Marine Biotechnology Research Center, State Key Laboratory of Microbial Technology, Shandong University, Qingdao, China.
MOE Key Laboratory of Evolution and Marine Biodiversity, Frontiers Science Center for Deep Ocean Multispheres and Earth System & College of Marine Life Sciences, Ocean University of China, Qingdao, China.
Nat Commun. 2024 Jun 12;15(1):4999. doi: 10.1038/s41467-024-49453-0.
Cryptophytes are ancestral photosynthetic organisms evolved from red algae through secondary endosymbiosis. They have developed alloxanthin-chlorophyll a/c2-binding proteins (ACPs) as light-harvesting complexes (LHCs). The distinctive properties of cryptophytes contribute to efficient oxygenic photosynthesis and underscore the evolutionary relationships of red-lineage plastids. Here we present the cryo-electron microscopy structure of the Photosystem II (PSII)-ACPII supercomplex from the cryptophyte Chroomonas placoidea. The structure includes a PSII dimer and twelve ACPII monomers forming four linear trimers. These trimers structurally resemble red algae LHCs and cryptophyte ACPI trimers that associate with Photosystem I (PSI), suggesting their close evolutionary links. We also determine a Chl a-binding subunit, Psb-γ, essential for stabilizing PSII-ACPII association. Furthermore, computational calculation provides insights into the excitation energy transfer pathways. Our study lays a solid structural foundation for understanding the light-energy capture and transfer in cryptophyte PSII-ACPII, evolutionary variations in PSII-LHCII, and the origin of red-lineage LHCIIs.
隐藻是通过二次内共生从红藻进化而来的原始光合生物。它们已经开发出了别藻蓝蛋白-叶绿素 a/c2 结合蛋白（ACPs）作为光收集复合物（LHCs）。隐藻的独特特性有助于高效的产氧光合作用，并强调了红藻质体的进化关系。在这里，我们展示了来自隐藻 Chroomonas placoidea 的光系统 II（PSII）-ACPII 超复合物的冷冻电子显微镜结构。该结构包括一个 PSII 二聚体和十二个 ACPII 单体，形成四个线性三聚体。这些三聚体在结构上类似于红藻 LHCs 和与光系统 I（PSI）结合的隐藻 ACPI 三聚体，表明它们具有密切的进化联系。我们还确定了一个叶绿素 a 结合亚基 Psb-γ，它对于稳定 PSII-ACPII 结合是必不可少的。此外，计算计算提供了对激发能量转移途径的深入了解。我们的研究为理解隐藻 PSII-ACPII 中的光能捕获和转移、PSII-LHCII 中的进化变化以及红藻质体 LHCII 的起源奠定了坚实的结构基础。
