Nat. Plants 4, 218–224 (2018)

Photosynthesis involves three integral membrane complexes that mediate the transport of electrons initiated by light absorption. In the final steps of this electron transport chain, one of these complexes, photosystem I (PSI), transfers electrons to the carrier protein ferredoxin (Fd) via the PSI subunit PsaC. Although the electron transport complex formed between PSI and Fd has been previously investigated by electron microscopy, cross-linking, and EPR, Kubota-Kawai et al. now present a detailed X-ray crystal structure of the cyanobacterial complex, providing insights into the interaction surfaces between PSI and Fd. Additional mutagenesis, flash-absorption spectroscopy, and solution NMR further validate the importance of individual Fd residues for the interactions that mediate complex formation. Comparison of the PSI–Fd complex structure with that of PSI alone also reveals a relay of conformational changes in the peripheral subunits that occur upon Fd binding, resulting in translocation of PsaF from the stromal side of the membrane to the lumenal side. These results contribute to a more detailed understanding of PSI function and may also facilitate future engineering efforts.

Credit: Nat. Plants