Substitutions in PBP2b from β-Lactam-resistant Streptococcus pneumoniae Have Different Effects on Enzymatic Activity and Drug Reactivity

J Biol Chem. 2017 Feb 17;292(7):2854-2865. doi: 10.1074/jbc.M116.764696. Epub 2017 Jan 6.


Pneumococcus resists β-lactams by expressing variants of its target enzymes, the penicillin-binding proteins (PBPs), with many amino acid substitutions. Up to 10% of the sequence can be modified. These altered PBPs have a much reduced reactivity with the drugs but retain their physiological activity of cross-linking the peptidoglycan, the major constituent of the bacterial cell wall. However, because β-lactams are chemical and structural mimics of the natural substrate, resistance mediated by altered PBPs raises the following paradox: how PBPs that react poorly with the drugs maintain a sufficient level of activity with the physiological substrate. This question is addressed for the first time in this study, which compares the peptidoglycan cross-linking activity of PBP2b from susceptible and resistant strains with their inhibition by different β-lactams. Unexpectedly, the enzymatic activity of the variants did not correlate with their antibiotic reactivity. This finding indicates that some of the numerous amino acid substitutions were selected to restore a viable level of enzymatic activity by a compensatory molecular mechanism.

Keywords: Streptococcus; antibiotic resistance; cell wall; enzyme kinetics; peptidoglycan.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Cephalosporins / metabolism
  • Drug Resistance, Bacterial / drug effects*
  • Penicillin-Binding Proteins / chemistry
  • Penicillin-Binding Proteins / genetics
  • Penicillin-Binding Proteins / metabolism*
  • Protein Denaturation
  • Recombinant Proteins / chemistry
  • Recombinant Proteins / genetics
  • Recombinant Proteins / metabolism
  • Sequence Homology, Amino Acid
  • Streptococcus pneumoniae / drug effects*
  • Streptococcus pneumoniae / metabolism
  • beta-Lactams / pharmacology*


  • Cephalosporins
  • Penicillin-Binding Proteins
  • Recombinant Proteins
  • beta-Lactams
  • nitrocefin

Associated data

  • PDB/2WAF
  • PDB/2WAD