Figure 1.

Chemotaxis signalling pathway in (a) E. coli and (b) R. sphaeroides (adapted from [8]). Blue arrows indicate phosphotransfer. (a) In E. coli, attractant binding to the transmembrane receptors inhibits CheA autophosphorylation. Subsequently, CheA-P transfers the phospho group to CheY, allowing CheY-P to bind flagellar motors for ‘tumbling’. CheZ phosphatase dephosphorylates CheY-P to enable ‘running’. CheR and CheB are antagonistic proteins that fine-tune sensitivity of the receptors by methylation and demethylation, respectively. (b) In R. sphaeroides, transmembrane chemoreceptors can sense external concentration of attractants, and the cell presumably responds by CheA₂ autophosphorylation. CheA₂-P then transfers phospho groups to a range of response regulators including CheY₃, CheY₄, CheY₆, CheB₁ and CheB₂. Cytosolic chemoreceptors may sense the internal metabolic state. When cytosolic cluster is activated, CheA₃ and CheA₄ cooperate to phosphorylate CheY₆ and CheB₂. (Online version in colour.)