known glycosyltransferases utilize sugar nucleotides as donors, wherease sugar nucleotide donors are generally absent in the extracellular environment. Thus, the "transglycosylation" with sialic acid donated by free saccharides or glyconjugates other than sugar nucleotides has not been previously demonstrated or accepted. Trypanosoma. cruzi, an obligatory intracellular protozoan parasite that causes Chagas" disease in humans (de Souza, W. Int Rev. Cytol. 86.:197-283 (1984)); Marsden, P.D. et al.. The Biology of Parasitism, Englund, P.T. et al. , eds, Alan R. Liss, New York, 1988, pp. 77-92) divides in the cytoplasm of mammalian cells as amastigotes. At the end of the intracellular cycle, the amastigotes transform into trypomastigotes, which enter the circulation. The trypomastigotes can invade a wide variety of mammalian cells using an energy-requiring receptor-mediated mechanism (Zingales, B. et al. , Curr. Topics Microbiol. Immunol. 112:129-152 (1985); de Araujo- orge, T.C. Mem. Inst. Oswald Cruz .84:441-462 (1989); Schenkman, S. et al. Cell 55:157-165; Schenkman, S. et al. Infect. Immun. 59:645-654 (1991)). However, the nature of the T. cruzi ligand(s) and target cell receptor(s) remains controversial (Ouaissi, M.A. et al. Science 234:603-607 (1986); de Arruda, M.V. et al. Eur. J. Biochem. 182:413-421 (1989) ; Abuin, G. et al. Mol. Biochem. Parasitol. 35:229-237 (1989); Yoshida, N. et al. Infect. Immun. 57:1663-1667 * 5 (1989) ;Rimoldi. M.T. et al. J. Clin. Invest. 84:1982-1989 (1989); • Boschetti, M.A. et al. Mol. Biochem. Parasitol. 24:175-184 ■ * • - (1987) . Sialic acid probably protects parasites from attack by the host complement system. Thus, sialidase or neuraminidase 10 treatment is expected to enhance the sensitivity of blood stream T. cruzi trypomastigotes to lysis by complement (Kipnis, T.L. et al. Proc. Nat'l Acad. Sci. USA 78:602-605 (1981)). This may be related to the fact that sialic acid can inhibit the assembly of the C3-convertase C3b,Bb (Kazatchkine, M.D. et al. J. Immunol. 15 122.:75-81 (1979)) and thereby control complement activity on the surface of certain bacteria (Jarvis, G.A. et al. Infect. Immun. 55:174-180 (1987); Edwards, M.S. et al. J. Immunol. 128:1278-1783 (1982) ) . Interestingly, Neisseria gonorrheae acquires sialic acid from the host and becomes serum resistant (Nairn, C . et 20 al. J. Gen. Microbiol. 134:3295-3306 (1988)). Pereira and his colleagues have described a T. cruzi neuraminidase which plays a role in invasion (Pereira, M.E.A., Science 219:1444- (1983); Pereira, M.E.A. et al.. Mol. Biochem. Parasitol. :20.:183- (1986)). This enzyme is developmentally 25 regulated with maximal activity in trypomastigotes, is located on the surface of the parasite where it can chemically desialylate the surfaces of various host target cells. The enzyme has an apparent molecular weight of 66 kDa (Harth, G. , et al.. Proc. Natl. Acad. Sci. USA :8320-8324 (1985); Pereira, 30 M.E.A. et al.. J. Exp. Med. 174:179-191 (1991)) and consists of a set of apparently glycosylated polypeptides whose range in size * depends on the parasite strain or clone (Prioli, R.P. et al. J. Immunol. 144:4384-4391 (1990) ; Pereira, 1991, supra) and ranges between 120 and 222 Kda, some of which appear to be tri ers. DNA 35 encoding one isoform of this neuraminidase of tissue culture trypomastigotes has recently been isolated and sequenced (Pereira, 1991, supra) . The deduced amino acid sequence encoded by this DNA includes the following characteristics: a catalytic domain in the N-terminus which resembles bacterial neuraminidases, including two YWTD motifs; a domain similar to fibronectin III modules having GTP-binding consensus sequences; a long terminal tandem repeating structure rich in Ser, Thr and Pro residues; and a hydrophobic stretch of 35 amino acids at the extreme C-terminus which could mediate anchorage of the neuraminidase to the cell surface via a glycosylphosphatidyl-inositol linkage. T. cruzi do not appear to synthesize sialic acid de novo (Schauer, R. et al. Z. Physiol. Chem. 364:1053-1057 (1983)), but rather scavenge it from glycoproteins in the external environment (Previato, J.O. et al. Mol. Biochem. Parasitol. 16:85-96 (1985); Zingales, B. et al. Mol. Biochem. Parasitol. 26:135-144 (1987)). Previato and colleagues suggested the presence of a sialyl transferase-like enzyme in T. cruzi epimastigotes. However, the enzyme, its substrate, or the parasite acceptor molecules were not characterized or were, at best, characterized incompletely (Zingales et al.. 1985, supra: Previato et al.. supra) . Glycoconiucrates of Sialic Acid Linked in an at(2→3) Linkage to Galactose and their Biomedical Significance A structure known as the Lewis x antigen (Le x ) is a t e t ras a c charide hav ing t he f o rmul a NeuNAcα!2→3Gal01→4Fucα!l-*3GlcNAc- and is found on the terminal portions of the carbohydrate chains in cell surface glycoproteins and glycolipids. Le x is transiently expressed as an antigenic determinant in the mouse embryo, hence its original designation as stage-specific antigen-l (SSEA-1) (Gooi, H.C. et al. , Nature 292.:156-158 (1981)) . This molecule is now known to be identical with CD15, a granulocyte differentiation marker. The sialylated derivative of Le x , termed "sialyl Le, " is the ligand for a group of cell adhesion molecules or adhesins, termed "selectins" or "LECCAMs" (leukocyte endothelial cell:cell adhesion molecules) (Larsen, E. et al. , Cell 63:467-474 (1990); Lowe, J.B. et al. , Cell 63:475-484 (1990); Phillips, M.L. et al.. Science 250:1130-1132 (1990); Walz, G. et al.. Science 250:1132-1135 (1990)) . The interaction of the N-terminal lectin domain of LECCAMs with sialyl Le x involves specific recognition of ligands sialylθ!(2→3)galactose (Walz, G. et al. Science T 250:1132-1135 (1990); for review, see Brandley, B.K. et al. Cell .63 . :861-863 (1990)). This constitutes one of the first well-defined physiological roles for carbohydrate-binding proteins (lectins) in humans. LECCAMs may have a role in trypomastigote infections, since, to invade muscle and nervous system cells, trypomastigotes have to traverse vascular endothelial cells, which transiently bear surface membrane receptors of the LECCAM family (Osborn, L. Cell £2:3-6 (1990)). The precise role of the LECCAM-sialyl Le interaction depends on the particular LECCAM involved. Platelet activation-dependent granulocyte external membrane protein (PADGEM, also known as GMP-140 or CD62) is expressed on platelets and endothelial cells after stimulation with thrombin or histamine and recruits leukocytes to the site of tissue injury. PADGEM is pre-synthesized within the cell and externalized immediately upon stimulation. In contrast, endothelial leukocyte adhesion molecule-1 (ELAM-1)) is produced after induction with inflammatory cytokines such as interleukin-lβ and tumor necrosis factor- a, or with bacterial endotoxins. The third sialyl-Le x binding protein, Leukocyte Adhesion Molecule-1 (LAM-1, also known as gp90 and LECCAM-1) is expressed on leukocytes such as neutrophils, but not on endothelial cells. The understanding of the LECCAM-sialyl Le x interactions has led to initial development of therapeutics to treat various pathologies mediated by leukocytes. Such pathologies comprise a variety of acute conditions, including septic shock, transplant rejection, traumatic shock, and myocardial infarction, as well as chronic conditions, for example, autoimmune disease, rheumatoid arthritis, asthma, psoriasis, and other inflammatory states. As an example, ELAM-1-carbohydrate interaction can be blocked by molecular mimics of either the ELAM-1 protein or its ligand. Such mimics can be antibodies, soluble carbohydrates or analogues of either of the above. Indeed, sialyl-Le x in either soluble form or on glycolipids in liposomes can block leukocyte adhesion (Hodgson, J. , Bio/Technology 9:609-613 (1991). An important goal of carbohydrate-based drug development is the synthesis of the sialyl Le x ligand. Using a molecular biologic approach, it was found that the expression of the cDNA encoding a human fucosyltransferase in non-myeloid cells conferred ELAM-1- ependent cell adhesion activity (Lowe, J.B. et al. , Cell 63:475-484 (1990)). However, the main obstacle to progress in the area of carbohydrate-based pharmaceuticals is that carbohydrates and their analogues are notoriously difficult to make. The addition of one monosaccharide to another or to a growing oligosaccharide chain by chemical synthesis requires a large number of separate steps, which is both difficult and expensive and serves as a disincentive to the pharmaceutical industry. Thus there is a well-recognized need in the art for methods which permit economic production of carbohydrate-based drugs, such as those containing oligosaccharides or their derivatives. As discussed above, enzymatic synthesis of a natural complex carbohydrate, such as sialyl Le x , can be accomplished by the appropriate purified or genetically engineered glycosyltransferases. While sialyl transferase enzymes capable of forming ΝeuΝAcα2→3Gal structures are known, they require that the sialic acid be donated by nucleotide sugars, typically CMP-sialic acid (Paulson, J.C. et al.. Meth. Enzymol. 138:162-168 (1987) ) . Accordingly, there is a long standing need to provide simpler or more readily available forms of sialic acid can be utilized to create such α;2-3 linkages. In addition, sialic acid has other important functions, such as increasing the half life of glycoconjugates or cells in body fluids or tissues. In the absence of the terminal sialic acid of glycoconjugates, such as cell membrane glycoproteins or glycolipids, the terminal galactose or glucose of such glycoconjugates are recognized by specific cell receptors and these glycoconjugates are removed from the circulation, body fluids or tissues. Accordingly, there is also a need to provide methods for increasing the half life of glycoconjugates in body fluids or tissues. Citation of documents herein is not intended as an admission that any of the documents cited herein is pertinent prior art, or an admission that the cited documents is considered material to the patentability of the claims of the present application. All statements as to the date or representation as to the contents of these documents is based on the information available to the applicant and does not constitute any admission as to the correctness of the dates or contents of these documents. SUMMARY OF THE INVENTION It is an object of the present invention to overcome the discrepancies of the prior art. It has now been discovered that novel trans-sialidase enzymes and enzymatically active polypeptides as fragments or derivatives thereof, have the capacity to attach to a sugar chain a sialic acid residue to a free or cell membrane associated glycoconjugate or saccharide, using sialic acid bound directly from extrinsic glycoconjugates or saccharides, other than nucleotide phosphates, such as cytosine monophosphates (CMPs, including, but not limited to cytidine, cytidylate, deoxycytidine and deoxycytidylates. The present invention thus provides the advantage of using sialic acid donors other than sialydated nucleotide phosphates, which facilitates and reduces the cost and effort required to sialydate biological molecules, such as biologically active molecules. The further advantage of sialydating biologically active molecules is that the added sialic acid residues are expected to increase the half lives of these molecules for therapeutic use and for storage of such molecules. This advantage is based on the fact that degradation of biological molecules is often due to loss of sialic acid residues and the degradation mechanisms in organisms can be based on detection of loss of sialic acids from biological molecules, which detection results in further active degradation and elimination of such molecules. Accordingly, the present invention may provide methods for processing drugs, proteins, polysaccharides, lipids or conjugates thereof, with a trans-sialidase polypeptide of the present invention for the purpose of increasing the half life of such drugs, proteins, polysaccharides, lipids or conjugates thereof, in vivo, in vitro, or in situ. Accordingly, this discovery of the present invention provides novel trans-sialidase polypeptides having trans- sialidase activity, and methods of use, that can be practiced by one of ordinary skill in the art without undue experimentation, based on the teachings and guidance presented herein. Thus, various embodiments of commercially useful applications of trans-sialidase polypeptides and methods of the present invention, can be practiced by the skilled artisan, based on the non-limiting examples and teaching and guidance presented herein. The present invention also provides for the use new sialic acid donor molecules, in contrast to the conventional sugar nucleotides as donor molecules. Inparticular, sialidase enzymes and methods of the present invention provide for the attachment of a sialic acid in an Q.2-3 linkage to a lactosyl group, such as a galactosyl or glucosyl group, as a non-limiting example. As presented above, it has also now been discovered that trans-sialidase polypeptides according to the present invention do not utilize cytidine 5' monophospho-N acetylneuraminic acid (CMP-NeuNAc) as a donor substrate, but readily transfer sialic acid from exogenously supplied o.(2-»3) -sialylsaccharides or from synthetic sialic acid conjugates, such as methyl-umbelliferyl-N- acetyl-neuraminic acid or p-nitro-phenyl-N-acetyl-neuraminic acid, which donor groups can be saccharides or parts of glycoconjugates such as saccharides, glycoproteins or glycolipids. Such glycoconjugates can be in free form or attached to cell membranes, in vivo, in situ or in vitro. This novel and unusual trans-sialidase may provide the trypanosomal epitope Ssp-3 with structural features required for target cell recognition. This epitope is specific to plasma membrane of the infective, trypomastigote stage of trypanosomes generally, such as T. cruzi or T. brucei , but is not present on amastigotes or insect forms of the parasite. Molecules bearing the Ssp-3 epitope may interact with cell adhesion molecules of the LECCAM family during the trypomastigote's migration within the host. Ssp-3 is sialylated by an enzymatic activity of a T. cruzi trans-sialidase polypeptide of the present invention. An assay has further been discovered to quantitate Ti-ypanosoma attachment, as well as a method utilizing panels of monoclonal antibodies (mAbs) to surface membrane components of infective trypomastigote forms of this parasite. MAbs have also been provided that inhibit parasite attachment to cells, and that reacted (in a Western blot) with a group of molecules migrating as a broad band between 60 and 250 kDa, having a peak of intensity around 160 kDa (Schenkman, S. et al. Exp. Parasitol. 72:76-86 (1991) ) . This same group of antibodies was additionally discovered to be immunoprecipitated by mAb 3C9, which defines the trypomastigote-specific Ssp-3 epitope (Andrews, N.W. et al. Exp. Parasitol. _64 . :474-484 (1987) ) . Ssp-3 is also bound by mAbs 46, 50 and 87 (Schenkman, S. et al.. supra) . Ssp3 is sialylated by the activity of T. cruzi trans-sialidase. The present invention provides novel trans-sialidase polypeptides obtainable by recombinant expression in a host, or by purification from organisms which produce such trans-sialidase polypeptides, such as from prokaryotes or eukaryotes, including bacteria, yeast and parasites, preferably from Trypanoso a trypomastigotes, such as T. cruzi , or T. brucei . A trans- sialidase polypeptide of the present invention specifically transfers sialic acid from either extrinsic or endogenous parasite glycoconjugates to form a sialylated structure. As a non-limiting example, in T. cruzi , this structure acts as a developmen ally regulated surface epitope involved in the parasitic invasion of host cells. According to one aspect of the present invention, a t^ ns-sialidase polypeptide is provided comprising substantially the amino acid sequence of Figure 18, wherein said trans- sialidase amino acid from the gene which has trans-sialidase activity, and is less than 100% homologous to the TCNA peptide sequence of Figure 23. In a preferred embodiment, the trans- sialidase amino acid sequence comprises the amino acid sequence of Figure 18. In another preferred embodiment, a trans-sialidase polypeptide is provided wherein an acceptor glycoconjugate for the polypeptide comprises an acceptor terminal group Galβl→z-R 1 or Glcβl→z-R 1 , wherein z is 3, 4 or 6 and R 1 is selected from glucose, fructose, gluconic acid, mannose, methoxygalactose, methoxyglucose, N-acetyl galactose, N-acetyl glucose, or arabinose. In another embodiment, the acceptor conjugate further comprises a member selected from a monosaccharide, a disaccharide, an oligosaccharide, a glycoprotein or a glycolipid, and wherein the acceptor glycoconjugate is in soluble form or is associated with a cell membrane or a liposome. In another aspect of the present invention, a sialic acid donor for the polypeptide is provided that is selected from a terminal NeuNAco.2→3Gal- or NeuNAcα.2→3Glc-containing donor glycoconjugate. In a preferred embodiment, the donor glycoconjugate comprises a donor terminal group NeuNAcα2→3Galβl→z-R l or NeuNAco.2→3Glc/3l→z-R 1 , wherein z is 3, 4 or 6 and wherein R 1 is selected from glucose, fructose, gluconic acid, mannose, methoxygalactose, methoxyglucose, N-acetyl galactose, N-acetyl glucose, or arabinose. In another preferred embodiment, the donor glycoconjugate further comprises a member selected from a monosaccharide, a disaccharide, an oligosaccharide, a glycoprotein or a glycolipid. In still another aspect of the present invention, an isolated or recombinant nucleic acid is provided, comprising a nucleotide sequence encoding a trans-sialidase polypeptide according to the present invention, optionally included in an expression vehicle, and/or a host transformed or transfected with the nucleic acid, wherein the host is a bacterium or a eukaryote, such as a mammalian cell. In another aspect of the present invention, a method for transferring sialic acid from a terminal o;2→3 linked donor glycoconjugate to a carbohydrate acceptor glycoconjugate is provided, comprising reacting a trans-sialidase polypeptide according to claim 1 with the sialic acid donor to transfer the sialic acid from the donor to the acceptor. Preferably, the acceptor glycoconjugate comprises an acceptor terminal group Galøl→z-R 1 or Glcβl→z-R 1 , wherein z is 3, 4 or 6 and R 1 is selected from glucose, fructose, gluconic acid, mannose, methoxygalactose, methoxyglucose, N-acetyl galactose, Ν-acetyl glucose, or arabinose. Preferably, the acceptor conjugate further comprises a member selected from a monosaccharide, a disaccharide, an oligosaccharide, a glycoprotein or a glycolipid, wherein the acceptor glycoconjugate is in soluble form or is associated with a cell membrane or a liposome. In another preferred embodiment, the acceptor terminal group is selected from /?-D-Gall→3j3-D-GalNAc-, |S-D-Gall-»4j3-D-GalNAc-, 3-D-Glcl→3/?-D- GalNAc, /3-D-Glcl→4j8-D-GalNAc-, ?-D-Gall→3jS-D-GlcNAc-, jS-D- Gall→43-D-GlcNAc, jS-D-Glcl→3jS-D-GlcNAc- or /3-D-Glcl→4/J-D-GlcNAc. Also preferably, the donor glycoconjugate is selected from a terminal NeuNAcα2→3Gal- or NeuNAcα.2-»3Glc-containing donor glycoconjugate, and the donor glycoconjugate sialic acid donor may preferably comprise a donor terminal group NeuNAcα2→3Gal/?l-»z- R 1 or NeuNAcα.2→3Glc/3l→z-R\ wherein z is 3, 4 or 6 and R 1 is selected from glucose, fructose, gluconic acid, mannose, methoxygalactose, methoxyglucose, N-acetyl galactose, N-acetyl glucose, or arabinose. Preferably, the donor glycoconjugate further comprises a member selected from a monosaccharide, a disaccharide, an oligosaccharide, a glycoprotein or a glycolipid. Preferably, R 1 may further comprises a fucosyl side chain, wherein the fucosyl side chain is optionally added to the acceptor glycoconjugate after the transfer of the sialic acid to the acceptor. Also, the acceptor glycoconjugate may be a Lewis type antigen. In still another embodiment, the terminal NeuNAco;2→3Gal- or NeuNAcα.2-»3Glc- comprises a C9 deoxy or methoxy. Other objects, features and advantages of the present invention will become apparent to those skilled in the art from the following detailed description. It should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the present invention, are given by way of illustration and not limitation. Many changes and modifications within the scope of the present invention may be made without departing from the spirit thereof, and the invention includes all such modifications. BRIEF DESCRIPTION OF THE DRAWINGS Figures 1A-1F are flow cytometry scans showing the effect of bacterial (V. cholerae) sialidase on the binding of mAbs 3C9, 46, and 14 to live trypomastigotes. Panels a, c and e show binding in the absence of sialidase. Panels b, d and f show binding in the presence of sialidase. T. cruzi trypomastigotes isolated from culture supernatants of LLC-MK 2 cells were incubated for 2 hrs with 50 mU/ml active sialidase (b. d and f) , or heat-inactivated enzyme (a, c, and e) . The parasites were stained by immunofluorescence with either mAb 3C9 at 5 μg/ml (a and b) , mAb 46 at 1 μg/ml (c and d) or mAb 14 at 5 μg/ml (e and f> . Figures 2A-2F are flow cytometry scans showing acquisition by trypomastigotes of epitopes recognized by mAb 3C9 and mAb 46 following incubation with conjugated sialic acid. Purified slender T. cruzi trypomastigotes from culture supernatants were incubated for 3 hr with 1 mM sialic acid (a and b) , 1 mM 0.(2-3) -sialyllactose (c and d) , and 0.5 mg/ml fetuin (e and f) . At the end of the incubation, the parasites were washed, stained by immunofluorescence using mAb 46 or 3C9 as primary antibodies, and analyzed. Figure 3 is a graph showing the kinetics of sialic acid transfer to live trypomastigotes. BSA trypomastigotes were incubated at 4°C with 0.1 mM a (2-3)sialyllactose (Panel A), or at 37°C with 1 mM α(2-3) sialyllactose (Panel B) . At the times shown, the parasites were diluted with cold 0.2% BSA, centrifuged, and washed with 0.2% BSA-DMEM at 4°C. Staining with mAb 3C9 (indirect immunofluorescence) or with FITC-labeled peanut agglutinin (PNA) (direct immunofluorescence) was analyzed by FACS- In Panel A, the ordinate represents the relative increase in 3C9 mean fluorescence. In Panel B, the ordinate represents the actual fluorescence measurement. Figure 4 shows western blots and SDS-PAGE patterns which demonstrate that the Ssp-3 epitope is restored after incubation of BSA trypomastigotes with 0.