Abstract
Histidine kinases are key regulators in the bacterial two-component systems that mediate the cellular response to environmental changes. The vast majority of the sensor histidine kinases belong to the bifunctional HisKA family, displaying both kinase and phosphatase activities toward their substrates. The molecular mechanisms regulating the opposing activities of these enzymes are not well understood. Through a combined NMR and crystallographic study on the histidine kinase HK853 and its response regulator RR468 from Thermotoga maritima, here we report a pH-mediated conformational switch of HK853 that shuts off its phosphatase activity under acidic conditions. Such a pH-sensing mechanism is further demonstrated in the EnvZ-OmpR two-component system from Salmonella enterica in vitro and in vivo, which directly contributes to the bacterial infectivity. Our finding reveals a broadly conserved mechanism that regulates the phosphatase activity of the largest family of bifunctional histidine kinases in response to the change of environmental pH.
Highlights
Histidine kinases are key regulators in the bacterial two-component systems that mediate the cellular response to environmental changes
As T264 of HK853cp is at least 5 Å away from either K105 or the K105-interacting fluorine atom (F2) of BeF3−-modified D53, we suggest that the chemical entity causing the chemical shift perturbation of the K105-interacting fluorine atom (F2) is a T264-mediated water molecule, which in turn forms a hydrogen bond with the F2 fluorine atom; this water molecule is likely the catalytic water molecule that interacts with H260 of HK853 in the trans χ1 rotameric configuration of the catalytically active state at high pH (Fig. 3, upper right panel)
Our study represents a complementary regulatory mechanism of bifunctional histidine kinases that inactivates the phosphatase activity through a pH-gated conformational switch (Fig. 3)
Summary
Histidine kinases are key regulators in the bacterial two-component systems that mediate the cellular response to environmental changes. Through a combined NMR and crystallographic study on the histidine kinase HK853 and its response regulator RR468 from Thermotoga maritima, here we report a pH-mediated conformational switch of HK853 that shuts off its phosphatase activity under acidic conditions Such a pH-sensing mechanism is further demonstrated in the EnvZ-OmpR two-component system from Salmonella enterica in vitro and in vivo, which directly contributes to the bacterial infectivity. Our study reveals a pH-mediated conformational change, involving a sidechain rotameric switch of the catalytic histidine residue that inactivates the phosphatase activity of HK853 Such a mechanism mediates the phosphatase activity of the classical EnvZ bifunctional histidine kinase, of the HisKA family, from Salmonella enterica in vitro; the transcriptional response genes of the EnvZ/OmpR TCS are upregulated at low pH in cells, consistent with the pH-gated inactivation of the EnvZ a Signal
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