title: His166 is the Schiff base proton acceptor in attractant phototaxis receptor sensory rhodopsin I.
abstract: Photoactivation of attractant phototaxis receptor sensory rhodopsin I (SRI) in Halobacterium salinarum entails transfer of a proton from the retinylidene chromophore's Schiff base (SB) to an unidentified acceptor residue on the cytoplasmic half-channel, in sharp contrast to other microbial rhodopsins, including the closely related repellent phototaxis receptor SRII and the outward proton pump bacteriorhodopsin, in which the SB proton acceptor is an aspartate residue salt-bridged to the SB in the extracellular (EC) half-channel. His166 on the cytoplasmic side of the SB in SRI has been implicated in the SB proton transfer reaction by mutation studies, and mutants of His166 result in an inverted SB proton release to the EC as well as inversion of the protein's normally attractant phototaxis signal to repellent. Here we found by difference Fourier transform infrared spectroscopy the appearance of Fermi-resonant X-H stretch modes in light-minus-dark difference spectra; their assignment with (15)N labeling and site-directed mutagenesis demonstrates that His166 is the SB proton acceptor during the photochemical reaction cycle of the wild-type SRI-HtrI complex.
authors.affiliation: Department of Frontier Materials, Nagoya Institute of Technology , Showa-ku, Nagoya 466-8555, Japan.
authors.forename: Jun
authors.initials: J
authors.lastname: Sasaki
authors.forename: Hazuki
authors.initials: H
authors.lastname: Takahashi
authors.forename: Yuji
authors.initials: Y
authors.lastname: Furutani
authors.forename: Oleg A
authors.initials: OA
authors.lastname: Sineshchekov
authors.forename: John L
authors.initials: JL
authors.lastname: Spudich
authors.forename: Hideki
authors.initials: H
authors.lastname: Kandori
mesh_terms: D019617:Halobacterium salinarum / Q000378:metabolism; D025602:Halorhodopsins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D006639:Histidine / Q000737:chemistry*; D016297:Mutagenesis, Site-Directed; D009587:Nitrogen Isotopes; D011522:Protons; D012545:Schiff Bases / Q000737:chemistry; D025603:Sensory Rhodopsins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D017550:Spectroscopy, Fourier Transform Infrared
chemical_list: D025602:Halorhodopsins; D009587:Nitrogen Isotopes; D011522:Protons; C061497:SRI protein, Halobacterium; D012545:Schiff Bases; D025603:Sensory Rhodopsins; D006639:Histidine