Mutants with defective phosphatase activity show no phosphorylation-dependent oligomerization of CheZ: The phosphatase of bacterial chemotaxis

Abstract

CheZ is the phosphatase of CheY, the response regulator in bacterial chemotaxis. The mechanism by which the activity of CheZ is regulated is not known. We used cheZ mutants of Salmonella typhimurium, which had been isolated by Sockett et al. (Sockett, H., Yamaguchi, S., Kihara, M., Irikura, V. M., and Macnab, R. M. (1992) J. Bacteriol. 174, 795-806), for cloning the mutant cheZ genes, overexpressing and purifying their products. We then measured the phosphatase activity, binding to CheY and to phosphorylated CheY (CheY∼P), and CheY∼P-dependent oligomerization of the mutant CheZ proteins. While all the mutant proteins were defective in their phosphatase activity, they bound to CheY and CheY∼P as well as wild-type CheZ. However, unlike wild-type CheZ, all the four mutant proteins failed to oligomerize upon interaction with CheY∼P. On the basis of these and earlier results it is suggested that (i) oligomerization is required for the phosphatase activity of CheZ, (ii) the region defined by residues 141-145 plays an important role in mediating CheZ oligomerization and CheY∼P dephosphorylation but is not necessary for the binding to CheY∼P, (iii) the oligomerization and hence the phosphatase activity are regulated by the level of CheY∼P, and (iv) this regulation plays a role in the adaptation to chemotactic stimuli.