Overcoming resistance to beta-lactamase inhibitors: comparing sulbactam to novel inhibitors against clavulanate resistant SHV enzymes with substitutions at Ambler position 244

Biochemistry. 2007 Oct 9;46(40):11361-8. doi: 10.1021/bi700792a. Epub 2007 Sep 12.


Amino acid changes at Ambler position R244 in class A TEM and SHV beta-lactamases confer resistance to ampicillin/clavulanate, a beta-lactam/beta-lactamase inhibitor combination used to treat serious infections. To gain a deeper understanding of this resistance phenotype, we investigated the activities of sulbactam and two novel penem beta-lactamase inhibitors with sp2 hybridized C3 carboxylates and bicyclic R1 side chains against a library of SHV beta-lactamase variants at the 244 position. Compared to SHV-1 expressed in Escherichia coli, all 19 R244 variants exhibited increased susceptibility to ampicillin/sulbactam, an important difference compared to ampicillin/clavulanate. Kinetic analyses of SHV-1 and three SHV R244 (-S, -Q, and -L) variants revealed the Ki for sulbactam was significantly elevated for the R244 variants, but the partition ratios, kcat/kinact, were markedly reduced (13 000 --> <or=500). A timed inactivation-mass spectrometry analysis of SHV inhibited by sulbactam showed that SHV-1 beta-lactamase was unmodified at 15 min. A parallel experiment with R244S demonstrated 70 and 88 +/- 3 Da fragments of sulbactam covalently attached to the beta-lactamase. We also observed that the Ki values of penems 1 and 2 were increased for R244 variants compared to those for SHV; however, these inhibitors effectively restored ampicillin susceptibility in vitro. Compared to that of sulbactam, the kcat/kinact values of penems for SHV-1 and R244S were low (<or=2), and unfragmented adducts of each penem were covalently attached to SHV-1 and R244S when studied using the timed inactivation-mass spectrometry method. The R244S mutation affects beta-lactamase inactivators differently, but resistance can be overcome by designing penem inhibitors with strategic chemical properties that improve affinity and impair turnover.

Publication types

  • Comparative Study
  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Amino Acid Substitution
  • Ampicillin / chemistry
  • Ampicillin / pharmacology
  • Clavulanic Acid / chemistry
  • Clavulanic Acid / pharmacology*
  • Drug Resistance, Bacterial / genetics
  • Enzyme Inhibitors / chemistry
  • Enzyme Inhibitors / pharmacology*
  • Kinetics
  • Mass Spectrometry
  • Molecular Structure
  • Plasmids / genetics
  • Protein Structure, Secondary
  • Spectrometry, Mass, Electrospray Ionization
  • Structure-Activity Relationship
  • Sulbactam / chemistry
  • Sulbactam / pharmacology*
  • beta-Lactam Resistance / genetics
  • beta-Lactamase Inhibitors*
  • beta-Lactamases / genetics


  • Enzyme Inhibitors
  • beta-Lactamase Inhibitors
  • Clavulanic Acid
  • Ampicillin
  • beta-lactamase PIT-2
  • beta-Lactamases
  • Sulbactam