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 regulat or, CheY, mediated by a histidine kinase (CheA) and a specific phosphatase (CheZ). While it is known that CheA activity is regulated, via the receptor s, by chemotactic stimuli, the input that may regulate CheY dephosphorylati on by CheZ has not been found. We measured, by using stopped-flow fluoromet ry, the kinetics of CheZ-mediated dephosphorylation of CheY. The onset of d ephosphorylation was delayed by similar to 50 ms after mixing phosphorylate d CheY (CheY similar to P) with CheZ, and a distinct overshoot was observed in the approach to the new steady state of CheY similar to P. The delay an d overshoot were not observed in a hyperactive mutant CheZ protein (CheZ54R C) that does not support chemotaxis in vivo and appears to be constitutivel y active. CheZ activity was cooperative with respect to CheY similar to P, with a Hill-coefficient of 2.5. The observed delayed modulation of CheZ act ivity and its cooperativity suggest that the phosphatase activity is regula ted at the level of CheY similar to 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. (C) 1998 Academi c Press.