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bioRxiv · 10.1101/2022.03.01.482405

Structure of cyanobacterial photosystem I complexed with Cytochrome c6 and Ferredoxin at 1.97 A resolution

Li, J.·Hamaoka, N.·Makino, F.·Kawamoto, A.·Lin, Y.·Rögner, M.·Nowaczyk, M. M.·Lee, Y.-H.·Namba, K.·Gerle, C.·Kurisu, G.
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Abstract

Photosystem I (PSI) is a light driven electron pump transferring electrons from Cytochrome c6 (Cyt c6) to Ferredoxin (Fd). An understanding of this electron transfer process is hampered by a paucity of structural detail concerning the binding of Fd and the bound Cyt c6. Here we describe the high resolution cryo-EM structure of Thermosynechococcus elongatus BP-1 PSI in complex with Fd and Cyt c6. In our structure Cyt c6 is loosely bound in a non-productive site on the periphery of the complex. Side chain interactions at the PSI:Fd interface are visualized in detail. The structure explains the properties of mutants of PsaE and PsaC and suggests a molecular switch for the dissociation of Fd upon reduction. Calorimetry-based thermodynamic analyses confirms a single binding site for Fd and demonstrates that PSI:Fd complexation is purely driven by entropy. A reaction cycle for the efficient transfer of electrons from Cyt c6 to Fd via PSI is proposed.

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Li, J., Hamaoka, N., Makino, F., Kawamoto, A., Lin, Y., Rögner, M., Nowaczyk, M. M., Lee, Y.-H., Namba, K., Gerle, C., Kurisu, G.. 2022-03-02. Structure of cyanobacterial photosystem I complexed with Cytochrome c6 and Ferredoxin at 1.97 A resolution. https://doi.org/10.1101/2022.03.01.482405

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