PDF(Pubmed)
Abstract：
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.
摘要：
隐生植物是由红藻通过次生内共生进化而来的祖先光合生物。他们已经开发了四氧嘧啶-叶绿素a/c2结合蛋白（ACP）作为光捕获复合物（LHC）。隐生植物的独特特性有助于有效的氧气光合作用，并强调了红色谱系质体的进化关系。在这里，我们介绍了来自隐藻嗜铬单胞菌的光系统II（PSII）-ACPII超复合物的低温电子显微镜结构。该结构包括PSII二聚体和形成四个线性三聚体的十二个ACPII单体。这些三聚体在结构上类似于红藻LHC和与光系统I（PSI）相关的隐藻ACPI三聚体，表明了它们紧密的进化联系。我们还确定了Chla-结合亚基，psb-γ,对于稳定PSII-ACPII关联至关重要。此外，计算计算提供了对激发能量转移途径的见解。我们的研究为理解隐生植物PSII-ACPII中的光能捕获和传输奠定了坚实的结构基础。PSII-LHCII的进化变异，以及红色谱系LHCIs的起源。
