The photosystem I supercomplex from a primordial green alga Ostreococcus tauri harbors three light-harvesting complex trimers
The photosystem I supercomplex from a primordial green alga Ostreococcus tauri harbors three light-harvesting complex trimers
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DOI：
10.1101/2022.11.08.515661
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发表时间：
2022-11
期刊：
影响因子：
7.7
通讯作者：
A. Ishii;Jianyu Shan;X. Sheng;Eunchul Kim;A. Watanabe;Makio Yokono;C. Noda;Chihong Song;K. Murata;Zhenfeng Liu;J. Minagawa
中科院分区：
文献类型：
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作者：
A. Ishii;Jianyu Shan;X. Sheng;Eunchul Kim;A. Watanabe;Makio Yokono;C. Noda;Chihong Song;K. Murata;Zhenfeng Liu;J. Minagawa
作为一种普遍存在于海洋中的微微型浮游植物和早期分枝的绿色藻类，尾牡蛎是研究光合作用中捕光系统功能进化的模式植物。在这里，我们报告的结构和功能的O。Tauri光系统I（PSI）超复合物在低光下，在那里它通过组装光捕获复合物I（LHCI）和prasinophyte特异性光捕获复合物（Lhcp）来扩大其光子吸收能力。其结构表现出植物型和绿色藻类型PSI超复合体的混合特征，由PSI核心、一侧连接的Lhca 1-Lhca 4-Lhca 2-Lhca 3带和另一侧在PsaG和PsaH之间关联的Lhca 5-Lhca 6异二聚体组成。有趣的是，九个Lhcp亚基，包括一个Lhcp 1单体与磷酸化的氨基末端苏氨酸和八个Lhcp 2单体，寡聚成三个三聚体和关联PSI的第三侧Lhca 6和PsaK之间。Lhcp 1的磷酸化和PSI的捕光能力受到可逆的光适应，这表明OtPSI-LHCI-Lhcp超复合物的形成可能是由于光强度变化诱导的状态转换机制。值得注意的是，该超复合物在77 K荧光光谱中没有表现出远红峰，这可能是由于OtLhca 1 -4中叶绿素a603-a609对的弱耦合。
As a ubiquitous picophytoplankton in the ocean and an early-branching green alga, Ostreococcus tauri is a model prasinophyte species for studying the functional evolution of the light-harvesting systems in photosynthesis. Here, we report the structure and function of the O. tauri photosystem I (PSI) supercomplex in the low light, where it expands its photon-absorbing capacity by assembling with the light-harvesting complexes I (LHCI) and a prasinophyte-specific light-harvesting complex (Lhcp). Its architecture exhibits hybrid features of the plant-type and the green algal-type PSI supercomplexes, consisting of a PSI core, a Lhca1-Lhca4-Lhca2-Lhca3 belt attached on one side and a Lhca5-Lhca6 heterodimer associated on the other side between PsaG and PsaH. Interestingly, nine Lhcp subunits, including one Lhcp1 monomer with a phosphorylated amino-terminal threonine and eight Lhcp2 monomers, oligomerize into three trimers and associate with PSI on the third side between Lhca6 and PsaK. The Lhcp1 phosphorylation and the light-harvesting capacity of PSI were subjected to reversible photoacclimation, suggesting that the formation of OtPSI–LHCI–Lhcp supercomplex is likely due to a state transition-like mechanism induced by light intensity change. Notably, this supercomplex did not exhibit far-red peaks in the 77 K fluorescence spectra, which is possibly due to weak coupling of the chlorophyll a603-a609 pair in OtLhca1-4.