Two cases of protease-inhibitor interfaces. (a) The interface between a carboxypeptidase a2 (EC number: 220.127.116.11) and a metallocarboxypeptidase inhibitor ([PDB:1DTD], resolution: 1.65 Å, wetness: 0.055, rWBL: 0.998). (b) The interface between a beta-trypsin (EC number: 18.104.22.168) and its inhibitor ([PDB:2PTC], resolution: 1.9 Å, wetness: 0.029, rWBL: 0.954). The figures only show the enzyme part (in surface) and the interfacial water (in spheres). Non-interface part is colored green. In (a), there are 4 layers of nested-rings in interface: O0 (red), O1 (brown), O2 (yellow) and O3 (blue). In (b), there are 5 layers of nested-rings: O0 (magenta), O1 (red), O2 (brown), O3 (yellow) and O4 (blue). Active site residues  are shown in sticks and mesh.
Li et al. BMC Bioinformatics 2012 13:51 doi:10.1186/1471-2105-13-51