CELL SIGNALING BY GLYCOSYL-PHOSPHATIDYLIN OSITOL ANCHORED PROTEINS

Recently a novel mechanism has been described for the hydrophobic atta chment of proteins to membranes which is shared by membrane proteins o f widely differing origins and functions. The hydrophobic anchor is a glycosyl-phosphatidylinositol (GPI) which is covalently attached to th e polypeptide chain. GPI-anchored proteins have been reported to resid e in clusters collected over small membrane invaginations called caveo lae. GPI-anchored proteins constitute an exceptionally diverse family of membrane molecules functioning in such processes as nutrient uptake , cell adhesion, catalysis, and membrane signalling events. A growing body of biochemical evidence indicates that they play a key role in th e recently discovered potocytosis process, act as intracellular sortin g signals, cause activation of Src-family kinase-mediated signalling p athways. Their hydrolysis, yielding inositolphosphoglycans and diacylg lycerol, is one of the earliest intracellular events generated in resp onse to growth factors, insulin or lipoproteins.