Kinetic features of L,D-transpeptidase inactivation critical for β-lactam antibacterial activity.

Abstract : Active-site serine D,D-transpeptidases belonging to the penicillin-binding protein family (PBPs) have been considered for a long time as essential for peptidoglycan cross-linking in all bacteria. However, bypass of the PBPs by an L,D-transpeptidase (Ldt(fm)) conveys high-level resistance to β-lactams of the penam class in Enterococcus faecium with a minimal inhibitory concentration (MIC) of ampicillin >2,000 µg/ml. Unexpectedly, Ldt(fm) does not confer resistance to β-lactams of the carbapenem class (imipenem MIC = 0.5 µg/ml) whereas cephems display residual activity (ceftriaxone MIC = 128 µg/ml). Mass spectrometry, fluorescence kinetics, and NMR chemical shift perturbation experiments were performed to explore the basis for this specificity and identify β-lactam features that are critical for efficient L,D-transpeptidase inactivation. We show that imipenem, ceftriaxone, and ampicillin acylate Ldt(fm) by formation of a thioester bond between the active-site cysteine and the β-lactam-ring carbonyl. However, slow acylation and slow acylenzyme hydrolysis resulted in partial Ldt(fm) inactivation by ampicillin and ceftriaxone. For ampicillin, Ldt(fm) acylation was followed by rupture of the C(5)-C(6) bond of the β-lactam ring and formation of a secondary acylenzyme prone to hydrolysis. The saturable step of the catalytic cycle was the reversible formation of a tetrahedral intermediate (oxyanion) without significant accumulation of a non-covalent complex. In agreement, a derivative of Ldt(fm) blocked in acylation bound ertapenem (a carbapenem), ceftriaxone, and ampicillin with similar low affinities. Thus, oxyanion and acylenzyme stabilization are both critical for rapid L,D-transpeptidase inactivation and antibacterial activity. These results pave the way for optimization of the β-lactam scaffold for L,D-transpeptidase-inactivation.
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PLoS ONE, Public Library of Science, 2013, 8 (7), pp.e67831. 〈10.1371/journal.pone.0067831〉
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Soumis le : jeudi 26 mai 2016 - 09:18:35
Dernière modification le : jeudi 24 mai 2018 - 12:02:02

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Sébastien Triboulet, Vincent Dubée, Lauriane Lecoq, Catherine M Bougault, Jean-Luc Mainardi, et al.. Kinetic features of L,D-transpeptidase inactivation critical for β-lactam antibacterial activity.. PLoS ONE, Public Library of Science, 2013, 8 (7), pp.e67831. 〈10.1371/journal.pone.0067831〉. 〈hal-01321589〉

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