The core Gpi (glycophosphatidylinositol) structure is synthesized on the lumenal face of the ER from phosphatidylinisitol (PI), UDP-GlcNAc, Dol-P-mannose and phosphoethanolamine. This core is modified due to addition of different sugar residues. It depends on the species and the protein to which it is attached.
Target protein becomes anchored to the membrane surface when the amine group of GPI-phosphoethaholamine nucleophically attacks a specific amino-acyl groups of the protein near its C-terminus. It occurs in the ER. Then the anchored proteins move to the Golgi. Finally they are directed to the exterior surface of the plasma membrane (GPI acts as a targeting signal).
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Biosynthesis of glycoproteins
Role of glycoproteins