2.3 History and current status of C-GlcNAc and other glycosylation in China
C-glycosylation refers to the process by which a molecule of mannose group is connected to the C-2 position of the tryptophan indole ring through a C-C bond to modify the protein. This glycosylation mostly occurs on the first tryptophan residue of the W-X-X-W-W-X-X-C or W-X-X-F sequence[19]. This glycosylation is rare in living organisms.
Glycosylphosphatidylinositol, the fifth type of sugar chain, is the only way for proteins to bind to the cell membrane. Unlike general lipid modification components, its structure is extremely complex. Many cell receptors, differentiation antigens and some biologically active proteins have been shown to bind to cell membranes through glycosylphosphatidylinositol (GPI) structure. The core structure of GPI is composed of ethanolamine phosphate, three mannosides, glucosamine, and cellolipids. The C-terminus of the anchoring protein is bridged to the core glycan by ethanolamine phosphate, which is highly conserved. At the same time, another phospholipid structure connects the GPI anchor to the cell membrane. The core glycan formed by C-glycosylation can be modified by a variety of side chains, such as ethanolamine anchored groups, mannose, galactose, sialic acid or other sugar groups.