Chapter 7 Synthesis and Processing of Asparagine-Linked Oligosaccharides of Glycoproteins

Abstract

Publisher Summary This chapter discusses three stages in the synthesis of asparagine-linked carbohydrates: (1) synthesis of the large lipid-linked oligosaccharide, (2) glycosylation of asparagine residues by the transfer of oligosaccharide from lipid to protein, and (3) processing of protein-linked oligosaccharides to yield mature high-mannose and complex glycopeptides. The asparagine-linked oligosaccharides of cell surface and extracellular glycoproteins are a heterogeneous class of molecules that can be divided in two basic types. High-mannose structures have a Man 2 GlcNAc 2 inner core at the reducing end and two to six additional mannose residues in a peripheral three-branched structure. Complex oligosaccharides also have a Man 3 GlcNAc 2 inner core and in addition contain a fucose residue and two to four terminal trisaccharide branches containing N -acetylglucosamine, galactose, and sialic acid. Both types of oligosaccharides show microheterogeneity; a number of related structures are usually found in a single purified glycoprotein preparation. The number of mannose residues in high-mannose oligosaccharides is variable, whereas complex oligosaccharides show variability in sialic acid and fucose content.