Mechanistic Basis for ATP-Dependent Inhibition of Glutamine Synthetase by Tabtoxinine-β-lactam

Biochemistry. 2018 Jan 9;57(1):117-135. doi: 10.1021/acs.biochem.7b00838. Epub 2017 Oct 31.


Tabtoxinine-β-lactam (TβL), also known as wildfire toxin, is a time- and ATP-dependent inhibitor of glutamine synthetase produced by plant pathogenic strains of Pseudomonas syringae. Here we demonstrate that recombinant glutamine synthetase from Escherichia coli phosphorylates the C3-hydroxyl group of the TβL 3-(S)-hydroxy-β-lactam (3-HβL) warhead. Phosphorylation of TβL generates a stable, noncovalent enzyme-ADP-inhibitor complex that resembles the glutamine synthetase tetrahedral transition state. The TβL β-lactam ring remains intact during enzyme inhibition, making TβL mechanistically distinct from traditional β-lactam antibiotics such as penicillin. Our findings could enable the design of new 3-HβL transition state inhibitors targeting enzymes in the ATP-dependent carboxylate-amine ligase superfamily with broad therapeutic potential in many disease areas.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adenosine Triphosphate / metabolism*
  • Azetidines / isolation & purification
  • Azetidines / metabolism
  • Azetidines / pharmacology*
  • Bacterial Toxins / biosynthesis
  • Bacterial Toxins / isolation & purification
  • Bacterial Toxins / pharmacology*
  • Catalysis
  • Chromatography, Liquid
  • Escherichia coli / drug effects
  • Escherichia coli / enzymology*
  • Escherichia coli / growth & development
  • Escherichia coli Proteins / antagonists & inhibitors*
  • Glutamate-Ammonia Ligase / antagonists & inhibitors*
  • Mass Spectrometry
  • Microbial Sensitivity Tests
  • Nuclear Magnetic Resonance, Biomolecular
  • Phosphorylation
  • Pseudomonas syringae / metabolism


  • Azetidines
  • Bacterial Toxins
  • Escherichia coli Proteins
  • tabtoxinine beta-lactam
  • Adenosine Triphosphate
  • Glutamate-Ammonia Ligase