(2-3)sialyllactose. In Experiment 1, T. cruzi trypomastigotes cultured in medium containing serum (lane a) or BSA (lanes b-e) were incubated for 15 min at 37°C with 1 mM sialic acid (lane b) , for 15 min at 4°C with l mM α(2-3) -sialyllactose (lane c) , or for 1 and 5 min at 37°C with 1 mM sialyllactose (lanes d and e) . At the end of the incubations, the parasites were washed, boiled in SDS sample buffer, and the binding of the mAb 3C9 was assayed by Western blotting. In Experiment 2, T. cruzi trypomastigotes obtained from cells grown in serum-containing medium were washed, boiled in SDS sample buffer, subjected to SDS-PAGE and transferred to nitrocellulose. One nitrocellulose strip was treated for 3 hr at room temperature with 10 mU/ml C. perfringens sialidase (lane f) , whereas the other strip was treated with boiled sialidase (lane g) . The strips were then washed and parasite antigens revealed with mAb 3C9. In Experiment 3, BSA trypomastigotes were incubated with [ 3 H]sialyllactose and extracted. Twenty percent of the lysate was mixed with concentrated sample buffer and analyzed directly by SDS-PAGE (lane h) . The remaining lysate was precleared with Sepharose 4B beads. The supernatant was divided in two aliquots and immunoprecipitated with mAb 3C9 (lane i) or mAb 27 (lane j) . The immunoprecipitated materials were analyzed by SDS-PAGE and fluorography. The standards correspond to myoglobin (200 kd) , β- galactosidase (116 kd) , phosphorylase b (93 kd) , BSA (66,kd) , and ovalbumin (43 kd) . Figure 5 is a graph showing the partial purification of T. cruzi trans-sialidase. A total detergent extract obtained from 4 x 10 9 frozen trypomastigotes was subjected to affinity chromatography on concanavalin A-Sepharose. The eluate was dialyzed and loaded into a Mono Q FPLC column. After extensive washing, the trans-sialidase activity (circles) was eluted with a NaCl gradient. The solid line represents the optical density at 280 nm and the dotted line the NaCl concentration. Figure 6 is a graph showing the silica gel thin-layer chromatography pattern of the reaction products of T. cruzi trans-sialidase. NP40 extracts of trypomastigotes were incubated with 1 mM α;(2-3)sialyllactose and [ 14 C]lactose, and the reaction product was isolated by elution from a QAE-Sephadex A50 column. The eluate was lyophilized and analyzed by chromatography in silica gel 60 plates using ethanol-n-butanol-pyridine-water- acetic acid (100:10:10:30:3 [v/v] ) . The standards α(2-3) sialyllactose (a), α. (2-6) sialyllactose (b) , α.(2-3)sialyllactosamine (c) , and α(2-6)sialyllactosamine (d) , were visualized with the orcinol ferric chloride spray reagent (Veh, R.W. et al. J. Chromat. 212:313-322 (1981)). The reaction product of T. cruzi πrans-sialidase (e) was visualized by spraying with En 3 Hance™ followed by autoradiography. Figure 7 is a series of photomicrographs showing that mammalian cells donate sialic acid for T. cruzi trans-sialidase. The photographs demonstrate immunofluorescence staining with mAb 3C9 of serum-grown or BSA trypomastigotes either attached to poly-L-lysine treated glass coverslips (a and c) or incubated with 3T3 fibroblasts for 30 min at 37°C (b and d) . BSA trypomastigotes are shown in (a) and (b) , and serum-grown trypomastigotes are shown in (c) and (d) . Figure 8 is a series of radioimmunoprecipitations or Western blots showing heterogeneity of the molecules recognized by mAb 39 specific for T. cruzi trans-sialidase. Lysates made from trypomastigotes labeled for 3 h with [ 35 S] -methionine and cysteine were immunoprecipitated with a control antibody (lane a) or with mAb 39 (lane b) . Lane c is a Western blot of total trypomastigote extracts, revealed with mAb 39. Supernatants of cultures of trypomastigotes were immunoprecipitated with mAb 39, then subjected to Western blotting and revealed either with mAb 39 (lane d) , with a rabbit antiserum to the cross-reactive determinant of the variant surface glycoprotein of African trypomastigotes (lane e) , or with normal rabbit serum (lane f) . Figure 9 is a chromatographic pattern showing that trans-sialidase and neuraminidase have similar physico-chemical properties. Shown are trans-sialidase (closed circles) and neuraminidase (open circles) activities following NaCl elution from a Mono Q FPLC column which had been equilibrated with 20 mM Tris-HCl pH 8.0. The input was a sample of enzyme purified from culture supernatants by affinity chromatography with mAB 39. The input is analyzed in the two lanes of the inset shown on the left side of the figure, which show the affinity-purified enzyme stained with Coomassie blue and silver nitrate. The right inset shows the results of SDS-PAGE and silver staining of the fractions eluted at the corresponding positions in the abscissa. Absorbance (O.D.) at 280 nm and/or salt concentrations are represented by dashed and dotted lines as indicated in the right ordinates. Figure 10 is a chromatographic pattern showing that trans-sialidase and neuraminidase have similar physico-chemical properties. Shown are trans-sialidase (closed circles) and neuraminidase (open circles) activities of fractions obtained by gel filtration on a Superose 12-Superose 6 FPLC column. The input was an eluate obtained by affinity chromatography of a T. cruzi extract on immobilized Concanavalin-A. Also indicated in the abscissa are positions of eluted protein standards and their molecular weights. Figure 11 is a chromatographic pattern showing that trans-sialidase and neuraminidase have similar physico-chemical properties. Shown are trans-sialidase (closed circles) and neuraminidase (open circles) activities of fractions eluted from an FPLC phenyl-Superose column by decreasing ammonium sulfate concentrations. The input was a sample of T. cruzi BSA culture supernatant. Figure 12 is a graph showing the effect of pH on the activity of trans-sialidase and neuraminidase enzymatic activity. Activity of pooled fractions eluting from the mono Q column (see Figure 9) was measured using sialyllactose and [ ~ 4C] -lactose (circles) or methyl-umbelliferyl-N-acetyl-neuraminic acid or p- nitro-phenyl-N-acetyl-neuraminic acid (triangles) as substrates in presence of 20 mM MES buffer (pH 5-6.5), 20 mM Hepes buffer (pH 7-7.5) and 20 mM Tris-HCl buffer (pH 8.0-9.0). Figure 13 is a graph showing that methyl-umbelliferyl-N-acetyl-neuraminic acid or p-nitro-phenyl-N-acetyl-neuraminic acid are sialic acid donors. Mono Q-affinity purified enzyme was incubated with 1 mM sialyllactose for the indicated times in the presence of 1 mM (open circles) or 0.1 mM (closed circles) methyl-umbelliferyl-N- acetyl-neuraminic acid or p-nitro-phenyl-N-acetyl-neuraminic acid. The amount of formed [ 14 C] -sialyllactose was determined after incubation at 25°C. Figure 14 is a graph showing that 4-methyl-umbelliferone is not a sialic acid acceptor. Mono Q-affinity purified enzyme was incubated at 25°C in the presence of 1 mM sialyllactose and 8 μM [ 14 C] -lactose in the presence of the indicated concentrations of lactose or 4-methylumbelliferone. After 30 min the amount of [ I4 C] -sialyllactose formed during the reaction was determined. Figure 15 is a graph showing a kinetic analysis of the neuraminidase and trans-sialidase reactions. Affinity purified enzyme (50 ng protein) was incubated for various periods of time at 25°C in 20 mM Hepes buffer pH 7.0, in the presence of 100 n oles of sialyllactose and 80 nmoles of lactose mixed with [ I4 C] -lactose, in a final volume of 0.l ml. At the end of the reaction, 0.04 ml was used to measure the amount of free sialic by TBA-HPLC method (closed circles), and 0.06 ml was used to measure the amount of [^C] -sialyllactose produced (open circles) . The sialic acid produced in the absence of lactose is also indicated (triangles) . The results are expressed in nmoles of sialyllactose or sialic acid produced per 0.1 ml of the reaction. Figure 16 is a graph showing that lactose inhibits the release of sialic acid. Experimental conditions are as described for Figure 15, except that incubation was for 30 minutes, and final concentrations of lactose mixed with [ I C] -lactose varied as indicated in the abscissa. The synthesis of [ 14 C] -sialyllactose (open circles) or release of sialic acid (closed circles) are indicated. Figure 17. Nucleotide sequence of portion of trans- sialidase imparting trans-sialidase and/orneuraminidase activity (SEQ ID NO:3) . Figure 18: Amino Acid sequence of portion of trans- sialidase impartingtrans-sialidaseand/orneuraminidase activity (SEQ ID N0:4) . Figure 19. Restriction maps of isolated trans-sialidase clones. The restriction maps of the inserts from eight lambda clones which expressed protein recognized by the antibody against trans-sialidase are indicated, along with a map of the neuraminidase clones (NA) of Periera, et. al., 1991. Clones labelled 121, 151, and 154 were chosen for further study. Abbreviations; E R , EcoRI; Pm, Pmll; Pv, PvuII; Ps, PstI; S, SacII; X, Xhol. Figure 20. Restriction maps of trans-sialidase clones. The top line (NA) represents a restriction map of the neuraminidase gene of Pereira, et. al., 1991. The lower three lines are maps of the inserts from clones 121, 151, and 154. Restriction enzyme sites common to all four genes are indicated below each line, and sites which differ amongst the four genes are indicated below each line. Clones 121 and 151 were negative for trans-sialidase activity, and 154 was positive for trans-sialidase activity. Abbreviations; Ba, BamH I; E N , EcoN I; E R , EcoR I; H, Hind III; K, Kpn I; M, Mlu I; Pm, Pml I; Ps, Pst I; Pv, Pvu II; S, Sac II; SUBSTITUTE SHEET X, Xho I . Figure 21. In order to identify the region of the gene in clone 154 which is necessary for trans-sialidase activity, recombinant constructs were generated using portions of clones 121/151, whose protein products are not enzymatically active, and clone 154, whose encoded protein product is enzymatically active. These recombinant plasmid constructs were transfected into E. coli and extracts of the transfectants were assayed for both trans-sialidase and neuraminidase activities. Lines labelled 121/151, and 154 represent the original clones of each trans- sialidase gene. Recombinant are indicated by listing first the source of the 5' portion of the construct, then the restriction site used to join the two DNA pieces, then the source of the 3' portion of the construct. Clones 121 and 151 are considered together since their restriction maps were identical. The results of the enzymatic assays are indicated on the right. The portion of the gene here defined by Bgl II and EcoN I sites encodes amino acid sequences which are necessary for trans- sialidase activity. Figure 22. Nucleotide sequence of that portion of the trans-sialidase gene necessary for enzymatic activity. The nucleotide sequence of Bgl II to EcoN I fragments was determined for clones 121, 151, and 154, and are presented here compared to the sequence of the same region of the neuraminidase gene of Pereira, et. al., 1991. Lines labelled TCNA represent the neuraminidase sequence of Pereira (SEQ ID NO:5) , 121 indicates the sequence of both 121 and 151 which were identical in this region (SEQ ID NO:6), and 154 represents the sequence of clone 154 (SEQ ID NO:7) . Dots below the TCNA sequence indicate identical nucleotides, and differences from the neuraminidase sequence are indicated. The Bgl II and EcoN I sites are also indicated. The gene in clone 154 is distinct from the neuraminidase and 121/151 genes at the nucleotide level. Figure 23. Predicted amino acid sequence of part of the trans-sialidase protein encoded by the Bgl II to EcoN I fragment, SEQ ID NO: 8 corresponds to TCNA, SEQ ID NO:9 corresponds to 121, and SEQ ID NO:10 corresponds to 154. A comparison of the amino acid sequence of the predicted proteins encoded by neuraminidase SUBSTITUTE SHEET and trans-sialidase genes are presented, with labellings as in figure 4. Dots below the TCNA sequence indicate amino acid identity, while differences are indicated with the substituted amino acid. Again, the protein encoded by clone 154 is distinct from neuraminidase of Pereira et. al. and from proteins encoded by clones 121 and 151. Figures 24A-B. Purification and determination of the molecular weight of the T. brucei trans-sialidase (A) Trans- sialidase activity (solid line) and optical density at 280 nm (dotted line) of fractions eluted with an NaCl gradient from a Mono Q FPLC column equilibrated with 20 mM Tris-HCl, pH 8. NaCl concentrations are represented by a dashed line. The input was an enzyme sample purified from an NP-40 lysate by Con A-affinity chromatography. The result of SDS-PAGE and silver staining of a pool of the fractions with trans-sialidase activity is shown in the left lane of the inset in part B of figure. (B) Trans- sialidase activity (solid line) and optical density at 280 nm (dotted line) of fractions obtained by gel filtration on Superose 12 - Superose 6 FPLC columns run in tandem. The input was a sample of the T. brucei enzyme purified by the ion-exchange chromatography illustrated in A above. The inset shows the result of SDS-PAGE and silver staining of the input sample (first lane) or of fractions corresponding to positions in the graph indicated by the hatched arrows. Figures 25A-B. Ability of different compounds to donate sialic acid to lactose in the presence T. brucei (closed circles) or _ ____ cruzi (open symbols) trans-sialidases. ,4 C-lactose (0.36 nmoles) was incubated with the indicated amounts of potential sialic acid donors and Con A-purified T. brucei or T. cruzi trans-sialidases as described in the Materials and Methods. (A) Sialyl(α.2-3)lactose (circles) . sialyl (α.2-6)lactose (triangles) and colominic acid (Squares). (B) Sialyl(α.2-9) (α2-3)lactose- ceramide (circles) and fetuin (triangles) . (C) 4- methylumbelliferyl-N-acetylneuraminic acid (circles) and N- acetylneuraminic acid (triangles) . Figures 26A-B. Inhibition of sialylation of radiolabelled lactose by saccharides [ , C] -lactose (7.2 μm) , sialyllactose (1 mM) and the indicated amounts of non-radioactive saccharides were incubated with T. brucei (closed symbols) or T. cruzi (open symbols) trans-sialidases. Radioactivity associated with sialic acid was separated by anion-exchange chromatography and measured in a β counter. Trans-sialidases were purified from NP- 40 trypomastigote lysates by Con A-affinity chromatography. (A) Lactose (circles) and melibiose (triangles) . (B) β-methyl- galactose (circles) and o.-methyl-galactose (triangles) . Figure 27. Thin-layer chromatography on silica gel of different saccharides sialylated by T. brucei trans-sialidase. One hundred nmoles of lactose (lane a) , β-methylgalactose (lane b) , stachyose (lane e) or melibiose (lane f.) were incubated with 15 nmoles of [sialic-9- 3 H)sialyllactose in the presence of T. brucei trans-sialidase (purified by Con A-affinity and anion- exchange chromatographies) for 210 min at room temperature. The products of the reaction were isolated by elution from a QAE- Sephadex column and analyzed by chromatography on silica gel, followed by fluorography. The arrow indicates the position that free sialic acid migrated to. Figure 28. Lack of reactivity of T. brucei trans-sialidase with antibodies to T. cruzi trans-sialidase. T. brucei (closed symbols) or T. cruzi (open symbols) ΝP-40 lysates were immunoprecipitated with the indicated volumes of protein A- agarose beads bearing T. cruzi-antibodies. The total volume of agarose beads was always brought to 27 μl by the addition of non- coated beads. (A) Immunoprecipitation with the anti-T. cruzi trans-sialidase mAb 39. (B) Immunoprecipitation with rabbit antibodies against purified T. cruzi trans-sialidase (circles) or with rabbit antibodies against a synthetic peptide corresponding to the first 19 amino-terminal amino acid residues of the T. cruzi trans-sialidase (triangles) . Figure 29. SDS-PAGE of T. brucei surface molecules sialylated by the addition of radiolabeled sialyllactose. Live T. brucei trypanomasigotes were incubated with [ 3 H] -sialyllactose and lysed with NP-40. Lysate samples were untreated (lanes a and d) , treated with sialidase (lanes b and e) , treated with sialidase buffer (lanes c and f . ) .and subjected to SDS-PAGE. The gel was impregnated with sodium salicylate and stained with coomassie blue (lane a, b and c.) . The presence of radioactive molecules in the same gel was revealed by fluorography (lane d, e and f.) . A lysate sample was subjected to western blotting utilizing an anti-procyclin mAb (lane g;) . Numbers in the left correspond to positions of molecular weight standards. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention relates to novel trans-sialidase enzymes and polypeptides having trans-sialidase activity, in vitro, in vivo, or ins situ. Additionally, a trans-sialidase polypeptide according to the present invention is also provided as expressed in a host from a nucleic acid sequence encoding such a polypeptide. Additionally, methods are provided for isolating trans-sialidase polypeptides of the present invention, as well as for isolated recombinant or purified polypeptides and using for synthetic or pharmacological applications, especially for the attachment of sialic acid residues to glycoproteins, glycolipids and saccharides, in soluble form or associated with cell membranes or other protein or lipid structures, such as the non-limiting examples of antibodies or liposomes. The present invention resides in the discovery transialidase polypeptides or purified polypeptides having at least some trans- sialidase activity, including recoverable amounts of such polypeptides, which may be isolateable from the genus Trypanosoma, such as T. cruzi or T. brucei. A trans-sialidase polypeptide may comprise at least a portion of the amino acid sequence depicted in Figure 18 which is less than 100% homologous with the TCNA amino acid sequence shown in Figure 23. Accordingly, the present invention is not limited to the examples presented herein, but encompasses all trans-sialidase polypeptides as described herein, encoding nucleic acids and methods of making and using such polypeptides, which can be provided by one of ordinary skill in the art using known method stops without undue experimentation, based on the teaching and guidance presented herein. As a non-limiting example, the invention is directed to an isolated, naturally occurring trans-sialidase enzyme or a recombinant trans-sialidase polypeptide derived therefrom, having at least one of trans-sialidase activity and neuraminidase activity. A trans-sialidase polypeptide of the present invention may be less than 100%, and preferably less than 99, 98, 97, 96, 95, 94, 93. 92, 91, 90, 88, 87% homologous to the TCNA amino acid sequence depicted in Figure 23. The present invention thus provides naturally occurring, chemically synthesized or recombinantly produced trans-sialidase active polypeptides containing at least a portion of the amino acid sequence of a trypanosoma trans-sialidase indicates that the protein has been purified away from at least 90% (on a weight basis), and preferably from at least 92, 94, 95, 97 or 99% of other proteins and glycoproteins with which it is natively associated, and is therefore substantially free of them. Such purification can be obtained according to known method steps as a non-limiting example, by the following steps: (a) treating a biological sample containing the trans-sialidase in a manner which provides releases the trans-sialidase polypeptide in at least partially soluble form; (b) removing insoluble material from the medium to yield a supernatant containing the trans-sialidase polypeptide; (c) performing lectin affinity chromatography of the supernatant obtained in step (b) to yield a first eluate; (d) performing anion exchange chromatography of the first eluate, yielding a second eluate, the second eluate comprising the trans-sialidase polypeptide substantially free of other proteins with which it is natively associated. Sources of such trans-sialidase polypeptides of the present invention, including fragments of such polypeptides, include samples containing proteins having trans-sialidase activity which are then provided according to the present invention in a form not found in nature. Such sources may include the genus Trypanosoma, such as the non-limiting examples of T. cruzi , T. brucei . As a further non-limiting example, such a process presented above can additionally be provided, wherein: (i) the biological sample comprises Trypanosoma. trypomastigotes and the treating comprises lysis in the presence of one or more proteinase inhibitors; (ii) the removing is by centrifugation for 10 minutes at 10,000 x g; (iii) the lectin affinity chromatography is performed with a concanavalin A-sepharose column and the first eluate is eluted with about 0.5 M α-methylmannoside; (iv) the anion exchange chromatography is performed with a FPLC Mono Q (HR5/5) column and said is eluted with a NaCl gradient (v) . The active peak of the FPLC MonoQ is subjected to molecular sieving chromatography. Alternatively, as a non-limiting example, a recombinant trans-sialidase polypeptide according to the present invention can be produced in prokaryotic or eukaryotic host cells as described herein. This method has the advantage that the enzyme of the present invention, secreted by a host such as a bacterium, yeast, insect or mammalian host, such as bacteria, growing in protein-free medium, is already in much purer form than that in a biological sample such as trypomastigotes or an extract thereof. Such a recombinantly produced trans-sialidase polypeptide of the present invention can be further purified in fewer steps than presented above using conventional purification techniques such as immunoadsorbent columns bearing monoclonal antibodies reactive against the enzyme, as would be obtainable by one of ordinary skill in the art using conventional techniques, without undue experimentation, based on the teaching and guidance presented herein. See, e.g. Ausubel et al, eds Current Protocols in Molecular Biology Wiley Interscience, New York (1987, 1992) and Sambrook et al. Molecular Cloning: A Laboratory Manual 2nd edition, Cold Spring Harbor Press, N.Y. (1989) . As shown, e.g., by Tables 5-11 in Example X below, a trans- sialidase polypeptides of the present invention may utilize acceptors having at least one of the following non-limiting characteristics: (a) acceptors having saccharides containing terminal β- linked but not α.