A PAS domain binds asparagine in the chemotaxis receptor McpB in Bacillus subtilis.
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 four-helical 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. A modified 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 K(D) to asparagine of 14 mum, 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.
Glekas
George D
GD
Department of Biochemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA.
Foster
Richard M
RM
Cates
Joseph R
JR
Estrella
Jeffrey A
JA
Wawrzyniak
Michael J
MJ
Rao
Christopher V
CV
Ordal
George W
GW
D000595:Amino Acid Sequence; D001216:Asparagine / Q000378:metabolism*; D001412:Bacillus subtilis / Q000166:cytology* / Q000378:metabolism*; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D001665:Binding Sites; D002151:Calorimetry; D002633:Chemotaxis; D029968:Escherichia coli Proteins / Q000737:chemistry / Q000378:metabolism; D000071677:Histidine Kinase; D008024:Ligands; D008565:Membrane Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D000072236:Methyl-Accepting Chemotaxis Proteins; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016296:Mutagenesis; D009154:Mutation; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D017386:Sequence Homology, Amino Acid
D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D008024:Ligands; D008565:Membrane Proteins; D000072236:Methyl-Accepting Chemotaxis Proteins; D001216:Asparagine; D000071677:Histidine Kinase; C000607608:cheA protein, E coli