Determination of glycosyl-phosphatidylinositol membrane protein anchorage

A diverse range of proteins are modified by the post-translational covalent attachment of a glycosyl-phosphatidylinositol (GPI) membrane anchor. Hydro pathy plots and other computer algorithms can be used to predict the presen ce of a GPI anchor attachment signal in the nascent polypeptide chain. Howe ver, the presence of a GPI anchor on the mature protein requires experiment al evidence, including sensitivity of the protein to release from cells or membranes with bacterial phosphatidylinositol-specific phospholipase C, rec ognition by anti-cross-reacting determinant antibodies, or metabolic labell ing with components of the anchor. GPI-anchored proteins are resistant to s olubilisation with detergents such as Triton X-100 due to their association with cholesterol and glycosphingolipids in membrane domains known as lipid rafts. This detergent insolubility can be used to provide evidence for the presence of a GPI anchor on a protein and to isolate lipid rafts.