title: An archaeal photosignal-transducing module mediates phototaxis in Escherichia coli.
abstract: Halophilic archaea, such as Halobacterium salinarum and Natronobacterium pharaonis, alter their swimming behavior by phototaxis responses to changes in light intensity and color using visual pigment-like sensory rhodopsins (SRs). In N. pharaonis, SRII (NpSRII) mediates photorepellent responses through its transducer protein, NpHtrII. Here we report the expression of fusions of NpSRII and NpHtrII and fusion hybrids with eubacterial cytoplasmic domains and analyze their function in vivo in haloarchaea and in eubacteria. A fusion in which the C terminus of NpSRII is connected by a short flexible linker to NpHtrII is active in phototaxis signaling for H. salinarum, showing that the fusion does not inhibit functional receptor-transducer interactions. We replaced the cytoplasmic portions of this fusion protein with the cytoplasmic domains of Tar and Tsr, chemotaxis transducers from enteric eubacteria. Purification of the fusion protein from H. salinarum and Tar fusion chimera from Escherichia coli membranes shows that the proteins are not cleaved and exhibit absorption spectra characteristic of wild-type membranes. Their photochemical reaction cycles in H. salinarum and E. coli membranes, respectively, are similar to those of native NpSRII in N. pharaonis. These fusion chimeras mediate retinal-dependent phototaxis responses by Escherichia coli, establishing that the nine-helix membrane portion of the receptor-transducer complex is a modular functional unit able to signal in heterologous membranes. This result confirms a current model for SR-Htr signal transduction in which the Htr transducers are proposed to interact physically and functionally with their cognate sensory rhodopsins via helix-helix contacts between their transmembrane segments.
authors.affiliation: Department of Microbiology and Molecular Genetics, University of Texas-Houston Medical School, Houston, Texas 77030, USA.
authors.forename: K H
authors.initials: KH
authors.lastname: Jung
authors.forename: E N
authors.initials: EN
authors.lastname: Spudich
authors.forename: V D
authors.initials: VD
authors.lastname: Trivedi
authors.forename: J L
authors.initials: JL
authors.lastname: Spudich
mesh_terms: D019843:Archaeal Proteins / Q000235:genetics / Q000502:physiology*; D001426:Bacterial Proteins / Q000235:genetics / Q000502:physiology; D002338:Carotenoids / Q000235:genetics / Q000502:physiology*; D002628:Chemoreceptor Cells; D004926:Escherichia coli / Q000235:genetics*; D029968:Escherichia coli Proteins; D019617:Halobacterium salinarum / Q000235:genetics; D008027:Light; D008124:Locomotion; D008565:Membrane Proteins / Q000235:genetics / Q000502:physiology; D011956:Receptors, Cell Surface; D011993:Recombinant Fusion Proteins / Q000502:physiology; D015398:Signal Transduction; D014169:Transformation, Bacterial
chemical_list: D019843:Archaeal Proteins; D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; C434451:HtrII protein, Natronobacterium pharaonis; D008565:Membrane Proteins; D011956:Receptors, Cell Surface; D011993:Recombinant Fusion Proteins; C057331:Tar protein, E coli; C057635:Tsr protein, Bacteria; C434450:phototaxis receptor sensory rhodopsin II, Natronobacterium pharaonis; D002338:Carotenoids