Jiang Han-Wei, Gisriel Christopher J, Cardona Tanai, Flesher David A, Brudvig Gary W, Ho Ming-Yang
Department of Life Science, National Taiwan University, Taipei 10617, Taiwan (Republic of China).
Department of Chemistry, Yale University, New Haven, CT 06511.
Proc Natl Acad Sci U S A. 2025 May 20;122(20):e2427090122. doi: 10.1073/pnas.2427090122. Epub 2025 May 14.
Thylakoid-free cyanobacteria are thought to preserve ancestral traits of early-evolving organisms capable of oxygenic photosynthesis. However, and until recently, photosynthesis studies in thylakoid-free cyanobacteria were only possible in the model strain , limiting our understanding of photosynthesis evolution. Here, we report the isolation, biochemical characterization, cryo-EM structure, and phylogenetic analysis of photosystem I (PSI) from a recently discovered thylakoid-free cyanobacterium, , a distant relative of the genus . We find that PSI exhibits a distinct carotenoid composition and has one conserved low-energy chlorophyll site, which was lost in . Furthermore, PSI in thylakoid-free cyanobacteria has changed at the sequence level to a degree comparable to that of other strains, yet its subunit composition and oligomeric form might be identical to that of the most recent common ancestor of cyanobacteria. This study therefore provides a glimpse into the ancient evolution of photosynthesis.
无类囊体蓝细菌被认为保留了能够进行光合放氧的早期进化生物的祖先特征。然而，直到最近，无类囊体蓝细菌中的光合作用研究仅能在模式菌株中进行，这限制了我们对光合作用进化的理解。在此，我们报告了从最近发现的无类囊体蓝细菌（一种与该属亲缘关系较远的蓝细菌）中分离出的光系统I（PSI）的分离、生化特性、冷冻电镜结构及系统发育分析。我们发现该PSI呈现出独特的类胡萝卜素组成，并且有一个保守的低能叶绿素位点，该位点在[具体菌株名称缺失]中丢失。此外，无类囊体蓝细菌中的PSI在序列水平上的变化程度与其他菌株相当，但其亚基组成和寡聚形式可能与蓝细菌最近共同祖先的相同。因此，这项研究让我们得以一窥光合作用的古老进化历程。
