Retinylidene Proteins: Structures and Functions from Archaea to Humans

Abstract

Retinylidene proteins, containing seven membrane-embedded alpha-helices that form an internal pocket in which the chromophore retinal is bound, are ubiquitous in photoreceptor cells in eyes throughout the animal kingdom. They are also present in a diverse range of other organisms and locations, such as archaeal prokaryotes, unicellular eukaryotic microbes, the dermal tissue of frogs, the pineal glands of lizards and birds, the hypothalamus of toads, and the human brain. Their functions include light-driven ion transport and phototaxis signaling in microorganisms, and retinal isomerization and various types of photosignal transduction in higher animals. The aims of this review are to examine this group of photoactive proteins as a whole, to summarize our current understanding of structure/function relationships in the best-studied examples, and to report recent new developments.

In Vivo Application of Optogenetics for Neural Circuit Analysis

“…Microbial opsins can be broadly categorized into transport rhodopsins and sensory rhodopsins. 9 Transport rhodopsins include light-driven chloride pumps (halorhodopsins) and light-driven proton pumps (e.g., bacteriorhodopsins, archaerhodopsins, proteorhodopsins, etc.). Sensory rhodopsins include sensory rhodopsins I and II (phototaxis receptors in prokaryotes), channelrhodopsins (phototaxis receptors in algae), and others that mediate a variety of cellular functions (for reviews on opsin structure and function, see refs 9 and 10).…”

“…In the dark state, all-trans retinal binds to a conserved lysine residue within the seventh transmembrane domain, forming a protonated Schiff base. 9 Upon absorption of a photon, photoisomerization of alltrans retinal to 13-cis retinal causes a sequence of protein conformational changes, which results in the transport of ions across the membrane. Different intermediate states during each photochemical cycle (photocycle) have been well studied for many microbial opsins, and each intermediate state can be distinguished based on the absorption spectrum determined by the overall structure of the protein.…”

Terrestrial models for extraterrestrial life: methanogens and halophiles at Martian temperatures

“…This capability has recently been discovered among a wide variety of Archaea, bacteria, and Eukaryotes and may represent an ancient form of metabolism, which may possibly have co-evolved with chlorophyllbased photosynthesis (Wickramasinghe 1976;Spudich et al 2000;Bielawski et al 2004;DasSarma 2006). The ability of extremely halophilic Archaea to thrive under anoxic conditions renders this group of organisms suitable as models for a variety of extraterrestrial habitat scenarios.…”

A light-driven proton pump from Haloterrigena turkmenica: Functional expression in Escherichia coli membrane and coupling with a H+ co-transporter

“…During this linear and cycling photochemical reaction (photocycle), bR transports one proton from the cytoplasm to the extracellular medium. In addition to bR, three other kinds of the retinal proteins (archaeal rhodopsins) are expressed in the same strain H. salinarum [3], and they are structurally similar to one another; they have seven transmembrane helices (A-G) with a chromophore (all-trans retinal) bound to a lysine residue on helix G via a protonated Schiff base. In addition, photo-excitation undergoes a photocycle for all archaeal rhodopsins.…”