Crystal structure of the red light-activated channelrhodopsin Chrimson

Nat Commun. 2018 Sep 26;9(1):3949. doi: 10.1038/s41467-018-06421-9.


Channelrhodopsins are light-activated ion channels that mediate cation permeation across cell membranes upon light absorption. Red-light-activated channelrhodopsins are of particular interest, because red light penetrates deeper into biological tissues and also enables dual-color experiments in combination with blue-light-activated optogenetic tools. Here we report the crystal structure of the most red-shifted channelrhodopsin from the algae Chlamydomonas noctigama, Chrimson, at 2.6 Å resolution. Chrimson resembles prokaryotic proton pumps in the retinal binding pocket, while sharing similarity with other channelrhodopsins in the ion-conducting pore. Concomitant mutation analysis identified the structural features that are responsible for Chrimson's red light sensitivity; namely, the protonation of the counterion for the retinal Schiff base, and the polar residue distribution and rigidity of the retinal binding pocket. Based on these mechanistic insights, we engineered ChrimsonSA, a mutant with a maximum activation wavelength red-shifted beyond 605 nm and accelerated closing kinetics.

Publication types

  • Evaluation Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Channelrhodopsins / chemistry*
  • Channelrhodopsins / genetics
  • Channelrhodopsins / metabolism
  • Chlamydomonas
  • Genetic Engineering
  • Molecular Structure
  • Protons
  • Schiff Bases / metabolism


  • Channelrhodopsins
  • Protons
  • Schiff Bases