Phosphatidylinositol-glycan biosynthesis class S protein
PIG-S is one of several key, core, components of the glycosylphosphatidylinositol (GPI) trans-amidase complex that mediates GPI anchoring in the endoplasmic reticulum. Anchoring occurs when a protein's C-terminal GPI attachment signal peptide is replaced with a pre-assembled GPI. Mammalian GPITransamidase consists of at least five components: Gaa1, Gpi8, PIG-S, PIG-T, and PIG-U, all five of which are required for function. It is possible that Gaa1, Gpi8, PIG-S, and PIG-T form a tightly associated core that is only weakly associated with PIG-U. The exact function of PIG-S is unclear.