Kato Koji, Kumazawa Minoru, Nakajima Yoshiki, Suzuki Takehiro, Dohmae Naoshi, Shen Jian-Ren, Ifuku Kentaro, Nagao Ryo
Research Institute for Interdisciplinary Science and Graduate School of Environmental, Life, Natural Science and Technology, Okayama University, Okayama 700-8530, Japan.
Graduate School of Agriculture, Kyoto University, Kyoto 606-8502, Japan.
Sci Adv. 2025 May 16;11(20):eadv7488. doi: 10.1126/sciadv.adv7488.
Red algae exhibit unique photosynthetic adaptations, characterized by photosystem I (PSI) supercomplexes containing light-harvesting complexes (LHCs), forming PSI-LHCI supercomplexes. In this study, we solved the PSI-LHCI structure of NIES-3638 at 2.19-angstrom resolution using cryo-electron microscopy, revealing a PSI monomer core associated with seven LHCI subunits. Structural analysis uncovered the absence of phylloquinones, the common secondary electron acceptor in PSI of photosynthetic organisms, suggesting adaptation to a benzoquinone-like molecule. Phylogenetic analysis suggests that retains traits characteristic of an ancestral red alga, including distinctive LHCI binding and interaction patterns. Variations in LHCI composition and interactions across red algae, particularly in red-lineage chlorophyll /-binding-like protein and red algal LHCs, highlight evolutionary divergence and specialization. These findings not only deepen our understanding of red algal PSI-LHCI diversification but also enable us to predict features of an ancestral red algal PSI-LHCI supercomplex, providing a framework to explore evolutionary adaptations from an ancestral red alga.
红藻表现出独特的光合适应特征，其特点是光系统I（PSI）超复合物包含捕光复合物（LHCs），形成PSI-LHCI超复合物。在本研究中，我们使用冷冻电子显微镜以2.19埃的分辨率解析了NIES-3638的PSI-LHCI结构，揭示了与七个LHCI亚基相关的PSI单体核心。结构分析发现光合生物PSI中常见的二级电子受体叶醌不存在，这表明其适应了类似苯醌的分子。系统发育分析表明，其保留了原始红藻的特征，包括独特的LHCI结合和相互作用模式。红藻中LHCI组成和相互作用的变化，特别是在红系叶绿素/-结合样蛋白和红藻LHCs中的变化，突出了进化分歧和特化。这些发现不仅加深了我们对红藻PSI-LHCI多样化的理解，还使我们能够预测原始红藻PSI-LHCI超复合物的特征，为探索原始红藻的进化适应提供了一个框架。
