αIIbβ3 headpiece-fibrinogen γ-module complex showing interactions between residues on the αIIb helix segment L151-D159 and fibrinogen γ-module. (A) Snapshot at 230 ns from MD simulations of a representative structure of cluster 2 showing a relaxed model of fibrinogen binding to αIIbβ3. Fibrinogen γ-module, αIIb, and β3 are colored in gray, blue, and red, respectively. The last 7 amino acids of fibrinogen are colored in yellow. The important contact region identified is highlighted with a green circle. (B) A zoom-in view of the contacts in the 230 ns snapshot is shown from a slightly different perspective and with fibrinogen residue 291-306 removed for clarity. Direct and water-mediated hydrogen bonds are indicated with dotted lines.