Glycosyltransferases involved in elongation of N-glycosidically linked oligosaccharides of the complex or N-acetyllactosamine type.

Abstract

This chapter discusses the glycosyltransferases that carry out the elongation of complex N-glycosyl oligosaccharides. Glycoproteins contain high-mannose oligosaccharides, complex oligosaccharides, or both. The (Man)5(GlcNAc)2-Asn intermediate is the starting point for all complex N-glycosyl oligosaccharides. A series of Golgi apparatus-localized glycosyltransferases and α-mannosidases act on this compound to produce several classes of complex structures. The key enzyme in the initiation of complex oligosaccharide synthesis is called UDP-GlcNAc: α-D-mannoside βl-2-N-acetylglucosaminyltransferase I (GlcNAc-transferase I). GlcNAc-transferase I adds a GlcNAc in βl-2 linkage to the Man-αl-3 arm o..