Biosynthesis of Glycoproteins

Vijay, Inder

Abstract

Glycoproteins participate in a wide spectrum of biological recognition phenomena. Pathological states, e.g., malignancy, atherosclerosis and many autosomal recessive disorders are accompanied with marked alterations in glycoprotein metabolism. The largest class of glycoproteins is the asparagine-linked type with well conserved carbohydrate side chains. The biosynthesis of these proteins involves a stepwise, lipid-linked assembly of a tetradecasaccharide, Glc3Man9(GlcNAc)2, its en bloc transfer to the nascent polypeptides in the RER and a series of postranslational modifications of the sugar residues, in both RER and the Golgi. Previous work from our laboratory has established structural details of the stepwise lipid-linked assembly of the oligosaccharide unit in the lactating bovine mammary tissue. In the proposed plan, the enzymology of a number of steps in the microsomes of the lactating bovine mammary tissue would be investigated. Initial studies on the hormonal regulation of lipid-linked assembly and transfer reactions in an in vitro mammogenesis-lactogenesis model of the rat mammary tissue would be investigated. Recently, some interesting features of glycoprotein biosynthesis in protozoa have been described. A brief investigation related to glycoprotein biosynthesis in the protozoan Crithidia fasciculata will be undertaken. Finally, isolation and characterization of a novel Alpha1,3-mannosidase secreted by a soil microorganism will be attempted. The availability of such an enzyme would be invaluable for conducting biosynthetic and structural studies on mannosyloligosaccharides and glycoproteins since this is the only missing enzyme among the battery of biochemical tools currently used for such studies.