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Title: Structural Basis of Activity against Aztreonam and Extended Spectrum Cephalosporins for Two Carbapenem-Hydrolyzing Class D β-Lactamases from Acinetobacter baumannii

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 themore » enhancement of substrate spectrum of class D β-lactamases, but may also provide a map for β-lactam improvement.« less
 [1] ;  [1] ;  [1] ;  [1] ;  [2] ;  [3] ;  [1] ;  [3] ;  [4] ;  [2] ;  [1] ;  [1]
  1. Grand Valley State Univ., Allendale, MI (United States). Dept. of Chemistry
  2. Grand Valley State Univ., Allendale, MI (United States). Dept. of Cell and Molecular Biology
  3. Case Western Reserve Univ., Cleveland, OH (United States). Dept. of Medicine, Pharmacology, Biochemistry, and Molecular Biology and Microbiology
  4. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). UT/ORNL Center for Molecular Biophysics, Biosciences Division
Publication Date:
OSTI Identifier:
Grant/Contract Number:
AC02-06CH11357; 1R15AI082416; R15AI094489; 1I01BX001974; R01AI100560; R01 AI063517; P41GM103712; 085P1000817
Accepted Manuscript
Journal Name:
Additional Journal Information:
Journal Volume: 54; Journal Issue: 10; Journal ID: ISSN 0006-2960
American Chemical Society (ACS)
Research Org:
Argonne National Lab. (ANL), Argonne, IL (United States). Advanced Photon Source (APS)
Sponsoring Org:
USDOE Office of Science (SC)
Country of Publication:
United States