Microbial rhodopsin

Microbial rhodopsin, also known as type-I rhodopsin, is a active membrane protein composed of seven transmembrane alpha-helices with a retinal chromophore. It includes light-driven proton pumps, ion pumps and ion channels, as well as light sensors. Microbial rhodopsins are found in all three domains of life: Archaea, Bacteria, and Eukaryota, as well as in viruses. It is rare in complex multicellular organisms.

Rhodopsin was originally a synonym for "visual purple", a visual pigment (light-sensitive molecule) found in the retinas of frogs and other vertebrates, used for dim-light vision, and usually found in rod cells. This is still the meaning of rhodopsin in the narrow sense. In the broad sense, rhodopsin refers to any molecule consisting of an opsin and a chromophore (generally a variant of retinal). The term bacterial rhodopsin originally referred to the first microbial rhodopsin discovered, known today as bacteriorhodopsin. The first bacteriorhodopsin turned out to be of archaeal origin, from Halobacterium salinarum. Since then, other microbial rhodopsins have been discovered, rendering the term bacterial rhodopsin ambiguous.

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