High-resolution crystal structure of the thrombin FPR–α-thrombin·FVa2 complex. (A) The 2 thrombin monomers in the asymmetric unit are represented by their secondary structure elements, colored blue and yellow, respectively. Their cognate FV peptides are given with all their nonhydrogen side chain atoms in green and pink, respectively. The FPR moieties covalently bound to thrombin active-site residues His⁵⁷/Ser¹⁹⁵ are depicted color-coded (carbon, gray; nitrogen, blue; oxygen, red). The thrombin molecule to the bottom left is shown in standard orientation, that is, macromolecular substrate residues would run from left to right in productive complexes with the proteinase. (B) Detail of the initial electron density map calculated after rigid-body refinement of the 2 thrombin molecules is shown around exosite I (contoured at 1 σ), with the final FVa2 model superimposed. The side chains of a few critical residues are labeled.