Characterization of the CheA(S)/CheZ complex: A specific interaction resulting in enhanced dephosphorylating activity on CheY-phosphate

The cheA gene encodes two overlapping polypeptides with a common carboxyl terminus: CheA(L) and CheA(S). CheA(L) plays a central role in the Escherichia coli chemotaxis signalling pathway by autophosphorylation and transferring the phosphate to both CheY and CheB. On the other hand, the physiological functions of CheA(S) remain unknown. We have observed that overproduction of CheA(S) in wild-type cells increased counterclockwise-biased flagellar rotation, and this effect is dependent on the presence of CheZ. CheZ specifically facilitates CheY-phosphate (CheY-P) dephosphorylation and generates a smooth swimming signal. A physical interaction was detected between CheZ and CheA(S) in wild-type cell lysates by immunoprecipitation. The CheA(S)/CheZ interaction does not require other chemotaxis components, as we could form the complex using purified CheA(S) and CheZ proteins. The ability of CheA(S) to bind to CheZ depends on its being in the reduced state. We found that under non-reducing conditions, CheA(S) appears to form intermolecular disulphide bonds and loses the ability to bind to CheZ. Finally, the CheA(S)/CheZ complex formed in vitro shows a greater dephosphorylating activity on CheY-P than does free CheZ.