N-Glycans

Excerpt

N-glycans are covalently attached to protein at asparagine (Asn) residues by an N-glycosidic bond. Five different N-glycan linkages have been reported, of which N-acetylglucosamine to asparagine (GlcNAcβ1-Asn) is the most common. This chapter describes only the GlcNAcβ1-Asn N-glycans, their general structure, the steps in their synthesis and processing, and the origins of their structural diversity. Terminal sugars that determine much of the diversity of N-glycans are referred to only briefly because they are described in detail in Chapter 13. Similarly, a discussion of glycosylation-mediated quality control of protein folding is reserved for Chapter 36, and the synthesis of the mannose-6-phosphate (Man-6-P) recognition determinant necessary for targeting lysosomal hydrolases to lysosomes is described in Chapter 30. Congenital disorders of glycosylation that arise from defects in N-glycan synthesis are discussed in Chapter 42.