Phosphate flow in the chemotactic response system of Helicobacter pylori

It is well established that motility is an essential virulence trait of the human gastric pathogen Helicobacter pylori. Accordingly, chemotaxis contributes to the ability of H. pylori to colonize in animal infection models. Chemotactic signal transduction in H. pylori differs from the enterobacterial paradigm in several respects. In addition to a separate CheY response regulator protein (CheY1) H. pylori contains a CheY-like receiver domain (CheY2) which is C-terminally fused to the histidine kinase CheA. Furthermore, the genome of H. pylori encodes three CheV proteins consisting of an N-terminal CheW-like domain and a C-terminal receiver domain, while there are no orthologues of the chemotaxis genes cheB, cheR and cheZ. To obtain insight into the mechanisms controlling the chemotactic response of H. pylori we investigated the phosphotransfer reactions between the purified two-component signalling modules in vitro. We demonstrate that both CheY1 and CheY2 are phosphorylated by CheA~P and that the three CheV proteins mediate the dephosphorylation of CheA~P, but with a clearly reduced efficiency as compared to CheY1 and CheY2. Furthermore, our data indicate retrophosphorylation of CheAY2 by CheY1~P suggesting a role of CheY2 as a phosphate sink to modulate the half-life of CheY1 ~P.