-linked galactopyranosyl residues; (b) Gal (/3l-3)GlcNAc bonds have greater activity than SUBSTITUTE SHEET Gal (jSl-4)GlcNAc which have greater activity than Gal (βl-6)GlcNAc; (c) chain elongation of acceptor does not alter reactivity; and (d) addition of fucosyl side chains close to the terminal galactose of acceptor impairs reactivity A trans-sialidase of the present invention also may utilize trans-sialidase donors 24 having at least one of the following non-limiting characteristics: (a) having N-acetylsialic acid (SA) (α2-3)Gal but not (α.2-6) or (α.2-9) ; (b) having SA in terminal position but not in side chain; (c) having SA(α2-3)0Gal (1-4) is more readily reacted by a trans-sialidase of the present invention than with SA(α2- 3)j8Gal(l-3) and S (α.2-3)0Gal (1-6) (d) having chain elongation does not alter reactivity; (e) having fucosyl side chains close to the terminal galactose impairs reactivity; (f) having modifications of sialic acid (NeuNAc) : changes in C9 (deoxy or methoxy) do not alter ability to donate; changes in C4 (deoxy or methoxy) , C7 (deoxy) and C8 (deoxy or epi) impairs ability to donate sialic acid. (g) synthetic neuraminic acid conjugates, such as methyl umbelliferyl-N-acetyl-neuraminic acid or p-nitro-phenyl-N-acetyl- neuraminic acid. Accordingly, acceptors of sialic acid provided according to methods of the present invention include saccharides, glycoproteins and glycolipids having terminal saccharides selected from a Galβl-4-R 1 or Galβl-3-R 1 , wherein R 1 is selected from glucose, fructose, gluconic acid, mannose, methoxygalactose, methoxyglucose, N-acetyl galactose, N-acetyl glucose, arabinose, which can be produced using conventional methods, modified based on the teaching and guidance presented herein. See, e.g., Auge et al Carb. Res. 200:257-268 (1990) . It will be understood that the naturally occurring trans-sialidase of the present invention can be biochemically purified from several protozoal sources. For preparation of naturally occurring enzyme, T. cruzi , T. brucei are a preferred source. Alternatively, because the gene for the trans-sialidase can be isolated or synthesized, the polypeptide can be synthesized substantially free of other proteins or glycoproteins of mammalian origin or of parasitic origin in a prokaryotic organism or in a convenient non-mammalian eukaryotic cell system, if desired. As intended by the present invention, a recombinant trans-sialidase molecule produced in mammalian cells, such as transfected COS, NIH-3T3, or CHO cells, for example, is either a naturally occurring protein sequence or a functional derivative thereof. Where a naturally occurring protein or glycoprotein is produced by recombinant means, it is provided substantially free of the other proteins and glycoproteins with which it is natively associated. Alternatively, methods are well known for the chemical synthesis of polypeptides of desired sequence on solid phase supports or carriers and their subsequent separation from the support. A "chemical derivative" of the trans-sialidase contains additional chemical moieties not normally a part of the protein. Covalent modifications of the peptide are included within the scope of this invention. Such modifications may be introduced into the molecule by reacting targeted amino acid residues with an organic derivatizing agent that is capable of reacting with selected side chains or terminal residues. Derivatization with bifunctional agents is useful for cross-linking the protein to a water-insoluble support matrix or to other macromolecular carriers. Commonly used cross-linking agents include, e.g., l,l-bis(diazoacetyl) -2-phenylethane, glutaraldehyde, N-hydroxysuccinimide esters, for example, esters with 4-azidosalicylic acid, homobifunctional imidoesters, in¬ cluding disuccinimidyl esters such as 3 , 3 ! - dithiobis(succin-imidylpropionate) , and bifunctional maleimides such as bis-N-maleimido-1,8-octane. Derivatizing agents such as methyl-3 - [ (p-azidophenyl) dithio]propioimidate yield photoactivatable intermediates that are capable of forming crosslinks in the presence of light. Alternatively, reactive water-insoluble matrices such as cyanogen bromide-activated carbohydrates and the reactive substrates described in U.S. SUBSTITUTESHEET Patent Nos. 3,969,287; 3,691,016; 4,195,128; 4,247,642; 4,229,537; and 4,330,440 are employed for protein immobilization. Other modifications include hydroxylation of proline and lysine, phosphorylation of hydroxyl groups of seryl or threonyl residues, methylation of the alpha-amino groups of lysine, arginine, and histidine side chains, acetylation of the N-terminal amine, and, in some instances, amidation of the C-terminal carboxyl groups (T.E. Creighton, Proteins: Structure and Molecule Properties. W.H. Freeman & Co., San Francisco, pp. 79-86 (1983)). Such derivatized moieties may improve the solubility, biological half life, and the like. In additional embodiments of the present invention, a DNA sequence encoding a trans-sialidase molecule or a functional derivative thereof, and methods and hosts useful for expressing the DNA sequence, are provided, wherein DNA is provided that is capable of being expressed in a host such that a polypeptide having at least trans-sialidase activity is expressed which polypeptide comprises at least a portion of the amino acid sequence depicted in Figure 18 and which polypeptide sequence is less than 100% homologous to the TCNA amino acid sequence depicted in Figure 23. In a preferred embodiment, the DNA comprises the nucleotide sequence shown in Figure 17 or a portion thereof which encodes a trans-sialidase polypeptide having at least some trans- sialidase activity and which polypeptide comprises an amino acid sequence corresponding to the TCNA amino acid sequence depicted in Figure 23, but which polypeptide has less than 100% homology to the TCNA amino acid sequence. The recombinant DNA molecules of the present invention can be produced through any of a variety of means, such as, for example, DNA or RNA synthesis, or more preferably, by application of recombinant DNA techniques. Techniques for detecting, cloning, synthesizing, recombining and expressing such molecules are conventional, e.g., as disclosed by Wu, R. , et al. (Prog. Nucl. Acid. Res. Molec. Biol. 21:101-141 (1978)); Ausubel et al, eds. Current Protocols in Molecular Biology Wiley Interscience, New York (1987, 1992) ; Sambrook et al. , Molecular Cloning: A Laboratory Manual. Second Edition, Cold Spring Harbor Press, Cold SUBSTITUTESHEET Spring Harbor, NY (1989) , the contents of which references are entirely incorporated by reference. Oligonucleotides representing a portion of the trans-sialidase-encoding DΝA sequence are useful for screening for the presence of the gene encoding this protein and for the cloning of the trans-sialidase gene or yet undiscovered genes having sufficient sequence homology. Techniques for synthesizing such oligonucleotides are disclosed by, for example, Wu, R. , e_t al.. Prog. Νucl. Acid. Res. Molec. Biol. 21:101-141 (1978)). Such oligonucleotide probes include at least 10-15 nucleotides corresponding to the nucleotide sequence of Figure 17. In a preferred embodiment, such oligo probes which selectively hybridize to a trans-sialidase polypeptide of the present invention do not hybridize under high stringency conditions to a nucleotide sequence corresponding to the TCΝA nucleotide sequence depicted in Figure 22. Such an oligonucleotide, or set of oligonucleotides, capable of selectively hybridizing to a nucleotide sequence encoding a trans-sialidase polypeptide of the present invention is thus used to identify alternative trans-sialidase polypeptide encoding nucleic acids by conventional methods (see, Sambrook et al.. supra. and Ausubel et al, supra) . A suitable oligonucleotide, or set of oligonucleotides, which is capable of encoding a fragment of the trans-sialidase gene (or which is complementary co such an oligonucleotide, or set of oligonucleotides) is identified (using the above-described procedure) , synthesized, and hybridized by means well known in the art, against a DΝA or, more preferably, a cDΝA preparation derived from cells which are capable of expressing the trans-sialidase gene. Single stranded oligonucleotide molecules complementary to the "most probable" trans-sialidase-encoding sequences can be synthesized using procedures which are well known to those of ordinary skill in the art (Belagaje, R. , et al.. J. Biol. Chem. 254:5765-5780 (1979); Maniatis, T. , et al.. In: Molecular Mechanisms in the Control of Gene Expression. Νierlich, D.P., e al., Eds., Acad. Press, Y (1976); Wu, R. , et al.. Prog. Νucl. Acid Res. Molec. Biol. 21:101-141 (1978); Khorana, R.G. , Science 203:614-625 (1979)). Additionally, DΝA SUBSTITUTE SHEET synthesis may be achieved through the use of automated synthesizers. Techniques of nucleic acid hybridization are disclosed by Sambrook et al. (supra) , and by Haymes, B.D. , et al. (In: Nucleic Acid Hybridization. A Practical Approach. IRL Press, Washington, DC (1985)), which reference is herein incorporated by reference. In a alternative way of cloning the trans-sialidase gene, a library of expression vectors is prepared by cloning DNA or, more preferably, cDNA (from a cell capable of expressing trans-sialidase) into an expression vector. A preferred source is a T. cruzi cDNA library, such as a lambda λgtll library or a T7 library such a ExLox™. The library is then screened for members capable of expressing a protein which binds to anti-trans-sialidase antibody, and which has a nucleotide sequence that is capable of encoding polypeptides that have the same amino acid sequence as trans-sialidase, or fragments thereof. In this embodiment, genomic DNA or, preferably mRNA, is extracted and purified from a cell which is capable of expressing trans-sialidase protein. cDNA is produced from the mRNA using standard procedures. The purified genomic DNA or cDNA is fragmentized (by shearing, endonuclease digestion, etc.) to produce a pool of DNA or cDNA fragments. Fragments from this pool of genomic DNA or mRNA derived cDNA are then cloned into an expression vector in order to produce a library of expression vectors whose members each contain a unique cloned genomic DNA or cDNA fragment. An "expression vector" is a vector which (due to the presence of appropriate transcriptional and/or translational control sequences) is capable of expressing a DNA (or cDNA) mole- cule which has been cloned into the vector and of thereby pro¬ ducing a polypeptide or protein. Expression of the cloned sequences occurs when the expression vector is introduced into an appropriate prokaryotic or eukaryotic host cell. Procedures for preparing cDNA and for producing a genomic library are disclosed by Sambrook., supra; and Ausubel, supra . A DNA sequence encoding the trans-sialidase of the present invention, or its functional derivatives, may be recombined with vector DNA in accordance with conventional techniques, including blunt-ended or staggered-ended termini for ligation, restriction enzyme digestion to provide appropriate termini, filling in of cohesive ends as appropriate, alkaline phosphatase treatment to avoid undesirable joining, and ligation with appropriate ligases. Techniques for such manipulations are disclosed by Sambrook et al., supra, and Ausubel, supra and are well known in the art. A nucleic acid molecule, such as DNA, is said to be "capable of expressing" a polypeptide if it contains nucleotide sequences which contain transcriptional and translational regulatory information and such sequences are "operably linked" to nucleo¬ tide sequences which encode the polypeptide. An operable linkage is a linkage in which the regulatory DNA sequences and the DNA sequence sought to be expressed are connected in such a way as to permit gene expression. The precise nature of the regulatory regions needed for gene expression may vary from organism to organism, but shall in general include a promoter region which, in prokaryotes, contains both the promoter (which directs the initiation of RNA transcription) as well as the DNA sequences which, when transcribed into RNA, will signal the initiation of protein synthesis. Such regions will normally include those 5' -non-coding sequences involvedwith initiation of transcription and translation, such as the TATA box, capping sequence, CAAT sequence, and the like. If desired, the non-coding region 3' to the gene sequence coding for the protein may be obtained by the above-described methods. This region may be retained for its transcriptional termination regulatory sequences, such as termination and polyadenylation. Thus, by retaining the 3' -region naturally contiguous to the DNA sequence coding for the protein, the transcriptional termination signals may be provided. Where the transcriptional termination signals are not satisfactorily func¬ tional in the expression host cell, then a 3' region functional in the host cell may be substituted. Two DNA sequences (such as a promoter region sequence and a trans-sialidase-encoding sequence) are said to be operably linked if the nature of the linkage between the two DNA sequences does not (1) result in the introduction of a frame-shift mutation, (2) interfere with the ability of the promoter region sequence to direct the transcription of the trans-sialidase gene sequence, or (3) interfere with the ability of the trans-sialidase gene sequence to be transcribed by the promoter region sequence. A promoter region would be operably linked to a DNA sequence if the promoter were capable of effecting transcription of that DNA sequence. Thus, to express the protein, transcriptional and translational signals recognized by an appropriate host are necessary. A promoter is a DNA sequence which is capable of binding RNA polymerase and promoting the transcription of an "operably linked" nucleic acid sequence. Certain RNA polymerases exhibit a high specificity for such promoters. The RNA polymerases of the bacteriophages T7, T3, and SP-6 are especially well characterized, and exhibit high promoter specificity. The promoter sequences which are specific for each of these RNA polymerases also direct the polymerase to transcribe only one strand of a duplex DNA template. The selection of which strand is transcribed is determined by the orientation of the promoter sequence. This selection determines the direction of transcrip- tion since RNA is only polymerized enzymatically by the addition of a .nucleotide 5' phosphate to a 3' hydroxyl terminus. Two sequences of a nucleic acid molecule are said to be "operably linked" when they are linked to each other in a manner which either permits both sequences to be transcribed onto the same RNA transcript, or permits an RNA transcript, begun in one sequence to be extended into the second sequence. Thus, two sequences, such as a promoter sequence and any other "second" sequence of DNA or RNA are operably linked if transcription com¬ mencing in the promoter sequence will produce an RNA transcript of the operably linked second sequence. In order to be "operably linked" it is not necessary that two sequences be immediately adjacent to one another. The promoter sequences useful in the present invention may be either prokaryotic, eukaryotic or viral. Suitable promoters are repressible, or, constitutive. Examples of suitable prokaryotic promoters include promoters capable of recognizing the T4 (Malik, S. et al.. J. Biol. Chem. 263:1174-1181 (1984); Rosenberg, A.H. et al.. Gene 59:191-200 (1987); Shinedling, S. et al.. J. Molec. Biol. 195:471-480 (1987) ; Hu, M. et al. , Gene 42 . :21-30 (1986)), T3, Sp6, and T7 (Chamberlin, M. et al. , Nature 228:227-231 (1970) ; Bailey, J.N. et al.. Proc. Natl. Acad. Sci. (U.S.A.) 80:2814-2818 (1983); Davanloo, P. et al.. Proc. Natl. Acad. Sci. (U.S.A.) 81:2035-2039 (1984)) polymerases; the P R and P L promoters of bacteriophage lambda (The Bacteriophage Lambda. Hershey, A.D., Ed., Cold Spring Harbor Press, Cold Spring Harbor, N (1973); Lambda II. Hendrix, R.W. , Ed., Cold Spring Harbor Press, Cold Spring Harbor, NY (1980) ) ; the trp. recA, heat shock, and lacZ promoters of E. colir the α.-amylase (Ulmanen, I., et al.. J. Bacteriol. 162:176-182 (1985)) and the σ-28-specific promoters of B. subtilis (Gilman, M.Z., et al. , Gene 32:11-20 (1984) ) ; the promoters of the bacteriophages of Bacillus (Gryczan, T.J., In: The Molecular Biology of the Bacilli. Academic Press, Inc., NY (1982)); Streptomvces promoters (Ward, J.M., et al.. Mol. Gen. Genet. 203:468-478 (1986)); the int promoter of bacteriophage lambda; the bla promoter of the β-lactamase gene of pBR322, and the CAT promoter of the chloram- phenicol acetyl transferase gene of pPR325, etc. Prokaryotic promoters are reviewed by Glick, B.R., (J. Ind. Microbiol. 1:277-282 (1987)); Cenatiempo, Y. (Biochimie 68:505-516 (1986)); Watson, J.D. et al. (In: Molecular Biology of the Gene. Fourth Edition, Benjamin Cummins, Menlo Park, CA (1987) ) ; and Gottesman, S. (Ann. Rev. Genet. 18:415-442 (1984)). Preferred eukaryotic promoters include the promoter of the mouse metallothionein I gene (Hamer, D., et al.. J. Mol. APPI. Gen. 1:273-288 (1982)); the TK promoter of Herpes virus (McKnight, S., Cell 31:355-365 (1982)); the SV40 early promoter (Benoist, C, et al. , Nature (London) 290:304-310 (1981)); and the yeast gal4 gene promoter (Johnston, S.A. , et al. , Proc. Natl. Acad. Sci. (USA) 79.:6971-6975 (1982); Silver, P.A. , et al.. Proc. Natl. Acad. Sci. (USA) 81:5951-5955 (1984)). All of the above listed references are incorporated by reference herein. Strongpromoters are preferred. Examples of such preferred promoters are those which recognize the T3, SP6 and T7 polymerases, the P L promoter of bacteriophage lambda, the recA promoter and the promoter of the mouse metallothionein I gene. A most preferred promoter for eukaryotic expression of trans-sialidase is an SV40 early promoter. This invention is also directed to an antibody specific for an epitope of trans-sialidase and the use of such antibody to detect the presence of, or measure the quantity or concentration of, trans-sialidase in a biological sample, including a cell or tissue, a cell or tissue extract, or a biological fluid, or as a pharmaceutic. For the following description, see, e.g., Harlow, supra, Sambrook, supra and Ausubel, supra, which references are entirely incorporated buy reference. The term "antibody" is meant to include polyclonal antibod¬ ies, monoclonal antibodies (mAbs), chimeric antibodies (chAbs) , and anti-idiotypic (anti-Id) antibodies. Polyclonal antibodies are heterogeneous populations of antibody molecules derived from the sera of animals immunized with an antigen. Thus, the production of a polyclonal antiserum specific for the trans-sialidase protein of the present invention can be achieved by conventional techniques well known to one of skill in the art. Standard reference works setting forth the general principles of immunology, which are hereby entirely incorporated by reference, include Roitt, I., Essential Immunology. 6th Ed., Blackwell Scientific Publications, Oxford (1988); Roitt, I. et al.. Immunology. C.V. Mosby Co., St. Louis, MO (1985) ; Klein, J. , Immunology: The Science of Self-Nonself Discrimination. John Wiley & Sons, New York, NY (1982)); Kennett, R., et al.. ; and Eisen, H.N., (In: Microbiology. 3rd Ed. (Davis, B.D., et al.. Harper & Row, Philadelphia (1980)); Paterson, P.Y., Textbook of Immunopathology (Miescher et al.. eds.), Grune and Stratton, New York, pp. 179-213 (1986). Monoclonal antibodies (mAbs) are a substantially homogeneous population of antibodies to specific antigens. MAbs specific for the trans-sialidase protein or glycoprotein of the present invention may be obtained by methods known to those skilled in the art. In a preferred embodiment polypeptides corresponding to the amino acid sequence set forth in Figure 18 are used as antigens for generating MAbs according to the present invention which can be used to purify or detect trans-sialidase polypeptides of the present invention. See, for example Kohler and Milstein, Nature 256:495-497 (1975); U.S. Patent No. 4,376,110; E. Harlow et al. , Antibodies: A Laboratory Manual. Cold Spring Harbor Laboratory Publications, Cold Spring Harbor, NY, 1988; Monoclonal Antibodies and Hybridomas: A New Dimension in Biological Analyses, Plenum Press, New York, NY (1980)); Campbell, A., "Monoclonal Antibody Technology," In: Laboratory Techniques in Biochemistry and Molecular Biology. Volume 13 (Burdon, R. , et al. , eds.), Elsevier, Amsterdam (1984), which references are hereby entirely incorporated by reference) . Such antibodies may be of any immunoglobulin class including IgG, IgM, IgE, IgA, and any subclass thereof. A hybridoma producing the mAbs of this invention may be cultivated in vitro or in vivo. Production of high titers of mAbs in vivo production makes this the presently preferred method of production. Briefly, cells from the individual hybridomas are injected intraperitoneally (i.p.) into pristane-primed BALB/c mice to produce ascites fluid containing high concentrations of the desired mAbs. MAbs may be purified from such ascites fluids, or from culture supernatants, using column chromatography methods well known to those of skill in the art. Chimeric antibodies are antibody molecules, different portions of which are derived from different animal species, such as those having variable region derived from a murine mAb and a human immunoglobulin constant region. Chimeric antibodies and methods for their production are known in the art ( Cabilly et al. , Proc. Natl. Acad. Sci. USA 81:3273-3277 (1984); Morrison et al. , Proc. Natl. Acad. Sci. USA 81:6851-6855 (1984); Boulianne et al. , Nature 312:643-646 (1984); Neuberger et al. , Nature 314:268-270 (1985) ; Taniguchi et al.. European Patent Application 171496 (2/19/85) ; Sahagan et al.. J. Immunol. 