2. "Potentially-active" amino acid residues, defined to be found within 3 Å from any atom in the ligand structure (thus being capable of significantly-interacting with the latter; see, for instance, section 2.2 in Ref. ) were selected via 'CONTACT' calculations included in the CCP4 suite. 3. Residues found in the preceding stage for each crystal structure were then simply taken alongside the corresponding bound ligand to create the final active-site + ligand geometries used throughout this paper.