title: Spectroscopic studies of a sensory rhodopsin I homologue from the archaeon Haloarcula vallismortis.
abstract: Sensory rhodopsin I (SRI) functions as a dual receptor regulating both negative and positive phototaxis. It transmits light signals through changes in protein-protein interactions with its transducer protein, HtrI. The phototaxis function of Halobacterium salinarum SRI (HsSRI) has been well characterized using genetic and molecular techniques, whereas that of Salinibacter ruber SRI (SrSRI) has not. SrSRI has the advantage of high protein stability compared with HsSRI and, therefore, provided new information about structural changes and Cl(-) binding of SRI. However, nothing is known about the functional role of SrSRI in phototaxis behavior. In this study, we expressed a SRI homologue from the archaeon Haloarcula vallismortis (HvSRI) as a recombinant protein which uses all-trans-retinal as a chromophore. Functionally important residues of HsSRI are completely conserved in HvSRI (unlike in SrSRI), and HvSRI is extremely stable in buffers without Cl(-). Taking advantage of the high stability, we characterized the photochemical properties of HvSRI under acidic and basic conditions and observed the effects of Cl(-) on the protein under both conditions. Fourier transform infrared results revealed that the structural changes in HvSRI were quite similar to those in HsSRI and SrSRI. Thus, HvSRI can become a useful protein model for improving our understanding of the molecular mechanism of the dual photosensing by SRI.
authors.affiliation: Department of Frontier Materials, Nagoya Institute of Technology, Showa-ku, Nagoya 466-8555, Japan.
authors.forename: Jin
authors.initials: J
authors.lastname: Yagasaki
authors.forename: Daisuke
authors.initials: D
authors.lastname: Suzuki
authors.forename: Kunio
authors.initials: K
authors.lastname: Ihara
authors.forename: Keiichi
authors.initials: K
authors.lastname: Inoue
authors.forename: Takashi
authors.initials: T
authors.lastname: Kikukawa
authors.forename: Makoto
authors.initials: M
authors.lastname: Sakai
authors.forename: Masaaki
authors.initials: M
authors.lastname: Fujii
authors.forename: Michio
authors.initials: M
authors.lastname: Homma
authors.forename: Hideki
authors.initials: H
authors.lastname: Kandori
authors.forename: Yuki
authors.initials: Y
authors.lastname: Sudo
mesh_terms: D041963:Bacteroidetes / Q000737:chemistry; D019613:Haloarcula / Q000737:chemistry*; D019617:Halobacterium salinarum / Q000737:chemistry; D025602:Halorhodopsins / Q000737:chemistry* / Q000302:isolation & purification; D006863:Hydrogen-Ion Concentration; D055550:Protein Stability; D025603:Sensory Rhodopsins / Q000737:chemistry*; D013056:Spectrophotometry, Ultraviolet; D017550:Spectroscopy, Fourier Transform Infrared; D040681:Structural Homology, Protein
chemical_list: D025602:Halorhodopsins; D025603:Sensory Rhodopsins; C099613:sensor rhodopsin csR-3, Haloarcula vallismortis