Eukaryotic rhodopsins

Microbial Rhodopsins Archaeal Rhodopsins Bacterial Rhodopsins Eukaryotic Rhodopsins. 124-2... 

Lawson, M.A., Zacks, D.N., Derguini, F., Nakanishi, K., and Spudich, J.L., Retinal analog restoration of photophobic responses in a blind Chlamydomonas reinhardtii mutant Evidence for an archae-bacterial like chromophore in a eukaryotic rhodopsin, Biophys. /., 60, 6,1490, 1991. 

The interphotoreceptor retinoid-binding protein (Borst et al., 1989) functions in the regeneration of rhodopsin in the mammalian visual cycle. It is exclusive to vertebrates yet contains a repeated structure that has been found singly in bacterial and plant tail-specific proteases (TSPc) (Silber et al., 1992) and the archaeal tricorn protease (Tamura et al., 1996). The eukaryotic homologs of TSPc are likely to be inactive as... 

At the start of the twenty-first century, the pace of membrane protein structure determinations is clearly accelerating (Figure 1). With the exceptions of rhodopsin (Palczewski et al., 2000) and the calcium ATPase (Toyoshima et al., 2000), however, eukaryotic channels, transporters, and receptors are conspicuously absent from the list of known membrane protein structures. These two exceptions, as proteins of naturally high abundance, highlight the current reality that no structure has been determined for an overexpressed eukaryotic membrane protein. This situation reflects the present difficulties in the reliable overexpression of membrane proteins, particularly those of eukaryotic organisms. Just as the development 20 years ago of overexpression systems for water-soluble proteins revolutionized the structure determinations of this class of proteins, advances in membrane protein expression will be essential to successful realization of the goal of routine structural analysis of membrane proteins. 

The photoreceptor molecules used by different microorganisms for light perception vary significantly and fall in different classes including BLUE proteins, cryptochromes, phototropins, phytochromes, and rhodopsins. Other prokaryotic and eukaryotic organisms use photoactive yellow proteins (PYP) which contain a 4-hydroxycinnamate chromophore (21)., chlorophylls, carotenoids, phycobilins, and pterins. Hypericins have been found to be involved in photoorientation of ciliates (22). 

Even though rhodopsin and bacteriorhodopsin appear to differ fundamentally in their function, mode of action, structure, and photochemistry, it has been suggested (Stoeckenius et ai, 1979) that the two proteins did not evolve independently. One possibility is that the halobacteria may have acquired bacteriorhodopsin by gene transfer from a eukaryote (Stoeckenius et al., 1979). However, a preliminary report by Hargrave et al. (1983) claims that no statistically significant sequence homology can be found. Thus, the resemblance between these proteins appears to be only superficial. 

Podesta, A., Marangoni, R., ViUani, C., and Colombetti, G., A rhodopsin-hke molecule on the plasma-membrane of Fabrea salina, J. Eukaryot. Microbiol, 41, 565,1994. 

Because microbial rhodopsins are present in aU three domains of hfe, progenitors of these proteins may have existed in the early phases of evolution, before the divergence of archaea, eubacteria, and eukaryotes. 

Bieszke, J.A., Spudich, E.N., Scott, K.L., Borkovich, K.A., and Spudich, J.L., A eukaryotic protein, NOP-1, binds retinal to form an archaeal rhodopsin-like photochemically reactive pigment. Biochemistry, 38, 43, 14,138, 1999. 

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