A PAS domain binds asparagine in the chemotaxis receptor McpB in Bacillus subtilis

George D. Glekas, Richard M. Foster, Joseph R. Cates, Jeffrey A. Estrella, Michael J. Wawrzyniak, Christopher V. Rao, George W. Ordal

Research output: Contribution to journalArticle

Abstract

During chemotaxis toward asparagine by Bacillus subtilis, the ligand is thought to bind to the chemoreceptor McpB on the exterior of the cell and induce a conformational change. This change affects the degree of phosphorylation of the CheA kinase bound to the cytoplasmic region of the receptor. Until recently, the sensing domains of the B. subtilis receptors were thought to be structurally similar to the well studied Escherichia coli fourhelical bundle. However, sequence analysis has shown the sensing domains of receptors from these two organisms to be vastly different. Homology modeling of the sensing domain of the B. subtilis asparagine receptor McpB revealed two tandem PAS domains. McpB mutants having alanine substitutions in key arginine and tyrosine residues of the upper PAS domain but not in any residues of the lower PAS domain exhibited a chemotactic defect in both swarm plates and capillary assays. Thus, binding does not appear to occur across any dimeric surface but within a monomer.Amodified capillary assay designed to determine the concentration of attractant where chemotaxis is most sensitive showed that when Arg-111, Tyr-121, or Tyr-133 is mutated to an alanine, much more asparagine is required to obtain an active chemoreceptor. Isothermal titration calorimetry experiments on the purified sensing domain showed a KD to asparagine of 14 μM, with the three mutations leading to less efficient binding. Taken together, these results reveal not only a novel chemoreceptor sensing domain architecture but also, possibly, a different mechanism for chemoreceptor activation.

Original languageEnglish (US)
Pages (from-to)1870-1878
Number of pages9
JournalJournal of Biological Chemistry
Volume285
Issue number3
DOIs
StatePublished - Jan 15 2010

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology

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