Sialic acids are found in a diverse group of oligosaccharides attached to glycoproteins and glycolipids. At least ten sialyltransferases are required to account for the biosynthesis of the variety of structures observed. Five sialyltransferases have been purified to homogeneity by the applicant and collaborators and each has a strict acceptor specificity which limits its transfer of sialic acid from CMP-sialic acid to produce a sialyloligosaccharide of defined sequence. The unique specificity of these enzymes make them ideal reagents to modify oligosaccharides of glycoproteins and glycolipids. A number of biological processes are mediated by recognition of oligosaccharides that contain essential sialic acid residues. To date, purified sialyltransferases have been instramental in understanding the molecular basis for the inactivation of a hepatic binding protein by neuraminidase, the expression of the human M and N blood group antigens, and in the demonstration that influenza and other animal viruses recognize cell surface sialyloligosaccharides of defined sequence as receptor determinants. In the proposed research three additional sialyltransferases, that synthesize the terminal GalBeta1yield3(NeuAcAlpha2yield6)G1cNAc-sequence on asparagine-linked oligosaccharides of glycoproteins and the NeuAcAlpha2yield8NeuAcAlpha2yield3Gal- and NeuAcAlpha2yield3GalBeta1yield4Glc-cermide sequences on gangliosides, will be purified to homogeneity. Enzymes will be purified by affinity chromatography on CDP-hexanolanine agarose, a donor substrate analog and on adsorbants containing their acceptor substrates. The substrate specificity and enzymatic properties of each sialyltransferase will be characterized and compared to those of other purified sialyltransferases to establish its role in the biosynthesis of glycoprotein and glycolipid oligosaccharides, and to determine its suitability to serve as a specific reagent to examine the biological roles of the sialic acids.
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