β-Lactams are the most successful antibacterials, but their effectiveness is threatened by resistance, most importantly by production of serine- and metallo-β-lactamases (MBLs). MBLs are of increasing concern because they catalyze the hydrolysis of almost all β-lactam antibiotics, including recent-generation carbapenems. Clinically useful serine-β-lactamase inhibitors have been developed, but such inhibitors are not available for MBLs. l-Captopril, which is used to treat hypertension via angiotensin-converting enzyme inhibition, has been reported to inhibit MBLs by chelating the active site zinc ions via its thiol(ate). We report systematic studies on B1 MBL inhibition by all four captopril stereoisomers. High-resolution crystal structures of three MBLs (IMP-1, BcII, and VIM-2) in complex with either the l- or d-captopril stereoisomer reveal correlations between the binding mode and inhibition potency. The results will be useful in the design of MBL inhibitors with the breadth of selectivity required for clinical application against carbapenem-resistant Enterobacteriaceae and other organisms causing MBL-mediated resistant infections.

The αββα metallo β-lactamase (MBL) fold (MBLf) was first observed in bacterial enzymes that catalyze the hydrolysis of almost all β-lactam antibiotics, but is now known to be widely distributed. The MBL core protein fold is present in human enzymes with diverse biological roles, including cell detoxification pathways and enabling resistance to clinically important anticancer medicines. Human (h)MBLf enzymes can bind metals, including zinc and iron ions, and catalyze a range of chemically interesting reactions, including both redox (e.g., ETHE1) and hydrolytic processes (e.g., Glyoxalase II, SNM1 nucleases, and CPSF73). With a view to promoting basic research on MBLf enzymes and their medicinal targeting, here we summarize current knowledge of the mechanisms and roles of these important molecules.

Background: The nucleases hSNM1A and hSNM1B are implicated in DNA interstrand cross-link repair.Results: hSNM1A and hSNM1B were biochemically characterized using undamaged and cross-linked DNA. A real-time assay for the nucleases suitable for inhibitor identification was developed.Conclusion: Preferential hSNM1A activation by high molecular weight and cross-linked DNA was observed.Significance: This work provides a basis for hSNM1A inhibitor development for improved cancer therapy.