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Publication Abstract from PubMed

OXA-48 carbapenemase has rapidly spread in many countries worldwide with several OXA-48-variants being described, differing by a few amino acid (AA) substitutions or deletions, mostly in the beta5-beta6 loop. While single AA substitutions have only a minor impact on OXA-48 hydrolytic profiles, others with 4 AA deletions result in loss of carbapenem hydrolysis and gain of expanded-spectrum cephalosporin (ESC) hydrolysis. We have replaced the beta5-beta6 loop of OXA-48 with that of OXA-18, a clavulanic-acid inhibited oxacillinase capable of hydrolyzing ESCs but not carbapenems. The hybrid enzyme OXA-48Loop18 was able to hydrolyze ESCs and carbapenems (although with a lower kcat), even though the beta5-beta6 loop was longer and its sequence quite different from that of OXA-48. The kinetic parameters of OXA-48Loop18 were in agreement with the MIC values. X-ray crystallography and molecular modeling suggest that the conformation of the grafted loop allows the binding of bulkier substrates, unlike that of the native loop, expanding the hydrolytic profile. This seems to be due not only to differences in AA sequence, but also to the backbone conformation the loop can adopt. Finally, our results provide further experimental evidence for the role of the beta5-beta6 loop in substrate selectivity of OXA-48-like enzymes and additional details on the structure-function relationship of beta-lactamases, demonstrating how localized changes in these proteins can alter or expand their function, highlighting their plasticity.

Substrate Specificity of OXA-48 after beta5-beta6 Loop Replacement.,Dabos L, Zavala A, Bonnin RA, Beckstein O, Retailleau P, Iorga BI, Naas T ACS Infect Dis. 2020 Mar 19. doi: 10.1021/acsinfecdis.9b00452. PMID:32156115^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.