ligand binding sensor domain of NarX and NarQ, and related chemoreceptors
The periplasmic ligand binding sensor domain of NarX and NarQ is a histidine kinase receptor that responds to nitrate and nitrite to effect regulation of anaerobic respiration in various bacteria and similar proteins. It forms a homodimer and binds to ligands such as nitrate via the dimerization interface, a feature that appears to be conserved in this domain superfamily. NarX-NarL sensor-response regulator pair, along with NarQ-NarP, control Escherichia coli gene expression in response to nitrate and nitrite. NarX has been shown to exhibit a clear kinetic preference for NarL over NarP, whereas NarQ exhibits a relatively slight kinetic preference for NarL. There is asymmetry in the Nar cross-regulation network with NarQ shown to interact similarly with both response regulators, while NarX interacts preferentially with NarL.
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