Fig. 1. (A) Outline mode of action of metallo-β-lactamases (MBLs); (B–E) views from MBL crystal structures highlighting potentially mobile regions. Views of (B) IMP-1 (B1 MBL, PDB ID: 1JJT),²⁰ (C) CphA (B2 MBL, PDB ID: ; 1X8I)¹⁷ and the (D) ‘open’ and (E) ‘closed’ forms of SPM-1 (B1 MBL, ‘open’ PDB ID: ; 2FHX¹⁴ and ‘closed’ PDB ID: ; 4BP0) highlighting the different mobile regions (L3 loop (blue), L10 loop (red) and α3 region (green)) that characterize the MBL subfamilies. A longer L3 loop (blue) is characteristic of the di-Zn B1 MBLs. The B2 MBLs using mono-zinc ion are characterised by an elongated α3 region (green) and a shorter L3 loop (blue). In the case of the B1 MBLs only SPM-1 has an elongated α3 loop (green) and a short L3 loop (blue).