• Clean Technology
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• v.17 no.3
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• pp.280-282
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• 2011

Capture and conversion of abundant solar energy using biotechnology will be essential for the development of sustainable and future energy. Photosynthesis is used for the production of biofuels such as biohydrogen. In this study, lightharvesting xanthorhodopsin consisting of retinal and salinixanthin was isolated from a photosynthetic microorganism Salinibacter ruber by aqueous two phase extraction. To stabilize the light-harvesting machine, artificial xanthorhodopsin-liposome system was reconstructed to have photoelectron absorption activity.

• Journal of Microbiology and Biotechnology
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• v.30 no.5
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• pp.633-641
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• 2020

Microbial rhodopsins are a superfamily of photoactive membrane proteins with the covalently bound retinal cofactor. Isomerization of the retinal chromophore upon absorption of a photon triggers conformational changes of the protein to function as ion pumps or sensors. After the discovery of proteorhodopsin in an uncultivated γ-proteobacterium, light-activated proton pumps have been widely detected among marine bacteria and, together with chlorophyll-based photosynthesis, are considered as an important axis responsible for primary production in the biosphere. Rhodopsins and related proteins show a high level of phylogenetic diversity; we focus on a specific class of bacterial rhodopsins containing the '3 omega motif.' This motif forms a stack of three non-consecutive aromatic amino acids that correlates with the B-C loop orientation and is shared among the phylogenetically close ion pumps such as the NDQ motif-containing sodium-pumping rhodopsin, the NTQ motif-containing chloride-pumping rhodopsin, and some proton-pumping rhodopsins including xanthorhodopsin. Here, we reviewed the recent research progress on these 'omega rhodopsins,' and speculated on their evolutionary origin of functional diversity.

• Rapid Communication in Photoscience
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• v.2 no.2
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• pp.60-63
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• 2013

Rhodopsins belong to a family of membrane-embedded photoactive retinylidene proteins. One opsin gene was isolated from ${\beta}$-proteobacterium (IMCC9480) which had been collected at the North Pole. It is very similar to Xanthorhodopin (XR) of HTCC2181. In this study, we carried out basic characterization of the rhodopsin. It has ${\lambda}max$ of 536, 554, and 546 nm at pH 4.0, 7.0, and 10.0, respectively. Since the pKa of its proton acceptor is around 6.27, we measured its proton pumping activity and photocycling rate at pH 8.0. It has a typical proton acceptor (D99) and donor (E110) which mediate proton translocation from intracellular to extracellular region when deduced from the sequence alignments. On the basis of in vitro proton pumping activity, it was proposed to have fast photocycling rate with M and O intermediates, indicating that it is a typical ion-pumping rhodopsin. Since the XR has not yet been expressed in any other heterologous expression system, we tried to get much more information about the XR through the XR-homologue rhodopsin.