Retinal proteins - visual pigments, bacterial ion pumps and sensory photoreceptors, are usually thought of as single chromophore molecular machines. Accordingly the retinal molecule acts both to harvest the light, and to translate it into biological activity. Recently discovered proteins show that this is not always the case. The Xanthorhodopsin proton pump, which was discovered in Salinibacter Ruber, is equipped with an associated carotenoid which was shown by methods of fluorescence spectroscopy to act as a light harvesting antenna, boosting the action spectrum of the protein deeper to the blue, and greatly enhancing its overall ability to utilize ambient light. Investigation of this process was later extended to the time domain both in our lab and in that of Sundstrom and Polivka. In those experiments the ultrafast nature of the carotenoid light harvesting was demonstrated, and the high efficiency of energy transfer to the retinal moiety quantified directly. In the talk I will report photo-selective ultrafast experiments on other retinal proteins which demonstrate the generality of this light harvesting strategy. The Gloeobacter rhodopsin proton pump, expressed in e-coli, was reconstituted with the same salinixanthine carotenoid antenna which is naturally synthesized in Xanthorhodopsin. Measures for energy transfer efficiency to the retinal will be presented, and the generality and consequences of this strategy for enhancing solar energy harvesting in retinal proteins will be discussed.

Light harvesting bichromophoric retinal proteins

247th National Meeting (2014)

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