title: Receptor sensitivity in bacterial chemotaxis.
abstract: Chemoreceptors in Escherichia coli are coupled to the flagella by a labile phosphorylated intermediate, CheY approximately P. Its activity can be inferred from the rotational bias of flagellar motors, but motor response is stochastic and limited to a narrow physiological range. Here we use fluorescence resonance energy transfer to monitor interactions of CheY approximately P with its phosphatase, CheZ, that reveal changes in the activity of the receptor kinase, CheA, resulting from the addition of attractants or repellents. Analyses of cheR and/or cheB mutants, defective in receptor methylation/demethylation, show that response sensitivity depends on the activity of CheB and the level of receptor modification. In cheRcheB mutants, the concentration of attractant that generates a half-maximal response is equal to the dissociation constant of the receptor. In wild-type cells, it is 35 times smaller. This amplification, together with the ultrasensitivity of the flagellar motor, explains previous observations of high chemotactic gain.
authors.affiliation: Department of Molecular and Cellular Biology, Harvard University, Cambridge, MA 02138, USA.
authors.forename: Victor
authors.initials: V
authors.lastname: Sourjik
authors.forename: Howard C
authors.initials: HC
authors.lastname: Berg
mesh_terms: D018407:Bacterial Physiological Phenomena; D001426:Bacterial Proteins; D002633:Chemotaxis; D004305:Dose-Response Relationship, Drug; D029968:Escherichia coli Proteins; D000071677:Histidine Kinase; D008565:Membrane Proteins / Q000737:chemistry / Q000502:physiology*; D000072236:Methyl-Accepting Chemotaxis Proteins; D008745:Methylation; D016202:N-Methylaspartate / Q000031:analogs & derivatives* / Q000494:pharmacology; D010766:Phosphorylation; D011485:Protein Binding; D013050:Spectrometry, Fluorescence; D013997:Time Factors
chemical_list: D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D008565:Membrane Proteins; D000072236:Methyl-Accepting Chemotaxis Proteins; C000607606:cheY protein, E coli; D016202:N-Methylaspartate; C037699:2-methylaspartic acid; D000071677:Histidine Kinase; C000607608:cheA protein, E coli