New Insights into the Evolutionary History of Type 1 Rhodopsins

Abstract

Type 1 (archaeal) rhodopsins and related rhodopsin-like proteins had been described in a few halophile archaea, gamma-proteobacteria, a single cyanobacteria, some fungi, and a green alga. In exhaustive database searches, we detected rhodopsin-related sequences derived not only from additional fungal species but also from organisms belonging to three groups in which opsins had hitherto not been described: the alpha-proteobacterium Magnetospirillum magnetotacticum, the cryptomonad alga Guillardia theta, and the dinoflagellate Pyrocystis lunula. Putative plant and human type 1 rhodopsin sequences found in the databases are demonstrated to be contaminants of fungal origin. However, a highly diverged sequence supposedly from the plant Oryza sativa was found that is, together with the Pyrocystis sequence, quite similar to gamma-proteobacterial rhodopsins. These close relationships suggest that at least one horizontal gene transfer event involving rhodopsin genes occurred between prokaryotes and eukaryotes. Alternative hypotheses to explain the current phylogenetic range of type 1 rhodopsins are suggested. The broader phylogenetic range found is compatible with an ancient origin of type 1 rhodopsins, their patchy distribution being caused by losses in multiple lineages. However, the possibility of ancient horizontal transfer events between distant relatives cannot be dismissed.

A Microbial Rhodopsin with a Unique Retinal Composition Shows Both Sensory Rhodopsin II and Bacteriorhodopsin-like Properties

“…Presumably, the slower phototactic response of FIGURE 6. A, light-driven pH changes in spheroplast vesicles containing HwBR or MR (50 mM MgSO 4 , 150 mM NaCl, initial pH ϳ6.5). On and Off indicate the onset and offset of illumination (with yellow light, Ͼ500 nm for HwBR and Ͼ460 nm for MR), and the negative signal corresponds to a decrease in pH (outward proton transport).…”

Evolution of GPCR: Change and continuity

“…First, both prokaryotic and eukaryotic 7TM proteins have evolved independently for hundreds of millions of years with strongly different generation times, environmental selection, susceptibilities to mutations and modes of genetic rearrangement [18]. Secondly, at least for type 1 microbial rhodopsins, there is good evidence for lateral gene transfer events across great evolutionary distances and even between prokaryotes and eukaryotes that further complicates the analysis of phylogenic relations [19,20]. As introns in protein-coding regions are uncommon in prokaryotes, extant gene structure analyses can only guide eukaryotic phylogenetic analysis.…”

How to make an eye

“…These subcellular organelles probably first evolved in cyanobacteria (Gartner and Losi, 2003), and have been maintained either within or associated with chloroplasts (the endosymbiotic descendants of these bacteria), in green algae such as Chlamydomonas and Volvox (Ebnet et al, 1999;Dieckmann, 2003;Dyall et al, 2004). Eye organelles containing rhodopsin are also present in dinoflagellates (Greuet, 1965;Francis, 1967;Okamoto and Hastings, 2003;Ruiz-Gonzalez and Marin, 2004), single-celled eukaryotes that have now lost the chloroplasts in which these eyespots presumably originated. Gehring made the intriguing suggestion that dinoflagellates might themselves have been engulfed by larger creatures, such as Cnidarians, and may thus be the source of the opsins and eye pigments of higher organisms.…”