ABSTRACT
The hydrogen bond network in the metal site is largely conserved. In particular, the peptide NH of an Asn residue next to the upstream His ligand is hydrogen-bonded to the bound Cys sulfur atom in most BCPs (Table 2 ). This hydrogen bond is relevant for maintaining the geometry of the metal site. In some BCPs, a second hydrogen bond is formed between the SY(Cys) and a backbone NH located two residues ahead of the Cys in the sequence (Table 2 ). This residue is substituted by a Pro in other BCPs, thus lacking this second hydrogen bond.
