In cyanobacteria, high light photoactivates the orange carotenoid protein (OCP) that binds to antennae complexes, dissipating energy and preventing the destruction of the photosynthetic apparatus. At low light, OCP is efficiently deactivated by a poorly understood action of the dimeric fluorescence recovery protein (FRP). Here, we engineer FRP variants with defined oligomeric states and scrutinize their functional interaction with OCP. Complemented by disulfide trapping and chemical crosslinking, structural analysis in solution reveals the topology of metastable complexes of OCP and the FRP scaffold with different stoichiometries. Unable to tightly bind monomeric FRP, photoactivated OCP recruits dimeric FRP, which subsequently monomerizes giving 1:1 complexes. This could be facilitated by a transient OCP-2FRP-OCP complex formed via the two FRP head domains, significantly improving FRP efficiency at elevated OCP levels. By identifying key molecular interfaces, our findings may inspire the design of optically triggered systems transducing light signals into protein-protein interactions.

中文翻译：

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OCP-FRP蛋白复合物拓扑结构提出了一种控制蓝细菌高耐光性的机制。

在蓝细菌中，强光会激活与天线复合体结合的橙色类胡萝卜素蛋白（OCP），从而耗散能量并防止光合装置的破坏。在昏暗的光线下，OCP通过二聚体荧光恢复蛋白（FRP）的未知作用而有效地失活。在这里，我们设计具有定义的低聚状态的FRP变体，并研究它们与OCP的功能相互作用。通过二硫键捕获和化学交联的补充，溶液中的结构分析揭示了OCP和FRP支架具有不同化学计量比的亚稳配合物的拓扑结构。由于无法紧密结合单体FRP，光活化的OCP会募集二聚FRP，随后将其单体化，形成1：1的复合物。通过两个FRP头域形成的瞬态OCP-2FRP-OCP复合物可以促进这种情况，在提高的OCP水平下显着提高FRP效率。通过确定关键的分子界面，我们的发现可能会激发光触发系统的设计，这些系统将光信号转换为蛋白质与蛋白质的相互作用。