Photosynthesis Research Center, Key Laboratory of Photobiology, Institute of Botany, The Chinese Academy of Sciences, Beijing, 100093, China.
University of Chinese Academy of Sciences, Yuquan Road, Shijingshan District, 100049, Beijing, China.
Nat Commun. 2020 Oct 8;11(1):5081. doi: 10.1038/s41467-020-18867-x.
Diatom is an important group of marine algae and contributes to around 20% of the global photosynthetic carbon fixation. Photosystem I (PSI) of diatoms is associated with a large number of fucoxanthin-chlorophyll a/c proteins (FCPIs). We report the structure of PSI-FCPI from a diatom Chaetoceros gracilis at 2.38 Å resolution by single-particle cryo-electron microscopy. PSI-FCPI is a monomeric supercomplex consisting of 12 core and 24 antenna subunits (FCPIs), and 326 chlorophylls a, 34 chlorophylls c, 102 fucoxanthins, 35 diadinoxanthins, 18 β-carotenes and some electron transfer cofactors. Two subunits designated PsaR and PsaS were found in the core, whereas several subunits were lost. The large number of pigments constitute a unique and huge network ensuring efficient energy harvesting, transfer and dissipation. These results provide a firm structural basis for unraveling the mechanisms of light-energy harvesting, transfer and quenching in the diatom PSI-FCPI, and also important clues to evolutionary changes of PSI-LHCI.
硅藻是一种重要的海洋藻类，约占全球光合作用碳固定的 20%。硅藻的光系统 I（PSI）与大量的叶黄素-叶绿素 a/c 蛋白（FCPIs）有关。我们通过单颗粒冷冻电子显微镜报告了来自硅藻 Chaetoceros gracilis 的 PSI-FCPI 的结构，分辨率为 2.38Å。PSI-FCPI 是一个由 12 个核心和 24 个天线亚基（FCPIs）组成的单体超复合体，包含 326 个叶绿素 a、34 个叶绿素 c、102 个叶黄素、35 个二氢玉米黄质、18 个β-胡萝卜素和一些电子传递辅助因子。在核心中发现了两个命名为 PsaR 和 PsaS 的亚基，而其他一些亚基则丢失了。大量的色素构成了一个独特而巨大的网络，确保了高效的能量收集、转移和耗散。这些结果为揭示硅藻 PSI-FCPI 中的光能收集、转移和猝灭机制提供了坚实的结构基础，也为 PSI-LHCI 的进化变化提供了重要线索。