132:1066-1074 (1986); Liu et al.. Proc. Natl. Acad. Sci. USA .84:3439-3443 (1987); Sun et al.. Proc. Natl. Acad. Sci. USA 84:214-218 (1987); Better et al.. Science 240:1041- 1043 (1988)). These references are hereby entirely incorporated by reference. An anti-idiotypic (anti-Id) antibody is an antibody which recognizes unique determinants generally associated with the antigen-binding site of an antibody. An Id antibody can be prepared by immunizing an animal belonging to the same species and genetic type (e.g. mouse strain) as the source of the mAb with the mAb to which an anti-Id is being prepared. The immunized animal will recognize and respond to the idiotypic determinants of the immunizing antibody by producing an antibody to these idiotypic determinants (the anti-Id antibody) . The anti-Id antibody may also be used as an "immunogen" to induce an immune response in yet another animal, producing a so-called anti-anti-Id antibody. The anti-anti-Id may be epitop- ically similar or identical to the original mAb which induced the anti-Id. Thus, by using antibodies to the idiotypic determinants of a mAb, it is possible to identify other clones expressing antibodies of identical specificity. Accordingly, mAbs generated against the trans-sialidase of the present invention may be used to induce anti-Id antibodies in suitable animals, such as BALB/c mice. Spleen cells from such immunized mice are used to produce anti-Id hybridomas secreting anti-Id mAbs, using standard hybridoma technology mentioned above. Further, the anti-Id mAbs can be coupled to a carrier such as keyhole limpet hemocyanin (KLH) and used to immunize additional BALB/c mice. Sera from these mice will contain anti-anti-Id antibodies that have the binding properties of the original mAb specific for a trans-sialidase epitope. It will be appreciated that Fab and F(ab') 2 and other fragments, regions or portions thereof, of the antibodies useful in the present invention, may be used for the detection and quantitation of the trans-sialidase enzyme according to the methods disclosed herein for intact antibody molecules. Such fragments are typically produced by proteolytic cleavage, using enzymes such as papain (to produce Fab fragments) or pepsin (to produce F(ab') 2 fragments). The antibodies, or fragments of antibodies, useful in the present invention may be used to quantitatively or qualitatively detect the presence of cells or organisms which express the trans-sialidase protein. This can be accomplished by immunofluorescence techniques employing a fluorescently labeled antibody (see below) coupled with light microscopic, flow cytometric, or fluorometric detection. The antibodies (or fragments thereof) useful in the present invention may be employed histologically, as in immunofluores- cence or immunoelectron microscopy, for in situ detection of the trans-sialidase enzyme. In situ detection may be accomplished by removing a histological specimen from a subject and providing a labeled antibody of the present invention to such a specimen. The antibody (or fragment) is preferably provided by applying or by overlaying the labeled antibody (or fragment) to a biological sample. Through the use of such a procedure, it is possible to determine not only the presence of the trans-sialidase enzyme but also its distribution. Using the teachings of the present invention, those of ordinary skill will readily perceive that any of a wide variety of histological methods (such as staining procedures) can be modified in order to achieve such in situ detection. Such assays for trans-sialidase typically comprise incubating a biological sample, such as a biological fluid, a tissue extract, a tissue section, freshly harvested cells or cells which have been incubated in tissue culture, in the presence of a detectably labeled antibody capable of identifying the trans-sialidase, and detecting the antibody by any of a number of techniques well-known in the art. The biological sample may be treated with a solid phase support or carrier (which terms are used interchangeably herein) such as nitrocellulose, or other solid support which is capable of immobilizing cells, cell particles or soluble proteins. The support may then be washed with suitable buffers followed by treatment with the detectably labeled trans-sialidase-specific antibody. The solid phase support may then be washed with the buffer a second time to remove unbound antibody. The amount of bound label on said solid support may then be detected by conven¬ tional means. By "solid phase support or carrier" is intended any support capable of binding antigen or antibodies. Well-known supports, or carriers, include glass, polystyrene, polypropylene, poly¬ ethylene, dextran, nylon, amylases, natural and modified celluloses, polyacrylamides, gabbros, and magnetite. The nature of the carrier can be either soluble to some extent or insoluble for the purposes of the present invention. The support material may have virtually any possible structural configuration so long as the coupled molecule is capable of binding to an antigen or antibody. Thus, the support configuration may be spherical, as in a bead, or cylindrical, as in the inside surface of a test tube, or the external surface of a rod. Alternatively, the surface may be flat such as a sheet, test strip, etc. Preferred supports include polystyrene beads. Those skilled in the art will know many other suitable carriers for binding antibody or antigen, or will be able to ascertain the same by use of routine experimentation. The binding activity of a given lot of anti-trans-sialidase antibody may be determined according to well known methods. Those skilled in the art will be able to determine without undue experimentation. One of the ways in which the trans-sialidase-specific anti¬ body can be detectably labeled is by linking the same to an enzyme and use in an enzyme immunoassay (EIA) such as the enzyme-linked immunosorbent assay (ELISA) (see, for example, Voller, A., "The Enzyme Linked Immunosorbent Assay (ELISA)", Diagnostic Horizons 2:1-7, 1978)) (Microbiological Associates Quarterly Publication, Walkersville, MD) ; Maggio, E. (ed.), Enzyme Immunoassay. CRC Press, Boca Raton, FL, 1980) . In an EIA, the conjugated enzyme, when later exposed to an appropriate substrate, will react with the substrate in such a manner as to produce a chemical moiety which can be detected, for example, by spectrophotometric, fluorometric or direct visual means. Enzymes which can be used to detectably label the antibody include, but are not limited to, malate dehydrogenase, staphylococcal nuclease, delta-5-steroid isomerase, yeast alcohol dehydrogenase, alpha-glycerophosphatedehydrogenase, triosephosphateisomerase, horseradish peroxidase, alkaline phosphatase, asparaginase, glucose oxidase, beta-galactosidase, ribonuclease, urease, catalase, glucose-6- phosphate dehydrogenase, glucoamylase and acetylcholinesterase. The detection can be accomplished by calorimetric methods which employ a chromogenic substrate for the enzyme. Detection may also be accomplished by visual comparison of the extent of enzymatic reaction of a substrate in comparison with similarly prepared standards. Detection may be accomplished using any of a variety of other immunoassays. For example, by radioactively labeling the antibodies or antibody fragments, it is possible to detect trans-sialidase through the use of a radioimmunoassay (RIA) (see, for example, Weintraub, B., Principles of Radioimmunoassays. Seventh Training Course on Radioligand Assay Techniques, The Endocrine Society, March, 1986) . The radioactive isotope can be detected by such means as the use of a gamma counter or a scintillation counter or by autoradiography. It is also possible to label the antibody with a fluorescent compound. When the fluorescently labeled antibody is exposed to light of the proper wave length, its presence can then be detected due to the fluorescence emitted by the sample. Among the most commonly used fluorescent labelling compounds are fluorescein isothiocyanate, rhodamine, phycoerythrin, phycocy- anin, allophycocyanin, o-phthaldehyde and fluorescamine. The antibody can also be detectably labeled using fluo¬ rescence emitting metals such as 152 Eu, or others of the lan- thanide series. These metals can be attached to the antibody using such metal chelating groups as diethylenetriaminepenta- acetic acid (DTPA) or ethylenediaminetetraacetic acid (EDTA) . The antibody also can be detectably labeled by coupling it to a chemiluminescent compound. The presence of the chemilumi- nescent-tagged antibody is then determined by detecting the presence of luminescence that arises during the course of a chemical reaction. Examples of particularly useful chemi- luminescent labeling compounds are luminol, isoluminol, thero- matic acridinium ester, imidazole, acridinium salt and oxalate ester. Likewise, a bioluminescent compound may be used to label the antibody of the present invention. Bioluminescence is a type of chemiluminescence found in biological systems in which a catalytic protein increases the efficiency of the chemilumine¬ scent reaction. The presence of a bioluminescent protein is determined by detecting the presence of luminescence. Important bioluminescent compounds for purposes of labeling are luciferin, luciferase and aequorin. According to another aspect of the present invention, a method for treating a subject infected with a Trypa_nosoma is provided, comprising administering to the subject, as an animal TITUTESHEET (mammal or bird) or human an effective amount of an agent capable of inhibiting the activity of a trans-sialidase enzyme, since the survival of the trypomastigote in the human subject is expected to depend on the non-inhibited transialidase activity produced by the trypomastigote. In a preferred embodiment, the agent is an antibody specific for the trans-sialidase polypeptide or binding fragment or region of the antibody. In another preferred embodiment, the method for treating the animal includes the vaccination of the animal with therapeutic amount of therapeutic composition, comprising a trans-sialidase polypeptide derived from a trypomastigote trans-sialidase, binding fragment or region of a anti-idiotype antibody thereto, in an amount effective to induce an antibody specific for the trans-sialidase enzyme. The production of such antibodies in an animal in response to the vaccination, is expected to result in reduced or inhibited trypomastigote infection and/or trypanosomyiasis, and/or the killing or inhibition of the vector trypomastigotes due to the uptake of the anti-trans-sialidase antibodies into the vector which transmits the trypomastigote into the animal. As a non-limiting example, the tsetse fly (Genus, Glossina) is the vector of the trypomastigote T. brucei which causes the diseases (i) nagana in livestock and horses and (ii) sleeping sickness (Gambian and Rhodesian trypanosomiasis) in humans, and animals vaccinated with an T. brucei trans-sialidase polypeptide of the present invention would be expected to have reduced or inhibited infection by a T. brucei containing vector, as well as cause the reduced or substantially inhibited vector infection or transmission of T. brucei trypomasigotes. As another non-limiting example, the trypomastigote T. cruzi causes Chagas' disease (South American trypanosomiasis) in humans seen in Central and South America and is transmitted by the vector Triatoma or Reduviidae ("assassin" or "kissing" reduviid bugs, when bite wounds are infected with the feces of the insect which harbors the T. cruzi trypomastigote. See Berkow et al., eds.. The Merck Manual of Diagnosis and Therapy, Sixteenth Ed., pp. 234-235 (1992). Accordingly, the use of vaccination of animals using an anti-trans-sialidase vaccine of the present invention is expected to provide an effective means for treating and/or preventing the infection, or spread of infection, in animals of trypomastigote related diseases, such as Nagana. Such antibodies, as described herein are, provided as pharmaceutical compositions. Pharmaceutical compositions are also provided according to the present invention. For therapeutic or diagnostic applications, compositions including anti-trans-sialidase antibodies, fragments or regions thereof, according to the present invention, may be administered parenterally in combination with conventional injectable liquid carriers such as sterile pyrogen-free water, sterile peroxide-free ethyl oleate, dehydrated alcohol, or propylene glycol. Conventional pharmaceutical adjuvants for injection solution such as stabilizing agent, solubilizing agents and buffers, such as ethanol, complex forming agents such as ethylene diamine tetraacetic acid, tartrate and citrate buffers, and high- molecular weight polymers such as polyethylene oxide for viscosity regulation may be added. Such compositions may be injected intramuscularly, intraperitoneally, or intravenously. Further non-limiting examples of carriers and diluents include albumin and/or other plasma protein components such as low density lipoprotems, high density lipoproteins and the lipids with which these serum proteins are associated. These lipids include phosphatidyl choline, phosphatidyl serine, phosphatidyl ethanolamine and neutral lipids such as triglycerides. Lipid carriers also include, without limitation, tocopherol and retinoic acid. Additional lipid and lipoprotein drug delivery systems that may be included herein are described more fully in "Biological Approaches to Controlled Delivery of Drugs," Annals of the New York Academy of Sciences, 507. 775-88, 98-103 f and 252-271, which disclosure is hereby incorporated by reference. The compositions may also be formulated into orally administrable compositions containing one ormorephysiologically compatible carriers or excipients, and may be solid or liquid in form. These compositions may, if desired, contain conventional ingredients such as binding agents, for example, syrups, acacia, gelatin, sorbitol, tragacanth, or polyvinylpyrrolidone; fillers, such as lactose, mannitol, starch, calcium phosphate, sorbitol, cyclodextran, or methylcellulose; lubricants such as magnesium stearate, high molecular weight polymers such as polyethylene glycols, high molecular weight fatty acids such as stearic acid or silica; disintegrants such as starch; acceptable wetting agents as, for example, sodium lauryl sulfate. The oral compositions may assume any convenient form, such as tablets, capsules, lozenges, aqueous or oily suspensions, emulsions, or dry products suitable for reconstitution with water or other liquid medium prior to use. The liquid oral forms may, of course, contain flavors, sweeteners, preservatives such as methyl or propyl p-hydroxybenzoates; suspending agents such as sorbitol, glucose or other sugar syrup, methyl, hydroxymethyl, or carboxymethyl celluloses or gelatin; emulsifying agents such as lecithin or sorbitan monooleate or thickening agents. Non- aqueous compositions may also be formulated which comprise edible oils as, for example, fish-liver or vegetable oils. These liquid compositions may conveniently be encapsulated in, for example, gelatin capsules in a unit dosage amount. The pharmaceutical compositions of the present invention can also be administered by incorporating the active ingredient into colloidal carriers, such as liposomes. Liposome technology is well known in the art, having been described by Allison et al. in Nature 252: 252-254 (1974) and Dancy et al., J. Immunol. 120: 1109- 1113 (1978) . Alternatively, active-targeting vesicles can be used as carriers for the active components of the present invention by placing a recognition sequence, i.e., from an antibody, onto the vesicles such that it is taken up more rapidly by certain cell types, such as cancer cells (cf. Papahadjopoulou et al.; Annals of the New York Academy of Sciences. 507: 67-74 (1987)). As further embodiments of the present invention, the active components can be administered in the form of sustained release products, by incorporating the active components in a suitable polymer. It will be understood by the skilled practitioner that the compositions of the present invention may be administered in conjunction with, as well as formulated with, at least one other therapeutic agent to produce a combination composition and/or therapy effective for ameliorating pathologies associated with such infections. "In conjunction" is defined herein to mean the present compositions may be administered first and other G- protein receptor binding agents later, or vice versa. Therapeutic agents include, by way of non-limiting examples, neuroleptic agents as presented above. A particular aspect of the present invention comprises an antibody or portion thereof of the present invention in an effective unit dose form. By "effective unit dose" is meant a predetermined amount sufficient to bring about the desired T. cruzi and T. brucei inhibitory effect, which can be readily determined by one skilled in the art. The dosage of the compounds of the present invention or their pharmaceutically acceptable salts or derivatives will depend, of course, on the degree of T. cruzi inhibition desired. Dosages of pharmaceutically active compounds such as those disclosed in the present invention are conventionally given in amounts sufficient to bring about the desired inhibition relative to the condition being treated without causing undue burden upon the host. Having now generally described the invention, the same will be more readily understood through reference to the following examples, which are provided by way of illustration only, and are not intended to be limiting of the present invention. EXAMPLE I Parasite Growth and Preparation T. cruzi trypomastigotes, Y strain (Silva, L.H.P. et al. Folia Clin. Biol. 20:191-203 (1953)), were grown in cultures of LLC-MK 2 cells (American Type Culture Collection CCL-7) . Usually 75 cm 2 flasks, with subconfluent cultures of LLC-MK 2 cells, were infected with 5 x 10 6 trypomastigotes. The LLC-MK 2 cells were grown in low glucose Dulbecco's modified Eagle's medium (DMEM) with penicillin and streptomycin (GIBCO) , containing 10% fetal bovine serum (FBS) at 37°C in 5% C0 2 . Free parasites were removed 24 hr later, and the cultures were maintained in 10% FBS-DMEM. When indicated, the FBS-DMEM was removed during the third day following infection, the monolayers were washed twice with Hanks' solution, and the medium was replaced with DMEM containing 0.2% bovine serum albumin (Ultrapure, Boehringer Mannheim) and 20 mM HEPES (pH 7.4) (0.2% BSA-DMEM). There was no difference in numbers or morphology of parasites obtained from cultures in 0.2% BSA-DMEM (BSA trypomastigotes) or in FBS-DMEM. After the fifth day following infection, the culture supernatants contained trypomastigotes, intermediate forms, and amastigotes. To separate the trypomastigotes, the heterogeneous parasite suspensions were centrifuged at 2000 x g for 5 min and then incubated at 37°C. After 2 hr, the motile, slender, highly infective trypomastigotes were collected from supernatant. The contamination of this fraction with amastigotes and intermediate forms was less than 1%. Amastigotes were prepared by incubating trypomastigotes for 24-48 hr at 37°C in liver infusion tryptose (Ley, V. et al. J. Exp. Med. 168:649- 659 (1988)) containing 10% FBS. The metacyclic stage of T. cruzi was obtained from aged cultures of epimastigotes in the same medium at 28°C. The epimastigotes were removed by passage through a DE-52 (Whatman, UK) column (Teixeira, M.M.G. et al. Mol. Biochem. Parasitol. 18:271-282) . EXAMPLE II Presence of Sialic Acid in the Ssp-3 Epitope A. Antibodies and Reagents Monoclonal antibody (mAb) 3C9 (IgGl isotype) (Andrews, N.W. et al. Exp. Parasitol. £4:474-484 (1987)) was purified from ascitic fluids by DEAE-cellulose chromatography. MAbs 46 and 14 (IgG2a isotype) and mAbs 87, 50, and 27 (IgGl isotype) were generated as described by Schenkman, S. et al.. Exp. Parasitol. 22:76-86 (1991) and were purified from ascitic fluids by protein-A-Sepharose affinity chromatography. V. cholerae sialidase was obtained from GIBCO, protease-free V. cholerae sialidase was from Boehringer Mannheim, and protease-free C. perfringens sialidase was from Sigma. B. Immunofluorescence and Flow Cytometric Analysis Parasites (2.5 x 10 7 ) were resuspended in 250 μl of 0.2% BSA-DMEM at 4°C. An equal volume of antibody, diluted in 0.2% BSA-DMEM containing 0.05% NaN 3 , was added and the incubation proceeded for 30 min on ice. The suspension was then centrifuged for 2 min at 6000 rpm in a Beckman minifuge using a horizontal rotor. The supernatant was removed and the remaining pellet carefully resuspended in 100 μl of 0.2% BSA-DMEM, followed by addition of 900 μl of 4% paraformaldehyde in PBS. After at least 30 min at 4°C, the fixative was removed, and the parasites were resuspended and washed twice with 1 ml of cold 0.2% BSA-DMEM. The parasites were then incubated for 30 min with anti-mouse IgG conjugated with FITC. The suspensions were centrifuged, washed with 0.2% BSA-DMEM, resuspended in 50 μl of PBS, and postfixed with 450 μl of 4% paraformaldehyde. The mixtures were analyzed on a Becton Dickinson FACScan. To study the antigenic properties of intracellular parasites, BALB/3T3 fibroblasts, clone A31 (American Type Culture Collection CCL-163) were plated in 12 mm glass coverslips placed in 24-well plates and were infected. As a control, the parasites were directly attached to glass coverslips using 0.1% poly-L-lysine in PBS. Trypomastigotes were placed in contact with the coverslips for 30 min at 37°C. At the end of the incubation period, unbound parasites were removed by aspiration and the coverslips fixed for 1 hr with 4% paraformaldehyde in PBS. The preparations were washed with PBS, treated 1 min with 0.1% Triton X-100, washed again with PBS, and incubated for 30 min with 0.2% BSA-DMEM at room temperature. Preparations were incubated with 50 μg/ml MAb 3C9 and treated with an anti-mouse IgG antibody labeled with FITC. The stained parasites were examined under a fluorescence microscope. C. Results When live trypomastigotes were treated with Vibrio cholerae neuraminidase, or with protease-free Clostridiu perfringens neuraminidase, the immunofluorescence staining of the parasites with mAb 3C9 and 46 was abolished (Figure 1) . These antibodies recognize the Ssp-3-related epitopes that have been associated with trypomastigote attachment to host cells (Schenkman, S, et al. Exp. Parasitol. 22:76-86 (1991a)). The same treatment did not affect binding of the control mAb 14 to a different surface antigen of the trypomastigotes. To determine the origin of the sialic acid residues recognized by the mAbs, experiments were performed to test the reactivity of trypomastigotes from cells maintained in 0.2% BSA- DMEM ("BSA trypomastigotes") , as compared to cells maintained in medium with FBS, which contains sialyllated glycoproteins. As shown in Figure 2, mAbs 3C9 and 46 did not react with the BSA trypomastigotes. However, when these parasites were incubated for 3 hr at 37°C with 1 mM sialyllactose or 0.5 mg/ml fetuin (but not with l mM free N-acetylneuraminic acid) , more than 80% of parasite staining by mAb 3C9 was recovered. EXAMPLE III Sialic Acid Transfer In Vivo BSA trypomastigotes were washed in 0.2% BSA-DMEM, resuspended to 5 x 10 7 parasites per ml, and incubated at the indicated temperature with various concentrations of α(2-3)- sialyllactose, a(2-6) -sialyllactose, α(2-6) -sialyllactosamine (OxfordGlycosysterns) , CMP-sialic acid, sialyllactose (Boehringer Mannheim) , fetuin, asialofetuin, or synthetic sialic acid (Sigma) . Inhibitors were added to the parasites before addition of the sialic acid donor. Radiolabeled sialic acid was transferred to the parasites by incubating 4 x 10 8 trypomastigotes in 800 μl of 0.2% BSA-DMEM for 3 hr at 37°C with 0.5 μCi of [sialic-9- 3 H]o!(2-3) -sialyllactose. At the end of incubation the parasites were centrifuged and washed twice with Hanks' solution, lysed with 3% NP-40, 50 mM Tris-HCl (pH 7.4), 1 mM PMSF, 0.1 mM EDTA, and 5 μg/ml antipain, pepstatin, and leupeptin, and centrifuged 10 min at 10,000 x g. Figure 3 shows the kinetics of sialic acid transfer to live trypomastigotes at 4°C and 37°C. At either temperature, maximum reactivity with 3C9 was observed after 15 sec of incubation. In parallel with the appearance of the 3C9 epitope, reactivity of the BSA trypomastigotes with peanut agglutinin lectin (which recognizes terminal β-galactosyl residues) diminished (Figure 3B) . To document the transfer of sialic acid further, experiments tested the reactivity of MAb 3C9 with antigens transferred to nitrocellulose fromvarious preparations of trypomastigotes. For Western blots, the trypomastigote suspensions were pelleted for 2 min at 6000 rpm in a microfuge equipped with a horizontal rotor. The trypomastigotes were washed with Hank's solution, resuspended in SDS sample buffer, and boiled for 3 min. Samples containing the equivalent of 2 x 10 7 trypomastigotes were loaded onto 7.5% SDS-PAGE gels. After electrophoresis, the gels were blotted onto nitrocellulose paper. The paper was blocked with 1% BSA in PBS and incubated with 20 μg/ml MAb 3C9 in 1Q mM Tris-HCl, 0.15 M NaCl, and 0.05% Tween 20. Bound antibodies were detected with anti-mouse IgG conjugated to alkaline phosphatase (Sigma) , followed by incubation with 0.3 mg/ml nitroblue tetrazolium and 0.15 mg/ml 5-bromo-4-chloro-3-indolyl phosphate, in 0.1 M Tris-HCl (pH 9.5), 0.1 M NaCl, and 0.005 M MgCl 2 . In some cases, the nitrocellulose strips were pretreated with the neuraminidases in 0.05 M sodium acetate (pH 5.5) before incubation with mAb 3C9. As shown in Figure 4, the Ssp-3 epitope was present in parasites grown in serum (lane a) , but not in BSA trypomastigotes incubated with sialic acid (lane b) . As shown in lane a, Ssp-3 was expressed in molecules that migrated as a smear between 60 and 200 kd, with a few defined bands, the strongest at about 160 kd. When the BSA parasites were incubated with sialyllactose for 15 min at 0°C (lane c) , or for 1 and 5 min at 37°C (lanes d and e) , the reactivity with mAb 3C9 was regained. When the nitrocellulose strips with antigens from parasites grown in serum were treated with protease-free C. perfringens or V. cholerae neuraminidase, reactivity with 3C9 was lost (lane f) . EXAMPLE IV Total Amount of Sialic Acid in the Parasites The total amount of sialic acid in the parasites was measured by the thiobarbituric acid-HPLC assay. Trypomastigotes were washed three times in Hanks ' • solution and stored frozen at -70°C until analysis. Total cellular sialic acid was determined after hydrolysis of the cell pellets with 0.1 M HC1, using the thiobarbituric acid method and HPLC analysis (Powell, L.D. et al. Anal. Biochem. 