The membrane-integral sensor kinase DcuS of Escherichia coli consists of a periplasmically located sensory PASP domain, transmembrane helices TM1 and TM2, a cytoplasmic PASC domain and the kinase domain. Stimulus (C4-dicarboxylate) binding at PASP is required to stimulate phosphorylation of the kinase domain, resulting in phosphoryl transfer to the response regulator DcuR. PASC functions as a signaling device or a relay in signal transfer from TM2 to the kinase. Phosphorylated DcuR induces the expression of the target genes. Sensing by DcuS requires the presence of the C4-dicarboxylate transporter DctA during aerobic growth. DctA forms a sensor unit with DcuS, and a short C-terminal sequence of DctA forming the putative helix 8b is required for interaction with DcuS. Helix 8b contains a LDXXXLXXXL motif that is essential for function and interaction. DcuS requires the PASC domain for signal perception from DctA. Thus, DcuS and DctA form a DctA/DcuS sensory unit, and DcuS perceives stimuli from two different sites (PASP and DctA). The signal transfer pathways are supposed to merge at PASC. The fumarate/succinate antiporter DcuB takes over the role as a co-sensor of DcuS under anaerobic growth conditions.
©2012 by Walter de Gruyter Berlin Boston