title: Channelrhodopsin-2, a directly light-gated cation-selective membrane channel.
abstract: Microbial-type rhodopsins are found in archaea, prokaryotes, and eukaryotes. Some of them represent membrane ion transport proteins such as bacteriorhodopsin, a light-driven proton pump, or channelrhodopsin-1 (ChR1), a recently identified light-gated proton channel from the green alga Chlamydomonas reinhardtii. ChR1 and ChR2, a related microbial-type rhodopsin from C. reinhardtii, were shown to be involved in generation of photocurrents of this green alga. We demonstrate by functional expression, both in oocytes of Xenopus laevis and mammalian cells, that ChR2 is a directly light-switched cation-selective ion channel. This channel opens rapidly after absorption of a photon to generate a large permeability for monovalent and divalent cations. ChR2 desensitizes in continuous light to a smaller steady-state conductance. Recovery from desensitization is accelerated by extracellular H+ and negative membrane potential, whereas closing of the ChR2 ion channel is decelerated by intracellular H+. ChR2 is expressed mainly in C. reinhardtii under low-light conditions, suggesting involvement in photoreception in dark-adapted cells. The predicted seven-transmembrane alpha helices of ChR2 are characteristic for G protein-coupled receptors but reflect a different motif for a cation-selective ion channel. Finally, we demonstrate that ChR2 may be used to depolarize small or large cells, simply by illumination.
authors: Max-Planck-Institut für Biophysik, Marie-Curie-Strasse 15, 60439 Frankfurt, Germany. georg.nagel@mpibp-frankfurt.mpg.de
authors: Georg
authors: G
authors: Nagel
authors: Tanjef
authors: T
authors: Szellas
authors: Wolfram
authors: W
authors: Huhn
authors: Suneel
authors: S
authors: Kateriya
authors: Nona
authors: N
authors: Adeishvili
authors: Peter
authors: P
authors: Berthold
authors: Doris
authors: D
authors: Ollig
authors: Peter
authors: P
authors: Hegemann
authors: Ernst
authors: E
authors: Bamberg
mesh_terms: D020418:Algal Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D002412:Cations / Q000378:metabolism; D002460:Cell Line; D016825:Chlamydomonas reinhardtii / Q000235:genetics / Q000378:metabolism; D006224:Cricetinae; D005260:Female; D006801:Humans; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D015640:Ion Channel Gating / Q000528:radiation effects; D007473:Ion Channels / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008027:Light; D008564:Membrane Potentials; D009865:Oocytes / Q000378:metabolism; D018462:Photobiology; D015800:Protozoan Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D012243:Rhodopsin / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D014982:Xenopus laevis
chemical_list: D020418:Algal Proteins; D002412:Cations; D007473:Ion Channels; D015800:Protozoan Proteins; D011994:Recombinant Proteins; D012243:Rhodopsin