title: Platymonas subcordiformis Channelrhodopsin-2 Function: I. THE PHOTOCHEMICAL REACTION CYCLE.
abstract: The photocycle kinetics of Platymonas subcordiformis channelrhodopsin-2 (PsChR2), among the most highly efficient light-gated cation channels and the most blue-shifted channelrhodopsin, was studied by time-resolved absorption spectroscopy in the 340-650-nm range and in the 100-ns to 3-s time window. Global exponential fitting of the time dependence of spectral changes revealed six lifetimes: 0.60 μs, 5.3 μs, 170 μs, 1.4 ms, 6.7 ms, and 1.4 s. The sequential intermediates derived for a single unidirectional cycle scheme based on these lifetimes were found to contain mixtures of K, L, M, O, and P molecular states, named in analogy to photointermediates in the bacteriorhodopsin photocycle. The photochemistry is described by the superposition of two independent parallel photocycles. The analysis revealed that 30% of the photoexcited receptor molecules followed Cycle 1 through the K, M, O, and P states, whereas 70% followed Cycle 2 through the K, L, M, and O states. The recovered state, R, is spectrally close, but not identical, to the dark state on the seconds time scale. The two-cycle model of this high efficiency channelrhodopsin-2 (ChR) opens new perspectives in understanding the mechanism of channelrhodopsin function.
authors.affiliation: From the Department of Chemistry and Biochemistry, University of California, Santa Cruz, California 95064 and.
authors.forename: Istvan
authors.initials: I
authors.lastname: Szundi
authors.affiliation: the Center for Membrane Biology, Department of Biochemistry and Molecular Biology, University of Texas Medical School, Houston, Texas 77030.
authors.forename: Hai
authors.initials: H
authors.lastname: Li
authors.affiliation: From the Department of Chemistry and Biochemistry, University of California, Santa Cruz, California 95064 and.
authors.forename: Eefei
authors.initials: E
authors.lastname: Chen
authors.affiliation: From the Department of Chemistry and Biochemistry, University of California, Santa Cruz, California 95064 and.
authors.forename: Roberto
authors.initials: R
authors.lastname: Bogomolni
authors.affiliation: the Center for Membrane Biology, Department of Biochemistry and Molecular Biology, University of Texas Medical School, Houston, Texas 77030 John.L.Spudich@uth.tmc.edu.
authors.forename: John L
authors.initials: JL
authors.lastname: Spudich
authors.affiliation: From the Department of Chemistry and Biochemistry, University of California, Santa Cruz, California 95064 and kliger@ucsc.edu.
authors.forename: David S
authors.initials: DS
authors.lastname: Kliger
mesh_terms: D000460:Chlorophyta / Q000737:chemistry / Q000235:genetics / Q000378:metabolism* / Q000528:radiation effects; D007700:Kinetics; D008027:Light; D010777:Photochemistry; D012243:Rhodopsin / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*
chemical_list: D012243:Rhodopsin
keywords: channelrhodopsin; optogenetics; photocycle; photoreceptor; phototaxis; protein dynamic; rhodopsin; time-resolved spectroscopy; ultraviolet-visible spectroscopy (UV-Vis spectroscopy)