Phosphorylation of the response regulator CheV is required for adaptation to attractants during Bacillus subtilis chemotaxis

In the Gram-positive soil bacterium Bacillus subtilis, the chemoreceptors a re coupled to the central two-component kinase CheA via two proteins, CheW and CheV. CheV is a two-domain protein with an N-terminal CheW-like domain and a C-terminal two-component receiver domain. In this study, we show that CheV is phosphorylated in vitro on a conserved aspartate in the presence o f phosphorylated CheA (CheA-P). This reaction is slower compared with the p hospho-transfer reaction between CheA-P and one other response regulator of the system, CheB. CheV-P is also highly stable in comparison with CheB-P. Both of these properties are more pronounced in the full-length protein com pared with a truncated form composed only of the receiver domain, that is, deletion of the CheW-like domain results in increase in the rate of the pho spho-transfer reaction and decrease in stability of the phosphorylated prot ein. Phosphorylation of CheV is required for adaptation to the addition of the chemoattractant asparagine. In tethered-cell assays, strains expressing an unphosphorylatable point mutant of cheV or a truncated mutant lacking t he entire receiver domain are severely impaired in adaptation to the additi on of asparagine. Both of these strains, however, show near normal counterc lockwise biases, suggesting that in the absence of the attractant the chemo receptors are efficiently coupled to CheA kinase by the mutant CheV protein s. Inability of the CheW-like domain of CheV to support complete adaptation to the addition of asparagine also suggests that unlike CheW this domain b y itself may lead to the formation of signaling complexes that stay overact ive in the presence of the attractant. A possible structural basis for this feature is discussed.