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<p>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 <i>Cyanidium caldarium</i> 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 <i>Cd. caldarium</i> strain. Comparative sequence analysis revealed substantial divergence in both PSI and LHCI proteins between the NIES-551 strain and <i>Cyanidiococcus yangmingshanensis</i> NIES-2137, a strain recently reclassified from <i>Cd. caldarium</i>. Pigment profiling of PSI-LHCI showed similar species across strains, yet carotenoid-to-chlorophyll <i>a</i> ratios were lower in NIES-551. 77-K fluorescence-emission spectra of PSI-LHCI highlighted a red-shifted emission peak in NIES-551 (734&#xa0;nm) relative to NIES-2137 (727&#xa0;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.</p>

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Comparative analysis of biochemical and sequence features of PSI-LHCI supercomplexes from Cyanidium caldarium NIES-551 and Cyanidiococcus yangmingshanensis NIES-2137

  • 期刊论文

  • 发表日期：

    2025年9月17日

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  • Ibuki Y. Takahashi,
  • Takehiro Suzuki,
  • Shunsuke Hirooka,
  • Naoshi Dohmae,
  • Shin-ya Miyagishima,
  • Ryo Nagao

摘要

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.