Green algae and plants rely on light-harvesting complex II (LHCII) to collect photon energy for oxygenic photosynthesis. In Chlamydomonas reinhardtii, LHCII molecules associate with photosystem II (PSII) to form various supercomplexes, including the C2S2M2L2 type, which is the largest PSII-LHCII supercomplex in algae and plants that is presently known. Here, we report high-resolution cryo-electron microscopy (cryo-EM) maps and structural models of the C2S2M2L2 and C2S2 supercomplexes from C. reinhardtii. The C2S2 supercomplex contains an LhcbM1-LhcbM2/7-LhcbM3 heterotrimer in the strongly associated LHCII, and the LhcbM1 subunit assembles with CP43 through two interfacial galactolipid molecules. The loosely and moderately associated LHCII trimers interact closely with the minor antenna complex CP29 to form an intricate subcomplex bound to CP47 in the C2S2M2L2 supercomplex. A notable direct pathway is established for energy transfer from the loosely associated LHCII to the PSII reaction centre, as well as several indirect routes. Structure-based computational analysis on the excitation energy transfer within the two supercomplexes provides detailed mechanistic insights into the light-harvesting process in green algae.

中文翻译：

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绿藻光系统 II 光收集的结构洞察。

绿藻和植物依靠光捕获复合物 II (LHCII) 来收集光子能量以进行有氧光合作用。在莱茵衣藻中，LHCII 分子与光系统 II (PSII) 结合形成各种超复合体，包括 C2S2M2L2 型，这是目前已知的藻类和植物中最大的 PSII-LHCII 超复合体。在这里，我们报告了来自莱茵衣藻的 C2S2M2L2 和 C2S2 超复合物的高分辨率低温电子显微镜 (cryo-EM) 图和结构模型。C2S2 超复合物在强结合的 LHCII 中包含一个 LhcbM1-LhcbM2/7-LhcbM3 异源三聚体，LhcbM1 亚基通过两个界面半乳糖脂分子与 CP43 组装。松散和适度关联的 LHCII 三聚体与次要天线复合体 CP29 密切相互作用，形成与 C2S2M2L2 超复合体中的 CP47 结合的复杂子复合体。建立了从松散关联的 LHCII 到 PSII 反应中心的能量转移的显着直接途径，以及一些间接途径。基于结构的计算分析对两个超级复合物中的激发能量转移提供了详细的机制见解，以了解绿藻中的光捕获过程。