Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States.
Department of Biology and Biotechnology, University of Pavia, 27100 Pavia, Italy.
J Am Chem Soc. 2021 Oct 27;143(42):17577-17586. doi: 10.1021/jacs.1c07385. Epub 2021 Oct 14.
Plants use energy from the sun yet also require protection against the generation of deleterious photoproducts from excess energy. Photoprotection in green plants, known as nonphotochemical quenching (NPQ), involves thermal dissipation of energy and is activated by a series of interrelated factors: a pH drop in the lumen, accumulation of the carotenoid zeaxanthin (Zea), and formation of arrays of pigment-containing antenna complexes. However, understanding their individual contributions and their interactions has been challenging, particularly for the antenna arrays, which are difficult to manipulate in vitro. Here, we achieved systematic and discrete control over the array size for the principal antenna complex, light-harvesting complex II, using near-native in vitro membranes called nanodiscs. Each of the factors had a distinct influence on the level of dissipation, which was characterized by measurements of fluorescence quenching and ultrafast chlorophyll-to-carotenoid energy transfer. First, an increase in array size led to a corresponding increase in dissipation; the dramatic changes in the chlorophyll dynamics suggested that this is due to an allosteric conformational change of the protein. Second, a pH drop increased dissipation but exclusively in the presence of protein-protein interactions. Third, no Zea dependence was identified which suggested that Zea regulates a distinct aspect of NPQ. Collectively, these results indicate that each factor provides a separate type of control knob for photoprotection, which likely enables a flexible and tunable response to solar fluctuations.
植物利用太阳的能量，但也需要防止多余能量产生有害的光产物。绿色植物中的光保护作用，称为非光化学猝灭（NPQ），涉及能量的热耗散，并由一系列相互关联的因素激活：腔室中的 pH 值下降、类胡萝卜素玉米黄质（Zea）的积累和含有色素的天线复合物的阵列形成。然而，理解它们各自的贡献及其相互作用一直具有挑战性，特别是对于天线阵列，在体外很难操纵。在这里，我们使用称为纳米盘的近天然体外膜实现了主要天线复合物——光捕获复合物 II 的阵列大小的系统和离散控制。每个因素对耗散水平都有明显的影响，这可以通过荧光猝灭和超快叶绿素到类胡萝卜素能量转移的测量来表征。首先，阵列尺寸的增加导致耗散的相应增加；叶绿素动力学的剧烈变化表明，这是由于蛋白质的变构构象变化。其次，pH 值下降会增加耗散，但仅在存在蛋白质-蛋白质相互作用的情况下。第三，未发现 Zea 的依赖性，这表明 Zea 调节 NPQ 的一个独特方面。总的来说，这些结果表明，每个因素都为光保护提供了一种单独的控制旋钮，这可能使植物能够对太阳波动做出灵活和可调节的反应。
