Beryllium fluoride exchange rate accelerated by Mg²⁺ as discovered by ¹⁹F NMR

Rational modulation of the enzymatic intermediates for tuning the phosphatase activity of histidine kinase HK853

Histidine kinase (HK) of two-component signal transduction system (TCS) is a potential drug target for treating bacterial infections, and most HKs are bifunctional. We have previously identified the HXXXT motif of HK in HisKA subfamily to perform the phosphatase activity, but the specific working mechanism of the threonine is not well understood. In this paper, we use the phosphate group analog BeF₃^- to capture the enzymatic intermediates between HK853 and RR468 from Thermotoga maritima during dephosphorylation, and demonstrate that the T264 site is essential for populating capable near attack conformers (NAC) between enzyme and substrate to facilitate catalysis. Importantly, mutations at this site can modulate the phosphatase activity of HK. Our results help to understand the TCS signal transduction mechanisms and provide a reference for drug design.

A pH-gated conformational switch regulates the phosphatase activity of bifunctional HisKA-family histidine kinases

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.

Bacteria adapt to changing environmental conditions through signal transduction mediated by the two-component system (TCS). Here, the authors combine X-ray crystallography and NMR studies to characterize a pH-gated conformational switch that regulates the phosphatase activity of TCS bifunctional histidine kinases.