157:179-185 (1986)). Samples of BSA trypomastigotes, before and after incubation with sialyllactose, contained 3.2 and 19.4 pmol of sialic acid per 10 6 parasites, respectively. Trypomastigotes grown in the presence of serum also contained relatively high amounts of sialic acid (12.2 pmol/10 6 parasites). To demonstrate directly that the sialic acid detected in the Ssp-3 epitope originated from sialyllactose, BSA trypomastigotes were incubated at 37°C for 3 hr with sialyllactose, lysed with detergent, and one sample of the lysate was analyzed directly by SDS-PAGE (Figure 4, lane h) . The remaining lysate was immunoprecipitated with the 3C9 MAb before SDS-PAGE (lane i) . For immunoprecipitation, extracts were incubated with mAb coupled to CNBr-Sepharose 4B for 3 hr at 4°C. The beads were washed and processed as described in Andrews et al. (supra) , and the precipitated material was loaded onto 7.5% SDS-PAGE gels. Autoradiographs of both samples show diffuse bands, similar to the appearance of the Ssp-3-bearing molecules on Western blots (see above) . The mAb 3C9 only immunoprecipitated about 10% of the sialylated, radiolabeled molecules. The remaining 90% was expected to contain sialic acid-containing epitopes distinct from that recognized by mAb 3C9. Alternatively or additionally, the sialic acid is expected to have been enzymatically released from the Ssp-3 epitope during the experimental manipulations. EXAMPLE V Biochemical Specificity in the Transfer of Sialic Acid to Live Trypomastigotes Table 1 shows some of the requirements for the transfer of sialic acid to live crypomastigoces. The parasites acquired sialic from 0.(2-3) -sialyl-lactose at concentrations as low as 10 μM. In contrast, α(2-6) -sialyllactose, CMP-sialic acid, and colominic acid (α(2-8) -polysialic acid) were not sialyl donors, even at concentrations as high as l mM. Fetuin also donated sialic acid. The transfer was not prevented by azide. The presence of 10 mM EDTA in the incubation medium was also without effect. Fixation of trypomastigotes with paraformaldehyde only partially blocked the reaction. In contrast, lactose inhibited the sialic acid transfer at concentrations much lower than those of galactose or melibiose. Other monosaccharides, such as N- acetylglucosamine, glucose, and N-acetylgalactosamine, were poor inhibitors. TABLE 1 Specificity and Characteristics of T. cruzi Trans-Sialidase Reaction in Live Parasites mAb 3C9 Stain Experimental Conditions Relative Fluorescence b Control UO Sialic acid 1 mM 12 α(2-3) -sialyllactose 1 mM 333 a.(2-3) -sialyllactose 0.1 mM Ϊ7.1 a(2-3) -sialyllactose 0.001 mM 12 a(2-3) -sialyllactose 0.0001 mM 1.8 CMP-sialic acid 1 mM 3.4 Colominic acid 0.3 mg/ml 3.0 Fetuin 1 mg/ml 23.0 Asialofetuin 1 mg/ml 2.0 0.(2-3) -sialyllactose 1 mM + 0.05% NaN 3 31.0 a(2-3) -sialyllactose 1 mM + 10 EDTA 2L8 α(2-3) -sialyllactose 1 mM/fixed T. cruzi" 5.1 Sialic acid 1 mM/fixed T. cruzi* 08 a. (2-3) -sialyllactose 20 μM + 10 mM lactose _L2 α(2-3) -sialyllactose 20 μM + 1 mM lactose 2.7 α(2-3) -sialyllactose 20 μM + 0.1 mM galactose 14.0 (2-3) -sialyllactose 20 μM + 10 mM galactose 5.7 0!(2-3) -sialyllactose 20 μM + 1 mM galactose 21.9 or(2-3) -sialyllactose 20 μM + 10 mM melibiose 22.3 Purified slender T. cruzi trypomastigotes (5 x 10 7 /ml) , obtained from culture supernatant of LLC-MK 2 cells grown in 0.2% BSA-DMEM, were incubated for 30 min at 37°C in 0.2% BSA-DMEM with the indicated reagents. At the end of the incubation the parasites were washed, and the immunofluorescence staining by MAb 3C9 was assayed by FACs. Values shown are the increase in the mean fluorescence relative to the staining of parasites incubated in 0.2% BSA-DMEM alone (control) . Trypomastigotes were washed in Hanks' solution and incubated with 4% paraformaldehyde in PBS at 4°C for 30 min. The trypomastigotes were washed with 0.2% BSA-DMEM before incubation with α(2-3) -sialyllactose or sialic acid. EXAMPLE VI Purification and Characterization of the T. cruzi Trans-Sialidase A. Trans-Sialidase Activity Trans-sialidase activitywas determined by incubating trypomastigote lysates (or preparations of purified enzyme, as described below) in 50 mM PIPES buffer (pH 7.0) (Sigma) in the presence of a sialic acid donor and [N-acetyl-D-l- 3 H- glucosamine.N-acetyllactosamine (10 Ci/mmol) (Passaniti, A. et al. J. Biol. Chem. 263:7591-7603 (1988)) or [D-glucose-1- 1 C] -lactose (60 mCi/mmol) (Amersham) . Radiolabeled α(2-3) -sialyllactose was prepared by incubating 25 μCi of [sialic-9- 3 H]CMP-sialic acid (20 Ci/mmol; New England Nuclear) with 0.15 M lactose in the presence of mammalian α2-3Galβl-3GalNAc sialyltransferase. The standard assay contained 1 mM sialyllactose and 25,000 to 40,000 cpm of the radioactive substrate in a final volume of 50 μl. This mixture was incubated 30 min at 37°C, and the reaction was terminated by addition of 1 ml of water followed by passage through a 1 ml QAE-Sephadex A50 column, also equilibrated in water. The radioactive oligosaccharides were eluted with 1 ml of 1 M ammonium formate. Activity is expressed as eluted cpm. For characterization of pH effect, the following Sigma buffers at 50 mM were used: pH 5.5 and 6.0, MES; pH 6.7 and 7.0, PIPES; pH 7.5, HEPES; and pH 8.5, Tris-HCl. B. Purification of Trans-Sialidase To purify the trans-sialidase, 5 x 10 9 trypomastigotes were lysed at 4°C in 5 ml of 3% n-octyl glucopyranoside (Sigma), 50 mM Tris-HCl (pH 7.4), 0.1 mM EDTA, 0.1 mM PMSF, and 5 μg/ml leupeptin, pepstatin, and antipain. The insoluble material was removed by centrifugation (10 min at 10,000 x g) , and the supernatant was adjusted to 0.5M NaCl, 1 mM of CaCl 2 , and MnCl 2 . The supernatant was incubated with 2 ml of concanavalin A- Sepharose equilibrated with 0.3% n-octyl glucopyranoside, 0.5 M NaCl, and 50 M Tris-HCl (pH 7.4) . After washing with 25 mil of the equilibration buffer, the enzyme was eluted with 0.5 M a- methylmannoside in the same buffer. The eluate was dialyzed with 10 mM Tris -HC1 (pH 8.0) and applied into Mono Q FPLC column HR 5/5 (Pharmacia-LKB) preequilibrated in the same buffer. After the absorbance had decreased below 0.002, the enzyme was eluted with a gradient of NaCl. C. Results To isolate a Trypanosoma trans-sialidase, the present inventors developed a quantitative assay based on the incorporation of sialic acid into radiolabeled N-acetyllactosamine or lactose, and retention of the product by an anion exchange column. Using this assay, the enzyme was purified from n-octyl glucoside lysates of trypomastigotes by affinity chromatography on concanavalin A-Sepharose, followed by FPLC separation on Mono Q (Figure 5) . Enzymatic activity was recovered in a single peak. The purification achieved was about 100-fold and the recovery was 10% of the initial activity in the crude extracts. The enzyme itself did not express the Ssp-3 epitope, since mAb 3C9 linked to Sepharose beads was unable to deplete trans-sialidase from total trypomastigote extracts. The specificity of the enzyme in the total extracts, or in the partially purified preparation, was identical to that observed in living parasites. Both in vitro and in vivo, the enzyme utilized as sialic acid donor α- (2-3) -sialyllactose, but does not utilize as a sialylic acid donor 0.(2-6) -sialyllactose, CMP-sialic acid, or free sialic acid at 1 mM. The purified enzyme was active at neutral or alkaline pH, but the activity was substantially reduced below pH 6.0 (Table 2, below) . Almost 100% of the trans-sialidase activity was present on the surface membrane of the trypomastigotes. If live parasites were first treated with trypsin, the lysate was enzymatically inactive. The stage specificity of the enzyme was also analyzed (Table 2) . Metacylcic trypomastigotes, the infective insect stage of the parasite, contained substantial levels of the trans-sialidase. Enzymatic activity was much SUBSTIT reduced in extracts of amastigotes, which correspond to the intracellular, dividing form of the parasite. Amastigotes grown in vitro (Andrews et al.. supra) include a small number of intermediate forms between trypomastigote and amastigote, which could account for the low levels of trans-sialidase activity. TABLE 2 Specificity of T. cruzi Trans-Sialidase In Vitro Sialyllactosamine Produced (counts per minute) Total Eurifieri Source Substrate Amount a e Enz me 0.(2-3) -sialyllactose α.(2-3) -sialyllactose α(2-3) -sialyllactose α.(2-6) -sialyllactose 0.(2-3) -sialyllactosamine Q;(2-6) -sialyllactosamine CMP-sialic acid Sialic acid B α.(2-3) -sialyllactose 1 mM 640 nt α{2-3) -sialyllactose 1 mM 8340 nt α(2-3) -sialyllactose 1 mM 3750 nt E 0.(2-3) -sialyllactose 1 mM 1330 nt A α(2-3) -sialyllactose 1 mM pH 5.5 pH 6.5 pH 6.7 pH 7.0 pH 7.5 pH 8.5 SOURCE: A - trypomastigotes; B - trypsin- treated trypomastigotes; live trypomastigotes were washed twice with Hanks' solution, resuspended to 5 x 10 7 /ml, and incubated for 30 min with 0.1 mg/ml trypsin. At the end of the incubation, 0.2 mg/ml soybean trypsin inhibitor was added, and the parasites were washed and extracted as described above. C - control trypsin-treated trypomastigotes; as above except without trypsin D - metacyclic trypomastigotes; E - amastigotes. nt = not tested After extraction or purification 5 μl of the lysate or of the purified enzyme from trypomastigotes (fraction 64 of the Mono Q column) , was incubated as described above. The novel trypomastigote-derived trans-sialidase of the present invention has the following characteristics, and additional characteristics presented in the following examples. Following purification from concanavalinA-Sepharose, it migrates as a sharp peak in Mono Q, indicating that it is single molecule. The purified enzyme retains the properties displayed in vivo by the parasite-associated enzyme. Its substrates must contain an α(2-3) -linked terminal sialic acid end unit, thus distinguishing it from other known enzymes that transfer sialic acid moieties (Paulson, J.C. etal. J. Biol. Chem. 264:17615-17618 (1989)), all of which require CMP-sialic acids. Futhermore, its activity can be inhibited by β-galactosides. In addition, the enzyme is active at low temperatures, is independent of divalent cations, and has a pH optimum in the physiologic range. EXAMPLE VII T. cruzi Trans-sialidase Reaction Products To identify the reaction product(s) of a Trypanosoma trans-sialidase, parasite extracts were incubated with nonradioactive α(2-3) -sialyllactose and [ ,4 C]lactose, labeled in the glucose portion ( [D-glucose-l- 1 C] -lactose, 60 mCi/mmol, Amersham) . The mixture was subjected to anion exchange chromatography to retain charged oligosaccharides, which were eluted with 1 M ammonium formate and analyzed by thin-layer silica gel chromatography, followed by autoradiography. Radioactive α.(2- 3) -sialyllactose was the only product detected (Figure 6) . If [ 3 H]N-acetyl-lactosamine was used as the sialyl in place of lactose, only α(2-3) -sialyllactosamine was detected on the thin-layer chromatography plate. EXAMPLE VIII A Trypanosoma Trans-Sialidase Transfers Sialic Acid from Mammalian Cell Surface Glycoproteins The trypomastigote trans-sialidase was also able to utilize cell surface glycoproteins as sialic acid donors. For example, flow cytometric analysis of BSA trypomastigotes following incubation with a suspension of human erythrocytes indicated a significant increase in mAb 3C9 reactivity. Perhaps of greater biological significance, the BSA trypomastigotes acquired sialic acid during invasion of target cells. In the experiment illustrated in Figure 7, BSA trypomastigotes or trypomastigotes grown in serum-containing medium were incubated for 30 min at 37°C with murine 3T3 fibroblasts. After removal of the extracellular parasites, the infected cells were reacted with mAb 3C9 and examined by immunofluorescence. Figure 7 shows that both types of intracellular parasites reacted with the antibody. As a control, both types of parasite were incubated on slides coated with poly-L-lysine, but lacking any additional cells. BSA trypomastigotes attached to glass were not recognized by 3C9. Reactivity of the various Ssp-3-specific mAbs with the Ssp-3 epitope is strong in parasites grown in serum but very weak in trypomastigotes developing inside the host cells, or on the BSA trypomastigotes. Within seconds of contact with medium containing either serum, fetuin, or sialyllactose, the BSA trypomastigotes acquire macromolecular-bound sialic acid and express the Ssp-3 epitope. The exact structure of Ssp-3 epitope is unknown. Several lines of evidence indicate that it contains a sialylα(2→3)galactose structure. First, recognition of Ssp-3 is strictly sialic acid-dependent, as shown by its sensitivity to sialidase both in vivo and following transfer of Ssp-3-bearing molecules to nitrocellulose. Second, trans-sialidase enzyme of the present invention, either bound to or derived from a Trypanosoma, transfers sialic acid to galactose-bearing oligosaccharides in vitro, forming α(2→3) -linked but not α(2→6) -linked sialic acid. Third, the sialic acid transfer is inhibited by galactose and lactose. Fourth, peanut agglutinin reacts strongly with BSA trypomastigotes, but the reactivity diminishes progressively following incubation of the parasites with sialyllactose and incorporation of sialic acid into Ssp-3. In vitro, the reaction product of the trans-sialidase enzyme of the present invention, sialyllactose, can be identical to the substrate (see Figure 6) . This finding points to the possible relationship between the trans-sialidase of this invention and the T. cruzi sialidases described elsewhere (Pereira, supra; Harth, G. et al. Proc. Natl. Acad. Sci. USA 84:8320-8324 (1987)). It is possible that the invasive blood stages of T. cruzi bear two separate sialic acid-targeted enzymes, a sialidase and a trans-sialidase. Alternatively, a single regulated enzyme, might be able to either remove or transfer sialic acid to modulate specific parasite functions. It is important to note that the trans-sialidase of the present invention is found on the parasite surface membrane (or in the flagellar pocket) , evidenced by its sensitivity to trypsin in live parasites. The speed of sialic acid transfer at 4°C, and in the presence of metabolic inhibitors, raised the possibility that the Ssp-3-bearing molecules were sialylating themselves. This possibility was ruled out by the observation that the purified trans-sialidase protein does not express the Ssp-3 epitope. The enzyme may be closely associated with its substrate on the trypomastigote surface membrane, may be secreted and act from the outside. By altering the sialic acid content of the host glycoproteins or glycolipids, the trans-sialidase may contribute to the pathology of Chagas' disease. Several findings suggest that the Ssp-3 epitope, by virtue of its sialic acid residue, participates in target cell recognition. Fab fragments of Ssp-3-specific antibodies inhibit attachment of the parasite to mammalian cells (Schenkman et al.. 1991a, supra) . Infectivity of trypomastigotes increases substantially following incubation with sialic acid-containing macromolecules (Piras, M.M. et al. Mol. Biochem. Parasitol. 22.:135-143 (1987)), and by inhibition of the parasite's own membrane-associated sialidase with mAbs (Prioli, R.P. et al. J. Immunol. 144:4384-4391 (1990) ) . On the other hand, treatment of target cells with bacterial sialidase decreases trypomastigote infectivity (de Titto, E.H. et al. Acta Trop. (Basel) 44:273-282 (1987) ; de Araujo-Jorge, supra) . EXAMPLE IX SUBSTITUTE SHEET Depletion of Enzyme Activities by mAbs METHODS Parasites T. cruzi trypomastigotes, Y strain (Silva. L.H.P. et al. , Folia Clin. Biol. 2^:191-203 (1953)), were grown in cultures of LLC-MK 2 cells (ATCC-CCL-7, Rockville, MD) . Usually 75 cm 2 flasks, with sub-confluent cultures of LLC-MK2 cells were infected with 5 X 10 6 trypomastigotes. The LLC-MK2 cells were grown in low glucose Dulbecco's modified Eagle's medium with penicillin and streptomycin (DMEM, Gibco, Grand Island, NY) , containing 10% fetal bovine serum (FBS) at 37°C, 5% C0 2 . Free parasites were removed 24 hours later, and the cultures maintained in 10% FBS-DMEM. When indicated, the FBS-DMEM was removed during the 3rd day following infection, the monolayers were washed twice with Hanks' solution, and the medium replaced with DMEM containing 0.2% BSA (ultrapure, Boehringer Mannhein, Indianapolis, IN) and 20 mM Hepes, pH 7.4 (0.2% BSA-DMEM). After the 5th day following the initial infection, the trypomastigotes were harvested from culture supernatants. Culture supernatants were collected from parasites grown in FBS (FBS-supernatant) or in 0.2% BSA (BSA-supernatant) . I munodepletion Experiments Frozen pellets of trypomastigotes were lysed in 1% NP40, 50 mM Tris-HCl pH 7.4, l mM phenylmethylsulfonyl fluoride, 0.1 mM EDTA and 10 μg/ml of antipain, pepstatin and leupeptin (100 μl/1 X 10 8 trypomastigotes) , and the lysates cleared by 5 min centrifugation at 10,000 g. Fractions of 60 μl of the lysates were incubated 30 min with 20 μg of mAb 39 or mAb TCN2 pre-adsorbed on protein-A Sepharose. The mAb 39 (IgG2b) (Schenkman, S. et al.. Exp. Parasitol. 22.:76-86 (1991)) was purified by protein A-Sepharose from ascites fluids. Tissue culture supernatants of hybridoma cells secreting mAb TCN2 anti-T. cruzi neuraminidase were provided by Dr. M. Pereira (Tufts University, MA) . Purified mAb 2C2, which recognizes the Ssp-4 antigen of amastigotes (Andrews, N.W. et al. J. Ex . Med. 167:300-314 (1988)), was used as control. At the end of incubations, the beads were removed by centrifugation, washed twice, resuspended in PBS, and assayed for trans-sialidase and neuraminidase activities. Immunoprecipitation, SDS-PAGE and Western blotting Trypomastigotes (2 x 10 8 ) were washed in methionine, cysteine-free MEM, containing 10% dialysed fetal bovine serum. The parasites were resuspended in 4 ml of the same medium, and after a starvation period of 30 min, incubated with 0.5 mCi of a mixture of 3 S S-methionine and 3 5 S-cysteine (ICN) for 3 h at 37°C. After washing three times in Hanks' buffered salt solution, trypomastigotes were lysed with the same buffer used to purify the enzymes. This lysate, as well as culture supernatants, were pre-treated with an irrelevant IgG and protein A-Sepharose, centrifuged and the cleared supernatants incubated for 1 hr with 5 μl of ascites fluid containing mAb 39 or an irrelevant control monoclonal antibody. The immune complexes were collected by incubation with 50 μl of a 50% suspension of protein A-Sepharose. The samples were then processed as described (Andrews, N.W. et al.. Exp. Parasitol. 64:474-484 (1987)), and loaded into 6.5% SDS-PAGE gels. The radioactive bands were detected after fluorography using Amplify (Amersham) . Non-radioactive samples were detected on SDS gels by silver staining (Ansorge, W. , In: Electrophoresis '82 (D. Stathakos, editor) , Walter de Gruyer, Berlin, 1983, pp 235-242), Coomassie blue R250 staining, or Western blotting. For Western blots of trypomastigote cellular antigens, parasite suspensions were centrifuged in a microfuge, the pellet washed with Hanks' solution, resuspended in SDS-sample buffer and boiled for 3 min. Samples containing the equivalent of 2 x 10 7 trypomastigotes were loaded onto 6.5% SDS-PAGE gels and subjected to Western blotting. Bound antibodies were detected with anti-mouse IgG conjugated to alkaline phosphatase (Sigma) , followed by incubation with 0.3 mg/ml of nitroblue tetrazolium and 0.15 mg/ml of 5-bromo-4-chloro-3-indolyl phosphate, in 0.1 M Tris-HCl pH 9.5, 0.1 M NaCl and 0.005 M MgCl 2 . In some cases the Western blots of immunoprecipitated FBS-supernatants or trypomastigote cellular antigens were revealed with rabbit antibodies to the cross-reactive determinant (Cross, G.A.M. , Annu. Rev. Cell Biol. 6:1-39 (1990); Ferguson, M.A.J. et al.. Annu. Rev. Biochem. 57:285-320 (1988)), supplied by Dr. M. Davitz, New York University Medical Center. Measurement of Enzymatic Activities A. Trans-sialidase activity This activity was assayed in a final volume of 50 μl, in 20 mM of the indicated buffers (Sigma Chemical Co., St. Louis, MO), sialyllactose and [D-glucose-1- ,4 C] lactose (60 mCi/mmol) (Amersham Corporation, Arlington Heights, ID . The standard assay contained 20 mM Hepes buffer, pH 7.0, 1 mM sialyllactose (50 nmoles) and 25,000 to 40,000 cpm of the radioactive substrate (0.4 nmoles). This mixture was incubated 30 min at room temperature, and the reaction terminated by addition of 1 ml of water, followed by passage through 0.5 ml QAE-Sephadex, A25 or A50 column, also equilibrated in water. Activity was expressed in counts per minute, or as moles of sialyllactose eluted from the column following elution with 0.5 ml of 1 M ammonium formate. In the experiments designed to measure the initial velocity of the reaction, the amounts of the generated [ 14 C] -sialyllactose were determined when the formation of the product was linear with respect to time. B. Neuraminidase activity This activity was determined by measuring the fluorescence of 4-methylumbelliferone (4MU) released by the hydrolysis of lmM 4-methylumbelliferyl-N-acetylneuraminic acid (MuNana) . The assays were performed in 50 μl of 20 mM Hepes buffer, pH 7.0, or in other indicated buffers. After 3 h of incubation at 25°C, the reactions were terminated by adding 200 μl of 0.1 M Tris-HCl pH 9.5, 0.1 M NaCl, 2 mM MgCl 2 . The fluorescence was measured at 420 nm using excitation at 365 nm in a Titertek Fluoroskan II (Flow Laboratories Inc. , McLean, VA) , and expressed in fluorescence units. Alternatively, neuraminidase activity was assayed by measuring the amount of free sialic acid released from sialyllactose using the thiobarbituric acid method (Powell, L.D. et al.. Anal. Biochem. 