Structural study of the chlorophyll between Lhca8 and PsaJ in an Antarctica green algal photosystem I-LHCI supercomplex revealed by its atomic structure

作者：Pi-Cheng Tsai, Koji Kato, Jian‐Ren Shen, Fusamichi Akita · 发表于：Biochimica et Biophysica Acta (BBA) - Bioenergetics · 年份：2025 · DOI：10.1016/j.bbabio.2025.149543 · 被引用次数：6 · 研究领域：Photosynthetic Processes and Mechanisms、Microbial Community Ecology and Physiology、Polar Research and Ecology

Coccomyxa subellipsoidea is an oleaginous, non-motile unicellular green microalga isolated from Antarctica, and is an attractive candidate for CO 2 fixation and biomass production. C. subellipsoidea is the first polar green alga whose genome has been sequenced. Understanding the structure of photosystems from C. subellipsoidea can provide more information about the conversion of light energy into chemical energy under extreme environments. Photosystems I (PSI) is one of the two photosystems highly conserved from cyanobacteria to vascular plants, and associates with a large amount of outer light-harvesting complex (LHC) which absorb light energy and transfer them to the core complex. Here, we determined the structure of the PSI-10 LHCIs and PSI-8 LHCIs supercomplexes from C. subellipsoidea at 1.92 Å and 2.06 Å resolutions by cryo-electron microscopy, respectively. The supercomplex is similar to PSI-LHCI from other green algae, whereas a large amount of water molecules is observed in our structure because of the high-resolution map. Two novel chlorophylls (Chls), Chl a 321 in Lhca4 and Chl a 314 in Lhca8, are observed at the lumenal side in our structure, in which Lhca8-Chl a 314 provides a potential excitation energy transfer (EET) pathway between the inner-belt of LHCI and the core at the lumenal side. A total of three major EET pathways from LHCIs to PSI core are proposed, and C. subellipsoidea might adapt to the extreme environment by transferring energy in these three diff...