Figure 1. Classical glycosylation types found on mammalian proteins.

This figure depicts common N-linked and O-linked glycoprotein structures as well as terminal Lewis antigens structures. The key glycosyltransferases responsible for the addition of specific glycans are also indicated. Secreted and membrane-bound glycoproteins exhibit N-glycans with β-GlcNAc linked to Asn as oligomannose, complex or hybrid forms. O-glycans are linked through α-GalNAc to Ser/Thr with various core structures and extensions. Terminal structures of N-linked and O-linked glycans are often sialylated and fucosylated to generate Lewis-type antigen glycosylation. Single β-O-GlcNAc is found on many cytosolic, nuclear and mitochondrial proteins.