Solubilization and Characterization of ß-Mannosyltransferase from Pig Aorta

Glycosyltransferase in general play a very important role in the post-translational modification of number of biomolecules including glycoproteins. The glycosylation of the protein occurs in the endoplasmic reticulum and is carried out by at least 14 different types of membrane bound glycosyltransferases. It is now well established that glycosylation of protein occurs either at serine or threonine residues (O-glycosylation) or at asparagine residue (N-glycosylation) of proteins. To date there is no definite demonstration of the presence of O-mannosylation of proteins in higher eukaryotes. However, it is a common feature in yeast and other fungal strain, indicating that glycosyltransferases are species-specific as well as tissue-specific. In higher eukaryotes the Nglycosylation is the major post translational process, initiated by the synthesis of a large lipid oligosaccharide, Glc3-Man9-GlcNAc2-PP-Dolichol. This represents the immediate precursor of carbohydrate unit involved in the biosynthesis of glycoproteins. The large oligosaccharide is then transferred from the lipid oligosaccharide to the acceptor lipid by the oligosaccharide transferase. ß-Mannosyltransferase is the key enzyme of the dolichol pathway that catalyzes the transfer of mannose to the chitobiose lipid (GlcNAc2-PP-Dol), acceptor substrate from GDP-mannose. This enzyme has been purified to near homogeneity and characterized from pig aorta tissue, using different chromatography techniques, and studying its properties.