112:179-185 (1986)). RESULTS To determine whether the trans-sialidase and neuraminidase were antigenically cross-reactive, trypomastigote lysates were immunoprecipitated with mAb TCN2 specific for the neuraminidase (8) , and with a series of mAbs to other T. cruzi surface antigens. Supernatants and precipitates were then assayed for enzymatic activity. As shown in Table 3, mAbs 39 and TCN2 (but not the control mAb 2C2) immunoprecipitated both neuraminidase and trans-sialidase from the parasite extracts. Most or all activities were recovered in the pellets, suggesting that the mAbs 39 and TCN2 bind to epitopes outside the enzymatic sites. Table 3 Depletion of trans-sialidase and neuraminidase activity from Trypanosoma cruzi trypomastigote lysates with mAbs Trans-sialidase activity Neuraminidase activity ( I4 C) -sialyllactose Methylumbelliferone (cpm) Fluorescence (%) Pellet Supernatant Pellet Supernatant Total lysate 8100 (100%) 2.9 (100%) mAb 39 7053 (87%) 0 (0%) 2.9 (100%) 0 (0%) mAb TCN2 4880 (71%) 0 (0%) 2.7 (100%) 0.1(3%) mAb cont 230 (2%) 6467 (80%) 0 (0%) 1.8 (62%) Frozen T. cruzi trypomastigotes were resuspended in 1% NP40 containing 50 mM Tris-HCl pH 7.4, 1 mM PMSF, 10 μg/ml of leupeptin, pepstatin, antipain (100 μ.l/1 X 10 8 trypomastigotes), and the lysates cleared by 5 min centrifugation at 10000 x g. Fractions of 60 μ.1 of the lysate were incubated 30 min with 20 μ.g of the indicated antibody pre-adsorbed to 30 μ.1 of protein-A Sepharose. At the end of incubations, the beads were removed by centrifugation, washed twice and resuspended in PBS. Aliquots containing comparable volumes of the initial lysate, the washed beads, and the first supernatant of the immuπodeplet on reaction were assayed for trans-sialidase reaction with 1 M sialyllactose for 30 min, or for neuraminidase reaction with 1 mM 4-methylumbelliferyl sialic acid for 3 h at room temperature. Next, mAb 39 was used to immunoprecipitate lysates of trypomastigotes which had been metabolically labeled with 35 S-methionine and 35 S-cysteine. As shown in Figure 8, this mAb specifically recognizes several radiolabeled bands having an Mr ranging between 120-220 kDa (lanes a,b) . A similar, complex pattern was seen in Western blots of total extracts of the parasite (lane c) , although some bands had different intensity. Trans-sialidase is released by trypomastigotes. Trypomastigotes were incubated at 37°C in DME-10% FBS, and at different time points, samples were removed and centrifuged. The supernatants and detergent extracts of the pellets were assayed for trans-sialidase activity. As shown in Table 4, there was a progressive increase of enzymatic activity in the supernatant. The activity in the pellets remained constant at least for a few hours, most likely reflecting the biosynthetic activity documented in Figure 8 (lane b) . After three hours, about half of the trans-sialidase activity was found in the culture supernatant. The enzymatic activity was not removed by centrifugation of the supernatants for one hour at 100,000 x g, indicating that the enzyme was released in a soluble form. TABLE 4 Release of Trans-sialidase into the Culture Supernatant of T. cruzi Trypomastigotes Activity (cpm + SD) Time (min) Supernatant Trypomastigotes 0 374 ± 24 4517 ± 166 30 1146 ± 14 5482 ± 159 60 1558 ± 297 5824 ± 451 120 1589 ± 41 4428 ± 245 180 2058 ± 78 4340 ± 270 T. cruzi trypomastigotes were washed three times at 4°C with 10% FBS-DMEM and incubated at 37°C at 5 x 10 7 parasites/ml. At the indicated times the parasites were centrifuged at 10,000 x g. Triplicate enzymatic determinations were made in the supernatants and in lysates of the pellets. The pellets were lysed in 1% NP40 containing 50 mM Tris-HCl pH 7.4, 1 mM PMSF and 10 μg/ml of leupeptin, pepstatin and antipain (1 ml per 5 x 10 7 parasites) . To determine whether the trans-sialidase was linked to the membrane by glycosylphosphatydilinositol (GPI) , as is the case with T. cruzi neuraminidase, a Western blot of the soluble form of trans-sialidase was revealed with an antiserum to the "cross-reactive determinant" (CRD) (Cross, 1990, supra; Ferguson et al.. 1988, supra) , an epitope characteristic of GPI-anchored proteins which is only revealed following cleavage of the anchor by a phosphatydilinositol-specific phospholipase C. As shown in Figure 8 (lanes d, e) , the same bands were revealed by mAb 39 and by the antiserum to CRD. If, however, total extracts of trypomastigotes were subjected to Western blotting, no reactivity with the antiserum to CRD was detected. The results shown in Table 4 above indicate similarities between the properties of the trans-sialidase of the present invention and the neuraminidase in antigenic cross-reactivity, migration in SDS-PAGE as bands of 120-220 Mr, GPI anchoring and rapid secretion into the culture medium. EXAMPLE X Purification of the Trans-sialidase and Neuraminidase and Comparison of their Activities Because of the complexity of the immunoprecipitation patterns described above, the trans-sialidase and neuraminidase enzymatic activities could reside in separate and distinct molecules. To resolve this issue, T. cruzi extracts or culture supernatants were subjected to several different chromatographic procedures. In every instance, the two enzymatic activities coincided. METHODS A. Enzyme Purification and Chromatography Trans-sialidase and neuraminidase activities were purified from pellets of parasites stored at -70°C, or from BSA-supernatants filtered through a 0.22 μm Millipore filter. Pellets containing 5 x 10 9 trypomastigotes were lysed at 4°C in 5 ml of 1% NP-40. 50 mM Tris-HCl, pH 7.4, 0.1 mM EDTA, 0.1 mM PMSF, 5 μg/ml of leupeptin, pepstatin and antipain. The viscous lysate was sonicated 3 times for 15 sec and the insoluble material was removed by centrifugation for 10 min at 10,000 x g. The supernatant was adjusted to 0.5 M NaCl, 1 mM of CaCl 2 , MgCl 2 , and MnCl 2 , and was incubated with 2 ml of Concanavalin A-Sepharose equilibrated with 0.1% NP-40, 0.5 M NaCl, 50 mM Tris-HCl pH 7.4. After washing with 25 ml of the equilibration buffer, the enzyme was eluted after an overnight incubation with 0.5 M α-methyl-D-mannoside in the same buffer. The eluate was filtered through a G-25 column equilibrated with 20 mM Tris-HCl pH 8.0 and applied into a mono-Q FPLC column HR5/5 (Pharmacia-LKB Biotechnology Inc., Piscataway, NJ) pre-equilibrated in the same buffer. After the absorbance had decreased below 0.002, the enzyme was eluted with a gradient of NaCl. In another experiment, a sample of the Concanavalin A eluate was subjected to sizing chromatography on Superose 12 HR 10/30 and Superose 6 HR 10/30 FPLC columns (Pharmacia-LKB) connec ed in series, equilibrated in 50 mM Tris/HCl containing 0.004% BSA, and pre-calibrated with proteins of molecular weights between 29 and 669 kDa (Sigma) . Trans-sialidase and neuraminidase activities were also purified from BSA-supernatants by affinity chromatography on immobilized mAb 39, or by hydrophobic interaction on a phenyl-Superose FPLC column (Pharmacia-LKB) . The affinity chromatography was carried out after concentrating the culture supernatants about 2Ox by filtration through Amicon membranes with a molecular weight cutoff of 300 kDa. The concentrated material was then passed through an Affigel-Hz (Bio-Rad Laboratories, Richmond, CA) column containing immobilized mAb 39 (prepared accordingly to the manufacturer's instructions). The column was washed with 0.15 M NaCl, 50 mM Tris-HCl pH 7.4, 0.05% NP-40, and the enzyme eluted with 3.5 M MgCl 2 , 20 mM sodium phosphate pH 6.0. The fractions eluted from the column were immediately filtered through Sephadex-G25 equilibrated in 20 mM Tris-HCl pH 8.0 to remove the MgCl 2 , and then subjected to further purification on mono-Q FPLC column HR5/5 as described above. The hydrophobic interaction chromatography was performed as follows. Fourteen ml of BSA-supernatant were diluted 1:2 with 50 mM phosphate buffer pH 7, containing 3.4 M ammonium sulfate, and applied to a phenyl-Superose HR 5/5 FPLC column pre-equilibrated with 50 mM phosphate buffer pH 7, containing 1.7 M ammonium sulfate. When the absorbance had decreased below 0.002, the bound enzymatic activities were eluted with a gradient of decreasing ammonium sulfate concentration. The collected 0.5 ml fractions were filtered through Sephadex G-25 columns pre-equilibrated with 50 mM Tris-HCl pH 7.4 containing 0.02% BSA to remove the ammonium sulfate. RESULTS Chromatographic Analysis The results of some of these experiments are summarized in Figures 9-11. Figure 9 shows the elution pattern from a MonoQ FPLC column. The input was a sample of a ET preparation isolated by affinity chromatography on immobilized mAb 39. The purity of the input is documented Figure 9: identical bands were observed by Coomassie-blue or silver staining (inset on the left of the Figure) , and by Western blotting revealed with mAb 39 (Figure 8) . The individual fractions eluted from the column were also run on SDS-PAGE and stained with silver (inset on the right of Figure 9) . All fractions displayed both enzymatic activities, and contained a family of polypeptides with Mr ranging from 120 to 220 kDa. Nevertheless, the composition of individual fractions was not the same. Lower molecular weight bands eluted first from the MonoQ. Identical results were obtained when total detergent lysates of trypomastigotes (rather than mAb 39-affinity purified enzyme) were subjected to chromatography on Concanavalin A-Sepharose, followed by ion exchange chromatography on a Mono Q. On Superose columns (Figure 10) , which separate proteins on the basis of size, the two enzymatic activities were detected in a broad peak, in a position corresponding to molecular weights greater than 700 kDa. In addition, small peaks of enzymatic activity eluted in positions corresponding to lower molecular weights. These results suggest that the enzymes form oligomers, as also pointed out by Pereira et al. for T. cruzi neuraminidase (Pereira, M.E.A. et al. , J. Exp. Med. 174:179-191 C1991)) . Chromatography on phenyl-Superose columns, which separate molecules on the basis of hydrophobic interactions, also failed to distinguish between the two activities (Figure 2C) . Effect of pH and Temperature on Enzymatic Activities Trans-sialidase and neuraminidase activities showed maximal velocities between pH 6.5 and 7.5, and very little activity at pH below 5.5, or above 9.5 (Figure 12) . A similar pH dependence was observed using several different preparations of enzyme, including total trypomastigote lysates, Mono Q fractions of trypomastigote lysates, or enzymes bound to immobilized mAbs 39 or TCN2. Incubation of affinity purified fractions, or total lysates, for 30 min at 56°C destroyed both enzymatic activities. No differences were found in the activities of either enzyme at temperatures between 4°C and to 37°C. Kinetic Analysis of the Enzymatic Activities The experiments illustrated in Figures 13- were performed in order to determine whether the same or different enzymes transfer and hydrolyse linked sialic acid. Figure 13 shows that methyl-umbelliferyl-N-acetyl-neuraminic acid, orp-nitro-phenyl- N-acetyl-neuraminic acid, the substrate used to assay the T„ cruzi neuraminidase activity, can also serve as a sialic acid donor to [ 14 C] -lactose; that is, the two reactions can be coupled. On the other hand 4-methyl-umbelliferone, the fluorescent product of the neuraminidase reaction, cannot function as an acceptor of sialic acid: at concentrations up to 10 mM it does not inhibit the transfer of sialic acid from sialylactose to [ 14 C] -lactose (Figure 14) . These findings raised the possibility that the trans-sialidase can function as a neuraminidase, provided that the reaction mixture does not contain a glycan acceptor (or contains a poor acceptor) of the removed sialic acid. To study this question further, the kinetics of sialic acid release from sialyllactose, and the formation of [ 14 C] -sialyllactose were measured simultaneously in reaction mixtures containing radioactive lactose. The velocity of transfer of sialic acid was much greater than the velocity of its release. In the presence of 1 mM [ 14 C] -lactose and 1 mM sialyllactose (100 nmoles of each in a total volume of 100 μl) , about 23 nmoles of [ 14 C] -sialyllactose were produced, but only 0.5 nmoles of free sialic acid were released, in one hour. In the absence of lactose, however, the amount of free sialic acid produced increased to about 2.5 moles (Figure 15). In other experiments, the incubation time was fixed at 30 minutes, the effect of increasing the concentration of lactose in the incubation medium was measured. As shown in Figure 16, the release of free sialic acid decreased from 2 to about 0.5 nmoles as the lactose concentration increased from 0 to 100 nmoles. The remote possibility that the lactose inhibited neuraminidase activity was excluded by the finding that the release of 4-methyl-umbelliferone from methyl-umbelliferyl-N-acetyl- neuraminic acid (or p-nitro-phenyl-N-acetyl-neuraminic acid) was not affected by addition of up to 10 mM lactose to the incubation medium. Taken together, the above results suggest that the sialic acid donor binds to the trans-sialidase and forms a sialylated intermediate. The bound sialic acid can then be transferred to water in a typical hydrolysis reaction, or transferred to an appropriate oligosaccharide acceptor, such as lactose. The trans-sialidase/neuraminidase appears to provide at least two enzymes; the enzyme from the Y strain of T. cruzi migrates on SDS-polyacrylamide gels as a group of 120 to 220 Mr bands. The interpretation that this heterogeneity reflects the presence of genetic variants in the parasite population is unlikely, since SDS-PAGE patterns of the trans-sialidase from six independent Y strain clones gave identical results. These bands are most likely not degradation products, since the SDS-boiled extracts of the trypomastigotes contained several protease inhibitors. Moreover, additional incubation of the extracts at 37°C did not alter the pattern of migration in SDS-PAGE. Instead, as suggested in (Pereira, 1991, supra) , the bands can be the products of different genes. The trans-sialidase/neuraminidase is part of a gene family. Its sequence is about 80% identical to a polymorphic GPI-anchored antigen named "shed acute phase protein", or SAPA (Affranchino, J.L. et al.. Mol. Biochem. Parasitol. 34.:221-228 (1989) ; Pollevick, G.D. et al. , Mol. Biochem. Parasitol. 47:247-250 (1991) ) . SAPA is glycosylated (Pollevick et al.. supra) , and Southern blotting of T. cruzi chromosomes separated by pulse-field gel electrophoresis and probed with a SAPA clone gave a complicated pattern, indicating the existence of several SAPA loci distributed among different chromosomes (Henriksson, J. et al.. Mol. Biochem. Parasitol. 42:213-224 (1990)). Each of the SAPA genes contains tandem repeats, and the number of repeats varies among the different genes, further contributing to the heterogeneity of the members of the family (Macina, R.A. et al. , FEBS Lett. 257:365-368 (1989)). In addition, the 120-220 Mr products share sequence homology with an antigenically distinct 85 Mr family of trypomastigote surface antigens (Kahn, S. et al. , J. EXP. Med. 172:589-597 (1990); Kahn, S. et al.. Proc. Natl- Acad. Sci. USA 8J5.4481-4485 (1991); Fouts, D.L. et al.. Mol. Biochem. Parasitol. 4£:189-200 (1991); Peterson, D.S. et al.. EMBO J. .8:3911-3916 (1989); Takle, G.B. et al. , Mol. Biochem. Parasitol. 48:185-198 (1991); Takle, G.B. et al.. Mol. Biochem. Parasitol. 3_7:57-64 (1989)) and with bacterial neuraminidases (Roggentin, P. et al. , Glycoconjugate J. 6:349-353 (1989)). In short, the trans-sialidase and neuraminidase enzymes of a family of T. cruzi stage-specific proteins share sequence motifs with bacterial neuraminidases. This family contains two antigenically distinct group of proteins, one migrating in SDS-PAGE around 85 Mr, and the other between 120-220 Mr. Proteins belonging to the 120-220 Mr family have trans-sialidase and neuraminidase activities. It is well known that many glycosidases transfer glycosidic bonds, when appropriate donors and acceptors are provided (Hassid, W.Z. et al.. In: The Enzymes (P. D. Boyer et al. , eds) Academic Press, New York, 1962, pp 277-315). The kinetics of the transfer versus hydrolysis reactions are different for individual glycosidases, depending on the relative affinity of the glycosyl residue for the acceptor, versus its affinity for water. Although it is not clear for most glycosidases whether the transferase reactions have biological relevance, the trans-sialidase reaction predominates on the surface membrane of T. cruzi trypomastigotes in vivo. The Ssp-3 epitope, which is expressed only after sialic acid transfer reactions, is present on trypomastigotes isolated from blood of infected mice. Furthermore, when blood trypomastigotes are isolated from animals whose tissues contain N-glycolylneuraminic rather than N-acetyl-neuraminic acid, the parasites also contain only N-glycolylneuraminic acid (Previato, J.O. et al.. Mem. Inst. Oswaldo Cruz £JL:38 (1990)). While the enzyme is known to desialylate the membrane of myocardial cells, vascular endothelial cells, and erythrocytes (Libby, P. et al.. J. Clin. Invest. 27:127-135 (1986)), this result may in fact be due to transfer of sialic acid to unidentified acceptors. Isolation of DNA Clones Encoding the Trans-Sialidase The product of a single T. cruzi gene expressed in Escherichia coli appears to display both neuraminidase and trans-sialidase activities. A randomly sheared library of T. cruzi DNA was made in the expression vector, lambda ZapII, with an average insert size of 5-6 kb. An initial screening of 175,000 plaques was performed with two oligonucleotide probes representing the repeat units in the C- and N-terminal region sequences of the published sequence of the T. cruzi neuraminidase (Perreira et al. , 1991, supra) . The first oligonucleotide probe (PROBE 1) contained 11 of the most conserved codons of the twelve amino acid C-terminal repeat unit and had the sequence: PROBE 1: GAC AGC AGT GCC CAC AGT ACG CCC TCG ACT CCC (SEQ ID N0:1) . The other oligonucleotide probe PROBE 2) represented one of the N-terminal repeat units which bear amino acid sequence homology to C. perfringens neuraminidase (consensus amino acid sequence SXDXGXTW. Four such units are found in the T. cruzi neuraminidase gene, but the codon sequence of the units varies considerably. An oligonucleotide probe containing codons for the five most conserved amino acids, as well as three amino acids which vary from unit to unit was synthesized (corresponding to nucleotides 493-516 of (Perreira et al.. supra) and had the sequence: PROBE 2: TCG GAA GAT GAT GGC AAG ACG TGG (SEQ ID NO:2) . Replica filters were screened with both oligonucleotide probes and yielded three types of positive clones: Type 1: (8 clones) hybridized with the PROBE 1 only; Type 2: (15 clones) hybridized with the PROBE 2 only; and Type 3: (13 clones) hybridized with both PROBE 1 and PROBE 2. The phages containing the 13 Type3 clones were spotted onto a lawn of bacteria and were induced for protein expression with IPTG. The plagues were overlaid with nitrocellulose and the filter lifts were incubated with mAb 39. Nine antibody-positive lambda clones were converted into plasmid form. Restriction maps of the inserts indicate that at least two classes of genes have been isolated. Three different plasmids were v.hen modified by removal of most of the 5' noncoding sequence. One of the extracts of these modified bacterial clones was strongly positive for TS and neuraminidase activities as shown in Figures 1 and 2 (Uemura et al, EMBO J. 11:3837-3844, 1992) . The other extracts were inactive. Restriction maps of the DNA inserts from the enzymatically positive and negative recombinant clones have been generated. The positive clone differs from the negative clones, in that it has an additional EcoRI restriction site within the coding region. Limited sequence analysis, now being extended, demonstrates additional differences in the coding regions of the two types of genes. EXAMPLE XI Substrate specificity of a Trans-Sialidase of the Present Invention Trans-sialidase was purified from supernatants of infected cultures as described in the above Examples. The ability of sialylated molecules to act as donors of sialic acid was measured by incubating them with purified TS in 20 mM Hepes buffer, pH 7.2, in the presence of [D-glucose-l- 14 C] lactose by conventional methods (see, e.g., Passaniti, A. et al. J. Biol. Chem. 263:7591-7603 (1988)) . The ability of molecules to act as acceptors of sialic acid was measured by incubating them with a mixture of TS, sialyl-lactose and [D-glucose-l- 14 C] lactose. These mixtures were incubated for 30 min at 37 °C, and the reactions terminated by addition of 1 ml of water followed by passage through a 1 ml QAE-Sephadex A50 column. The radioactive oligosaccharides were eluted with 1 ml of 1 M ammonium formate, and counted. Table 5. Ability of various compounds to be acceptors of sialic acid. This is expressed as percent reduction in the synthesis of sialyl- 1 C-lactose in a reaction mixture containing TS, 1 mM sialyl-lactose, 25000 to 40000 cpm [D-glucose-l- 14 C] -lactose and different concentrations of potential acceptor molecules. Table 5 Disaccharides and Derivatives Saccharides Name Gal(01-4)Glc Gal(01-4)Fructose Gal(01-4)Gluconic Acid Gal(j8l-4)GlcNac Gal(01 4)Man Gal(01 4)Glc- CH, Gal(01 -3)GlcNac Gal(01 -3)GalNAc Gal(01 -3)arabinose Gal(01 -3)Gal-0-CH 3 Gal(01 -6)Gal Gal(01 -6)GlcNAc Gal(oil -4)Gal Gal(α.1 -3)Gal-0-CH 3 13 GaKαα -6)Glc Melibiose Gal(αl -6)Gal Stachyose GalNAc (01-3)Gal-O-CH 3 Glc(01 -4)Glc Cellobiose Glc(Q!l -6)fructose Palatinose Glc(αl -4)Glc Maltose Glc(α!l -10)Fructose Sucrose Glc(αl -lα Glc o;,of-Trehalose GlcNAc (01-3)Gal-O-CH 3 GlcNAc (01-6)Gal GlcNAc (01-4)GlcNAc Chitobiose GlcNAc (01-6)GlcNAc GlcNAc (01-6)GlcNAc GlcNAc (01-6)Man-O-CH 3 Man(o_l -3)Man Table 6 Oligosaccharides Product Saccharides Concentraion (mM) .1 1 10 LNnT Gal(01-4)GlcNAc(01- 3)Gal(0-4)Glc 12 69 84 LNT Gal (01-3)GlcNAc(01-3) LNFP-II Gal(01-3)GlcNAc[Fuc(αl- 4)] (01-3)Gal(01-4)Glc 12 21 LNFP-III Gal(01-4)GlcNAc[Fuc(αl- 3)] (01-4)Glc 18 ND Lewis,. LNFP-V Gal (01-3)GlcNAc(01-4) [Fuc(αl-3)Glc 52 Table 7 Monosaccharides and derivatives* Product 10 Galactose ot-Methyl-Galactose -Methyl-Galactose ♦ Glucose(Glc) , Glucosamine (GlcN), Galactosamme (GallN), Fucose (Fuc) , N-Acetyl-Glucosamine (GlcNAc) , N-Acetyl-Galactosamme (GalNAc) , Mannose (Man) were all tested and found to be negative. SUBSTITUTESHEET Table 8 Ability of Ganglioside * compounds to be sialic acid donors Product Terminal saccharides Concentration (μM) 10_ 100 1000 SA(Q!2-3)Gal(01-4)GlcNAc (01-3) (Gal(01-3)Glc- ** 71 91 100 SA(Qi2-3)Gal(01-3)GlcNAc (01-3)Gal(01-4)Glc-R 23 42 55 SA(α2-3)Gal(01-4)GlcNAc[Fuc (αl-3)] (01-3)Glc(01-4)Gal- R, Sialyl-Lewis x 42 SA(θ!2-6)Gal(01-4)Glc-R SA(α2-6)Gal(01-3)GlcNAc(02-3) Gal(01-4)Glc-R SA(α2-8)SA(α2-3)Gal(01-4)Glc-R 8 ♦Expressed as percentage of cpm formed in the presence of 1 mM GSC-31 ♦* R = -0-CH 2 -CH(NH-CO-C 17 H 35 ) -CH0H-CH=CH-C13H27 Table 9 Ability of Oligiosaccharides* compounds to be sialic acid donors Product Saccharides Concentration (μM) 10 100 1000 10000 SL NeuNAc(α2-3)Gal(01-4)Glc 36 63 100 LST-a NeuNac(α2-3)Gal(01-3)GlcNAc [αl-3)]Glc 0 2 31 71 3'-S,3-FL NeuNac(α2-3)Gal(01-4)Fuc [Fuc(αl-3)]Glc 3 2 8 * Expressed as percentage of cpm formed in the presence of 1 mM SL Table 10 Ability of Ganglioside * compounds with terminal and non-terminal SA* to be sialic acid donors Product Terminal Saccharides Concentration (μM) 10 100 1000 monosialo-GM Gal (01-3)GalNAc (01-4)Gal [NeuNAc(α2-3)] (0l-4)Glc-Cer 6 monosialo-GM1 GalNAc( 1-4)Gal [NeuNAc ( 2-3) ] (Bl-4)Gle-Cer 10 10 monosialo-GM2 NeuNAc(α2-3)Gal (01-4) Glc-Cer 52 122 100 * Expressed as percentage of cpm formed in the presence of 1 mM GM3 Table 11 Ability of GM3-gangliosides with variations in the NeuNAc- molecule* to be sialic acid donors Product Terminal Saccharides Concentration (μM) 10 100 1000 GSC- Expressed as percentage of cpm formed in the presence of mM GSC- 17. EXAMPLE XII Novel trans-sialidase of Trypanosoma brucei procyclic trypanomastigotes: enzyme characterization and identification of procyclin as a sialic acid acceptor. MATERIALS AND METHODS Parasites. TREU 667-stock !