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<p>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 <i>Thermosynechococcus vestitus</i> 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 Mn<sub>4</sub>CaO<sub>5</sub> 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.</p>

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

  • 期刊论文

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  • 发表日期：

    2026年7月8日

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  • Ziyu Zhao,
  • Irene Vercellino,
  • Julian P. Whitelegge,
  • Karim Maghlaoui,
  • Wojciech Białek,
  • Peter J. Nixon,
  • Leonid A. Sazanov

摘要

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.