title: Structural Basis for Enhancement of Carbapenemase Activity in the OXA-51 Family of Class D β-Lactamases.
abstract: Class D β-lactamases of Acinetobacter baumannii are enzymes of the utmost clinical importance, producing resistance to last resort carbapenem antibiotics. Although the OXA-51-like enzymes constitute the largest family of class D β-lactamases, they are poorly studied and their importance in conferring carbapenem resistance is controversial. We present the detailed microbiological, kinetic, and structural characterization of the eponymous OXA-51 β-lactamase. Kinetic studies show that OXA-51 has low catalytic efficiency for carbapenems, primarily due to the low affinity of the enzyme for these substrates. Structural studies demonstrate that this low affinity results from the obstruction of the enzyme active site by the side chain of Trp222, which presents a transient steric barrier to an incoming carbapenem substrate. The Trp222Met substitution relieves this steric hindrance and elevates the affinity of the mutant enzyme for carbapenems by 10-fold, significantly increasing the levels of resistance to these antibiotics. The ability of OXA-51 to evolve into a robust carbapenemase as the result of a single amino acid substitution may, in the near future, elevate the ubiquitous enzymes of the OXA-51 family to the status of the most deleterious A. baumannii carbapenemases, with dire clinical consequences.
authors.affiliation: †Stanford Synchrotron Radiation Lightsource, Stanford University, Menlo Park, California 94025, United States.
authors.forename: Clyde A
authors.initials: CA
authors.lastname: Smith
authors.affiliation: ‡Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556, United States.
authors.forename: Nuno Tiago
authors.initials: NT
authors.lastname: Antunes
authors.affiliation: ‡Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556, United States.
authors.forename: Nichole K
authors.initials: NK
authors.lastname: Stewart
authors.affiliation: ‡Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556, United States.
authors.forename: Hilary
authors.initials: H
authors.lastname: Frase
authors.affiliation: ‡Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556, United States.
authors.forename: Marta
authors.initials: M
authors.lastname: Toth
authors.affiliation: §College of Science and Mathematics, California State University, San Marcos, California 92078, United States.
authors.forename: Katherine A
authors.initials: KA
authors.lastname: Kantardjieff
authors.affiliation: ‡Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556, United States.
authors.forename: Sergei
authors.initials: S
authors.lastname: Vakulenko
mesh_terms: D040981:Acinetobacter baumannii / Q000737:chemistry / Q000201:enzymology* / Q000378:metabolism; D001426:Bacterial Proteins / Q000378:metabolism*; D020134:Catalytic Domain; D007700:Kinetics; D008958:Models, Molecular; D011487:Protein Conformation; D013379:Substrate Specificity; D001618:beta-Lactamases / Q000737:chemistry / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D001618:beta-Lactamases; C577373:beta-lactamase OXA-51, Acinetobacter baumannii; C063912:carbapenemase