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© Ahmed Haouz
Cristaux d'une protéine de Mycobacterium tuberculosis produits dans le cadre du Grand Programme Horizontal sur la Tuberculose à l'Institut Pasteur. La caractérisation structurale de protéines mycobactériennes aide à une meilleure compréhension de la physiologie et de la pathogénicité des mycobactéries et fournit un point de départ pour la conception de nouveaux agents antibactériens.
Publication : The Journal of antimicrobial chemotherapy

Structural insights into the loss of penicillinase and the gain of ceftazidimase activities by OXA-145 β-lactamase in Pseudomonas aeruginosa

Scientific Fields
Diseases
Organisms
Applications
Technique

Published in The Journal of antimicrobial chemotherapy - 14 Nov 2015

Meziane-Cherif D, Bonnet R, Haouz A, Courvalin P

Link to Pubmed [PMID] – 26568564

J. Antimicrob. Chemother. 2016 Feb;71(2):395-402

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 Å and its superposition with that of OXA-10 showed that Trp-154 was shifted by 1.8 Å 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 α- or β-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.

http://www.ncbi.nlm.nih.gov/pubmed/26568564