FXI dimer colocalization of bound HK peptides. (A) Cartoon diagram of the apple domain saucer section shown in gray, blue, orange, and yellow for the A1, A2, A3, and A4 domains, respectively. The HK peptide is colored in dark blue and shown as sticks. (B) The FXI dimer bound to the HK peptide (blue sticks) is shown with the protease domain (white) and active-site residues (red spheres) for His413, Asp462, and Ser557. The distance between the HK peptides is indicated as 45 Å, and the vertical arrow shows the dimer axis. (C) Surface representation of the FXI dimer, with each subunit colored the same as in panel A, except the protease domain is red.