Localization of the phosphatase CheZ to the chemoreceptor patch of Escherichia coli
Peritrichously flagellated bacteria carry out chemotaxis by modulating the frequency of switching between smooth swimming and tumbling. The tumbling frequency is controlled by a signal transduction cascade in which transmembrane receptors modulate the activity of a histidine kinase CheA that transfers phosphate to its cognate response regulator CheY. The proteins of the chemotaxis signaling cascade are localized to clusters found primarily at the poles of cells. In this work, the localization of the CheZ protein, a phosphatase that dephosphorylates CheY~P, is examined. Using a CheZ-GFP fusion protein, we show that CheZ was localized to the polar receptor patch via interaction with the short form of CheA (CheAS). Aromatic residues of CheZ near one end of the elongated CheZ four-helix bundle were determined to be critical for localization. Aliphatic residues in CheAS were also determined to be critical for CheZ localization to the receptor patch and substitution of these residues conferred a tumble bias to swimming cells. A mechanism of CheZ localization is proposed in which the CheZ apical loop interacts with a binding site formed by dimerization of the P1 domain of CheAS. The potential role of CheZ localization as a means of coordinating the rotation state of peritrichously distributed flagella is discussed.