Figure 2.

N-glycan biosynthesis. Overview of the N-glycan biosynthesis pathways in the cell and in circulation as also occurs for immunoglobulin G glycosylation (4). In the left panel, the different cell compartments are illustrated with the different steps of synthesis indicated: 1. synthesis of lipid-linked precursor oligosaccharide, 2. En Bloc transfer to protein, 3. processing; 3a. initial trimming of sugar residues, 3b. trimming and modification of branch structure, 3c. addition of terminal sugar residues. In the right panel, the different involved glycosidases and glycosyltransferases listed at the position in the endoplasmic reticulum and Golgi apparatus where they proposed to be expressed. Extracellularly, glycosyltransferases and glycosidases are present in circulation, mainly editing the terminal sialic acid groups on glycans.