Structural Basis of Activity against Aztreonam and Extended Spectrum Cephalosporins for Two Carbapenem-Hydrolyzing Class D β-Lactamases from Acinetobacter baumannii
- Grand Valley State Univ., Allendale, MI (United States). Dept. of Chemistry
- Grand Valley State Univ., Allendale, MI (United States). Dept. of Cell and Molecular Biology
- Case Western Reserve Univ., Cleveland, OH (United States). Dept. of Medicine, Pharmacology, Biochemistry, and Molecular Biology and Microbiology
- Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). UT/ORNL Center for Molecular Biophysics, Biosciences Division
The carbapenem-hydrolyzing class D β-lactamases OXA-23 and OXA-24/40 have emerged world-wide as causative agents for β-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 β5-β6 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 β5-β6 loop, relieving the steric clash with the R1 side-chain carboxypropyl group of aztreonam and ceftazidime. We found that these results reveal worrying trends in the enhancement of substrate spectrum of class D β-lactamases, but may also provide a map for β-lactam improvement.
- Research Organization:
- Argonne National Laboratory (ANL), Argonne, IL (United States). Advanced Photon Source (APS)
- Sponsoring Organization:
- USDOE Office of Science (SC)
- Grant/Contract Number:
- AC02-06CH11357; 1R15AI082416; R15AI094489; 1I01BX001974; R01AI100560; R01 AI063517; P41GM103712; 085P1000817
- OSTI ID:
- 1178836
- Journal Information:
- Biochemistry, Vol. 54, Issue 10; ISSN 0006-2960
- Publisher:
- American Chemical Society (ACS)Copyright Statement
- Country of Publication:
- United States
- Language:
- ENGLISH
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