Halorhodopsin is a seven-transmembrane retinylidene protein from microbial rhodopsin family. It is a chloride-specific light-activated ion pump found in archaea known as halobacteria. It is activated by green light wavelengths of approximately 578nm. Halorhodopsin also shares sequence similarity to channelrhodopsin, a light-gated ion channel.
Halorhodopsin Cartoon Visualization by Jawahar Swaminathan and MSD staff at the European Bioinformatics Institute
Microbial rhodopsins, also known as bacterial rhodopsins, are retinal-binding proteins that provide light-dependent ion transport and sensory functions in halophilic and other bacteria. They are integral membrane proteins with seven transmembrane helices, the last of which contains the attachment point for retinal. Most microbial rhodopsins pump inwards, however "mirror rhodopsins" which function outwards. have been discovered.
Purple bacteriorhodopsin in Halobacteria at Cargill's salt evaporation ponds in San Francisco Bay, located at Newark, California