32] Covalent attachment of oligosaccharide-asparagine derivatives: Incorporation into glutamine residues with the enzyme transglutaminase

Abstract

Publisher Summary It is difficult to study the biological functions of oligosaccharide with naturally occurring glycoproteins because of the high degree of heterogeneity of the oligosaccharides in a glycoprotein. To remedy this problem, one approach is to prepare synthetic glycoprotein (neoglycoprotein) with a specific number of homogeneous oligosaccharides in specific positions on the polypeptide backbone. To accomplish this chemically is a monumental task, because it is difficult to control the extent and sites of reaction in chemical modification of proteins. The reaction specificity required to prepare the desired neoglycoprotein, however, fits the descriptions of the very nature of enzymatic reactions. This chapter describes the use of an enzyme, guinea pig liver transglutaminase (protein-glutamine γ-glutamyltransferase), to prepare neoglycoproteins. Using transglutaminase to prepare neoglycoprotein has one distinct drawback. As the lysine side chains of the protein acceptor must be blocked, the protein is at least partially denatured. Therefore, neoglycoproteins prepared by this method cannot be used as models to study the information encoded in the topological arrangement of the oligosaccharides.