Characterisation and directed evolution of novel metallo-β-lactamases - spr-1 and aim-1

Metallo-β-lactamases (MBLs) are zinc ion dependent enzymes that responsible for the emergence and spread of β-lactam resistance. The increasing number of novel members of this family is threatening to global health care. MBLs are divided into three subclasses, i.e. B1, B2 and B3. The recent discovery of an unusual MBL from Serratia proteamaculans (SPR-1) suggests the presence of an additional subgroup, i.e. B4. A database search reveals that SPR-1 has several homologues including a MBL from Cronobacter sakazakii, CSA-1. These MBLs have a unique active site and my employ a mechanism distinct from other MBLs. Characterisation of a novel B3 MBL from Pseudomonas aeruginosa in Adelaide, Australia, Adelaide Imipenemase-1 (AIM-1) suggests the presence of a super enzyme that is biochemically broad spectrum and physically stable. In this study, X-ray crystal structure of AIM-1 was solved and site-saturation mutagenesis was used for probing several interesting residues. Moreover, directed evolution was introduced for finding the prospective variants that have better activity against antibiotics. Variants found in this study suggest AIM-1 has the potential to increase activity against β- lactams antibiotics. Information gained from this study may also be useful in the design of inhibitors that could be used as anti-bacterial agents