Evidence that the methylesterase of bacterial chemotaxis may be a serine hydrolase

Joanna K. Krueger, J. Stock, C. E. Schutt

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CheB, the methylesterase of chemotactic bacteria, catalyzes the hydrolysis of glutamyl-methyl esters in bacterial chemoreceptor proteins. The two cysteines predicted by the amino acid sequence of CheB were replaced by alanine residues. The resulting mutants, Cys207-Ala, Cys309-Ala and a double cysteine mutant Cys207-Ala/Cys309-Ala, retained methylesterase activity, indicating that sulfhydryls are not crucial for CheB mediated catalysis. A homology search revealed a conserved serine active-site region between residues 162 and 166 which is homologous to the active-site region of acetylcholine esterases, suggesting that Ser164 of CheB is the active-site nucleophile. Oligonucleotide-directed mutagenesis was used to change the serine to a cysteine. This Ser164-Cys mutant had less than 2% of the wild-type activity. Unlike the serine proteinases which utilize a 'catalytic triad' mechanism, CheB does not have the conserved histidine and aspartic acid residues located in positions N-terminal to the active-site serine. In addition, CheB is not labeled with di-isopropylfluorophosphate, a potent inhibitor of other serine hydrolases. A novel mechanism is proposed for CheB involving substrate-assisted catalysis to account for these apparent anomalies.

Original languageEnglish (US)
Pages (from-to)322-326
Number of pages5
JournalBiochimica et Biophysica Acta (BBA)/Protein Structure and Molecular
Issue number3
StatePublished - Mar 12 1992

All Science Journal Classification (ASJC) codes

  • Molecular Biology
  • Structural Biology
  • Biophysics
  • Biochemistry


  • Active-site serine
  • Chemotaxis
  • Di-isopropylfluorophosphate
  • Methylesterase
  • Substrate-assisted catalysis


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