Binding of the integrin α_IIbβ₃ headpiece to the VWF D4-CK fragment. (A) Overall shape of the open α_IIbβ₃ headpiece (PDB code 2VDR and 3FCS), including the β-propeller and thigh domains in α_IIb and PSI, hybrid, βI, and I-EGF1 domains in β₃ subunit. Arrow shows the position of the RGD-binding site. (B) Superdex 200 gel filtration of VWF D4-CK, α_IIbβ₃ headpiece, and their complex in 5mM MnCl₂, 0.5mM CaCl₂, and 0.1M NaCl and in 20mM buffer of either Bis-Tris, pH 6.2, or HEPES, pH 7.4. (C) EM image of the complex of D4-CK with the α_IIbβ₃ headpiece at pH 6.2. (D) EM image of the complex of A3-CK with the α_IIbβ₃ headpiece at pH 6.2. (E) Representative class averages of complex of D4-CK with the α_IIbβ₃ headpiece. A schematic of integrin binding to VWF is shown to the right. Scale bars represent 50 nm in images and 10 nm in class averages.