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Publication Abstract from PubMed

The carbapenem-hydrolyzing class D beta-lactamases OXA-23 and OXA-24/40 have emerged worldwide as causative agents for beta-lactam antibiotic resistance in Acinetobacter species. Many variants of these enzymes have appeared clinically, including OXA-160 and OXA-225, which both contain a P --> S substitution at homologous positions in the OXA-24/40 and OXA-23 backgrounds, respectively. We purified OXA-160 and OXA-225 and used steady-state kinetic analysis to compare the substrate profiles of these variants to their parental enzymes, OXA-24/40 and OXA-23. OXA-160 and OXA-225 possess greatly enhanced hydrolytic activities against aztreonam, ceftazidime, cefotaxime, and ceftriaxone when compared to OXA-24/40 and OXA-23. These enhanced activities are the result of much lower Km values, suggesting that the P --> S substitution enhances the binding affinity of these drugs. We have determined the structures of the acylated forms of OXA-160 (with ceftazidime and aztreonam) and OXA-225 (ceftazidime). These structures show that the R1 oxyimino side-chain of these drugs occupies a space near the beta5-beta6 loop and the omega loop of the enzymes. The P --> S substitution found in OXA-160 and OXA-225 results in a deviation of the beta5-beta6 loop, relieving the steric clash with the R1 side-chain carboxypropyl group of aztreonam and ceftazidime. These results reveal worrying trends in the enhancement of substrate spectrum of class D beta-lactamases but may also provide a map for beta-lactam improvement.

Structural Basis of Activity against Aztreonam and Extended Spectrum Cephalosporins for Two Carbapenem-Hydrolyzing Class D beta-Lactamases from Acinetobacter baumannii.,Mitchell JM, Clasman JR, June CM, Kaitany KC, LaFleur JR, Taracila MA, Klinger NV, Bonomo RA, Wymore T, Szarecka A, Powers RA, Leonard DA Biochemistry. 2015 Mar 2. PMID:25710192^[1]

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