Model structure of αIIb superimposed on the crystal structure of α_vβ3. (A) Superimposition of α_vβ3 derived from the crystal structure (PDB:1jv2) and αIIb derived from the predicted models of the β-propeller, calf-1, and calf-2 domains. The α_v is shown in blue, GPIIIa (β3) in red, and GPIIb (αIIβ) in green. The interface between calf-1 and EGF-3 of β3 is circled, and the interface between calf-2 and EGF-4 of β3 is depicted in the square. (B) The interface between the calf-1 of GPIIb derived from the model and EGF-3 of GPIIIa derived from the crystal structure (red). The calf-2 backbone is shown in green and black; the black denotes the 50 amino acids deleted by del.20 mutation. The abolished contact with β3 is circled. (C) A region in the interface between β3 derived from the crystal structure (red) and calf-2 α_v derived from the crystal structure (blue) and αIIb derived from the model (green) and αIIb-alt.25 derived from model (gold). Notable is the profound displacement of His788 of GPIIb-alt.25; compare with His787 of normal GPIIb.