Two distinct intermolecular contacts between symmetry related molecules of β-FXIIa protease domain in the crystal packing. (A) First extensive interface. Ribbon representation of 2 protease domains shown in cyan and magenta. Contacting residues are labeled and shown as sticks. The residues of the neighboring molecule are denoted by the “′” mark. Salt bridges and hydrogen bonds are depicted by black dotted lines. Compound 1, buried in the active site, is shown as balls. Positions of the catalytic triad for both molecules and the heavy chain remnant for one molecule (on the right) are indicated. (B) Second contact region. The same as in panel A except the heavy chain remnant of the β-FXIIa molecule on the left (yellow cartoon) is shown in red.