Stabilizing effects of TAFI-IIYQ mutations. Mutations T325I (A) and T329I (B) form additional interactions with residues from the catalytic domain outside the dynamic flap. Mutations H333Q (C) and H335Y (D) stabilize the dynamic flap through interactions within the flap. Because the side chain conformation of Ile325 and Ile329 could not be determined unequivocally from the electron density, details of these interactions remain subject to speculation. Wild-type residues are shown in orange and mutated residues in cyan. H-bonds are shown as black dashes.