DIFFERENTIAL REGULATION OF SRC-FAMILY PROTEIN-TYROSINE KINASES IN GPIDOMAINS OF T-LYMPHOCYTE PLASMA-MEMBRANES

The association of glycosylphosphatidylinositol (GPI)-anchored cell su rface glycoproteins with Src-family protein tyrosine kinases was analy sed in intact T lymphocyte plasma membranes. Following subcellular fra ctionation without detergent, 25% of the recovered plasma membranes we re light density vesicles enriched in GPI-anchored glycoproteins and s phingolipids (GPI domains), while the remainder behaved as heavier den sity vesicles containing equal amounts of lipids and proteins. Qualita tively similar lipids were found in both vesicle types, but only light density vesicles made of 65-75% lipids yielded a Triton X-100 resista nt, sedimentable fraction containing GPI-linked glycoproteins and sphi ngolipids. The GPI-rich vesicles phosphotyrosylated an exogenous subst rate as efficiently as the denser vesicles, despite a low Lck and Fyn kinase content. Likewise, these kinases were more efficiently phosphor ylated in GPI domains than in denser vesicles. GPI domains thus could constitute plasma membrane ''hot spots'' where associated Src kinases assume an optimally active conformation that contributes to signaling via GPI-anchored cell surface glycoproteins. (C) 1996 Academic Press, Inc.