Photosynthesis Research Center, Key Laboratory of Photobiology, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China; University of Chinese Academy of Science, Yuquan Road, Shijingshan District, Beijing 100049, China.
China National Botanical Garden, Beijing 100093, China.
Structure. 2023 Oct 5;31(10):1247-1258.e3. doi: 10.1016/j.str.2023.08.001. Epub 2023 Aug 25.
Light-harvesting complexes of photosystem II (LHCIIs) in green algae and plants are vital antenna apparatus for light harvesting, energy transfer, and photoprotection. Here we determined the structure of a siphonous-type LHCII trimer from the intertidal green alga Bryopsis corticulans by X-ray crystallography and cryo-electron microscopy (cryo-EM), and analyzed its functional properties by spectral analysis. The Bryopsis LHCII (Bry-LHCII) structures in both homotrimeric and heterotrimeric form show that green light-absorbing siphonaxanthin and siphonein occupied the sites of lutein and violaxanthin in plant LHCII, and two extra chlorophylls (Chls) b replaced Chls a. Binding of these pigments expands the blue-green light absorption of B. corticulans in the tidal zone. We observed differences between the Bry-LHCII homotrimer crystal and cryo-EM structures, and also between Bry-LHCII homotrimer and heterotrimer cryo-EM structures. These conformational changes may reflect the flexibility of Bry-LHCII, which may be required to adapt to light fluctuations from tidal rhythms.
光合系统 II（PSII）的捕光复合物（LHCIIs）在绿藻和植物中是至关重要的天线装置，用于进行光捕获、能量传递和光保护。在这里，我们通过 X 射线晶体学和冷冻电镜（cryo-EM）确定了来自潮间带绿藻石莼的管状型 LHCII 三聚体的结构，并通过光谱分析分析了其功能特性。石莼 LHCII（Bry-LHCII）的同三聚体和异三聚体形式的结构表明，绿光吸收的硅甲藻黄素和硅甲藻素占据了植物 LHCII 中叶黄素和紫黄质的位置，并且两个额外的叶绿素 b 取代了叶绿素 a。这些色素的结合扩展了石莼在潮间带中对蓝绿光的吸收。我们观察到 Bry-LHCII 同三聚体晶体和 cryo-EM 结构之间以及 Bry-LHCII 同三聚体和异三聚体 cryo-EM 结构之间的差异。这些构象变化可能反映了 Bry-LHCII 的灵活性，这可能是适应潮汐节律引起的光波动所必需的。
