Phosphatidylinositol Glycan G (PIGG)

Many eukaryotic cell surface proteins are anchored to the membrane via glycosylphosphatidylinositol (GPI). GPI is synthesized from phosphatidylinositol by stepwise reactions and attached en bloc to nascent proteins.Yeast GPI7 is involved in the transfer of EtNP to the second mannose, but the corresponding mammalian enzyme has not yet been clarified. The human homolog of Gpi7p (hGPI7) forms a protein complex with PIG-F and is involved in the H7-to-H8 conversion. hGPI7 was associated with and stabilized by PIG-F, which is known to bind to and stabilize PIG-O, a protein homologous to hGPI7. PIG-O is a transferase that adds EtNP to the third mannose, rendering GPI capable of attaching to proteins. The overexpression of hGPI7 decreased the level of PIG-O and, therefore, decreased the level of EtNP transferred to the third mannose.