A NarX–Tar chimera mediates repellent chemotaxis to nitrate and nitrite

Abstract

SummaryMembrane receptors communicate between the external world and the cell interior. In bacteria, these receptors include the transmembrane sensor kinases, which control gene expression via their cognate response regulators, and chemoreceptors, which control the direction of flagellar rotation via the CheA kinase and CheY response regulator. Here, we show that a chimeric protein that joins the ligandbinding, transmembrane and linker domains of the NarX sensor kinase to the signalling and adaptation domains of the Tar chemoreceptor of Escherichia coli mediates repellent responses to nitrate and nitrite. Nitrate induces a stronger response than nitrite and is effective at lower concentrations, mirroring the relative sensitivity to these ligands exhibited by NarX itself. We conclude that the NarX-Tar hybrid functions as a bona fide chemoreceptor whose activity can be predicted from its component parts. This observation implies that ligand-dependent activation of a sensor kinase and repellent-initiated activation of receptorcoupled CheA kinase involve a similar transmembrane signal.

Analysis of the Role of the EnvZ Linker Region in Signal Transduction Using a Chimeric Tar/EnvZ Receptor Protein, Tez1

“…The resultant Taz (12) and Trz (13) are able to respond to aspartate and ribose in the medium, respectively, to activate ompC-lacZ in a concentration-dependent manner, suggesting that the chemoreceptors and EnvZ share a common signal transduction mechanism. Similar chimeric receptors have also been constructed using the periplasmic and transmembrane domain of Tar and the cytoplasmic domain of the human insulin receptor (14) or the periplasmic domain of the histidine kinase NarX and the cytoplasmic domain of Tar (15), further supporting a notion that there is a common mechanism widely used by signal transduction across the membrane in both prokaryotes and eukaryotes. Extensive studies on signal transduction through the transmembrane domain of chemotaxis receptors have been carried out, and various mechanisms have been proposed (16 -21).…”

Mutational Analysis of the Control Cable That Mediates Transmembrane Signaling in the Escherichia coli Serine Chemoreceptor

“…However, symmetric structural changes (amino acid replacements, disulfide bonds) in the periplasmic sensing domain or TM bundle can also mimic chemoeffector signaling effects (shifted outputs, altered adaptation responses) (6,7,22,23,25,71). Moreover, the hybrid transducer Nart, which carries the periplasmic sensing through the HAMP domains of NarX joined to the methylation and kinase control domains of Tar (64,65), mediates chemotactic responses to nitrate, whose binding causes quasisymmetric piston displacements (19). We conclude that symmetric conformational inputs most likely modulate HAMP signaling by the same mechanism as that used for asymmetric TM2 piston displacements.…”

Probing Conservation of HAMP Linker Structure and Signal Transduction Mechanism through Analysis of Hybrid Sensor Kinases

“…Similarly, although the Trg-EnvZ hybrid Trz responds to ribose with increased kinase activity, its sensitivity to ribose is approximately 100-fold lower than that of Trg (5). A further hybrid has been constructed between the sensory domain of NarX and the methylation domain of Tar with a fusion point at AS-2.11 (50). This protein responds to ligand (nitrate) as a repellent, while Tar responds to its ligands Asp and MBP-maltose as attractants (13).…”

“…Such hybrids have been made between different E. coli MCPs (16,24,40,51), Bacillus subtilis MCPs (25), the MCP Tar or Trg and the sensor kinase EnvZ (5,49), and the sensor kinase NarX and the MCP Tar (50). Most of these hybrids alter their output activity in response to ligand binding in their heterologous input domains.…”