The crystal structure of the Bz·α-thrombin·FVa2 complex corroborates FVa2 binding to exosite I residues. The tetramer found in the asymmetric unit is shown, with the 4 independent thrombin molecules represented by their major secondary structure elements colored green, purple, orange, and gray, respectively. The Van der Waals surfaces of the 4 monomers are superimposed in lighter tones of the same colors. The FVa2 peptides are given with all their nonhydrogen atoms, color-coded according to the bound thrombin moiety. The benzamidine molecules that occupy the S₁ pockets of thrombin are also shown as color-coded ball-and-stick models. Notice that the phenyl rings of Phe⁶⁶⁸ dock onto exosite I regions from cognate thrombin molecules.