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Structure of the plant photosystem I supercomplex at 2.6 Å resolution

Abstract

Four elaborate membrane complexes carry out the light reaction of oxygenic photosynthesis. Photosystem I (PSI) is one of two large reaction centres responsible for converting light photons into the chemical energy needed to sustain life. In the thylakoid membranes of plants, PSI is found together with its integral light-harvesting antenna, light-harvesting complex I (LHCI), in a membrane supercomplex containing hundreds of light-harvesting pigments. Here, we report the crystal structure of plant PSI–LHCI at 2.6 Å resolution. The structure reveals the configuration of PsaK, a core subunit important for state transitions in plants, a conserved network of water molecules surrounding the electron transfer centres and an elaborate structure of lipids bridging PSI and its LHCI antenna. We discuss the implications of the structure for energy transfer and the evolution of PSI.

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Figure 1: The structure of plant PSI–LHCI at 2.6 Å resolution.
Figure 2: The structure of the PsaK subunit suggests multiple conformations.
Figure 3: Lipid structure in PSI–LHCI, core asymmetry and a complete patch of lipids in the PSI–LHCI gap.
Figure 4: A small region determines the oligomeric state of LHC proteins.
Figure 5: Chlorophyll b molecules are located at the junctions of individual lhca subunits.
Figure 6: Chlorophyll b molecules are coordinated by a mixture of polar and hydrophobic interactions.
Figure 7: Förster rate calculations reveal the importance of the luminal-side pigment junctions.

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Acknowledgements

The authors would like to thank the ESRF, SLS and BESSYII synchrotrons for beam time and the staff scientists for excellent guide and relentless help. We would like to thank O. Rog for critical reading of the manuscript. This work is supported by a grant no. 293579—HOPSEP from the European Research Council, The Israel Science Foundation through grant no. 71/14 and by the I-CORE Program of the Planning and Budgeting Committee and The Israel Science Foundation (grant no. 1775/12).

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Y.M and N.N. performed experiments, analysed the data and wrote the paper. I.C. analysed the data. A.B. performed experiments.

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Correspondence to Yuval Mazor or Nathan Nelson.

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The authors declare no competing financial interests.

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Supplementary Figures 1–5, Supplementary Tables 1–3, Supplementary References. (PDF 1745 kb)

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Mazor, Y., Borovikova, A., Caspy, I. et al. Structure of the plant photosystem I supercomplex at 2.6 Å resolution. Nature Plants 3, 17014 (2017). https://doi.org/10.1038/nplants.2017.14

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