title: Photoreaction cycle of phoborhodopsin (sensory rhodopsin II) from Halobacterium salinarum expressed in Escherichia coli.
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 degrees 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.
authors.affiliation: Division of Engineering for Composite Functions, Muroran Institute of Technology, Muroran, Japan.
authors.forename: Gang
authors.initials: G
authors.lastname: Dai
authors.forename: Yoshikazu
authors.initials: Y
authors.lastname: Ohno
authors.forename: Yoichi
authors.initials: Y
authors.lastname: Ikeda
authors.forename: Jun
authors.initials: J
authors.lastname: Tamogami
authors.forename: Takashi
authors.initials: T
authors.lastname: Kikukawa
authors.forename: Naoki
authors.initials: N
authors.lastname: Kamo
authors.forename: Tatsuo
authors.initials: T
authors.lastname: Iwasa
mesh_terms: D003001:Cloning, Molecular; D004926:Escherichia coli / Q000235:genetics*; D019617:Halobacterium salinarum / Q000737:chemistry*; D025602:Halorhodopsins / Q000737:chemistry / Q000235:genetics / Q000528:radiation effects*; D055668:Photochemical Processes; D010777:Photochemistry; D010782:Photolysis; D025603:Sensory Rhodopsins / Q000737:chemistry / Q000235:genetics / Q000528:radiation effects*; D013696:Temperature
chemical_list: D025602:Halorhodopsins; D025603:Sensory Rhodopsins; C061508:sensory rhodopsin II protein, archaeal