Adenylate Charge Regulates Sensor Kinase CheS(3) To Control Cyst Formation in Rhodospirillum centenum

Rhodospirillum centenum forms metabolically dormant cysts under unfavorable growth conditions such as desiccation or nutrient starvation. The development of cysts is tightly regulated and involves a cyst-repressing chemotaxis-like signal transduction pathway called the Che(3) signaling cascade. The Che(3) cascade is comprised of a methyl chemoreceptor (MCP(3)), receptor-methylating/demethylating proteins CheB(3) and CheR(3), two CheW(3) linker proteins, a CheA(3)-CheY hybrid histidine kinase, and a single-domain response regulator, CheY(3). In addition to Che-like components, the Che(3) cascade also contains a second hybrid histidine kinase, CheS(3). Recent biochemical and genetic studies show that CheA(3) does not serve as a phosphor donor for CheY(3); instead, CheA(3) inhibits a CheS(3)→CheY(3) two-component system by phosphorylating an inhibitory receiver domain of CheS(3). In this study, we show that in addition to phosphorylation by CheA(3), the phosphorylation state of CheS(3) is also regulated by the cellular energy level as quantified by the molar ratio of ATP/(ATP + ADP). A 35% decrease in cellular energy is shown to occur in vivo upon a nutrient downshift that gives rise to cyst formation. When this energy decline is replicated in vitro, the phosphorylation level of CheS(3) is reduced by ~75%. Finally, we also show that ADP-mediated reduction of CheS(3) phosphorylation is a consequence of ADP enhancing autodephosphorylation of CheS(3).