Photosynthesis is one of the most fundamental biological processes on Earth. The light reactions of oxygenic photosynthesis begin with photon absorption and drive the photosynthetic electron transport chain from water to the final electron carrier protein, ferredoxin (Fd). Four major membrane protein complexes—Photosystem II (PSII), Cytochrome b₆f (Cyt b₆f), Photosystem I (PSI), and the NADH-like complex I (NDH-1)—operate within the thylakoid membrane to support this electron flow. Between these complexes, lipophilic and hydrophilic mobile electron carriers such as plastoquinone, plastocyanin, cytochrome c₆, and Fd mediate electron transfer. Although sunlight on Earth is highly variable, photosynthetic electron transfer reactions are finely regulated to balance concurrent redox processes and minimize the production of reactive oxygen species (ROS) around the light-absorbing reaction centers. To better understand these coordinated reactions, my laboratory has spent decades studying the structures of these electron transfer complexes using X-ray crystallography, cryo-electron microscopy, and NMR spectroscopy [1–9]. Recently, I have also investigated a novel protein shell that encloses the pyrenoid compartment, separating it from the thylakoid membrane [10]. In this seminar, I would like to present the structures of the Cyt b₆f complex, PSI, and the NDH-1 complex, and discuss their electron transfer reactions with their respective electron-transfer partners.

1. G Kurisu et al., Nature Structural Biology 8 (2), 117-121 (2001)
2. G Kurisu et al., Science 302 (5647), 1009-1014 (2003)
3. J Yan et al., PNAS 103 (1), 69-74 (2006)
4. N Muraki et al., Nature 465 (7294), 110-114 (2010)
5. R Mutoh et al., Biochemistry 54 (39), 6052-6061 (2015)
6. H Kubota-Kawai et al., Nature Plants 4 (4), 218-224 (2018)
7. J M Schuller et al., Science 363 (6424), 257-260 (2019)
8. O Çoruh et al., Communications Biology 4 (1), 304 (2021)
9. J Li et al., Communications Biology 5 (1), 951 (2022)
10. G Shimakawa et al., Cell 187 (27), 5919-5934 (2024)

Professor Genji Kurisu, Division of Protein Structural Biology, Institute for Protein Research － The University of Osaka