Omega Rhodopsins: A Versatile Class of Microbial Rhodopsins

J Microbiol Biotechnol. 2020 May 28;30(5):633-641. doi: 10.4014/jmb.1912.12010.


Microbial rhodopsins are a superfamily of photoactive membrane proteins with covalently bound retinal cofactor. Isomerization of the retinal chromophore upon absorption of a photon triggers conformational changes of the protein to function as ion pumps or sensors. After the discovery of proteorhodopsin in an uncultivated γ-proteobacterium, light-activated proton pumps have been widely detected among marine bacteria and, together with chlorophyll-based photosynthesis, are considered as an important axis responsible for primary production in the biosphere. Rhodopsins and related proteins show a high level of phylogenetic diversity; we focus on a specific class of bacterial rhodopsins containing the 3 omega motif. This motif forms a stack of three nonconsecutive aromatic amino acids that correlates with the B-C loop orientation, and is shared among the phylogenetically close ion pumps such as the NDQ motif-containing sodium-pumping rhodopsin, the NTQ motif-containing chloride-pumping rhodopsin, and some proton-pumping rhodopsins including xanthorhodopsin. Here, we reviewed the recent research progress on these omega rhodopsins, and speculated on their evolutionary origin of functional diversity..

Keywords: 3 omega motif; actinorhodopsin (ActR); chloride pump rhodopsin (ClR); microbial rhodopsin; sodium pump rhodopsin (NaR); xanthorhodopsin (XR).

Publication types

  • Review

MeSH terms

  • Amino Acid Motifs
  • Bacterial Proteins*
  • Models, Molecular
  • Protein Conformation
  • Rhodopsins, Microbial*


  • Bacterial Proteins
  • Rhodopsins, Microbial