Identification of a quinone-sensitive redox switch in the ArcB sensor kinase.

Escherichia coli senses and signals anoxic or low redox conditions in its growth environment by the Arc two-component system. Under anaerobic conditions, the ArcB sensor kinase autophosphorylates and transphosphorylates ArcA, a global transcriptional regulator that controls the expression of numerous operons involved in respiratory or fermentative metabolism. Under aerobic conditions, the kinase activity of ArcB is inhibited by the quinone electron carriers that act as direct negative signals. Here, we show that the molecular mechanism of kinase silencing involves the oxidation of two cytosol-located redox-active cysteine residues that participate in intermolecular disulfide bond formation, a reaction in which the quinones provide the source of oxidative power. Thus, a pivotal link in the Arc signal transduction pathway connecting the redox state of the quinone pool to the transcriptional apparatus is elucidated.