Penicillin-binding protein 2x of Streptococcus pneumoniae: three new mutational pathways for remodelling an essential enzyme into a resistance determinant |
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Authors: | Maurer Patrick Koch Barbara Zerfass Ilka Krauss Jan van der Linden Mark Frère Jean-Marie Contreras-Martel Carlos Hakenbeck Regine |
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Affiliation: | 1 Department of Microbiology, University of Kaiserslautern, Paul-Ehrlich Straße 23, D-67663 Kaiserslautern, Germany 2 Institut de Chimie B6, Université de Liège, B-4000 Liège, Belgium 3 Institut de Biologie Structurale Jean-Pierre Ebel (CEA/CNRS/UJF/PSB), Laboratoire des Protéines Membranaires, 41 rue Jules Horowitz, 38027 Grenoble, France |
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Abstract: | Mutations in the transpeptidase domain of penicillin-binding protein 2x (PBP2x) of Streptococcus pneumoniae that reduce the affinity to beta-lactams are important determinants of resistance to these antibiotics. We have now analyzed in vitro and in vivo properties of PBP2x variants from cefotaxime-resistant laboratory mutants and a clinical isolate. The patterns of two to four resistance-specific mutations present in each of the proteins, all of which are placed between 6.6 and 24 Å around the active site, fall into three categories according to their positions in the three-dimensional structure. The first PBP2x group is characterized by mutations at the end of helix α11 and carries the well-known T550A change and/or one mutation on the surface of the penicillin-binding domain in close contact with the C-terminal domain. All group I proteins display very low acylation efficiencies, ≤ 1700 M− 1 s− 1, for cefotaxime. The second class represented by PBP2x of the mutant C505 shows acylation efficiencies below 100 M− 1 s− 1 for both cefotaxime and benzylpenicillin and contains the mutation L403F at a critical site close to the active serine. PBP2x of the clinical isolate 669 reveals a third mutational pathway where at least the two mutations Q552E and S389L are important for resistance, and acylation efficiency is reduced for both beta-lactams to around 10,000 M− 1 s− 1. In each group, at least one mutation is located in close vicinity to the active site and mediates a resistance phenotype in vivo alone, whereas other mutations might exhibit secondary effects only in context with other alterations. |
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Keywords: | PBP, penicillin-binding protein GST, glutathione S-transferase MIC, minimal inhibitory concentration |
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