Cryo-EM structures of naturally occurring dimeric photosystem II complexes lacking the Mn4CaO5 cluster

article Cryo-EM structures of naturally occurring dimeric photosystem II complexes lacking the Mn4CaO5 cluster published yes Ziyu Zhao author a63fe682-9f3a-11ee-bf8c-cfdf919b9850 Irene Vercellino author 3ED6AF16-F248-11E8-B48F-1D18A9856A870000-0001-5618-3449 Julian P. Whitelegge author Karim Maghlaoui author Wojciech Białek author Peter J. Nixon author Leonid A Sazanov author 338D39FE-F248-11E8-B48F-1D18A9856A870000-0002-0977-7989 LeSa department Robust oxygenic photosynthesis requires the efficient assembly and repair of the multi-subunit oxygen-evolving photosystem II (PSII) complex. Previous cryogenic electron microscopy (cryo-EM) structures of PSII assembly/disassembly intermediates have relied on the analysis of deletion mutants or removal of PSII subunits in vitro. Here we report the cryo-EM structures of naturally occurring dimeric PSII intermediates from the cyanobacterium Thermosynechococcus vestitus at a resolution of about 2.2 Å. These intermediates contain inactive dimers lacking the oxygen-evolving complex (OEC) and semi-active dimers with the OEC present in one of the two monomers. Our structural data provide a mechanism for how assembly and disassembly of the Mn4CaO5 cluster is coordinated with the binding and release of the extrinsic proteins: restructuring of the C-terminal tail of D1 subunit during assembly or disassembly of the Mn cluster triggers conformational changes in D2, CP47 and CP43 to drive the binding/release of the extrinsic proteins. A combination of structural and mass spectrometry data also suggests that the inactive PSII complexes may include damaged complexes containing oxidized D1-His332, a monodentate ligand to one of the Mn ions of the OEC. https://research-explorer.ista.ac.at/download/22750/22843/2026_NatureComm_Zhao.pdf application/pdfno Springer Nature2026 eng Nature Communications 2041-1723 4242030710.1038/s41467-026-75324-x 17 Zhao, Ziyu, Irene Vercellino, Julian P. Whitelegge, Karim Maghlaoui, Wojciech Białek, Peter J. Nixon, and Leonid A Sazanov. “Cryo-EM Structures of Naturally Occurring Dimeric Photosystem II Complexes Lacking the Mn4CaO5 Cluster.” Nature Communications. Springer Nature, 2026. <a href="https://doi.org/10.1038/s41467-026-75324-x">https://doi.org/10.1038/s41467-026-75324-x</a>. Zhao Z, Vercellino I, Whitelegge JP, Maghlaoui K, Białek W, Nixon PJ, Sazanov LA. 2026. Cryo-EM structures of naturally occurring dimeric photosystem II complexes lacking the Mn4CaO5 cluster. Nature Communications. 17, 8433. Zhao, Z., Vercellino, I., Whitelegge, J. P., Maghlaoui, K., Białek, W., Nixon, P. J., & Sazanov, L. A. (2026). Cryo-EM structures of naturally occurring dimeric photosystem II complexes lacking the Mn4CaO5 cluster. Nature Communications. Springer Nature. <a href="https://doi.org/10.1038/s41467-026-75324-x">https://doi.org/10.1038/s41467-026-75324-x</a> Z. Zhao, I. Vercellino, J.P. Whitelegge, K. Maghlaoui, W. Białek, P.J. Nixon, L.A. Sazanov, Nature Communications 17 (2026). Zhao, Ziyu, et al. “Cryo-EM Structures of Naturally Occurring Dimeric Photosystem II Complexes Lacking the Mn4CaO5 Cluster.” Nature Communications, vol. 17, 8433, Springer Nature, 2026, doi:<a href="https://doi.org/10.1038/s41467-026-75324-x">10.1038/s41467-026-75324-x</a>. Z. Zhao et al., “Cryo-EM structures of naturally occurring dimeric photosystem II complexes lacking the Mn4CaO5 cluster,” Nature Communications, vol. 17. Springer Nature, 2026. Zhao Z, Vercellino I, Whitelegge JP, et al. Cryo-EM structures of naturally occurring dimeric photosystem II complexes lacking the Mn4CaO5 cluster. Nature Communications. 2026;17. doi:<a href="https://doi.org/10.1038/s41467-026-75324-x">10.1038/s41467-026-75324-x</a> 227502026-08-23T22:01:46Z2026-09-07T13:17:53Z