On the origins of arrestin and rhodopsin (PubMed)
Full length article. "... the arrestin clan is comprised of the Spo0M protein family in archaea and bacteria, and the arrestin and Vps26 families in eukaryotes." More information on rhodopsin and arrestin is available through the links, below.
"Rhodopsin, also known as visual purple, is a pigment of the retina that is responsible for both the formation of the photoreceptor cells and the first events in the perception of light. Rhodopsins belong to the G-protein coupled receptor family... " "Some prokaryotes express proton pumps called bacteriorhodopsin, proteorhodopsin, xanthorhodopsin to carry out phototrophy. Like rhodopsin, these contain retinal and have seven transmembrane alpha helices; however they are not coupled to a G protein."
"Arrestins are a small family of proteins important for regulating signal transduction." "Arrestins were first discovered as a part of a conserved two-step mechanism for regulating the activity of G protein-coupled receptors (GPCRs). In response to a stimulus, GPCRs activate heterotrimeric G proteins. In order to turn off this response, or adapt to a persistent stimulus, activated receptors need to be silenced." "Arrestin binding to the receptor blocks further G protein-mediated signaling ..."