高等植物光系统II，即PSII-LHCII，是由二十多个亚基构成的超大膜蛋白复合物，富含叶绿素和类胡萝卜素分子，也是自然界中唯一能够氧化水分子的物质。解析该超复合物三维结构对于光合作用机理研究具有重要意义。PSII-LHCII超复合物由外周捕光天线系统和核心放氧复合物两部分构成，目前人们纯化到的最大超复合物样品C2S2M2是由核心放氧复合物双体，4个主要捕光蛋白LHCII三体，和6个次要捕光蛋白CP29、CP26、CP24单体等亚基组成。但是整个超复合物仅有12埃低分辨率的负染电镜结果，其中各亚基的组装方式和色素网络排布仍未被揭示。本项目主要利用单颗粒冷冻电镜的最新技术，使用新型单电子计数探测器，并结合X射线晶体学分析，研究高等植物PSII-LHCII超复合物高分辨率的三维精细结构。在结构的基础上，深入开展生物功能分析实验，从中揭示高等植物光系统II高效吸能、传能和转能的分子机制。

Higher plant photosystem II, PSII-LHCII, is a large membrane-protein supercomplex, which is consisting of more than 20 subunits and rich in chlorophyll and carotenoid molecules. It is the unique system where water oxidation takes place in nature. It is of great significance to solve the three-dimensional structure of PSII-LHCII supercomplex for revealing the molecular mechanism of photosynthesis. The PSII-LHCII supercomplex of higher plants is composed by two main moieties: the peripheral antenna system and the core oxygen-evolving complex. The largest PSII supercomplex purified is C2S2M2, consisting of a dimer of the core oxygen-evolving complex, four copies of the major light-harvesting complex LHCII trimers, six copies of the minor light-harvesting complexes CP29, CP26 and CP24 monomers, and et al. However, the whole structure of PSII-LHCII supercomplex was solved by negative staining electron microscopy in very low resolution, only 12 angstroms. So the assembly mode of the different subunits and its pigment network remain unclear until now. This project takes the PSII-LHCII supercomplex of higher plants as the subject with the aim to study its high-resolution three-dimensional structure through the new technologies of Cryo-EM and single particle analysis, especially using the direct electron detector, combined with X-ray crystallography. On the basis of the high-resolution structures, the further assays of biological function on the PSII-LHCII supercomplex will be performed. It will help us to elucidate the molecular mechanism of the absorption, transition and conversion of light-energy of the PSII-LHCII supercomplex of higher plants.