MOD_N-GLC_1

N-glycosylation is the most common modification of secretory and membrane-bound proteins in eukaryotic cells. The whole process of N-glycosylation comprises more than 100 enzymes and transport proteins. The biosynthesis of all N-linked oligosaccharides begins in the ER with a large precursor oligosaccharid. The structure of this oligosaccharide [(Glc)3(Man)9(GlcNAc)2] is the same in plants, animals, and single cell eukaryotes. This precursor is linked to a dolichol, a long-chain polyisoprenoid lipid that act as a carrier for the oligosaccharide. The oligosaccharide is then transferred by an ER enzyme from the dodichol carrier to an asparagine residue on a nascent protein. The oligosaccharide chain is then processed as the glycoprotein moves through the Golgi apparatus. In some cases this modification involves attachment of more mannose groups, in other cases a more complex type of structure is attached.