Active site of hDNPEP. (A) |F
| omit map contoured at 3σ for zinc ions and ABH molecules. (B) Insertion of the β8-β9 loop from the neighboring subunit (magenta) completes the active site construction. Bonding interactions at (C) the binuclear metal catalytic centre and (D) the P1 substrate pocket in the hDNPEP structure. (E) Proposed catalytic mechanism for hDNPEP. The substrate peptide N-terminus is shown in both amine and its protonated form, which can engage in different interactions.