The organizing principle of the platelet glycoprotein IbIXV complex

The glycoprotein (GP)IbIXV complex is the platelet receptor for von Willebrand factor and many other molecules that are critically involved in hemostasis and thrombosis. The lack of functional GPIbIXV complexes on the platelet surface is the cause of BernardSoulier syndrome, a rare hereditary bleeding disorder that is also associated with macrothrombocytopenia. GPIbIXV contains GPIb, GPIb, GPIX and GPV subunits, all of which are typeI transmembrane proteins containing leucine-rich repeat domains. Although all of the subunits were identified decades ago, not until recently did the mechanism of complex assembly begin to emerge from a systematic characterization of inter-subunit interactions. This review summarizes the forces driving the assembly of GPIbIXV, discusses their implications for the pathogenesis of BernardSoulier syndrome, and identifies questions that remain about the structure and organization of GPIbIXV.