Transcriptional regulation and energetics of alternative respiratory pathways in facultatively anaerobic bacteria

AbstractThe facultatively anaerobic Escherichia coli is able to grow by aerobic and by anaerobic respiration. Despite the large difference in the amount of free energy that could maximally be conserved from aerobic versus anaerobic respiration, the proton potential and Δg′Phos are similar under both conditions. O2 represses anaerobic respiration, and nitrate represses fumarate respiration. By this the terminal reductases of aerobic and anaerobic respiration are expressed in a way to obtain maximal H+e− ratios and ATP yields. The respiratory dehydrogenases, on the other hand, are not synthesized in a way to achieve maximal H+e− ratios. Most of the dehydrogenases of aerobic respiration do not conserve redox enery in a proton gradient whereas the enzymes from anaerobic respiration do so. Thus transcriptional regulation of the respiratory pathways by electron acceptors has multiple effects on cellular energetics. The transcriptional regulation in response to O2 is effected by two transcriptional regulators, ArcA/B (aerobic respiratory control) and FNR (fumarate nitrate reductase regulator). FNR contains an O2-sensitive [4Fe4S]2+ cluster in the sensory domain and is converted to the transcriptional inactive state in the presence of (cytoplasmic) O2

Conversion of the Sensor Kinase DcuS to the Fumarate Sensitive State by Interaction of the Bifunctional Transporter DctA at the TM2/PASC-Linker Region

The membrane-bound C4-dicarboxylate (C4DC) sensor kinase DcuS of Escherichia coli typically forms a protein complex with the C4DC transporter DctA. The DctA × DcuS complex is able to respond to C4DCs, whereas DcuS without DctA is in the permanent ON state. In DctA, the C-terminal helix 8b (H8b) serves as the site for interaction with DcuS. Here the interaction site in DcuS and the related structural and functional adaptation in DcuS were determined. The Linker connecting transmembrane helix 2 (TM2) and the cytosolic PASC (Per-ARNT-SIM) domain of DcuS, was identified as the major site for interaction with DctA-H8b by in vivo interaction studies. The Linker is known to convert the piston-type transmembrane signaling of TM2 to a tilting motion which relies on a resolution of the Linker-Linker’ homodimer in the presence of C4DCs. Absence of DctA caused decreased cross-linking in the Linker, as identified by oxidative Cys-cross-linking. This response resembled structurally and functionally that of fumarate activation in the DctA × DcuS complex. Overall, formation of the DctA × DcuS complex is based on the interaction of the DcuS Linker with DctA H8b; the interaction is required to set DcuS in the C4DC-responsive state by stabilizing the linker-linker’ homodimer in DcuS. This work identifies DctA as a structural co-regulator of DcuS sensor kinase