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BP: Fachverband Biologische Physik

BP 14: Posters: Protein Structure and dynamics

BP 14.3: Poster

Tuesday, April 1, 2014, 09:30–12:30, P1

Photoswitchable Dynamics of the Orange Carotenoid Protein (OCP) in Living Cells of Synechocystis sp. PCC6803 — •Franz-Josef Schmitt¹, Evgeny Maksimov², Vladimir Z. Paschenko² und Thomas Friedrich¹ — ¹Institute of Chemistry, Biophysical Chemistry, TU Berlin, Straße des 17. Juni 135, D-10623 Berlin, Germany — ²Department of Biophysics, Biology Faculty, Lomonosov Moscow State University, 119991 Moscow, Russia

The cyanobacterium Synechocystis sp. PCC6803 contains a photoswitchable protein, the orange carotenoid protein (OCP) which undergoes conformational changes under illumination in the blue spectral regime. After activation by light the OCP binds to the membrane extrinsic phycobilisome (PBS) complexes and leads to non-photochemical quenching (NPQ) of the PBS fluorescence reducing the flow of energy into the photosystems (PS) under high light conditions as protection mechanism. We investigated the energy migration in the PS II by time- and wavelength-resolved fluorescence spectroscopy in a wide temperature range between 4 K and 300 K. The decay associated spectra calculated from the time resolved spectra were simulated by rate equation systems to analyse the pathway of energy migration in the PBS of Synechosystis sp. WT and two mutants that exhibit PBS of reduced complexity. The simulations show that NPQ of PBS by OCP occurs in the PBS core with an apparent time constant of about 100 ps. At kryostatic temperatures the efficient NPQ by OCP is hampered showing that the protein flexibility and/or mobility is essential for NPQ.