Interactions of ligands with endothelial cell receptors. This figure shows a putative scheme of the interaction between vβ3 and GPIb complex with vWF, vitronectin, and alboaggregins. The GPIb complex is composed of seven molecules. One molecule of GPV is flanked symmetrically by two molecules of GPIX, GPIb, and GPIbβ. vWF interaction with vβ3, mediated by the C1 domain, is inhibited by echistatin and MoAbs LJ1b and SZ2. Botrocetin alters the conformation of the A1 domain of vWF so that it can interact with GPIb complex. This interaction can be blocked by echicetin and by anti-GPIb MoAbs LJIb and SZ2. The GPIb complex and vβ3 cooperate in binding vWF, but each of these two receptors may independently bind specific ligands. Alboaggregins bind to the GPIb complex, and vitronectin binds to vβ3. Each of these interactions leads to cell spreading and cytoskeletal mobilization.