_____ brucei procyclic trypomastigotes (11) were formed in buffered semi-defined medium (BSM) cultures (12) containing 10% FCS (Hyclone Laboratories, Inc., Logan, UT) carried out at 26°C. Y strain _Y____ cruzi trypomatigotes (13) were grown in cultures of LLC-MK 2 cells (CCL- 7; American Type Culture Collection, Rockville, MD) with DMEM containing 10% FCS as described previously (10) . Enzyme ActivityAssays. Trans-sialidase activity was assayed as described previously (10) . Briefly, samples were tested in a final volume of 50 μl, in 20 mM of the indicated buffers (Sigma Chemical Co., St. Louis, MO) containing 50 nmoles of sialyl (02-3) lactose (Boehringer Mannheim Biochemicals, Indianapolis, IN) and 0.36 pmoles of (D-glucose-1-14C] -lactose (60 Ci/mol) Amersham Corp., Arlington Heights, IL) . This mixture was incubated for 40 minutes at room temperature and the reaction terminated by the addition of 1 ml of water and passage through a 0.5 ml QAE-Sephadex A50 column pre-equilibrated with water. Activity was expressed as cpm eluted from the columns with 0.5 ml of Iμ ammonium formate solution. In some assays 0.25 to 25 nmoles of sialyl(α2-6) lactose (Boehringer Mannheim Biochemicals), sialyl(α2-9)sialyl(α2-3)lactose-ceramide, N- acetylneuraminic acid (Sigma Chemical Co.) or 4- methylumbelliferyl-N-acetylneuraminic acid (Sigma Chemical Co.) were substituted for the sialyl (02-)lactose in order to test their potential ability to serve as sialic acid donors. In other assays 40 to 4,000 nmoles of lactose, stachyose, melibiose, Gal(01- (a) )Gal, 2-methyl-D-galactophyranoside, 0-methyl-D- galactopyranoside (Sigma Chemical Co.) Gal (01-4) [Fuc(αl-3)Glc (Oxford Glycosystems, Inc., Rosedale, NY) or 10 μm of cipric nitrate or mercuric acetate were added to the reaction mixture to assess their possible ability to serve as sialic acid acceptors or trans-sialidase inhibitors. Trans-sialidase activity was also demonstrated by measuring the transfer of 3H-labeled sialic acid residues from sialyllactose to different saccharides. [Sialic-9- 3 H] (α2-3) - sialyllactose was prepred by incubating 25 μl of [sialic -9- 3 H]CMP-sialic acid (26.2 Ci/mmol; NEN Research Products, Boston, MA) with 0.15 M lactose in the presence of porcine submaxillary α(2-3) -Gal0(l-3) -GalNac sialyltransferase (15). Fifteen nmoles of the labeled sialyllactose and 100 moles of potential sialic acid acceptors were incubated for 210 min at room temperature in 15 μl of 20 mM HEPES, pH 7, in the presence of purified trans- sialidase. The products of the reactions were isolated by elution from QEAE-Sephadex columns as described above, lyophilized and subjected to thin-layer chromatography (TLC) on silica gel 60 plates (Macherey-Nagel, Duren, Germany) using ethanol- n-butanol -pyridine -water -acetic acid [100:10:10:30:3 (v/v) ] . The sialylated compounds were visualized by spraying the TLC plates with En 3 Hance (NEN Research Products) , followed by fluorography. Saccharide purity was assesed by silica-gel TLC analysis of 1 μmol samples, followed by staining with orcinol- ferric chlordie (16) . Single bands were observed with meliviose, α(2-3)sialyllactose, α-methylgalactose, 0-methylgalactose and Gal (01-6)Gal. Sialidase activity was determined by measuring the fluorescence of 4-methylumbelliferone resulting from the hydrolysis of 4-methylumbelliferyl-N-acetylneuraminic acid (initial concentration of 1 mM in 50 μl of 20 mM HEPES buffer, pH 6.7), as described elsewhere (17). Labeling of Surface Components with Sialic Acid. 3 H- labeled sialyl(α2-3) lactose was prepared by incubating 25 μl of [sialic-9- 3 H]CMP-sialic acid (20 Ci/mmol; New England Nuclear), with 0.15 M lactose in the presence of mammalian α2-Gal01-3GalNac sialyltransferase (16) . Trypomastigotes (1.5 x 10 8 ) were washed once with cold BSM-G, left for 2 h at 26°C in BSM-G, washed 4 times more with cold BSM-G and resuspended with 250 μl of BSM-G containing 45 nmoles of 3 H-labeled sialyllactose. After 25 min incubation at room temperature, 30 more nmoles of 3 H-labeled sialyllactose were added to the parasites, which were further incubated for 3 min at room temperature and finally washed three times with cold BSM-G for the SDS-PAGE and western blotting or six time for the immunoprecipitation. ImmunoprecipitationandConA-AbsorptionExperiments. Parasites were lysed in 1.5% NP-40, 50 mM Tris-HCl, pH 7.4, 1 mM PMSF and 5 μg/ml of antipain, pepstatin and leupeptin (1 ml/10 9 parasites) . The lysates were cleared by centrifugation at lO r OOOg; for 5 min at 4°C. Forty μl fractions of the lysates were incubated for 1 h at 4°C with 3, 9 and 27 μl of protein A-agarose (Sigma Chemical Co.) pre-adsorbed with an excess of mAb 39 (anti- T. cruzi trans-sialidase; 10) . Immunoprecipitation. Parasites were lysed in 1.5% NP-40, 50 mM Tris-HCl, pH 7.4, 1 mM PMSF and 5 μg/ml of antipain, pepstatin and leupeptin (1 ml per 10 9 parasites) . The lysates were cleared by centrifugation at 10,000 g for 5 min at 4°C. Forty μl fractions of the lysates were incubated, with mixing, for 1 h at 4°C with 3, 9 and 27 μl of protein A-agarose (Sigma Chemical Co.) bearing adsorbed mAb 39 [anti-T. cruzi trans- sialidase (18)]. Eighty μl volumes of lysate were similarly incubated with protein A-agarose bearing rabbit antibodies against purified T. cruzi trans-sialidase (17) or rabbit antibodies against a synthetic peptide corresponding to the first 19 amino-terminal amino acid resiudes of the T. cruzi trans- sialidase (19) . In addition, lysates were prepared from T. brucei radiolabeled with 3 H-sialic acid resiudes (see below) in the presence of 1% BSA (Ultrapure, Boehringer MannheimBiochemicals) . These lysates were mixed with equal volumes of 1 M Tris/HCl, pH 8.6, 2% BSA, and left for 30 min at 56°C to inactivate trans- sialidase/sialidase activities. Sixty μl fractions of these lysates were incubated with 20 μl of protein A-agarose bearing 20 μl of mAb 137 [IgGl anti-procyclin, kindly supplied by Dr. T. Pearson, University of Victoria, Victoria, Canada (7)] or 20 μg of mAb 3C9 [IgGl anti-T. cruzi Ssp-e (9)] for 40 min at 4°C. The beads were then centrifuged, washed three times with 50 mM Tris/HCl pH 8.6, 285 mM NaCl, 0.3% BSA, and the bound antigen eluted with 0.1 M HCl/glycine, pH 3.1. The amount of radioactivity remaining in the extracts and in the eluates from the beads was measured i a 0 counter. Enzymepurification Trypomastigote lysates, prepared as described above, were purified by affinity chromatography on Con A-Sepharose (Pharmacia-LKB Biotechnology Inc., Piscataway, NJ) , followed by anion-exchange chromatography on a Mono-Q FPLC HR5/5 column (Pharmacia-LKB Biotechnology, Inc.), as described for the T. cruzi trans-sialidase (17) „ A sample of the purified enzyme was concentrated on a Centriprep-10 concentrator (Amicon, Beverly, MA) and further subjected to sizing chromoatogrpahy on Superose 12 HR 10/30 and 5 HR 10/30 columns (Pharmacia-LKB Biotechnology Inc.), connected in series (17) and pre¬ equilibrated with 40 mM Tris/HCl, pH 8, containing 0.1% NP-40. Protease and Sialidase Treatment Trypomastigotes were washed once with BSM and treated with 250 μg/ml of trypsin (Sigman Chemical Co) in DMEM for 20 min at 37°C, or with 1250 U/ml of pronase (Calbiochem Biochemicals, San Diego, CA) in DMEM for either 15 min at 37°C, for 30 min at room temperature, as indicated in the text. The trypsin digestion was terminated by the addition of soybean trypsin inhibitor (final concentration of 500 μg/ml; Sigma Chemical Co.). The parasites were further washed in DMEM containing 2 mg/ml BSA and 100 μg/ml soybean trypsin inhibitor. Pronase was removed by the addition of 50 volumes of ice-cold DMEM containing 30% FCS followed by washing with DMEM containing 15% FCS, at 4°C. NP-40 lysates of the protease-treated parasites were assayed for trans-sialidase activity. In controls, the trypsin was added to parasites in the presence of soy bean trypsin inhibitor, or the pronase added to the parasites concomitantly with the addition of the DMEM with FCS. In addition, the assays for trans-sialidase activity in lysates containing pronase were done at 4°C in the presence of 60 mg/ml of BSA. Con A-purified trans-sialidase was treated with 100 μg/ml of proteinase K (Sigma Chemical Co.), 250 μg/ml of trypsin or 1250 U/ml of pronase in DMEM for 20 min at 37°C. The proteinase K and the trypsin digestions were respectively terminated by the addition of either PMSF (2mM) and BSA (20 mg/ml) or soybean trypsin inhibitor (500 ug/ml) and BSA (30 mg/ml) . After pronase digestion, BSA (60 mg/ml) was added to the reaction mixture and assays for trans-sialidase activity performed immediately, at 4°C, in the presence of 75 mg/ml BSA. Trypomastigotes washed once with BSM-G were incubated for 2 h with 0.33 U/ml Vibrio cholera sialidase (Boehringer Mannheim Biochemicals) in BSM-G, pH 5.5, and washed five times with BSM-G. Some lysate samples were incubated with equal volumes of 1 U/ml sialidase, or of sialidase buffer, for 15 min at 37°C, before being subjected to SDS-PAGE (see below) . Labeling of Surface Components with Sialic Acid, trypomastigoes (1.4 x 10 8 ) were washed once with cold BSM-G, left for 2 h at 20°C in BSM-G, washed 4 times more with cold BSM-G and resuspended in 250 μl of BSM-G containing 45 nmoles of 3 H-labeled sialyllactose. After a 25 min incubation at room temperature, 30 nmoles of additional 3 H-labeled sialyllactose were added to the parasites and the incubation continued for 3 min at room temperature. The trypomastigotes were then washed three times with cold BSM-G and lysed with NP-40 for SDS-PAGE and immunoprecipitation. SDS-PAGE and Western Blotting. Samples of FPLC fractions, or of cell lysates containing the equivalent of 5 x 10° parasites labeled with 3 H-sialic acid, were applied to 7.5% SDS-PAGE gels under both reducing and non-reducing conditions (20) . Gels were either silver stained (21) or impregnated with 1 M sodium salicylate (22) , stained with coomassie blue and subjected to fluorography using an intensifying screen. For western blot analysis, separated proteins were transferred to nitrocellulose membranes and probed with mAbs 39 and 137. Bound antibodies were detected with an alkaline- phosphatase conjugate (17) . RESULTS Presence of Sialic Acid in T. brucei Procyclic Trypomastigotes. Initial experiments demonstrated the presence of sialic acid associated with the surface membrane of cultured, extensively washed T. brucei procyclic trypomastigotes. The total sialic acid content of parasite extracts, as compared to those of T. cruzi cell-derived trypomastigotes, is shown in Table 1. T. brucei contains more sialic acid than T. cruzi. Most of the sialic acid is surface-associated since it was removed from the live parasites by pronase or by sialidase treatment (Table 12) . Enzymatic treatments did not affect the motility of the parasites, as determined by light microscopy. These results, however, do not address the question of the origin of the surface-bound sialic acid. In order to investigate its possible acquisition from exogenous sources, trypomastigotes were treated with sialidase, re-incubated for 30 min at room temperature with α(2-3) -sialyllactose and extensively washed. As shown in Table l, their sialic acid content was restored. When α(2-3) -sialyl lactose was substituted for α(2-3) -sialyl lactose, however, much less sialic acid was found on the parasites (Table 12) , indicating that the sialylation reaction is specific and documenting the efficiency of the washing procedure to remove remaining free sialic acid, or sialic acid loosely bound to the parasites. Presence of Trans-sialidase in T. brucei Procyclic Trypomastigotes. In the following experiments, we assayed for the presence of trans-sialidase in NP-40 extracts of blood stage stumpy and slender trypomastigotes, and of procyclic trypomastigoes. Enzymatic activity was measured by the ability to transfer sialic acid from sialyllactose to radiolabeled lactose, forming labeled sialyllactose. As shown in Table 13, extracts of procyclics were active. The trans-sialidase activity per parasite was approximately five times less than that of T. cruzi trypomastigotes (not shown) . No significant activity was found in supernatants of procyclic cultures (Table 13) . Enzyme Purification. NP-40 lysates of T. brucei trypomastigotes were first subjected to Con A-affinity chromatography and elution with α-methyl-D-mannoside. Approximately 40% of the trans-sialidase activity was recovered. This material was then subjected to anion-exchange FPCL. Most enzymatic activity was eluted between 70 and 130 mM of NaCl (Fig. 24A) , with a recovery of approximately 85%. Reduced SDS-PAGE of this purified trans-sialidase showed two major bands with molecular weights of approximately 73 and 77 kDa and a faint band of approximately 48 kDa (Fig. 24B, insert, left lane) . In order to assess the molecular weight of its native form and further purify the trans-sialidase, Mono-Q fractions corresponding to the peak of enzymatic activity were pooled, concentrated by retention on a 10 kDa-cut-off membrane filter, and subjected to sizing chromatography on FPLC Superose 12 and Superose 6 columns connected in series. In several experiments, using different trans-sialidase preparations, enzymatic activity was detected in fractions corresponding to molecular weighcs ranging from approximately 66 kDa to more than 700 kDa. In the experiment illustrated in Fig. IB, the two major broad active peaks have molecular weights of approximately 180 and 660 kDa. In another run, a 66 kDa peak replaced the 180 kDa peak (not shown) . On one occasion, a fresh lysate produced only the 660 kDa peak (not shown) . These data suggest that the trans- sialidase has a propensity to self-aggregate. Reduced SDS-PAGE gels of fractions corresponding both to the 180 kDa and to the 660 kDa peaks, stained by silver, revealed a major band of approximately 73 kDa (Fig. 25B, inset) . In the fraction corresponding to the high molecular weight peak, a less intense band of approximately 77 kDa could also be seen. Two faint bands corresponding to molecular weights of approximately 63-67 kDa could also be seen. Under non-reducing conditions, however, a single band of approximately 63 kDa was observed (not shown) . Protease-Sensitivity and Surface Localization of the Trans-sialidase. Con A-purified T. brucei trans-sialidase was relatively resistant to treatment with 250 μg/ml of trypsin or with 100 μg/ml of proteinase K for 20 min at 37°C. Enzymatic activity was destroyed, however, by treatment with 1250 U/ml of pronase (Table 14) . Accordingly, treatment of live parasites with 1250 U/ml of pronase for 15 min at 37°C, but not with 250 μg/ml of trypsin for 20 min at 37°C, markedly reduced the trans- sialidase activity of subsequently prepared lysates (Table 14) . Substrate Specificity. The ability of different sialylated compounds to serve as sialic acid donors for purified T. brucei and T. cruzi trans-sialidases was assessed. Both enzymes and catalyzed the transfer to radiolabeled lactose of sialic acid from α(2-3) -sialyllactose, fetuin (Fig 25) and 4- methylumbelliferyl-N-acetylneuraminic acid (not shown) . In contrast, there was no sialylation of radiolabeled lactose when (2-3) -sialyllactose, colominic acid [poly-α(2-8) -neuraminic acid] , N-ace ylneuraminic acid or α(2-9) -sialysialyllactose were used as sialic acid donors (Fig. 25) . Next, various saccharides were assayed for their ability to inhibit sialic acid transfer by T. cruzi and T. brucei trans-sialidases. The addition of saccharides containing 0- 1inked, but not α-linked, galactopyranosyl residues reduced the transfer of sialic acid to radiolabeled lactose (Table 15) . 0- methylgalactose, but not α-methylgalactose, also inhibited the reaction. Gal(01-4) - [Fuc(αl-3) ]Glc had an intermediate inhibitory activity on the formation of radiolabeled sialyllactose by both enzymes, when compared with the other disaccharides (Table 15) . The dose-response curves comparing Gal (01-4)Glc (lactose) with Gal (αl-6)Glc (melibiose) and 0- methyl- with α-methyl-galactose, showed that 0-linked galactopyranosyl residues are at least 100 times more efficient in inhibiting the reaction than α-linked residues (Fig. 26) . To distinguish between competitive inhibition and inhibition of catalysis, selected saccharides were incubated with 3 H-labeled sialyllactose in the presence of purified enzyme. The formation of new sialyated molecules was revealed by TLC on silica-gel plates, followed by fluorography. This experiment documents the sialylation of Gal (01-6)Gal and 0-methylgalactose (Fig 27, lanes b and c) and, to a minor extent, of melibiose (Fig. 27 lane d) . The lower efficiency of sialylation of melibiose was associated with an increased production of free sialic acid. Therefore, similarly to the T. cruzi enzyme, the sialidase activity increases in the absence of good sialic acid acceptors. Absence of Reactivity of the Trans-Sialidase with T. cruzi-specific Monoclonal and Polyclonal Antibodies. In order to reveal a possible immunological cross-reactivity between the T. brucei and T. cruzi enzymes, we attempted to immunoprecipitate the T. brucei trans-sialidase activity with monoclonal and polyclonal antibodies specific for T. cruzi trans-sialidase. Even when used in amounts 4.5-to nine-fold higher than that necessary to immunoprecipitate an equally active T. cruzi trans- sialidase preparation, the antibodies failed to remove T. brucei enzymatic activity (Fig. 28) . Identification of Procyclin as a Sialic Acid Acceptor. To identify the sialic acid acceptor(s) on the T. brucei surface, live procyclic trypomastigotes were incubated with [ 3 H]sialyllactose. Fluorography of an SDS-PAGE gel carried out with a lysate of tse tse parasites showed only one radioactive band (Fig. 29, lane d) . Sialidase treatment of the lysate removed the radioactivity from the band (Fig. 29, lane e) , while treatment with control buffer had little effect (Fig. 29, lane f) , indicating that the sialic acid was covalently bound to surface molecules. This band had the same molecular weight, intensity and shape expected of a procyclin band (Fig. 29, lanes a, b and c) and reacted with a procyclin-specific mAb in western blotting (Fig. 29, lane g) . An extract prepared with [ 3 H]sialyllactose-labeled parasites was then immunoprecipiated with an anti-procyclin mAb. Most counts were immunoprecipitated, whereas no radioactivity was precipitated by a control mAb (Table 28) . SUBSTITUTESHEET Table 12. Presence of Sialic Acid in T. brucei Procyclic Trypomastigotes and its Removal by Enzymatic Treatment * As assessed by the thiobarbituric method arjd HPLC φ Trypomastigotes were washed once with BSM-G, incubated for 2 h ar 26 °C with 0.33 U/ml of Vibrio cholera sialidase in BSM, pH 5.7 and washed five times with BSM-G Sialidase-treated parasites were washed twice with BSM-G, incubated with ImM of sialyllactose in BSM-G for 40 min at 26°C and washed five times with BSM-G. Prepared from trypomastigotes that had been washed five times with BSM, incubated for 30 min at room temperature with 1250 U/ml of pronase in DMEM, pH 7.5, and washed once with BSM-G. Containing material released by treating trypomastigotes with pronase. Total number of lysed parasites in the aliquot assayed. $ All samples were assayed in duplicates; the background value (111 cpm, obtained in the absence of trans-sialidase) was subtracted. Variation between the duplicate values was less than 7% of the mean (lysates) or 18.6% of the mean (culture supernatant) . Thirty μl volumes of a supernatant from a procyclic trypomastigote culture with approximately 10 7 parasites per ml were assayed. TABLE 14 Comparison of the T. brucei and T. cruzi Trans-sialidases in Terms of the Effect of Adding Potential Acceptors or Inhibitors to the Enzymatic Assay Non-radioactive saccharides were added at a final concentration of 8 mM in a standard assay for trans- sialidase activity (1 mM sialyllactyose and 7.2 nM 14 C-lactose in 50 μl of 20 mM HEPES buffer, pH 7) . Trans-sialidase was purified from trypomastigotes by Con A-affinity chromatography as described in the footnote for Table 3 Percentage of reduction in cpm in relation to reactions carried out without non-radioactive saccharides (5532 cpm for the T. brucei enzyme, 4513 for the T. cruzi enzyme) . All samples were assayed in duplicates and the background value (72 cpm, obtained in the absence of trans-sialidase) subtracted. Variation between the duplicate values was in every case less than 16% of the mean. TABLE 15 Immunoabsorption with mAbs of Molecules Sialylated by the incubation of Live T. brucei Procyclic Trypomastigotes with [H 3 ] -Sialyllactose Amount of [H 3 ] m Amount of [H 3 ] in su ernatant pellet TABLE 16 Sialic acid contents and removal of sialic acid from T. brucei procyclic trypomastigotes by treatment with pronase. Amount of Source of sialic sialic Parasite Treatment acid acid 10 6 parasites in pmoles DISCUSSION A trans-sialidase according to the present invention, e.g., as obtained or sequenced from Trypanosomi trypomastigote, as described herein, may have a specificity such that the trans- sialidase transfers α(2-3) -linked, but not α(2-6)-, or α(2-9)- linked sialic acid residues to terminal 0-galactopyranosyl (and not to α-galactopyranosyl) residues. In this respect, the T. brucei trans-sialidase is strikingly similar to the T. cruzi trans-sialidase. Moreover, T. brucei trans-sialidase is inhibited by mercuric acetate and binds to Con A, again in agreement with findings on the T. cruzi. However, despite these functional and structural similarities, a T. cruzi trans-sialidase-specific mAb or polyclonal antibodies raised against the purified T. cruzi enzyme or against a synthetic peptide corresponding to this first 19 amino-terminal amino acids did not appear to have immunological cross-reactivity with the T. brucei enzyme. Also contrasting with the T. cruzi enzyme, the T. brucei trans-sialidase activity is relatively resistant to trypsin treatment and was not affected by treatment with proteinase K under the conditions described in this paper, raising the possibility that enzymatically active trypsin- and/or proteinase K-fragments of the T. brucei trans-sialidase could be used as irr-v-unogens for obtaining trans-sialidase-activity blocking ant_,:.odies. When trans-sialidase sequentially purified by Con A- affinity r^ FPLC ion-exchange chromatographies, which produced three banc m silver-stained SDS-PAGE gels, was applied to FPLC gel-filtration columns, trans-sialidase activity was eluted associated with fractions with a molecular weight of approximately 67,000 Da. SDS-PAGE of these fractions showed only a 73 kDa band. This is consistent with the molecular weight of a protein with sialidase activity recently described in T. brucei procycllic trypomastigotes (Eugstler, M. et al.. Mol. Biochem Parasitol. 