OXA-239 is a class D carbapenemase isolated from an Acinetobacter baumannii strain found in Mexico. This enzyme is a variant of OXA-23 with three amino acid substitutions in or near the active site. These substitutions cause OXA-239 to hydrolyze late-generation cephalosporins and the monobactam aztreonam with greater efficiency than OXA-23. OXA-239 activity against the carbapenems doripenem and imipenem is reduced ∼3-fold and 20-fold, respectively. Further analysis demonstrated that two of the substitutions (P225S and D222N) are largely responsible for the observed alteration of kinetic parameters, while the third (S109L) may serve to stabilize the protein. Structures of OXA-239 with cefotaxime, doripenem and imipenem bound as acyl-intermediates were determined. These structures reveal that OXA-239 has increased flexibility in a loop that contains P225S and D222N. When carbapenems are bound, the conformation of this loop is essentially identical with that observed previously for OXA-23, with a narrow active site that makes extensive contacts to the ligand. When cefotaxime is bound, the loop can adopt a different conformation that widens the active site to allow binding of that bulky drug. This alternate conformation is made possible by P225S and further stabilized by D222N. Taken together, these results suggest that the three substitutions were selected to expand the substrate specificity profile of OXA-23 to cephalosporins and monobactams. The loss of activity against imipenem, however, suggests that there may be limits to the plasticity of class D enzymes with regard to evolving active sites that can effectively bind multiple classes of β-lactam drugs.
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January 2018
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A 3D representation of the filamentous cyanobacteria Anabaena. In this issue, Sein-Echaluce et al. report on the molecular basis for the integration of environmental signals by FurB from Anabaena sp. PCC 7120; for details see pages 151–168.
Research Article|
January 11 2018
Multiple substitutions lead to increased loop flexibility and expanded specificity in Acinetobacter baumannii carbapenemase OXA-239
Thomas M. Harper;
Thomas M. Harper
1Department of Chemistry, Grand Valley State University, Allendale, MI 49401, U.S.A.
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Cynthia M. June;
Cynthia M. June
1Department of Chemistry, Grand Valley State University, Allendale, MI 49401, U.S.A.
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Magdalena A. Taracila;
Magdalena A. Taracila
2Department of Medicine, Case Western Reserve University, Cleveland, OH 44106, U.S.A.
3Research Service, Louis Stokes Veterans Affairs Medical Center, Cleveland, OH 44106, U.S.A.
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Robert A. Bonomo;
Robert A. Bonomo
2Department of Medicine, Case Western Reserve University, Cleveland, OH 44106, U.S.A.
3Research Service, Louis Stokes Veterans Affairs Medical Center, Cleveland, OH 44106, U.S.A.
4Department of Pharmacology, Case Western Reserve University, Cleveland, OH 44106, U.S.A.
5Department of Biochemistry, Case Western Reserve University, Cleveland, OH 44106, U.S.A.
6Department of Molecular Biology and Microbiology, Case Western Reserve University, Cleveland, OH 44106, U.S.A.
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Rachel A. Powers;
Rachel A. Powers
1Department of Chemistry, Grand Valley State University, Allendale, MI 49401, U.S.A.
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David A. Leonard
1Department of Chemistry, Grand Valley State University, Allendale, MI 49401, U.S.A.
Correspondence: David A. Leonard (leonardd@gvsu.edu)
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Biochem J (2018) 475 (1): 273–288.
Article history
Received:
September 11 2017
Revision Received:
December 07 2017
Accepted:
December 11 2017
Accepted Manuscript online:
December 11 2017
Citation
Thomas M. Harper, Cynthia M. June, Magdalena A. Taracila, Robert A. Bonomo, Rachel A. Powers, David A. Leonard; Multiple substitutions lead to increased loop flexibility and expanded specificity in Acinetobacter baumannii carbapenemase OXA-239. Biochem J 15 January 2018; 475 (1): 273–288. doi: https://doi.org/10.1042/BCJ20170702
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