4.2 Article

Deciphering the role of residues in the loops nearing the active site of OXA-58 in imparting beta-lactamase activity

Journal

MICROBIOLOGY-SGM
Volume 168, Issue 6, Pages -

Publisher

MICROBIOLOGY SOC
DOI: 10.1099/mic.0.001203

Keywords

antimicrobial resistance; beta-lactamase; omega loop; OXA beta-lactamase; thermal stability

Categories

Funding

  1. Department of Biotechnology (DBT), Government of India [BT/PR24255/NER/95/716/2017]
  2. Council of Scientific and Industrial Research (CSIR) [27 (0367) /20/EMR-II]

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This study investigates the mechanism and stability of OXA-58 carbapenemase. The results demonstrate that the residues in the putative omega loop play a significant role in the activity and stability of the enzyme.
The existence of OXA-58 carbapenemase alone or in combination with other beta-lactam resistance factors poses significant beta-lactam resistance. The exact mechanism of action of OXA type beta-lactamases is debatable due to the involvement of multiple residues within or outside the active site. In the present work, we have elucidated the relative role of residues present in the putative omega (W169, L170, K171) and beta 6-beta 7 (A226 and D228) loops on the activity of OXA-58 by substituting into alanine (and aspartate for A226) through site-directed mutagenesis. E. coli cells harbouring OXA-58, substituted at the putative omega loop, manifest a significant decrease in the beta-lactam resistance profile than that of the cells expressing OXA-58. Further, a reduction in the catalytic efficiency is observed for the purified variants of OXA-58 carrying individual substitutions in the putative omega loop than that of OXA-58. However, the addition of NaHCO3 (for carbamylation of K86) increases catalytic efficiency of the individual protein as revealed by nitrocefin hydrolysis assay and steady state kinetics. Moreover, W169A and K171A substitutions show significant effects on the thermal stability of OXA-58. Therefore, we conclude that the putative omega loop residues W169, L170 and K171, individually, have significant role in the activity and stability of OXA-58, mostly by stabilising carbamylated lysine of active site.

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