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.