Photosensory Functions of Channelrhodopsins in Native Algal Cells

Authors

  • Oleg A. Sineshchekov,

    Corresponding author
    1. Center for Membrane Biology, Department of Biochemistry and Molecular Biology, University of Texas Medical School, Houston, TX
    2. Biology Department, Moscow State University, Moscow, Russia
      *Corresponding authors email: oleg.a.sineshchekov@uth.tmc.edu (Oleg A. Sineshchekov), john.l.spudich@uth.tmc.edu (John L. Spudich)
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  • Elena G. Govorunova,

    1. Biology Department, Moscow State University, Moscow, Russia
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  • John L. Spudich

    Corresponding author
    1. Center for Membrane Biology, Department of Biochemistry and Molecular Biology, University of Texas Medical School, Houston, TX
      *Corresponding authors email: oleg.a.sineshchekov@uth.tmc.edu (Oleg A. Sineshchekov), john.l.spudich@uth.tmc.edu (John L. Spudich)
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  • This paper is part of the Proceedings of the 13th International Conference on Retinal Proteins, Barcelona, Spain, 15–19 June 2008.

*Corresponding authors email: oleg.a.sineshchekov@uth.tmc.edu (Oleg A. Sineshchekov), john.l.spudich@uth.tmc.edu (John L. Spudich)

Abstract

Photomotility responses in flagellate alga are mediated by two types of sensory rhodopsins (A and B). Upon photoexcitation they trigger a cascade of transmembrane currents which provide sensory transduction of light stimuli. Both types of algal sensory rhodopsins demonstrate light-gated ion channel activities when heterologously expressed in animal cells, and therefore they have been given the alternative names channelrhodopsin 1 and 2. In recent publications their channel activity has been assumed to initiate the transduction chain in the native algal cells. Here we present data showing that: (1) the modes of action of both types of sensory rhodopsins are different in native cells such as Chlamydomonas reinhardtii than in heterologous expression systems, and also differ between the two types of rhodopsins; (2) the primary function of Type B sensory rhodopsin (channelrhodopsin-2) is biochemical activation of secondary Ca2+-channels with evidence for amplification and a diffusible messenger, sufficient for mediating phototaxis and photophobic responses; (3) Type A sensory rhodopsin (channelrhodopsin-1) mediates avoidance responses by direct channel activity under high light intensities and exhibits low-efficiency amplification. These dual functions of algal sensory rhodopsins enable the highly sophisticated photobehavior of algal cells.

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