In vitro penicillinase activity of ?-lactamase OXA-143(P227S): pH effect

Resumo

Antibiotic resistance is a global threat. The Class D ?-lactamase OXA-143 has been described as an efficient penicillinase, oxacillinase, and carbapenemase. This Class of enzymes has an unusual lysine (K84) that in the carbamylated form acts as a general base. Recent studies performed in our laboratory showed that P227S is a positive mutation within the evolutionary pathway of the OXA-143 sub-family towards a more efficient carbapenemase. Once the mutant OXA-143(P227S) is an evolved version of OXA-143 it is important to analyze the effect of the buffer for the kinetic in vitro assays. Therefore, as the carboxylated lysine acts as a general base in the proposed covalent catalysis mechanism, in this study, we performed assays to investigate the effect of the pH in the structure and catalytic efficiency of the mutant OXA-143(P227S). Our results show a direct pH dependence on penicillinase activity, with an optimal range from pH 7 to 9. In addition, our findings also suggest the exchange of two hydrogens during the reaction with ampicillin. Furthermore, it was also observed a direct correlation between the catalytic efficiency in this pH range and the enzyme thermal stability.