Conserved ancillary residues situated proximally to the VIM-2 active site affect its metallo β-lactamase activity

Abstract

Verona-integron-metallo-β-lactamase (VIM-2) is one of the most widespread class B β-lactamase responsible for β-lactam resistance. Although active-site residues help in metal binding, the residues nearing the active-site possess functional importance. Here, to decipher the role of such residues in the activity and stability of VIM-2, the residues E146, D182, N210, S207, and D213 were selected through in-silico analyses and substituted with alanine using site-directed mutagenesis. The effects of substitution mutations were assessed by comparing the changes in the β-lactam susceptibility pattern of E. coli host cells expressing VIM-2 and its mutated proteins. VIM-2_N210A enhanced the susceptibility of the host by ~4-8 folds against penicillins and cephalosporins while the expression of VIM-2_D182A radically increased the susceptibility of the host. However, expression of VIM-2_E146A reduced the susceptibility of the host by 2-fold. Further, proteins were purified to homogeneity, and VIM_N210A and VIM_D182A displayed reduced thermal stability than VIM-2. Moreover, in vitro catalytic efficiencies of VIM-2_D182A were drastically reduced against all the β-lactams tested whereas the same were moderately reduced for VIM-2_N210A. Conversely, the catalytic efficiency was marginally altered for VIM_E146A. Overall, we infer that both N210A and D182A substitutions negatively affect the performance of VIM-2 by influencing substrate specificity and stability, respectively.