Proposed model for the dynamics of integrin αIIbβ3 on the resting human platelet membrane. On the surface of the resting human platelets, integrin αIIbβ3 has 3 major conformations: inactivated bent, intermediate, and homodimer. An RGD motif–containing ligand (red shooting star) binds to the bent conformation and keeps the ligand-binding site occupied when the molecule is inactive. The ligand releases whereas αIIbβ3 extends to the intermediate state. Two adjacent αIIbβ3 molecules in the intermediate state can form a homodimer on the surface. There is a dynamical conformational equilibrium between the intermediate state and the homodimer state of αIIbβ3 on the human platelets. (A) Diagram with solved integrin αIIbβ3 structures in their corresponding location. (B) Cartoon models of the molecule. The top panels of both panels A and B show the side view of the molecules in which the extracellular side is on the top and the intracellular side is on the bottom. The bottom panels of both panels A and B show the top view of the molecules where the platelet membrane (gray) lies on the bottom.