Target Synonyms and Classification: Proteorhodopsins (pRhodopsin, PR) are a subgroup of 50 identified members within the Ion-translocating Microbial Rhodopsin Family (MRF, TCDB: 3.E.1), which catalyzes light-driven ion translocation across microbial cytoplasmic membranes or serve as light receptors.
Function: Proteorhodopsins are light-driven H+ or Na+ pumps and have a mechanism very similar to Bacteriorhodopsin. Photon adsorption by covalently bound Retinal triggers a photocycle, which is coupled to ion translocation involving cation binding and release as well as intramolecular transfer of cations along specific amino acid residues.
Organism and Localization: Proteorhodopsins are found in marine planktonic bacteria, archaea, and eukaryotes (protae). They are the most abundant retinal-based photoreceptors and due to their function in energy conversion might be relevant in marine ecosystems.
Substrates and Inhibitors: Na+ pumping Proteorhodopsins have been described, but most PRs pump protons.
Related Transporters: All Rhodopsins share the properties of a covalently bound retinal coupling light adsorption with ion translocation. There are several bacterial sensory Rhodopsins, such as the Cl- pumping Halorhodopsin, the Na+ pumping Rhodopsin KR2, the H+ pumping Bacteriorhodopsin and Channelrhodopsin, which has a channel-like mechanism. Besides energy conversion, they play key roles in phototaxis. Rhodopsins are also found in vertebrates, where they belong to the class of G protein-coupled receptors. Here, they are commonly found in light-sensing organs and responsible for the eyesight in humans.