Activation of the AtoSC two-component system in the absence of the AtoC N-terminal receiver domain in E. coli.

The AtoSC two-component system in E. coli consists of the AtoS sensor kinase and the AtoC response regulator. It regulates positively the transcriptional activation of atoDAEB operon, encoding enzymes involved in short-chain fatty acid catabolism upon acetoacetate-mediated induction. AtoSC acting on atoDAEB operon, regulates the biosynthesis and the intracellular distribution of short-chain poly-(R)-3-hydroxybutyrate (cPHB). A phosphorylation-incompetent AtoC form was constructed lacking its N-terminal receiver domain, trAtoC, to study the effects of AtoC domains on cPHB biosynthesis and atoDAEB operon regulation. Both cPHB biosynthesis and atoDAEB gene expression were regulated positively by trAtoC in the absence of any inducer in E. coli of both atoSC (+) and ΔatoSC genotypes. The presence of acetoacetate or spermidine further promoted these trAtoC actions. Competitive regulatory functions between the full length AtoC and trAtoC were observed referring to atoDAEB and cPHB targets as well as growth of trAtoC-overproducing atoSC (+) cells on butyrate as the sole carbon source. trAtoC in contrast to the wild-type AtoC presented different modes of cPHB and atoDAEB regulation in the presence of compounds involved in fatty acid metabolism including CoA-SH, acetyl-CoA, sodium acetate or 3-hydroxybutyryl-CoA. These data provide evidence for a role of the AtoC N-terminal receiver domain in regulating the biological activities of AtoSC as well as additional mechanisms of interactions between the AtoSC constituents including their established inducers or new effectors towards the accomplishment of the AtoSC TCS signal transduction.