fig2

Figure 2. GPI anchor biosynthesis in the ER. Steps for GPI anchor biosynthesis and protein anchoring are shown^[44]. UDP denotes uracil diphosphate, PE denotes phosphatidylethanolamine, signal peptide denotes an N-terminal signal peptide that is not required for GPI anchorage, and GPI-SS denotes the GPI signal sequence that may be associated with the membrane before cleavage^[45,46]. Step 3 involves an unknown mechanism that allows for the movement of the phosphatidylinositol to the luminal side of the ER. Step 4 involves the addition of a fatty acid chain, while Step 5 involves lipid remodeling. Step 13 involves the cleavage of the GPI-SS and the addition of the protein onto the preassembled GPI anchor. The anchor is further modified and is released from a COPII-coated vesicle for trafficking to the Golgi.