Delineation of the region in the glycoprotein VI tail required for association with the Fc receptor γ-chain

Abstract

The glycoprotein VI (GPVI)·Fc receptor γ-chain (FcR γ-chain) complex is the major activation receptor for collagen on platelets. GPVI cross-linking mediates activation through tyrosine phosphorylation of an ITAM (immunoreceptor tyrosine-based activation motif) in the FcR γ-chain by Src family kinases. It has been previously shown that a transmembrane arginine and the cytoplasmic domain of GPVI are required for association with the FcR γ-chain in immortalized cell lines. In this study, we have delineated the regions in the GPVI tail that promote binding to FcR γ-chain and mediate functional responses to the snake venom convulxin by reconstitution of mutant forms of GPVI in RBL-2H3 cells. Sequential truncation of the cytoplasmic tail of GPVI revealed a major role for the basic region and a minor role for the juxtamembrane six amino acids in the association with FcR γ-chain and functional responses to convulxin. Analysis of selective deletions in the GPVI tail supported this conclusion. In addition, we show that the proline-rich domain is required for optimal Ca 2+ release, whereas it is dispensable for FcR γ-chain association.