title: Hydrogen-bonding changes of internal water molecules upon the actions of microbial rhodopsins studied by FTIR spectroscopy.
abstract: Microbial rhodopsins are classified into type-I rhodopsins, which utilize light energy to perform wide varieties of function, such as proton pumping, ion pumping, light sensing, cation channels, and so on. The crystal structures of several type-I rhodopsins were solved and the molecular mechanisms have been investigated based on the atomic structures. However, the crystal structures of proteins of interest are not always available and the basic architectures are sometimes quite similar, which obscures how the proteins achieve different functions. Stimulus-induced difference FTIR spectroscopy is a powerful tool to detect minute structural changes providing a clue for elucidating the molecular mechanisms. In this review, the studies on type-I rhodopsins from fungi and marine bacteria, whose crystal structures have not been solved yet, were summarized. Neurospora rhodopsin and Leptosphaeria rhodopsin found from Fungi have sequence similarity. The former has no proton pumping function, while the latter has. Proteorhodopsin is another example, whose proton pumping machinery is altered at alkaline and acidic conditions. We described how the structural changes of protein were different and how water molecules were involved in them. We reviewed the results on dynamics of the internal water molecules in pharaonis halorhodopsin as well. This article is part of a Special Issue entitled: Retinal Proteins - You can teach an old dog new tricks.
authors.affiliation: Department of Life and Coordination-Complex Molecular Science, Institute for Molecular Science, 38 Nishigo-Naka, Myodaiji, Okazaki 444-8585, Japan; Department of Structural Molecular Science, The Graduate University for Advanced Studies (SOKENDAI), 38 Nishigo-Naka, Myodaiji, Okazaki 444-8585, Japan; PRESTO, Japan Science and Technology Agency (JST), 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan. Electronic address: furutani@ims.ac.jp.
authors.forename: Yuji
authors.initials: Y
authors.lastname: Furutani
authors.affiliation: Department of Frontier Materials, Nagoya Institute of Technology, Showa-ku, Nagoya 466-8555, Japan. Electronic address: kandori@nitech.ac.jp.
authors.forename: Hideki
authors.initials: H
authors.lastname: Kandori
mesh_terms: D001436:Bacteriorhodopsins / Q000737:chemistry* / Q000378:metabolism; D019605:Euryarchaeota / Q000737:chemistry / Q000502:physiology; D025602:Halorhodopsins / Q000737:chemistry* / Q000378:metabolism; D006860:Hydrogen Bonding; D006863:Hydrogen-Ion Concentration; D017136:Ion Transport; D008027:Light; D055537:Light Signal Transduction; D008958:Models, Molecular; D009491:Neurospora / Q000737:chemistry / Q000502:physiology; D011487:Protein Conformation; D012243:Rhodopsin / Q000737:chemistry* / Q000378:metabolism; D025604:Rhodopsins, Microbial; D004718:Saccharomycetales / Q000737:chemistry / Q000502:physiology; D025603:Sensory Rhodopsins / Q000737:chemistry* / Q000378:metabolism; D017550:Spectroscopy, Fourier Transform Infrared / Q000379:methods; D014867:Water / Q000737:chemistry*
chemical_list: D025602:Halorhodopsins; D025604:Rhodopsins, Microbial; D025603:Sensory Rhodopsins; C413548:proteorhodopsin; D014867:Water; D001436:Bacteriorhodopsins; D012243:Rhodopsin
keywords: Hydrogen bond; Ion–protein interaction; Light-energy conversion; Proton pump; Vibrational spectroscopy