Interaction energies between beta-lactam antibiotics and E. coli penicillin-binding protein 5 by reversible thermal denaturation

Protein Sci. 2001 Jun;10(6):1254-9. doi: 10.1110/ps.52001.


Penicillin-binding proteins (PBPs) catalyze the final stages of bacterial cell wall biosynthesis. PBPs form stable covalent complexes with beta-lactam antibiotics, leading to PBP inactivation and ultimately cell death. To understand more clearly how PBPs recognize beta-lactam antibiotics, it is important to know their energies of interaction. Because beta-lactam antibiotics bind covalently to PBPs, these energies are difficult to measure through binding equilibria. However, the noncovalent interaction energies between beta-lactam antibiotics and a PBP can be determined through reversible denaturation of enzyme-antibiotic complexes. Escherichia coli PBP 5, a D-alanine carboxypeptidase, was reversibly denatured by temperature in an apparently two-state manner with a temperature of melting (T(m)) of 48.5 degrees C and a van't Hoff enthalpy of unfolding (H(VH)) of 193 kcal/mole. The binding of the beta-lactam antibiotics cefoxitin, cloxacillin, moxalactam, and imipenem all stabilized the enzyme significantly, with T(m) values as high as +4.6 degrees C (a noncovalent interaction energy of +2.7 kcal/mole). Interestingly, the noncovalent interaction energies of these ligands did not correlate with their second-order acylation rate constants (k(2)/K'). These rate constants indicate the potency of a covalent inhibitor, but they appear to have little to do with interactions within covalent complexes, which is the state of the enzyme often used for structure-based inhibitor design.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Acylation
  • Anti-Bacterial Agents / metabolism*
  • Bacterial Proteins*
  • Carrier Proteins / metabolism*
  • Cefoxitin / metabolism
  • Circular Dichroism
  • Cloxacillin / metabolism
  • Escherichia coli / metabolism*
  • Hexosyltransferases*
  • Imipenem / metabolism
  • Models, Chemical
  • Moxalactam / metabolism
  • Muramoylpentapeptide Carboxypeptidase / metabolism*
  • Penicillin-Binding Proteins
  • Peptidyl Transferases*
  • Protein Binding
  • Protein Denaturation
  • Spectrometry, Fluorescence
  • Temperature
  • Thermodynamics
  • beta-Lactams / metabolism*


  • Anti-Bacterial Agents
  • Bacterial Proteins
  • Carrier Proteins
  • Penicillin-Binding Proteins
  • beta-Lactams
  • Cefoxitin
  • Imipenem
  • Peptidyl Transferases
  • Hexosyltransferases
  • Muramoylpentapeptide Carboxypeptidase
  • Cloxacillin
  • Moxalactam