pH sensing in bacterial XXXX .

@entity6722 @entity3793 @entity492 @entity563 @entity717
Bacteria are able to sense a broad range of chemical and energetic stimuli and modulate their swimming behaviour to migrate to more favourable environments. Signal transduction in bacterial @entity6722 is mediated by a two-component system composed of a protein @entity3793 kinase, CheA, and a response regulator, CheY. The phosphorylated response regulator, P approximately CheY, binds to a protein at the flagellar motor, FliM, to cause reversals in @entity717 . The level of P approximately CheY is controlled by the activity of the kinase CheA, which is in turn regulated by membrane receptors at the cell surface. Membrane receptors such as the @entity492 receptor, Tar, are composed of two distinct regions: an extracellular sensing domain that binds stimulatory ligands, @entity492 in the case of Tar; and an intracellular signalling domain that forms a complex with the protein kinase CheA. What is the mechanism of transmembrane signalling? How does @entity492 binding to the sensing domain at the outside surface of the membrane translate into a change in kinase activity at the membrane cytosol interface? Recent results suggest that the mechanism depends on perturbations in lateral packing within an extensive array of receptors localized to patches at the cell poles. Receptor patching appears to depend on higher-order associations with the kinase CheA as well as an adaptor protein, CheW. It is difficult to assess the locus of pH effects within the context of even a simple signal transduction system like that involved in bacterial @entity6722 . Previous results with mutant strains have indicated that the @entity563 receptor, Tsr, is critical for pH sensing, but in vitro results do not support such a straightforward interpretation of the genetic data.
