Cryo-EM structures of naturally occurring dimeric photosystem II complexes lacking the Mn4CaO5 cluster Zhao, Ziyu Vercellino, Irene ; https://orcid.org/0000-0001-5618-3449 Whitelegge, Julian P. Maghlaoui, Karim Białek, Wojciech Nixon, Peter J. Sazanov, Leonid A ; https://orcid.org/0000-0002-0977-7989 ddc:570 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. Springer Nature 2026 info:eu-repo/semantics/article doc-type:article text http://purl.org/coar/resource_type/c_2df8fbb1 https://research-explorer.ista.ac.at/record/22750 https://research-explorer.ista.ac.at/download/22750/22843 Zhao Z, Vercellino I, Whitelegge JP, et al. Cryo-EM structures of naturally occurring dimeric photosystem II complexes lacking the Mn4CaO5 cluster. <i>Nature Communications</i>. 2026;17. doi:<a href="https://doi.org/10.1038/s41467-026-75324-x">10.1038/s41467-026-75324-x</a> eng info:eu-repo/semantics/altIdentifier/doi/10.1038/s41467-026-75324-x info:eu-repo/semantics/altIdentifier/e-issn/2041-1723 info:eu-repo/semantics/altIdentifier/pmid/42420307 info:eu-repo/semantics/openAccess