Projection structure of channelrhodopsin-2 at 6 Å resolution by electron crystallography

J Mol Biol. 2011 Nov 18;414(1):86-95. doi: 10.1016/j.jmb.2011.09.049. Epub 2011 Oct 5.


Channelrhodopsin-2 (ChR2) is the prototype of a new class of light-gated ion channels that is finding widespread applications in optogenetics and biomedical research. We present a 6-Å projection map of ChR2, obtained by cryo-electron microscopy of two-dimensional crystals grown from pure, heterologously expressed protein. The map shows that ChR2 is the same dimer with non-crystallographic 2-fold symmetry in three different membrane crystals. This is consistent with biochemical analysis, which shows a stable dimer in detergent solution. Comparison to the projection map to bacteriorhodopsin indicates a similar structure of seven transmembrane alpha helices. Based on the projection map and sequence alignments, we built a homology model of ChR2 that potentially accounts for light-induced channel gating. Although a monomeric channel is not ruled out, comparison to other membrane channels and transporters suggests that the ChR2 channel is located at the dimer interface on the 2-fold axis, lined by transmembrane helices 3 and 4.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Bacteriorhodopsins / chemistry*
  • Bacteriorhodopsins / metabolism
  • Channelrhodopsins
  • Cryoelectron Microscopy*
  • Crystallography, X-Ray
  • Humans
  • Ion Channels / chemistry*
  • Ion Channels / metabolism
  • Models, Molecular
  • Molecular Sequence Data
  • Mutation / genetics
  • Nerve Tissue Proteins / chemistry*
  • Nerve Tissue Proteins / genetics
  • Nerve Tissue Proteins / metabolism*
  • Protein Conformation
  • Protein Multimerization
  • Protein Structure, Secondary
  • Sequence Homology, Amino Acid


  • Channelrhodopsins
  • Ion Channels
  • Nerve Tissue Proteins
  • Bacteriorhodopsins