La Rocca Romain, Kato Koji, Tsai Pi-Cheng, Nakajima Yoshiki, Akita Fusamichi, Shen Jian-Ren
Research Institute for Interdisciplinary Science, and Advanced Research Field, Graduate School of Environmental, Life, Natural Science and Technology, Okayama University, Okayama, Japan.
Nat Commun. 2025 May 5;16(1):4175. doi: 10.1038/s41467-025-59512-9.
Haptophytes are unicellular algae that produce 30 to 50% of biomass in oceans. Among haptophytes, a subset named coccolithophores is characterized by calcified scales. Despite the importance of coccolithophores in global carbon fixation and CaCO production, their energy conversion system is still poorly known. Here we report a cryo-electron microscopic structure of photosystem II (PSII)-fucoxanthin chlorophyll c-binding protein (FCPII) supercomplex from Chyrostila roscoffensis, a representative of coccolithophores. This complex has two sets of six dimeric and monomeric FCPIIs, with distinct orientations. Interfaces of both FCPII/FCPII and FCPII/core differ from previously reported. We also determine the sequence of Psb36, a subunit previously found in diatoms and red algae. The principal excitation energy transfer (EET) pathways involve mainly 5 FCPIIs, where one FCPII monomer mediates EET to CP47. Our findings provide a solid structural basis for EET and energy dissipation pathways occurring in coccolithophores.
定鞭藻是单细胞藻类，在海洋中产生30%至50%的生物量。在定鞭藻中，一个名为颗石藻的子集以钙化鳞片为特征。尽管颗石藻在全球碳固定和碳酸钙生产中很重要，但其能量转换系统仍鲜为人知。在这里，我们报道了来自颗石藻代表物种罗斯科夫嗜冷绿藻的光系统II（PSII）-岩藻黄素叶绿素c结合蛋白（FCPII）超复合物的冷冻电子显微镜结构。该复合物有两组六个二聚体和单体FCPII，具有不同的方向。FCPII/FCPII和FCPII/核心的界面与先前报道的不同。我们还确定了Psb36的序列，Psb36是先前在硅藻和红藻中发现的一个亚基。主要的激发能量转移（EET）途径主要涉及5个FCPII，其中一个FCPII单体将EET介导至CP47。我们的发现为颗石藻中发生的EET和能量耗散途径提供了坚实的结构基础。
