Evolution of New Delhi metallo-{beta}-lactamase (NDM) in the clinic: Effects of NDM mutations on stability, zinc affinity, and mono-zinc activity [Microbiology] (Journal of Biological Chemistry)

Infections by carbapenem-resistant Enterobacteriaceae are difficult to manage owing to broad antibiotic resistance profiles and because of the inability of clinically used ?-lactamase inhibitors to counter the activity of metallo-?-lactamases often harbored by these pathogens. Of particular importance is New Delhi metallo-?-lactamase (NDM), which requires a di-nuclear zinc ion cluster for catalytic activity. Here, we compare the structures and functions of clinical NDM variants 1-17. The impact of NDM variants on structure is probed by comparing melting temperature and refolding efficiency and also by spectroscopy (UV-visible, 1H NMR, and EPR) of di-cobalt metalloforms. The impact of NDM variants on function is probed by determining the minimum inhibitory concentrations of various antibiotics, pre-steady-state and steady-state kinetics, inhibitor binding, and zinc dependence of resistance and activity. We observed only minor differences among the fully loaded di-zinc enzymes, but most NDM variants had more distinguishable selective advantages in experiments that mimicked zinc scarcity imposed by typical host defenses. Most NDM variants exhibited improved thermostability (up to ~10 °C increased Tm) and improved zinc affinity (up to ~10-fold decreased Kd, Zn2). We also provide first evidence that some NDM variants have evolved the ability to function as mono-zinc enzymes with high catalytic efficiency (NDM-15, ampicillin: kcat/Km = 5 × 106 m-1 s-1). These findings reveal the molecular mechanisms that NDM variants have evolved to overcome the combined selective pressures of ?-lactam antibiotics and zinc deprivation.