Research Institute for Interdisciplinary Science and Graduate School of Natural Science and Technology, Okayama University, Okayama, Japan.
Biomolecular Characterization Unit, RIKEN Center for Sustainable Resource Science, Saitama, Japan.
Nat Plants. 2019 Aug;5(8):890-901. doi: 10.1038/s41477-019-0477-x. Epub 2019 Jul 29.
Light-harvesting antenna systems in photosynthetic organisms harvest solar energy and transfer it to the photosynthetic reaction centres to initiate charge-separation and electron-transfer reactions. Diatoms are one of the important groups of oxyphototrophs and possess fucoxanthin chlorophyll a/c-binding proteins (FCPs) as light harvesters. The organization and association pattern of FCP with the photosystem II (PSII) core are unknown. Here we solved the structure of PSII-FCPII supercomplexes isolated from a diatom, Chaetoceros gracilis, by single-particle cryoelectron microscopy. The PSII-FCPII forms a homodimer. In each monomer, two FCP homotetramers and three FCP monomers are associated with one PSII core. The structure reveals a highly complicated protein-pigment network that is different from the green-type light-harvesting apparatus. Comparing these two systems allows the identification of energy transfer and quenching pathways. These findings provide structural insights into not only excitation-energy transfer mechanisms in the diatom PSII-FCPII, but also changes of light harvesters between the red- and green-lineage oxyphototrophs during evolution.
光合生物中的光捕获天线系统收集太阳能，并将其转移到光合作用反应中心，以启动电荷分离和电子转移反应。硅藻是重要的光合自养生物群之一，它们拥有岩藻黄素叶绿素 a/c 结合蛋白（FCP）作为光捕获器。然而，FCP 与光系统 II（PSII）核心的组织和关联模式尚不清楚。在这里，我们通过单颗粒冷冻电子显微镜解析了从硅藻角毛藻中分离得到的 PSII-FCPII 超复合物的结构。PSII-FCPII 形成同源二聚体。在每个单体中，两个 FCP 四聚体和三个 FCP 单体与一个 PSII 核心结合。该结构揭示了一个高度复杂的蛋白质-色素网络，与绿色型光捕获装置不同。比较这两个系统可以确定能量转移和猝灭途径。这些发现不仅为硅藻 PSII-FCPII 中的激发能转移机制提供了结构见解，也为红藻和绿藻光合自养生物在进化过程中光捕获器的变化提供了结构见解。
