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bioRxiv · 10.1101/2025.07.17.665390

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

Zhao, Z.·Vercellino, I.·Whitelegge, J. P.·Maghlaoui, K.·Nixon, P. J.·Sazanov, L. A.
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Abstract

Robust oxygenic photosynthesis requires the efficient assembly and repair of the multi-subunit oxygen-evolving photosystem II (PSII) complex. Previous electron cryo-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 have determined the cryo-EM structures of naturally occurring dimeric PSII intermediates from the cyanobacterium Thermosynechococcus vestitus at a resolution of 2.2 [A]. 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 indicates that the inactive PSII complexes are disassembly complexes and that oxidation of D1-His332, a monodentate ligand to one of the Mn ions of the OEC, is an early event in the photoinactivation of PSII.

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Zhao, Z., Vercellino, I., Whitelegge, J. P., Maghlaoui, K., Nixon, P. J., Sazanov, L. A.. 2025-07-17. Cryo-EM structures of naturally occurring dimeric photosystem II complexes lacking the Mn4CaO5 cluster. https://doi.org/10.1101/2025.07.17.665390

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