Structurally Distinct Cation Channelrhodopsins from Cryptophyte Algae

Biophys J. 2016 Jun 7;110(11):2302-2304. doi: 10.1016/j.bpj.2016.05.001. Epub 2016 May 24.


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.

Publication types

  • Letter
  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Cation Transport Proteins / genetics
  • Cation Transport Proteins / metabolism*
  • Cations, Monovalent / metabolism
  • Chlorophyta
  • Cryptophyta*
  • Evolution, Molecular
  • HEK293 Cells
  • Humans
  • Hydrogen / metabolism
  • Hydrogen-Ion Concentration
  • Light
  • Patch-Clamp Techniques
  • Polynucleotides / genetics
  • Polynucleotides / metabolism
  • Protons
  • Sensory Rhodopsins / genetics
  • Sensory Rhodopsins / metabolism*
  • Sodium / metabolism


  • Cation Transport Proteins
  • Cations, Monovalent
  • Polynucleotides
  • Protons
  • Sensory Rhodopsins
  • Hydrogen
  • Sodium