9SE6

Structure of Photosystem I from Chlamydomonas reinhardtii at 1.83 A resolution

Summary for 9SE6

• Entry DOI: 10.2210/pdb9se6/pdb
• Related: 9se7
• EMDB information: 54803
• Descriptor: Light-harvesting chlorophyll-a/b protein of photosystem I, type III, Photosystem I reaction center subunit II, chloroplastic, Photosystem I reaction center subunit IV, chloroplastic, ... (32 entities in total)
• Functional Keywords: photosystem i, chlamydomonas reinhardtii, cryoem, photosynthesis
• Biological source: Chlamydomonas reinhardtii; More
• Total number of polymer chains: 19
• Total formula weight: 697983.49

Authors

Mahapatra, G.P.,Schuller, J.M. (deposition date: 2025-08-15, release date: 2026-04-01, Last modification date: 2026-04-08)

Primary citation

Ogawa, Y.,Mahapatra, G.P.,Milrad, Y.,Schimpf, M.,Kurisu, G.,Hippler, M.,Schuller, J.M.
Cryo-EM structure of Chlamydomonas reinhardtii Photosystem I complexed with cytochrome c 6 .
Nat Commun, 2026

PubMed Abstract: Photosynthetic electron transfer relies on small soluble carriers that shuttle electrons between the cytochrome b₆f complex and Photosystem I (PSI). While copper-containing plastocyanin (Pc) serves this role in plants, the heme protein cytochrome c₆ (Cyt c₆) is also employed in algae and cyanobacteria. Here, we present a cryo-electron microscopy structure of a Cyt c₆:PSI complex from Chlamydomonas reinhardtii. We observe that the heme group of Cyt c₆ is positioned ~11 Å away from P700, stabilized by extensive contacts involving a N-terminal helix-loop-helix motif of PSAF, characteristic of eukaryotic PSI. Notably, the algal Cyt c₆ also retains an arginine residue (R66) which is crucial for cyanobacterial donor:PSI reactions. Our structure reveals the previously uncharacterized interactions involving this residue; it can form a putative electrostatic contact with PsaB-D623 while also contributing to a tri-planar π(cation)-π interactions with adjacent residues. Our findings provide a structural framework for understanding the mechanism and evolution of donor:PSI interactions.

PubMed: 41896549
DOI: 10.1038/s41467-026-70944-9

Experimental method

ELECTRON MICROSCOPY (1.83 Å)