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The Signaling State of Orange Carotenoid Protein
Authors:Eugene?G Maksimov  Evgeny?A Shirshin  Nikolai?N Sluchanko  Dmitry?V Zlenko  Evgenia?Y Parshina  Georgy?V Tsoraev  Konstantin?E Klementiev  Gleb?S Budylin  Franz-Josef Schmitt  Thomas Friedrich  Victor?V Fadeev  Vladimir?Z Paschenko  Andrew?B Rubin
Institution:1.Department of Biophysics, Faculty of Biology, M.V. Lomonosov Moscow State University, Moscow, Russia;2.Department of Quantum Electronics, Faculty of Physics, M.V. Lomonosov Moscow State University, Moscow, Russia;3.A.N. Bach Institute of Biochemistry, Russian Academy of Sciences, Moscow, Russia;4.Institute of Chemistry, Max-Volmer Laboratory of Biophysical Chemistry, Technical University Berlin, Berlin, Germany
Abstract:Orange carotenoid protein (OCP) is the photoactive protein that is responsible for high light tolerance in cyanobacteria. We studied the kinetics of the OCP photocycle by monitoring changes in its absorption spectrum, intrinsic fluorescence, and fluorescence of the Nile red dye bound to OCP. It was demonstrated that all of these three methods provide the same kinetic parameters of the photocycle, namely, the kinetics of OCP relaxation in darkness was biexponential with a ratio of two components equal to 2:1 independently of temperature. Whereas the changes of the absorption spectrum of OCP characterize the geometry and environment of its chromophore, the intrinsic fluorescence of OCP reveals changes in its tertiary structure, and the fluorescence properties of Nile red indicate the exposure of hydrophobic surface areas of OCP to the solvent following the photocycle. The results of molecular-dynamics studies indicated the presence of two metastable conformations of 3′-hydroxyechinenone, which is consistent with characteristic changes in the Raman spectra. We conclude that rotation of the β-ionylidene ring in the C-terminal domain of OCP could be one of the first conformational rearrangements that occur during photoactivation. The obtained results suggest that the photoactivated form of OCP represents a molten globule-like state that is characterized by increased mobility of tertiary structure elements and solvent accessibility.
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