Tsoraev Georgy V, Bukhanko Antonina, Budylin Gleb S, Shirshin Evgeny A, Slonimskiy Yury B, Sluchanko Nikolai N, Kloz Miroslav, Cherepanov Dmitry A, Shakina Yaroslava V, Ge Baosheng, Moldenhauer Marcus, Friedrich Thomas, Golub Maksym, Pieper Jörg, Maksimov Eugene G, Rubin Andrew B
Faculty of Biology, M.V. Lomonosov Moscow State University, 119234 Moscow, Russia.
Faculty of Physics, M.V. Lomonosov Moscow State University, 119991 Moscow, Russia.
J Phys Chem B. 2023 Mar 9;127(9):1890-1900. doi: 10.1021/acs.jpcb.2c07189. Epub 2023 Feb 17.
Most cyanobacteria utilize a water-soluble Orange Carotenoid Protein (OCP) to protect their light-harvesting complexes from photodamage. The Fluorescence Recovery Protein (FRP) is used to restore photosynthetic activity by inactivating OCP via dynamic OCP-FRP interactions, a multistage process that remains underexplored. In this work, applying time-resolved spectroscopy, we demonstrate that the interaction of FRP with the photoactivated OCP begins early in the photocycle. Interacting with the compact OCP state, FRP completely prevents the possibility of OCP domain separation and formation of the signaling state capable of interacting with the antenna. The structural element that prevents FRP binding and formation of the complex is the short α-helix at the beginning of the N-terminal domain of OCP, which masks the primary site in the C-terminal domain of OCP. We determined the rate of opening of this site and show that it remains exposed long after the relaxation of the red OCP states. Observations of the OCP transitions on the ms time scale revealed that the relaxation of the orange photocycle intermediates is accompanied by an increase in the interaction of the carotenoid keto group with the hydrogen bond donor tyrosine-201. Our data refine the current model of photoinduced OCP transitions and the interaction of its intermediates with FRP.
大多数蓝细菌利用水溶性橙色类胡萝卜素蛋白（OCP）来保护其光捕获复合体免受光损伤。荧光恢复蛋白（FRP）通过动态的OCP-FRP相互作用使OCP失活，从而恢复光合活性，这一多级过程仍未得到充分研究。在这项工作中，我们应用时间分辨光谱法证明，FRP与光活化的OCP之间的相互作用在光循环早期就开始了。与紧密的OCP状态相互作用时，FRP完全阻止了OCP结构域分离以及形成能够与天线相互作用的信号状态的可能性。阻止FRP结合和复合物形成的结构元件是OCP N端结构域起始处的短α螺旋，它掩盖了OCP C端结构域中的主要位点。我们测定了该位点的开放速率，并表明在红色OCP状态弛豫后很长时间它仍保持暴露状态。在毫秒时间尺度上对OCP转变的观察表明，橙色光循环中间体的弛豫伴随着类胡萝卜素酮基与氢键供体酪氨酸-201相互作用的增加。我们的数据完善了当前光诱导OCP转变及其中间体与FRP相互作用的模型。
