Takahashi Ibuki Y, Suzuki Takehiro, Hirooka Shunsuke, Dohmae Naoshi, Miyagishima Shin-Ya, Nagao Ryo
Faculty of Agriculture, Shizuoka University, Shizuoka, 422-8529, Japan.
Biomolecular Characterization Unit, RIKEN Center for Sustainable Resource Science, Saitama, 351-0198, Japan.
Photosynth Res. 2025 Sep 17;163(5):48. doi: 10.1007/s11120-025-01169-y.
Cyanidiophyceae represent basal, extremophilic taxa subdivided into several genetically distinct orders. While photosystem I supercomplexes containing light-harvesting complexes (PSI-LHCI) have been characterized in Cyanidioschyzonales and Galdieriales, their organization in Cyanidiales remains poorly understood. Here, we purified the PSI-LHCI supercomplex from Cyanidium caldarium NIES-551, and analyzed its biochemical and spectroscopic properties. SDS-PAGE and mass spectrometry identified canonical PSI and LHCI subunits. The chloroplast-encoded PSI proteins were identical to those of a previously sequenced Cd. caldarium strain. Comparative sequence analysis revealed substantial divergence in both PSI and LHCI proteins between the NIES-551 strain and Cyanidiococcus yangmingshanensis NIES-2137, a strain recently reclassified from Cd. caldarium. Pigment profiling of PSI-LHCI showed similar species across strains, yet carotenoid-to-chlorophyll a ratios were lower in NIES-551. 77-K fluorescence-emission spectra of PSI-LHCI highlighted a red-shifted emission peak in NIES-551 (734 nm) relative to NIES-2137 (727 nm), suggesting differences in pigment configuration and excitation-energy transfer. These findings indicate that PSI-LHCI in NIES-551 possesses lineage-specific pigment composition and LHCI organization. Together, these characteristics likely represent hallmarks of PSI-LHCI in Cyanidiales. Our results reinforce the evolutionary distinctiveness of Cyanidiales within Cyanidiophyceae and provide a foundation for future structural studies that will clarify the diversification of photosynthetic architecture in early-diverging red algae.
蓝藻纲代表基部的嗜极端生物分类群，可细分为几个基因上不同的目。虽然在蓝藻目和加尔迪藻目中已经对含有捕光复合体的光系统I超复合体（PSI-LHCI）进行了表征，但它们在蓝球藻目中的组织情况仍知之甚少。在这里，我们从嗜热栖热蓝藻NIES-551中纯化了PSI-LHCI超复合体，并分析了其生化和光谱性质。SDS-PAGE和质谱鉴定出了典型的PSI和LHCI亚基。叶绿体编码的PSI蛋白与先前测序的嗜热栖热蓝藻菌株的蛋白相同。比较序列分析表明，NIES-551菌株与阳明山蓝球藻NIES-2137（一种最近从嗜热栖热蓝藻重新分类的菌株）的PSI和LHCI蛋白存在显著差异。PSI-LHCI的色素分析表明，不同菌株的色素种类相似，但NIES-551中类胡萝卜素与叶绿素a的比例较低。PSI-LHCI的77-K荧光发射光谱突出显示，相对于NIES-2137（727 nm），NIES-551中发射峰发生了红移（734 nm），这表明色素构型和激发能转移存在差异。这些发现表明，NIES-551中的PSI-LHCI具有谱系特异性的色素组成和LHCI组织。总之，这些特征可能代表了蓝球藻目中PSI-LHCI的标志。我们的结果强化了蓝球藻目在蓝藻纲中的进化独特性，并为未来的结构研究奠定了基础，这些研究将阐明早期分化的红藻中光合结构的多样化。
