title: Structure of the light-driven chloride pump halorhodopsin at 1.8 A resolution.
abstract: Halorhodopsin, an archaeal rhodopsin ubiquitous in Haloarchaea, uses light energy to pump chloride through biological membranes. Halorhodopsin crystals were grown in a cubic lipidic phase, which allowed the x-ray structure determination of this anion pump at 1.8 angstrom resolution. Halorhodopsin assembles to trimers around a central patch consisting of palmitic acid. Next to the protonated Schiff base between Lys(242) and the isomerizable retinal chromophore, a single chloride ion occupies the transport site. Energetic calculations on chloride binding reveal a combination of ion-ion and ion-dipole interactions for stabilizing the anion 18 angstroms below the membrane surface. Ion dragging across the protonated Schiff base explains why chloride and proton translocation modes are mechanistically equivalent in archaeal rhodopsins.
authors.affiliation: Department of Membrane Biochemistry, Max-Planck-Institute for Biochemistry, Am Klopferspitz 18a, D-82152 Martinsried bei München, Germany.
authors.forename: M
authors.initials: M
authors.lastname: Kolbe
authors.forename: H
authors.initials: H
authors.lastname: Besir
authors.forename: L O
authors.initials: LO
authors.lastname: Essen
authors.forename: D
authors.initials: D
authors.lastname: Oesterhelt
mesh_terms: D001436:Bacteriorhodopsins / Q000737:chemistry* / Q000378:metabolism*; D001665:Binding Sites; D001693:Biological Transport, Active; D002462:Cell Membrane / Q000737:chemistry / Q000378:metabolism; D002712:Chlorides / Q000378:metabolism*; D003460:Crystallization; D018360:Crystallography, X-Ray; D003593:Cytoplasm / Q000737:chemistry / Q000378:metabolism; D019617:Halobacterium salinarum / Q000737:chemistry; D025602:Halorhodopsins; D006860:Hydrogen Bonding; D006863:Hydrogen-Ion Concentration; D016623:Ion Pumps / Q000737:chemistry* / Q000378:metabolism*; D017136:Ion Transport; D008027:Light; D008055:Lipids / Q000737:chemistry; D008958:Models, Molecular; D011487:Protein Conformation; D017510:Protein Folding; D020836:Protein Structure, Quaternary; D017433:Protein Structure, Secondary; D011522:Protons; D012545:Schiff Bases; D055672:Static Electricity; D013816:Thermodynamics
chemical_list: D002712:Chlorides; D025602:Halorhodopsins; D016623:Ion Pumps; D008055:Lipids; D011522:Protons; D012545:Schiff Bases; D001436:Bacteriorhodopsins