title: The structure of a doripenem-bound OXA-51 class D β-lactamase variant with enhanced carbapenemase activity.
abstract: OXA-51 is a class D β-lactamase that is thought to be the native carbapenemase of Acinetobacter baumannii. Many variants of OXA-51 containing active site substitutions have been identified from A. baumannii isolates, and some of these substitutions increase hydrolytic activity toward carbapenem antibiotics. We have determined the high-resolution structures of apo OXA-51 and OXA-51 with one such substitution (I129L) with the carbapenem doripenem trapped in the active site as an acyl-intermediate. The structure shows that acyl-doripenem adopts an orientation very similar to carbapenem ligands observed in the active site of OXA-24/40 (doripenem) and OXA-23 (meropenem). In the OXA-51 variant/doripenem complex, the indole ring of W222 is oriented away from the doripenem binding site, thereby eliminating a clash that is predicted to occur in wildtype OXA-51. Similarly, in the OXA-51 variant complex, L129 adopts a different rotamer compared to I129 in wildtype OXA-51. This alternative position moves its side chain away from the hydroxyethyl moiety of doripenem and relieves another potential clash between the enzyme and carbapenem substrates. Molecular dynamics simulations of OXA-51 and OXA-51 I129L demonstrate that compared to isoleucine, a leucine at this position greatly favors a rotamer that accommodates the ligand. These results provide a molecular justification for how this substitution generates enhanced binding affinity for carbapenems, and therefore helps explain the prevalence of this substitution in clinical OXA-51 variants.
authors.affiliation: Department of Chemistry, Grand Valley State University, Allendale, Michigan, 49401.
authors.forename: Cynthia M
authors.initials: CM
authors.lastname: June
authors.affiliation: Department of Chemistry, Grand Valley State University, Allendale, Michigan, 49401.
authors.forename: Taylor J
authors.initials: TJ
authors.lastname: Muckenthaler
authors.affiliation: Department of Chemistry, Grand Valley State University, Allendale, Michigan, 49401.
authors.forename: Emma C
authors.initials: EC
authors.lastname: Schroder
authors.affiliation: Department of Cell and Molecular Biology, Grand Valley State University, Allendale, Michigan, 49401.
authors.forename: Zachary L
authors.initials: ZL
authors.lastname: Klamer
authors.affiliation: Life Sciences Collaborative Access Team, Synchrotron Research Center, Northwestern University, Argonne, Illinois, 60439.
authors.forename: Zdzislaw
authors.initials: Z
authors.lastname: Wawrzak
authors.affiliation: Department of Chemistry, Grand Valley State University, Allendale, Michigan, 49401.
authors.forename: Rachel A
authors.initials: RA
authors.lastname: Powers
authors.affiliation: Department of Cell and Molecular Biology, Grand Valley State University, Allendale, Michigan, 49401.
authors.forename: Agnieszka
authors.initials: A
authors.lastname: Szarecka
authors.affiliation: Department of Chemistry, Grand Valley State University, Allendale, Michigan, 49401.
authors.forename: David A
authors.initials: DA
authors.lastname: Leonard
mesh_terms: D040981:Acinetobacter baumannii / Q000201:enzymology* / Q000235:genetics; D019943:Amino Acid Substitution; D001665:Binding Sites; D015780:Carbapenems / Q000737:chemistry*; D018360:Crystallography, X-Ray; D000077726:Doripenem; D056004:Molecular Dynamics Simulation; D020125:Mutation, Missense; D001618:beta-Lactamases / Q000737:chemistry* / Q000235:genetics
chemical_list: D015780:Carbapenems; D000077726:Doripenem; D001618:beta-Lactamases; C577373:beta-lactamase OXA-51, Acinetobacter baumannii
keywords: antibiotic resistance; carbapenem; crystal structure; β-lactamase