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Publication Abstract from PubMed

OBJECTIVES: We previously described extended-spectrum oxacillinase OXA-145 from Pseudomonas aeruginosa, which differs from narrow-spectrum OXA-35 by loss of Leu-155. The deletion results in loss of benzylpenicillin hydrolysis and acquisition of activity against ceftazidime. We report the crystal structure of OXA-145 and provide the basis of its switch in substrate specificity. METHODS: OXA-145 variants were generated by site-directed mutagenesis and purified to homogeneity. The crystal structure of OXA-145 was determined and molecular dynamics simulations were performed. Kinetic parameters were investigated in the absence and in the presence of sodium hydrogen carbonate (NaHCO3) for representative substrates. RESULTS: The structure of OXA-145 was obtained at a resolution of 2.3 A and its superposition with that of OXA-10 showed that Trp-154 was shifted by 1.8 A away from the catalytic Lys-70, which was not N-carboxylated. Addition of NaHCO3 significantly increased the catalytic efficiency against penicillins, but not against ceftazidime. The active-site cavity of OXA-145 was larger than that of OXA-10, which may favour the accommodation of large molecules such as ceftazidime. Molecular dynamics simulations of OXA-145 in complex with ceftazidime revealed two highly coordinated water molecules on the alpha- or beta-face of the acyl ester bond, between Ser-67 and ceftazidime, which could be involved in the catalytic process. CONCLUSIONS: Deletion of Leu-155 resulted in inefficient positioning of Trp-154, leading to a non-carboxylated Lys-70 and thus to loss of hydrolysis of the penicillins. Ceftazidime hydrolysis could be attributed to enlargement of the active site and to a catalytic mechanism independent of the carboxylated Lys-70.

Structural insights into the loss of penicillinase and the gain of ceftazidimase activities by OXA-145 beta-lactamase in Pseudomonas aeruginosa.,Meziane-Cherif D, Bonnet R, Haouz A, Courvalin P J Antimicrob Chemother. 2016 Feb;71(2):395-402. doi: 10.1093/jac/dkv375. Epub, 2015 Nov 14. PMID:26568564^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.