title: Structural basis for the slow photocycle and late proton release in Acetabularia rhodopsin I from the marine plant Acetabularia acetabulum.
abstract: Although many crystal structures of microbial rhodopsins have been solved, those with sufficient resolution to identify the functional water molecules are very limited. In this study, the Acetabularia rhodopsin I (ARI) protein derived from the marine alga A. acetabulum was synthesized on a large scale by the Escherichia coli cell-free membrane-protein production method, and crystal structures of ARI were determined at the second highest (1.52-1.80 Å) resolution for a microbial rhodopsin, following bacteriorhodopsin (BR). Examinations of the photochemical properties of ARI revealed that the photocycle of ARI is slower than that of BR and that its proton-transfer reactions are different from those of BR. In the present structures, a large cavity containing numerous water molecules exists on the extracellular side of ARI, explaining the relatively low pKa of Glu206(ARI), which cannot function as an initial proton-releasing residue at any pH. An interhelical hydrogen bond exists between Leu97(ARI) and Tyr221(ARI) on the cytoplasmic side, which facilitates the slow photocycle and regulates the pKa of Asp100(ARI), a potential proton donor to the Schiff base, in the dark state.
authors.affiliation: RIKEN Systems and Structural Biology Center, Yokohama 230-0045, Japan.
authors.forename: Munenori
authors.initials: M
authors.lastname: Furuse
authors.affiliation: College of Pharmaceutical Sciences, Matsuyama University, Matsuyama, Ehime 790-8578, Japan.
authors.forename: Jun
authors.initials: J
authors.lastname: Tamogami
authors.affiliation: RIKEN Systems and Structural Biology Center, Yokohama 230-0045, Japan.
authors.forename: Toshiaki
authors.initials: T
authors.lastname: Hosaka
authors.affiliation: Faculty of Advanced Life Science, Hokkaido University, Sapporo 060-0810, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Kikukawa
authors.affiliation: RIKEN Systems and Structural Biology Center, Yokohama 230-0045, Japan.
authors.forename: Naoko
authors.initials: N
authors.lastname: Shinya
authors.affiliation: RIKEN Systems and Structural Biology Center, Yokohama 230-0045, Japan.
authors.forename: Masakatsu
authors.initials: M
authors.lastname: Hato
authors.affiliation: RIKEN Systems and Structural Biology Center, Yokohama 230-0045, Japan.
authors.forename: Noboru
authors.initials: N
authors.lastname: Ohsawa
authors.affiliation: Department of Life Science and Institute of Biological Interfaces, Sogang University, Seoul 121-742, Republic of Korea.
authors.forename: So Young
authors.initials: SY
authors.lastname: Kim
authors.affiliation: Department of Life Science and Institute of Biological Interfaces, Sogang University, Seoul 121-742, Republic of Korea.
authors.forename: Kwang Hwan
authors.initials: KH
authors.lastname: Jung
authors.affiliation: Faculty of Advanced Life Science, Hokkaido University, Sapporo 060-0810, Japan.
authors.forename: Makoto
authors.initials: M
authors.lastname: Demura
authors.affiliation: College of Pharmaceutical Sciences, Matsuyama University, Matsuyama, Ehime 790-8578, Japan.
authors.forename: Seiji
authors.initials: S
authors.lastname: Miyauchi
authors.affiliation: College of Pharmaceutical Sciences, Matsuyama University, Matsuyama, Ehime 790-8578, Japan.
authors.forename: Naoki
authors.initials: N
authors.lastname: Kamo
authors.affiliation: RIKEN Systems and Structural Biology Center, Yokohama 230-0045, Japan.
authors.forename: Kazumi
authors.initials: K
authors.lastname: Shimono
authors.affiliation: RIKEN Systems and Structural Biology Center, Yokohama 230-0045, Japan.
authors.forename: Tomomi
authors.initials: T
authors.lastname: Kimura-Someya
authors.affiliation: RIKEN Systems and Structural Biology Center, Yokohama 230-0045, Japan.
authors.forename: Shigeyuki
authors.initials: S
authors.lastname: Yokoyama
authors.affiliation: RIKEN Systems and Structural Biology Center, Yokohama 230-0045, Japan.
authors.forename: Mikako
authors.initials: M
authors.lastname: Shirouzu
mesh_terms: D000076:Acetabularia / Q000737:chemistry*; D018360:Crystallography, X-Ray; D008027:Light; D008958:Models, Molecular; D010940:Plant Proteins / Q000737:chemistry*; D011487:Protein Conformation; D011522:Protons; D012243:Rhodopsin / Q000737:chemistry*
chemical_list: D010940:Plant Proteins; D011522:Protons; D012243:Rhodopsin
keywords: X-ray crystal structure; cell-free protein synthesis; light-driven ion pump; membrane protein; microbial rhodopsin