Fig. 5
pH-gated regulation of the phosphatase activity of the bifunctional histidine kinase EnvZ in Salmonella. a The schematic illustration depicting the different functions of EnvZ at different pHs during host cell invasion. The H243A and T247A point mutations abolish the kinase and phosphatase activities of EnvZ, respectively. b Sequence alignment of the α1 helix in EnvZ and HK853 from the same HisKA subfamily, with the HxxxT motif highlighted in red. Identical and conserved residues are indicated below the sequence alignment. c Differential phosphatase activities of EnvZcp detected by the Phos-tag gel shift assay at pH 5.0 and 8.0, respectively. d Detection of the expression of ssrA and ssrB genes by real-time fluorescence quantitative PCR at different pHs. The expression levels at pH 7.0 and 5.0 were shown in black and red, respectively. In each group, the expression level of the H243A mutant is normalized to 1.0 for comparison. e Macrophage infectivity of S. typhimurium LT2 and mutants. The infectivity was defined as the percentage of infected host cells. Error bars in d and e represent the standard deviation from quadruplet measurements