54: 21-30 (1992)). This sialidase activity is very likely a component of the trans-sialidase activity of the enzyme described herein, since, in addition to the molecular weight identity, it has basically the same substrate specificity, being more active on α(2-3) -linked sialyl residues than on α(2-6)- or α(2-8) -linked residues, is affected by chloride and mercury ions and is not present on bloodstreams forms of the parasite, as shown herein for the trans-sialidase. In fact, no discrimination of the trans-sialidase and sialidase activit-ies could be achieved in T. cruzi. In addition to the 67 kDa peak, activity was also detected in fractions corresponding to molecular weights ranging from 67 to more than 700 kDa SDS-PAGE gels of these fractions showed peptides with molecular weights of 73 and 77 kDa, suggesting that, as proposed for the T. cruzi trans-sialidase (14) , the enzyme may form oligomers or bind no-covalently to other molecules on the parasite surface. Although all trans- sialidase activity in this high molecular weight peak could be ascribed to the 73 kDa peptide, the 77 kDa peptide may also have trans-sialidase activity. It is also shown herein that procyclin, the main surface glycoprotein of African trypanosome procyclic trypomastigotes, is sialylated with the addition of α(2-3)linked sialic acid residues to live procyclic trypomastigotes. The fact that only one sialylated band was seen on an electrophoresis gel of a whole trypomastigote extract suggests that no other surface molecule is sialylated. Moreover, sialylation of procyclin takes place not only in the GPI-anchor, but also in another part of the molecule, since sialic acid residues are released in the supernatant when live parasites are treated with pronase. The total amount of sialic acid in T. brucei procylic trypomastigotes is five to six times higher than in T. cruzi cell-derived trypomastigotes. In T. cruzi a trans-sialidase product - the sialylated epitope Ssp-3 - was shown to participate in the process of cell penetration by the parasite (9) . A similar function for sialic acid in procyclin is unlikely, since T. brucei procyclic trypomastigotes multiply freely in the midgut of the tsetse fly (1) , and do not bind to the chitinous perithrophic membrane of the gut. However, its possible that the expression of the trans-sialidase and the consequent sialylation of procyclin by transfer of sialic acid residues from sialic acid donors in the blood meal would take place only four days after ingestion of the trypomastigotes by the fly and could therefore play a role in the penetration of the perithrophic membrane that happens from that day onwards (l) ,. As the T. cruzi trans- sialidase (10) , the T. brucei enzyme is on the parasite surface, as shown by its availability to proteolysis by pronase on live parasites, and it could itself be involved as a ligand in this penetration. On the other hand, its known that protection of bloodstream trypomastigotes against complement activation is mediated by the VSG coat (5) . As this coat is replaced by procyclin during the firs 48 h following ingestion by the fly (2, 3) , its possible that the sialic acid in procylin could maintain complement resistance and prevent lysis of the trypomastigotes by complement factors present in the present or in future blood meals. In this respect, it is of interest the finding that procyclic trypomastigotes are resistant to lysis by fresh bovine serum (Tomlison, unpublished results) . It would be of interest to determine how long would complement remain active in the sandfly midgut or crop. The possibility that trans-sialidase could play a role in parasite-host interactions raises the possibility that it could be used as immunogen for cattle from endemic areas in an attempt to produce antibodies that would interfere with the parasite development in the insect vector. All references cited herein, including journal articles or abstracts, published or corresponding U.S. or foreign patent applications, issued U.S. or foreign patents, or any other references, are entirely incorporated by reference herein, including all data, tables, figures, and text presented in the cited references. Additionally, the entire contents of the references cited within the references cited herein are also entirely incorporated by reference. Reference to known method steps, conventional methods steps, known methods or conventional methods is not in any way an admission that any aspect, description or embodiment of the present invention is disclosed, taught or suggested in the relevant art. The foregoing description of the specific embodiments will so fully reveal the general nature of the invention that others can, by applying knowledge within the skill of the art (including the contents of the references cited herein) , readily modify and/or adapt for various applications such specific embodiments, without undue experimentation, without departing from the general concept of the present invention. Therefore, such adaptations and modifications are intended to be within the meaning and range of equivalents of the disclosed embodiments, based on the teaching and guidance presented herein. It is to be understood that the phraseology or terminology herein is for the purpose of description and not of limitation, such that the terminology or phraseology of the present specification is to be interpreted by the skilled artisan in light of the teachings and guidance presented herein, in combination with the knowledge of one of ordinary skill in the art. SEQUENCE LISTING (1) GENERAL INFORMATION: (i) APPLICANT: NUSSENZWEIG, VICTOR SCHENKMAN, SERGIO VAN DEN KERKOV, PHILIP EICHINGER, Daniel (ii) TITLE OF INVENTION: TRANS-SIALIDASE AND METHODS OF USE AND MAKING THEREOF (iii) NUMBER OF SEQUENCES: 10 (iv) CORRESPONDENCE ADDRESS: (A) ADDRESSEE: Browdy and Neimark (B) STREET: 419 Seventh Street, N.W., Suite 300 (C) CITY: Washington (D) STATE: D.C. (E) COUNTRY: USA (F) ZIP: 20004 (v) COMPUTER READABLE FORM: (A) MEDIUM TYPE: Floppy disk (B) COMPUTER: IBM PC compatible (C) OPERATING SYSTEM: PC-DOS/MS-DOS (D) SOFTWARE: Patentln Release #1.0, Version #1.25 (vi) CURRENT APPLICATION DATA: (A) APPLICATION NUMBER: US 07/857,519 (B) FILING DATE: 24-MAR-1992 (C) CLASSIFICATION: (viii) ATTORNEY/AGENT INFORMATION: (A) NAME: TOWNSEND, GUY KEVIN (B) REGISTRATION NUMBER: 34,033 (C) REFERENCE/DOCKET NUMBER: NUSSENZWEIG IA (ix) TELECOMMUNICATION INFORMATION: (A) TELEPHONE: 202-628-5197 (B) TELEFAX: 202-737-3528 (C) TELEX: 248633 (2) INFORMATION FOR SEQ ID NO:l: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 33 base pairs (B) TYPE: nucleic acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (ii) MOLECULE TYPE: DNA (genomic) (xi) SEQUENCE DESCRIPTION: SEQ ID NO:i: GACAGCAGTG CCCACAGTAC GCCCTCGACT CCC 33 (2) INFORMATION FOR SEQ ID NO:2: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 24 base pairs (B) TYPE: nucleic acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear SUBSTITUTESHEET (ii) MOLECULE TYPE: DNA (genomic) (xi) SEQUENCE DESCRIPTION: SEQ ID NO:2: TCGGAAGATG ATGGCAAGAC GTGG 24 (2) INFORMATION FOR SEQ ID NO:3: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 500 base pairs (B) TYPE: nucleic acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (ii) MOLECULE TYPE: DNA (genomic) (xi) SEQUENCE DESCRIPTION: SEQ ID NO:3: GCGTCCAACG GGAATCTTGT GTACCCTGTG CAGGTTACGA ACAAAAAGAA GCIAAGTTTTT 60 TCCAAGATCT TCTACTCGGA AGACGAGGGC AAGACGTGGA AGTTTGGGGA GGGTAGGAGT 120 GATTTTGGCT GCTCTGAACC TGTGGCCCTT GAGTGGGAGG GGAAGCTCAT CATAAACACT 180 CGAGTTGACT ATCGCCGCCG TCTGGTGTAC GAGTCCAGTG ACATGGGGAA TTCGTGGGTG 240 GAGGCTGTCG GCACGCTCTC ACGTGTGTGG GGCCCCTCAC CAAAATCGAA CCAGCCCGGC 300 AGTCAGAGCA GCTTCACTGC CGTGACCATC GAGGGAATGC GTGTTATGCT CTTCACACAC 360 CCGCTGAATT TTAAGGGAAG GTGGCTGCGC GACCGACTGA ACCTCTGGCT GACGGATAAC 420 CAGCGCATTT ATAACGTTGG GCAACTATCC ATTGGTGATG AAAATTCCGC CTACAGCTCC 480 GTCCTGTACA AGGATGATAA 500 (2) INFORMATION FOR SEQ ID N0:4: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 166 amino acids (B) TYPE: amino acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (ii) MOLECULE TYPE: peptide (xi) SEQUENCE DESCRIPTION: SEQ ID N0:4: Ala Ser Asn Gly Asn Leu Val Tyr Pro Val Gin Val Thr Asn Lys Lys 1 5 10 15 Lys Gin Val Phe Ser Lys lie Phe Tyr Ser Glu Asp Glu Gly Lys Thr 20 25 30 Trp Lys Phe Gly Glu Gly Arg Ser Asp Phe Gly Cys Ser Glu Pro Val 35 40 45 Ala Leu Glu Trp Glu Gly Lys Leu lie lie Asn Thr Arg Val Asp Tyr 50 55 60 Arg Arg Arg Leu Val Tyr Glu Ser Ser Asp Met Gly Asn Ser Trp Val 65 70 75 80 Glu Ala Val Gly Thr Leu Ser Arg Val Trp Gly Pro Ser Pro Lys Ser SUBSTITUTESHEET 85 90 95 Asn Gin Pro Gly Ser Gin Ser Ser Phe Thr Ala Val Thr He Glu Gly 100 105 110 Met Arg Val Met Leu Phe Thr His Pro Leu Asn Phe Lys Gly Arg Trp 115 120 125 Leu Arg Asp Arg Leu Asn Leu Trp Leu Thr Asp Asn Gin Arg He Tyr 130 135 140 Asn Val Gly Gin Val Ser He Gly Asp Glu Asn Ser Ala Tyr Ser Ser 145 150 155 160 Val Leu Tyr Lys Asp Asp 165 (2) INFORMATION FOR SEQ ID NO:5: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 499 base pairs (B) TYPE: nucleic acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (ii) MOLECULE TYPE: DNA (genomic) (xi) SEQUENCE DESCRIPTION: SEQ ID NO:5: GCGTCCAACG GGAATCTTGT GTACCCTGTG CAGGTTACGA ACAAAAGGAA GCAAGTTTTC 60 TCCAAGATCT TCTACTCGGA AGATGATGGC AAGACGTGGA AGTTTGGGAA GGGTAGGAGC 120 GATTTTGGCT GCTCTGAACC TGTGGCCCTT GAGTGGGAGG GGAAGCTCAT CATAAACACC 180 CGAGTTGACT GGAAACGCCG TCTGGTGTAC GAGTCCAGTG ACATGGAGAA ACCGTGGGTG 240 GAGGCTGTCG GAACCGTCTC GCGTGTGTGG GGCCCCTCAC CAAAATCGAA CCAGCCCGGC 300 AGTCAGACGA GCTTCACTGC CGTGACCATC GAAGGAATGC GTGTGATGCT CTTCACACAC 360 CCGCTGAATT TTAAGGGAAG GTGCGTGCGC GACCGACTGA ACCTCTGGCT GACGGATAAC 420 CAGCGCATTT ATAACGTTGG GCAACTATCC ATTGGTGATG AAAATTCCGC CTACAGCTCC 480 GTCCTTACAA GGATGATAA 499 (2) INFORMATION FOR SEQ ID NO:6: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 500 base pairs (B) TYPE: nucleic acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (ii) MOLECULE TYPE: DNA (genomic) (xi) SEQUENCE DESCRIPTION: SEQ ID NO:6: GCGTCCAACG GGAATCTTGT GTACCCTGTG CAGGTTACGA ACAAAAAGAA GCLAAGTTTTT 60 TCCAAGATCT TCTACTCGGA AGATGATGGC AAGACGTGGA AGTTTGGGGA GGGTAGGAGC 120 GCTTTTGGCT GCTCTGAAGC TGTGGCCCTT GAGTGGGAGG GGAAGCTCAT CATAAACACT 180 CGAGTTGACT ATCGCCGCCG TCTGGTGTAC GAGTCCAGTG ACATGGGGAA TACGTGGCTG 240 GAGGCTGTCG GCACGCTCTC ACGTGTGTGG GGCCCCTCAC CAAAATCGAA CCAGCCCGGC 300 AGTCAGAGCA GCTTCACTGC CGTGACCATC GAGGGAATGC GTGTGATGCT CTTCACACAC 360 CCGCTGAATT TTAAGGGAAG GTGGCTGCGC GACCGACTGA ACCTCTGGCT GACGGATAAC 420 CAGCGCATTT ATAACGTTGG GCAACTATCC ATTGGTGATG AAAATTCCGC CCACAGCTCC 480 GTCCTGTACA AGGATGATAA 500 (2) INFORMATION FOR SEQ ID NO:7: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 500 base pairs (B) TYPE: nucleic acid (C) STRANDEDNESS: εingle (D) TOPOLOGY: linear (ii) MOLECULE TYPE: DNA (genomic) (xi) SEQUENCE DESCRIPTION: SEQ ID NO:7: GCGTCCAACG GGAATCTTGT GTACCCTGTG CAGGTTACGA ACAAAAAGAA GCAAGTTTTT 60 TCCAAGATCT TCTACTCGGA AGACGAGGGC AAGACGTGGA AGTTTGGGGA GGGTAGGAGT 120 GATTTTGGCT GCTCTGAACC TGTGGCCCTT GAGTGGGAGG GGAAGCTCAT CATAAACACT 180 CGAGTTGACT ATCGCCGCCG TCTGGTGTAC GAGTCCAGTG ACATGGGGAA TTCGTGGGTG 240 GAGGCTGTCG GCACGCTCTC ACGTGTGTGG GGCCCCTCAC CAAAATCGAA CCAGCCCGGC 300 AGTCAGAGCA GCTTCACTGC CGTGACCATC GAGGGAATGC GTGTTATGCT CTTCACACAC 360 CCGCTGAATT TTAAGGGAAG GTGGCTGCGC GACCGACTGA ACCTCTGGCT GACGGATAAC 420 CAGCGCATTT ATAACGTTGG GCAACTATCC ATTGGTGATG AAAATTCCGC CTACAGCTCC 480 GTCCTGTACA AGGATGATAA 500 (2) INFORMATION FOR SEQ ID NO:8: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 166 amino acids (B) TYPE: amino acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (ii) MOLECULE TYPE: peptide (xi) SEQUENCE DESCRIPTION: SEQ ID NO:8: Ala Ser Asn Gly Asn Leu Val Tyr Pro Val Gin Val Thr Asn Lys Arg 1 5 10 15 Lys Gin Val Phe Ser Lys He Phe Tyr Ser Glu Asp Asp Gly Lys Thr 20 25 30 Trp Lys Phe Gly Lys Gly Arg Ser Asp Phe Gly Cys Ser Glu Pro Val 35 40 45 Ala Leu Glu Trp Glu Gly Lys Leu He He Asn Thr Arg Val Asp Trp 50 55 60 Lys Arg Arg Leu Val Tyr Glu Ser Ser Asp Met Glu Lys Pro Trp Val 65 70 75 80 Glu Ala Val Gly Thr Val Ser Arg Val Trp Gly Pro Ser Pro Lys Ser 85 90 95 Asn Gin Pro Gly Ser Gin Thr Ser Phe Thr Ala Val Thr He Glu Gly 100 105 110 Met Arg Val Met Leu Phe Thr His Pro Leu Asn Phe Lys Gly Arg Cys 115 120 125 Val Arg Asp Arg Leu Asn Leu Trp Leu Thr Asp Asn Gin Arg He Tyr 130 135 140 Asn Val Gly Gin Val Ser He Gly Asp Glu Asn Ser Ala Tyr Ser Ser 145 150 155 160 Val Leu Tyr Lys Asp Asp 165 (2) INFORMATION FOR SEQ ID NO:9: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 166 amino acids (B) TYPE: amino acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (ii) MOLECULE TYPE: peptide (xi) SEQUENCE DESCRIPTION: SEQ ID NO:9: Ala Ser Asn Gly Asn Leu Val Tyr Pro Val Gin Val Thr Asn Lys Lys 1 5 10 15 Lys Gin Val Phe Ser Lys He Phe Tyr Ser Glu Asp Asp Gly Lys Thr 20 25 30 Trp Lys Phe Gly Glu Gly Arg Ser Ala Phe Gly Cys Ser Glu Arg Val 35 40 45 Ala Leu Glu Trp Glu Gly Lys Leu He He Asn Thr Arg Val Asp Tyr 50 55 60 Arg Arg Arg Leu Val Tyr Glu Ser Ser Asp Met Gly Asn Thr Trp Leu 65 70 75 80 Glu Ala Val Gly Thr Leu Ser Arg Val Trp Gly Pro Ser Pro Lys Ser 85 90 95 Asn Gin Pro Gly Ser Gin Ser Ser Phe Thr Ala Val Thr He Glu Gly 100 105 110 Met Arg Val Met Leu Phe Thr His Pro Leu Asn Phe Lys Gly Arg Trp 115 120 125 Leu Arg Asp Arg Leu Asn Leu Trp Leu Thr Asp Asn Gin Arg He Tyr 130 135 140 Asn Val Gly Gin Val Ser He Gly Asp Glu Asn Ser Ala His Ser Ser 145 150 155 160 Val Leu Tyr Lys Asp Asp 165 (2) INFORMATION FOR SEQ ID NO:10: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 166 amino acids (B) TYPE: amino acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (ii) MOLECULE TYPE: peptide (xi) SEQUENCE DESCRIPTION: SEQ ID NO:10: Ala Ser Asn Gly Asn Leu Val Tyr Pro Val Gin Val Thr Asn Lys Lys 1 5 10 15 Lys Gin Val Phe Ser Lys He Phe Tyr Ser Glu Asp Glu Gly Lys Thr 20 25 30 Trp Lys Phe Gly Glu Gly Arg Ser Asp Phe Gly Cys Ser Glu Pro Val 35 40 45 Ala Leu Glu Trp Glu Gly Lys Leu He He Asn Thr Arg Val Asp Tyr 50 55 60 Arg Arg Arg Leu Val Tyr Glu Ser Ser Asp Met Gly Asn Ser Trp Val 65 70 75 80 Glu Ala Val Gly Thr Leu Ser Arg Val Trp Gly Pro Ser Pro Lys Ser 85 90 95 Asn Gin Pro Gly Ser Gin Ser Ser Phe Thr Ala Val Thr He Glu Gly 100 105 110 Met Arg Val Met Leu Phe Thr His Pro Leu Asn Phe Lys Gly Arg Trp 115 120 125 Leu Arg Asp Arg Leu Asn Leu Trp Leu Thr Asp Asn Gin Arg He Tyr 130 135 140 Asn Val Gly Gin Val Ser He Gly Asp Glu Asn Ser Ala Tyr Ser Ser 145 150 155 160 Val Leu Tyr Lys Asp Asp 165

Claims: WHAT IS CLAIMED IS; 1. A method for transferring sialic acid from a terminal α2-»3 linked donor glycoconjugate to a carbohydrate acceptor glycoconjugate, comprising reacting a trans-sialidase polypeptide capable of transferring sialic acid from a terminal α2-»3 linked donor glycoconjugate to a carbohydrate acceptor glycoconjugate with said sialic acid donor to transfer said sialic acid from said donor to said acceptor. 2. A method according to claim 1, wherein said acceptor glycoconjugate comprises an acceptor terminal group Galβl→z-R 1 or wherein z is 3, 4 or 6 and R 1 is selected from glucose, fructose, gluconic acid, mannose, methoxygalactose, methoxyglucose, N-acetyl galactose, N-acetyl glucose, or arabinose. 3. A method according to claim 1, wherein said acceptor conjugate further comprises a member selected from a monosaccharide, a disaccharide, an oligosaccharide, a glycoprotein or a glycolipid, and wherein said acceptor glycoconjugate in soluble form or is associated with a cell membrane or a liposome. 4. A method according to claim 2, wherein said acceptor terminal group is selected from (S-D-Gall→3jS-D- GalNAc-, S-D-Gall→4jS-D-GalNAc-, /3-D-Glcl->3β-D-GalNAc, jβ-D- Glcl→4|8-D-GalNAc-, /S-D-Gall->3j3-D-GlcNAc- , jβ-D-Gall→4/3-D- GlcNAc, jS-D-Glcl→33-D-GlcNAc- or /?-D-Glcl-»4j5-D-GlcNAc. 5. A method according to claim 1, wherein said donor glycoconjugate is selected from a terminal NeuNAcα2-»3Gal- or NeuNAcα2→3Glc-containing donor glycoconjugate. 6. A method according to claim 3, wherein said donor glycoconjugate sialic acid donor comprises a donor terminal group NeuNAcα2→3Gal/?l→z-R 1 or NeuNAcα2→3Glc / 3l→z-R * , wherein z is 3, 4 or 6 and wherein R 1 is selected from glucose, fructose, gluconic acid, mannose, methoxygalactose, methoxyglucose, N-acetyl galactose, N-acetyl glucose, or arabinose. 7. A method according to claim l, wherein said donor glycoconjugate further comprises a member selected from a monosaccharide, a disaccharide, an oligosaccharide, a glycoprotein or a glycolipid. 8. A method according to claim 5, wherein R 1 further comprises a fucosyl side chain, wherein said fucosyl side chain is optionally added to said acceptor glycoconjugate after said transfer of said sialic acid to said acceptor. 9. A method according to claim 1, wherein said acceptor glycoconjugate is a Lewis type antigen. 10. A method according to claim 5, wherein said terminal NeuNAcα2→3Gal- or NeuNAcα2-»3Glc- comprises a C9 deoxy or methoxy. 11. A trans-sialidase according to claim 1, comprising a transialidase polypeptide derivable from a trypomastigote of the genus Trypanosoma. 12. A trans-sialidase according to claim 1, wherein said trypomastigote is selected from Trypanosoma cruzi or Trypanosoma brucei . 13. A transialidase polypeptide according to claim 2, wherein said trypomastigote is of the species Trypanosoma cruzi . 14. A transialidase polypeptide according to claim 2, wherein said trypomastigote is of the species Trypεinosoma brucei . 15. A trans-sialidase polypeptide according to claim 1, comprising a peptide having an amino acid sequence substantially corresponding to the amino acid sequence of Figure 18 (SEQ ID NO:2) . 16. A trans-sialidase polypeptide according to claim 5, comprising the amino acid sequence of Figure 18 (SEQ ID N0:2) . 17. A trans-sialidase polypeptide according to claim 1, wherein an acceptor glycoconjugate for said polypeptide comprises an acceptor terminal group Galβl→z-R 1 or Glcβl→z-R 1 , wherein z is 3, 4 or 6 and R 1 is selected from glucose, fructose, gluconic acid, mannose, methoxygalactose, methoxyglucose, N-acetyl galactose, N-acetyl glucose, or arabinose. 18. A trans-sialidase polypeptide according to claim 7, wherein said acceptor glycoconjugate further comprises a member selected from a monosaccharide, a disaccharide, an oligosaccharide, a glycoprotein or a glycolipid, and wherein said acceptor glycoconjugate in soluble form or is associated with a cell membrane or a liposome. 19. A trans-sialidase polypeptide according to claim 1, wherein a sialic acid donor for said polypeptide is selected from a terminal NeuNAcα2→3Gal- or NeuNAcα2→3Glc- containing donor glycoconjugate. 20. A trans-sialidase polypeptide according to claim 9, wherein said donor glycoconjugate comprises a donor terminal group NeuNAcα2-»3Galj8l→z-R 1 or NeuNAcα2→3Glc?l-»z-R 1 , wherein z is 3, 4 or 6 and wherein R 1 is selected from glucose, fructose, gluconic acid, mannose, methoxygalactose, methoxyglucose, N-acetyl galactose, N-acetyl glucose, or arabinose. 21. A trans-sialidase polypeptide according to claim 10, wherein said donor glycoconjugate further comprises a member selected from a monosaccharide, a disaccharide, an oligosaccharide, a glycoprotein or a glycolipid. 22. A trans-sialidase according to claim 1, wherein said polypeptide has trans-sialidase activity and is less than 100% homologous to the TCNA amino acid sequence of Figure 23A (SEQ ID NO:6) . 23. A nucleic acid consisting essentially of a nucleotide sequence encoding a trans-sialidase polypeptide according to claim 1. 24. A nucleic acid according to claim 11 which is an expression vehicle. 25. A host transformed or transfected with a nucleic acid according to claim 11. 26. A host according to claim 13, wherein said host is a bacterium or a eukaryote. 27. A host cell according to claim 14, wherein said host is a mammalian cell. 28. A process for purifying a trans-sialidase polypeptide according to claim 1 from a biological sample, comprising (a) treating the biological sample containing said trans-sialidase in a manner which releases said trans-sialidase polypeptide into solution; (b) removing insoluble material from said solution to yield a supernatant containing said trans-sialidase polypeptide; (c) performing lectin affinity chromatography of said supernatant obtained in step (b) to yield a first eluate; (d) performing anion exchange chromatography of said first eluate, yielding a second eluate, said second eluate comprising said trans-sialidase polypeptide in a form not found in nature. 29. A process according to claim 20, wherein: (i) said biological sample comprises a Trypanosoma trypomastigote or an extract thereof, and said treating comprises lysis in the presence of one or more proteinase inhibitors; (ii) said removing is by centrifugation for 10 minutes at 10,000 x g; (iii) said lectin affinity chromatography is performed with a concanavalin A-sepharose column and said first eluate is eluted with about 0.5 M α-methylmannoside; (iv) said anion exchange chromatography is performed with a FPLC Mono Q (HR5/5) column and said fourth second is eluted with a NaCl gradient. 30. A process for preparing a trans-sialidase polypeptide according to claim 1, comprising (a) culturing a host capable of expressing the DNA molecule of claim 13 under culturing conditions, such that said polypeptide is expressed by said host in recoverable amounts; (b) recovering said trans-sialidase polypeptide from said host or culture. 31. A method for assaying a trans-sialidase polypeptide according to claim 1, said method comprising (a) incubating a reaction mixture comprising said polypeptide, a sialic acid donor which is not a sugar nucleotide, and a labeled sialic acid acceptor glycoconjugate under conditions sufficient to permit transfer of sialic acid from said donor to said acceptor, yielding a labeled reaction product; (b) subjecting said reaction mixture to anion exchange chromatography and eluting said labeled reaction product; and (d) identifying said reaction product as indicative of the presence of said polypeptide having trans-sialidase activity. 32. A method according to claim 26, wherein said incubating is for 30 minutes at 37°C, said chromatography of step (c) is with a QAE-Sephadex A50 column, said elution is with 1 M ammonium formate. 33. A method according to claim 26, wherein said identifying is performed by silica gel thin-layer chromatography, followed by autoradiography compared to known standards. 34. An antibody comprising an antigen binding region capable of specifically binding a trans-sialidase polypeptide according to claim 1. 35. An antibody according to claim 32, wherein said antibody is monoclonal. 36. An antibody according to claim 32, wherein said antibody inhibits the trans-sialidase activity of said trans-sialidase polypeptide. 37. A method for treating a subject infected with a trypomastigote of the genus Trypanosoma, comprising administering to said subject an effective amount of a therapeutic agent capable of providing inhibition of the activity of a trans-sialidase polypeptide according to claim 1. 38. A method according to claim 32, wherein said method comprises vaccination of the subject with said therapeutic amount of said therapeutic agent, said therapeutic agent comprising a trans-sialidase polypeptide derived from a trypomastigote transialidase, binding fragment or region of a anti-idiotype antibody thereto, in an amount effective to induce in said subject an antibody specific for the transialidase enzyme. 39. A method according to claim 35, wherein said agent is an antibody specific for said trans-sialidase polypeptide or binding fragment of said antibody. 40. A method for detecting the presence in a biological sample of a trans-sialidase polypeptide obtainable from the membrane of Trypanosoiπa trypomastigotes, said trans- sialidase polypeptide having the property of catalyzing the transfer of sialic acid from a donor substrate containing an α(2→3) -linked terminal sialic acid residue to a carbohydrate acceptor substrate to yield a sialyl (α2→3) -linked product, said method comprising: (a) contacting said biological sample that is suspected of containing said trans-sialidase polypeptide with a binding molecule capable of binding to said transialidase polypeptide; and (b) detecting any of said molecule bound to said transialidase polypeptide. 41. A method according to claim 38, wherein said binding molecule is an antibody specific for said trans- sialidase polypeptide or a trans-sialidase polypeptide-binding fragment of said antibody. 42. A method according to claim 38, wherein said antibody is a monoclonal antibody

Inventors: EICHINGER DAN, NUSSENZWEIG VICTOR, SCHENKMAN SERGIO, VANDEKERCKHOVE FLIP, EICHINGER, DAN, NUSSENZWEIG, VICTOR, SCHENKMAN, SERGIO, VANDEKERCKHOVE, FLIP
Applicants: UNIV NEW YORK, NEW YORK UNIVERSITY
Application year: 1993
Main classification: C12Q1
IPC codes: A61K39, C07H3, C07H13, C07H15, C07K16, C12N9, C12N15, C12P19, C12P21