Photoreaction Cycle of Phoborhodopsin (Sensory Rhodopsin II) from Halobacterium salinarum Expressed in Escherichia coli |
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Authors: | Gang Dai Yoshikazu Ohno Yoichi Ikeda Jun Tamogami Takashi Kikukawa Naoki Kamo Tatsuo Iwasa |
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Affiliation: | 1. Division of Engineering for Composite Functions, Muroran Institute of Technology, Muroran, Japan;2. Division of Applied Science and Engineering, Muroran Institute of Technology, Muroran, Japan;3. Laboratory of Biophysical Chemistry, Faculty of Advanced Life Science, Hokkaido University, Sapporo, Japan;4. Laboratory of Biophysical Chemistry, Faculty of Advanced Life Science, Hokkaido University, Sapporo, Japan Current address: Naoki Kamo, College of Pharmaceutical Science, Matsuyama University, Matsuyama 790 5. 8578, Japan. |
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Abstract: | Phoborhodopsin (pR; also called sensory rhodopsin II, SRII) is a photoreceptor of negative phototaxis of halobacteria. The studies of photochemical properties of this pigment are not many because the amount of the pigment is small and the stability is low. Recently an expression system of phoborhodopsin from Halobacterium salinarum (called salinarum phoborhodopsin, spR; also HsSRII) in Escherichia coli and purification method has been developed (Mironova et al. [2005] FEBS Lett., 579, 3147–3151), which enables detailed studies on the photochemical properties of spR. In the present work, the photoreaction cycle of E. coli-expressed spR was studied by low-temperature spectroscopy and flash photolysis. Formations of K-, M-, O-like intermediates and P480 were reconfirmed as reported previously. New findings are as follows. (1) The K-like intermediate (P500) was a mixture of two photoproducts. (2) Formation of L-like intermediate (P482) was observed by low-temperature spectroscopy and flash photolysis at room temperature. (3) On long irradiation of spR at 20°C, formation of a new photoproduct P370 was observed and it decayed to the original spR in the dark with a decay half time of 190 min. Based on these results the similarities and dissimilarities between spR and ppR are discussed. |
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