Signal decay through a reverse phosphorelay in the arc two-component signal transduction system

Escherichia coli senses and signals anoxic or low redox conditions in its g rowth environment by the Are two-component system. Under those conditions, the tripartite sensor kinase ArcB undergoes autophosphorylation at the expe nse of ATP and subsequently transphosphorylates its cognate response regula tor ArcA through a His --> Asp --> His --> Asp phosphorelay pathway. In thi s study we used various combinations of wild-type and mutant ArcB domains t o analyze in vitro the pathway for signal decay. The results indicate that ArcA-P dephosphorylation does not occur by direct hydrolysis but by transfe r of the phosphoryl group to the secondary transmitter and subsequently to the receiver domain of ArcB. This reverse phosphorelay involves both the co nserved His-717 of the secondary transmitter domain and the conserved Asp-5 76 of the receiver domain of ArcB but not the conserved His-292 of its prim ary transmitter domain. This novel pathway for signal decay mag generally a pply to signal transduction systems with tripartite sensor kinases.