Microbial Rhodopsins: Diversity, Mechanisms, and Optogenetic Applications

Annu Rev Biochem. 2017 Jun 20;86:845-872. doi: 10.1146/annurev-biochem-101910-144233. Epub 2017 Mar 9.


Microbial rhodopsins are a family of photoactive retinylidene proteins widespread throughout the microbial world. They are notable for their diversity of function, using variations of a shared seven-transmembrane helix design and similar photochemical reactions to carry out distinctly different light-driven energy and sensory transduction processes. Their study has contributed to our understanding of how evolution modifies protein scaffolds to create new protein chemistry, and their use as tools to control membrane potential with light is fundamental to optogenetics for research and clinical applications. We review the currently known functions and present more in-depth assessment of three functionally and structurally distinct types discovered over the past two years: (a) anion channelrhodopsins (ACRs) from cryptophyte algae, which enable efficient optogenetic neural suppression; (b) cryptophyte cation channelrhodopsins (CCRs), structurally distinct from the green algae CCRs used extensively for neural activation and from cryptophyte ACRs; and

Keywords: anion channelrhodopsins; cation channelrhodopsins; ion pumps; optogenetics; photosensors; retinylidene proteins.

Publication types

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

MeSH terms

  • Chlorophyta / classification
  • Chlorophyta / genetics
  • Chlorophyta / metabolism
  • Evolution, Molecular
  • Gene Expression
  • Light
  • Light Signal Transduction
  • Membrane Potentials / physiology
  • Models, Molecular
  • Optogenetics / methods*
  • Photochemical Processes
  • Phylogeny
  • Plant Proteins / chemistry*
  • Plant Proteins / genetics
  • Plant Proteins / metabolism
  • Protein Conformation, alpha-Helical
  • Protein Conformation, beta-Strand
  • Protein Domains
  • Retinoids / chemistry*
  • Retinoids / metabolism
  • Rhodopsins, Microbial / chemistry*
  • Rhodopsins, Microbial / genetics
  • Rhodopsins, Microbial / metabolism
  • Sensory Rhodopsins / chemistry*
  • Sensory Rhodopsins / genetics
  • Sensory Rhodopsins / metabolism


  • Plant Proteins
  • Retinoids
  • Rhodopsins, Microbial
  • Sensory Rhodopsins
  • retinylidene chromophore