Effect of Lys84 carbamylation and chloride ion on OXA-143 dynamics and catalytic efficiency

Carbapenem-hydrolyzing Class-D {beta}-lactamase OXA-143 is known as an efficient carbapenemase, and the number of clinically isolated Acinetobacter baumannii carrying the OXA-143 gene has risen significantly since it was first identified in 2004. The inhibitory effect of chloride ions on OXA enzymes has been described in the literature; however, no study has been performed on the OXA-143 subfamily. Furthermore, there is no information available on the effect of carbamylation on the OXA dynamics. Here, we explored the effects of the absence and presence of carbamylated lysine on protein dynamics using Mass Spectrometry Hydrogen-Deuterium exchange (HDX) and Molecular Dynamics Simulation (MD). We also investigated the effect of chloride ions on the enzyme kinetics and thermal stability. Our results show that in the absence of the carboxy group, the active site of the enzyme and its surroundings are more flexible due to a lack of hydrogen bonds involving the modified lysine. Furthermore, chloride plays no role in the thermal stability or efficiency of the enzyme in the presence of bicarbonate. However, a decreased efficiency proportional to the chloride concentration was observed in a non-supplemented buffer.