Glutamate residues at positions 162nd and 164th influence the beta-lactamase activity of SHV-14 obtained from Klebsiella pneumoniae

Abstract

Extensive production of SHV-14 beta-lactamase makes Klebsiella pneumoniae resistant to beta-lactams. The presence of omega-loop has been reported to influence the beta-lactamase activity, which is also present in SHV-14. Its omega-loop has three glutamates in nearly alternating positions, 162, 164 and 167 but their concise role on the behaviour of SHV-14 is unknown. To uncover the influence of each glutamate on SHV-14, we replaced glutamates with alanine and estimated the effect of each mutation by assessing the change in beta-lactam sensitivities in the surrogate Escherichia coli cells and catalytic efficiencies for hydrolysis with the purified proteins. Upon expression, the clone of wild-type SHV-14 aggravated the resistance of host by 60–500 folds against penicillin and cephalosporin groups of antibiotics. However, the expression of mutated enzymes (especially E164A) substantially reduced the resistance level as compared to the wild-type, and the results were in synchrony with the estimated enzymatic efficiencies of wild-type and mutated proteins. Therefore, with further support from the in silico analysis, we hypothesize that mutation at the glutamate residues in the omega-loop of SHV-14 can considerably modulate the beta-lactam sensitivity and hydrolysis; thus, revealing the importance of such glutamates as the target for inhibitor design in future.