The sensor kinase DcuS of Escherichia coli: two stimulus input sites and a merged signal pathway in the DctA/DcuS sensor unit

摘要

The membrane-integral sensor kinase DcuS of Escherichia coli consists of a periplasmically located sensory PAS(P) domain, transmembrane helices TM1 and TM2, a cytoplasmic PAS(C) domain and the kinase domain. Stimulus (C-4-dicarboxylate) binding at PAS(P) is required to stimulate phosphorylation of the kinase domain, resulting in phosphoryl transfer to the response regulator DcuR. PAS(C) 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 C-4-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 PAS(C) domain for signal perception from DctA. Thus, DcuS and DctA form a DctA/DcuS sensory unit, and DcuS perceives stimuli from two different sites (PAS(P) and DctA). The signal transfer pathways are supposed to merge at PAS(C). The fumarate/succinate antiporter DcuB takes over the role as a co-sensor of DcuS under anaerobic growth conditions.