title: Penicillin-binding protein 2x of Streptococcus pneumoniae: three new mutational pathways for remodelling an essential enzyme into a resistance determinant.
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 A 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 alpha 11 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, <or=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.
authors.affiliation: Department of Microbiology, University of Kaiserslautern, Paul-Ehrlich Strasse 23, D-67663 Kaiserslautern, Germany.
authors.forename: Patrick
authors.initials: P
authors.lastname: Maurer
authors.forename: Barbara
authors.initials: B
authors.lastname: Koch
authors.forename: Ilka
authors.initials: I
authors.lastname: Zerfass
authors.forename: Jan
authors.initials: J
authors.lastname: Krauss
authors.forename: Mark
authors.initials: M
authors.lastname: van der Linden
authors.forename: Jean-Marie
authors.initials: JM
authors.lastname: Frère
authors.forename: Carlos
authors.initials: C
authors.lastname: Contreras-Martel
authors.forename: Regine
authors.initials: R
authors.lastname: Hakenbeck
mesh_terms: D002439:Cefotaxime / Q000494:pharmacology*; D006801:Humans; D008958:Models, Molecular; D046915:Penicillin-Binding Proteins / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism; D010458:Peptidyl Transferases / Q000235:genetics / Q000378:metabolism; D011008:Pneumococcal Infections / Q000382:microbiology; D017354:Point Mutation; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D013296:Streptococcus pneumoniae / Q000737:chemistry* / Q000187:drug effects*; D018440:beta-Lactam Resistance
chemical_list: D046915:Penicillin-Binding Proteins; C072223:PBP 2x protein, Streptococcus; D010458:Peptidyl Transferases; D002439:Cefotaxime