National Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, China.
University of Chinese Academy of Sciences, Beijing, China.
Nat Plants. 2019 Dec;5(12):1320-1330. doi: 10.1038/s41477-019-0543-4. Epub 2019 Nov 25.
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 CSML 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 CSML and CS supercomplexes from C. reinhardtii. The CS 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 CSML 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.
绿藻和植物依赖光捕获复合物 II（LHCII）来收集光子能量进行放氧光合作用。在莱茵衣藻中，LHCII 分子与光系统 II（PSII）结合形成各种超复合物，包括 CSML 型，这是目前已知的藻类和植物中最大的 PSII-LHCII 超复合物。在这里，我们报道了来自莱茵衣藻的 CSML 和 CS 超复合物的高分辨率冷冻电镜（cryo-EM）图谱和结构模型。CS 超复合物在强烈结合的 LHCII 中包含一个 LhcbM1-LhcbM2/7-LhcbM3 异三聚体，LhcbM1 亚基通过两个界面半乳糖脂分子与 CP43 组装。松散和中度结合的 LHCII 三聚体与较小的天线复合物 CP29 紧密相互作用，在 CSML 超复合物中形成与 CP47 结合的复杂亚复合物。建立了一条从松散结合的 LHCII 到 PSII 反应中心的能量转移的显著直接途径，以及几条间接途径。基于结构的计算分析表明，在这两个超复合物内的激发能量转移提供了有关绿藻光捕获过程的详细机制见解。
