Comparison of the structures of cZPI and ZPI. (A) Ribbon structure of cZPI (I2 space group) in gray with sheet A in blue, the cleaved reactive loop in red, helix A in orange, and helix G in purple. (B) Superposition of the PZ-binding sites of native (cyan) and cleaved (green) ZPI by aligning strand 6 of sheet A. The 4 key PZ-interacting residues are represented in stick.