title: Structurally Distinct Cation Channelrhodopsins from Cryptophyte Algae.
abstract: Microbial rhodopsins are remarkable for the diversity of their functional mechanisms based on the same protein scaffold. A class of rhodopsins from cryptophyte algae show close sequence homology with haloarchaeal rhodopsin proton pumps rather than with previously known channelrhodopsins from chlorophyte (green) algae. In particular, both aspartate residues that occupy the positions of the chromophore Schiff base proton acceptor and donor, a hallmark of rhodopsin proton pumps, are conserved in these cryptophyte proteins. We expressed the corresponding polynucleotides in human embryonic kidney (HEK293) cells and studied electrogenic properties of the encoded proteins with whole-cell patch-clamp recording. Despite their lack of residues characteristic of the chlorophyte cation channels, these proteins are cation-conducting channelrhodopsins that carry out light-gated passive transport of Na(+) and H(+). These findings show that channel function in rhodopsins has evolved via multiple routes.
authors.affiliation: Center for Membrane Biology and Department of Biochemistry and Molecular Biology, University of Texas Health Science Center at Houston, McGovern Medical School, Houston, Texas.
authors.forename: Elena G
authors.initials: EG
authors.lastname: Govorunova
authors.affiliation: Center for Membrane Biology and Department of Biochemistry and Molecular Biology, University of Texas Health Science Center at Houston, McGovern Medical School, Houston, Texas.
authors.forename: Oleg A
authors.initials: OA
authors.lastname: Sineshchekov
authors.affiliation: Center for Membrane Biology and Department of Biochemistry and Molecular Biology, University of Texas Health Science Center at Houston, McGovern Medical School, Houston, Texas. Electronic address: john.l.spudich@uth.tmc.edu.
authors.forename: John L
authors.initials: JL
authors.lastname: Spudich
mesh_terms: D000595:Amino Acid Sequence; D027682:Cation Transport Proteins / Q000235:genetics / Q000378:metabolism*; D002414:Cations, Monovalent / Q000378:metabolism; D000460:Chlorophyta; D044785:Cryptophyta; D019143:Evolution, Molecular; D057809:HEK293 Cells; D006801:Humans; D006859:Hydrogen / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D008027:Light; D018408:Patch-Clamp Techniques; D011119:Polynucleotides / Q000235:genetics / Q000378:metabolism; D011522:Protons; D025603:Sensory Rhodopsins / Q000235:genetics / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism
chemical_list: D027682:Cation Transport Proteins; D002414:Cations, Monovalent; D011119:Polynucleotides; D011522:Protons; D025603:Sensory Rhodopsins; D006859:Hydrogen; D012964:Sodium