Platelet Glycoprotein Ibβ/IX Mediates Glycoprotein Ibα Localization to Membrane Lipid Domain Critical for von Willebrand Factor Interaction at High Shear

The localization of the platelet glycoprotein GP Ib-IX complex (GP Ib alpha, GP Ib beta, and GP IX) to membrane lipid domain, also known as glycosphingolipid-enriched membranes (GEMs or raft) lipid domain, is essential for the GP Ib-IX complex mediated platelet adhesion to von Willebrand factor (vWf) and subsequent platelet activation. To date, the mechanism for the complex association with the GEMs remains unclear. Although the palmitate modifications of GP Ib beta and GP IX were thought to be critical for the complex presence in the GEMs, we found that the removal of the putative palmitoylation sites of GP Ib beta and GP IX had no effects on the localization of the GP Ib-IX complex to the GEMs. Instead, the disruption of GP Ib alpha disulfide linkage with GP Ib beta markedly decreased the amount of the GEM-associated GP Ib alpha without altering the GEM association of GP Ib beta and GP IX. Furthermore, partial dissociation with the GEMs greatly inhibited GP Ib alpha interaction with vWf at high shear instead of in static condition or under low shear stress. Thus, for the first time, we demonstrated that GP Ib beta/GP IX mediates the disulfide-linked GP Ib alpha localization to the GEMs, which is critical for vWf interaction at high shear.