Regulation of phosphatase activity in bacterial chemotaxis

Bacterial chemotaxis is the most studied model system for signaling by the widely spread family of two-component regulatory systems. It is controlled by changes in the phosphorylation level of the chemotactic response regulator, CheY, mediated by a histidine kinase (CheA) and a specific phosphatase (CheZ). While it is known that CheA activity is regulated, via the receptors, by chemotactic stimuli, the input that may regulate CheY dephosphorylation by CheZ has not been found. We measured, by using stopped-flow fluorometry, the kinetics of CheZ-mediated dephosphorylation of CheY. The onset of dephosphorylation was delayed by approximately 50 ms after mixing phosphorylated CheY (CheY approximately P) with CheZ, and a distinct overshoot was observed in the approach to the new steady state of CheY approximately P. The delay and overshoot were not observed in a hyperactive mutant CheZ protein (CheZ54RC) that does not support chemotaxis in vivo and appears to be constitutively active. CheZ activity was cooperative with respect to CheY approximately P, with a Hill-coefficient of 2.5. The observed delayed modulation of CheZ activity and its cooperativity suggest that the phosphatase activity is regulated at the level of CheY approximately P-CheZ interaction. This novel kind of interplay between a response regulator and its phosphatase may be involved in signal tuning and in adaptation to chemotactic signals.