title: Light-Dark Adaptation of Channelrhodopsin Involves Photoconversion between the all-trans and 13-cis Retinal Isomers.
abstract: Channelrhodopsins (ChR) are light-gated ion channels of green algae that are widely used to probe the function of neuronal cells with light. Most ChRs show a substantial reduction in photocurrents during illumination, a process named "light adaptation". The main objective of this spectroscopic study was to elucidate the molecular processes associated with light-dark adaptation. Here we show by liquid and solid-state nuclear magnetic resonance spectroscopy that the retinal chromophore of fully dark-adapted ChR is exclusively in an all-trans configuration. Resonance Raman (RR) spectroscopy, however, revealed that already low light intensities establish a photostationary equilibrium between all-trans,15-anti and 13-cis,15-syn configurations at a ratio of 3:1. The underlying photoreactions involve simultaneous isomerization of the C(13)═C(14) and C(15)═N bonds. Both isomers of this DAapp state may run through photoinduced reaction cycles initiated by photoisomerization of only the C(13)═C(14) bond. RR spectroscopic experiments further demonstrated that photoinduced conversion of the apparent dark-adapted (DAapp) state to the photocycle intermediates P500 and P390 is distinctly more efficient for the all-trans isomer than for the 13-cis isomer, possibly because of different chromophore-water interactions. Our data demonstrating two complementary photocycles of the DAapp isomers are fully consistent with the existence of two conducting states that vary in quantitative relation during light-dark adaptation, as suggested previously by electrical measurements.
authors.affiliation: Technische Universität Berlin , Institut für Chemie, Sekr. PC14, Straße des 17. Juni 135, D-10623 Berlin, Germany.
authors.forename: Sara
authors.initials: S
authors.lastname: Bruun
authors.affiliation: Leibniz-Institut für Molekulare Pharmakologie (FMP) , Robert-Rössle-Strasse 10, 13125 Berlin, Germany.
authors.forename: Daniel
authors.initials: D
authors.lastname: Stoeppler
authors.affiliation: Technische Universität Berlin , Institut für Chemie, Sekr. PC14, Straße des 17. Juni 135, D-10623 Berlin, Germany.
authors.forename: Anke
authors.initials: A
authors.lastname: Keidel
authors.affiliation: Technische Universität Berlin , Institut für Chemie, Sekr. PC14, Straße des 17. Juni 135, D-10623 Berlin, Germany.
authors.forename: Uwe
authors.initials: U
authors.lastname: Kuhlmann
authors.affiliation: Humboldt-Universität zu Berlin , Institut für Biologie, Invalidenstrasse 42, D-10115 Berlin, Germany.
authors.forename: Meike
authors.initials: M
authors.lastname: Luck
authors.affiliation: Leibniz-Institut für Molekulare Pharmakologie (FMP) , Robert-Rössle-Strasse 10, 13125 Berlin, Germany.
authors.forename: Anne
authors.initials: A
authors.lastname: Diehl
authors.affiliation: Leibniz-Institut für Molekulare Pharmakologie (FMP) , Robert-Rössle-Strasse 10, 13125 Berlin, Germany.
authors.forename: Michel-Andreas
authors.initials: MA
authors.lastname: Geiger
authors.affiliation: Department of Chemistry, Ludwig-Maximilians-Universität München , Butenandtstraße 5-13, 81377 München, Germany.
authors.forename: David
authors.initials: D
authors.lastname: Woodmansee
authors.affiliation: Department of Chemistry, Ludwig-Maximilians-Universität München , Butenandtstraße 5-13, 81377 München, Germany.
authors.forename: Dirk
authors.initials: D
authors.lastname: Trauner
authors.affiliation: Humboldt-Universität zu Berlin , Institut für Biologie, Invalidenstrasse 42, D-10115 Berlin, Germany.
authors.forename: Peter
authors.initials: P
authors.lastname: Hegemann
authors.affiliation: Leibniz-Institut für Molekulare Pharmakologie (FMP) , Robert-Rössle-Strasse 10, 13125 Berlin, Germany.
authors.forename: Hartmut
authors.initials: H
authors.lastname: Oschkinat
authors.affiliation: Technische Universität Berlin , Institut für Chemie, Sekr. PC14, Straße des 17. Juni 135, D-10623 Berlin, Germany.
authors.forename: Peter
authors.initials: P
authors.lastname: Hildebrandt
authors.affiliation: Humboldt-Universität zu Berlin , Institut für Biologie, Invalidenstrasse 42, D-10115 Berlin, Germany.
authors.forename: Katja
authors.initials: K
authors.lastname: Stehfest
mesh_terms: D000818:Animals; D000075402:Channelrhodopsins; D003623:Dark Adaptation / Q000502:physiology*; D004224:Diterpenes; D007313:Insecta; D007536:Isomerism; D010775:Photic Stimulation / Q000379:methods; D010843:Pichia; D012172:Retinaldehyde / Q000031:analogs & derivatives* / Q000737:chemistry
chemical_list: D000075402:Channelrhodopsins; D004224:Diterpenes; C525876:retinal dimer; C031338:13-cis-retinal; D012172:Retinaldehyde