Penicillin-binding protein 2x of Streptococcus pneumoniae: three new mutational pathways for remodelling an essential enzyme into a resistance determinant

J Mol Biol. 2008 Mar 7;376(5):1403-16. doi: 10.1016/j.jmb.2007.12.058. Epub 2008 Jan 4.


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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Cefotaxime / pharmacology*
  • Humans
  • Models, Molecular
  • Penicillin-Binding Proteins / chemistry*
  • Penicillin-Binding Proteins / genetics*
  • Penicillin-Binding Proteins / metabolism
  • Peptidyl Transferases / genetics
  • Peptidyl Transferases / metabolism
  • Pneumococcal Infections / microbiology
  • Point Mutation
  • Protein Structure, Secondary
  • Protein Structure, Tertiary
  • Streptococcus pneumoniae / chemistry*
  • Streptococcus pneumoniae / drug effects*
  • beta-Lactam Resistance*


  • Penicillin-Binding Proteins
  • PBP 2x protein, Streptococcus
  • Peptidyl Transferases
  • Cefotaxime

Associated data

  • PDB/1QME
  • PDB/1QMF