pH dependence of CheA autophosphorylation in Escherichia coli.

摘要: Chemotaxis by cells of Escherichia coli and Salmonella typhimurium depends upon the ability chemoreceptors called transducers to communicate with switch components flagellar motors modulate swimming behavior. This communication requires an excitatory pathway composed cytoplasmic signal transduction proteins, CheAL, CheAS, CheW, CheY, CheZ. Of these, autokinase CheAL is most central. Modifications or mutations that affect rate at which autophosphorylates result in profound chemotactic defects. Here we demonstrate pH can activity vitro. exhibits a bell-shaped dependence within range 6.5 10.0, consistent notion two proton dissociation events autophosphorylation kinetics: one characterized pKa about 8.1 another exhibiting 8.9. These vitro results predict decrease response reduction intracellular pH, should cause increased counterclockwise rotation. We observed such vivo for containing partially reconstituted chemotaxis system. Benzoate (10 mM, 7.0), weak acid when undissociated readily traverses membrane, causes from 7.6 7.3. In this reduction, expressing but not transducers, exhibited small reproducible increase fraction time they spun their counterclockwise. The added presence CheW Tar Trg resulted more dramatic response. significance our results, relationships regulation behavior, mechanisms might CheA are discussed.