Cryo-EM structure of the spinach cytochrome b 6 f complex at 3.6 Å resolution

Malone, Lorna A., Qian, Pu, Mayneord, Guy E., Hitchcock, Andrew, Farmer, David A., Thompson, Rebecca F., Swainsbury, David J.K., Ranson, Neil A., Hunter, C. Neil and Johnson, Matthew P. (2019) Cryo-EM structure of the spinach cytochrome b 6 f complex at 3.6 Å resolution. Nature, 575 (7783). pp. 535-539. ISSN 0028-0836

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The cytochrome b6 f (cytb6 f) complex has a central role in oxygenic photosynthesis, linking electron transfer between photosystems I and II and converting solar energy into a transmembrane proton gradient for ATP synthesis1–3. Electron transfer within cytb6 f occurs via the quinol (Q) cycle, which catalyses the oxidation of plastoquinol (PQH2) and the reduction of both plastocyanin (PC) and plastoquinone (PQ) at two separate sites via electron bifurcation2. In higher plants, cytb6 f also acts as a redox-sensing hub, pivotal to the regulation of light harvesting and cyclic electron transfer that protect against metabolic and environmental stresses3. Here we present a 3.6 Å resolution cryo-electron microscopy (cryo-EM) structure of the dimeric cytb6 f complex from spinach, which reveals the structural basis for operation of the Q cycle and its redox-sensing function. The complex contains up to three natively bound PQ molecules. The first, PQ1, is located in one cytb6 f monomer near the PQ oxidation site (Qp) adjacent to haem bp and chlorophyll a. Two conformations of the chlorophyll a phytyl tail were resolved, one that prevents access to the Qp site and another that permits it, supporting a gating function for the chlorophyll a involved in redox sensing. PQ2 straddles the intermonomer cavity, partially obstructing the PQ reduction site (Qn) on the PQ1 side and committing the electron transfer network to turnover at the occupied Qn site in the neighbouring monomer. A conformational switch involving the haem cn propionate promotes two-electron, two-proton reduction at the Qn site and avoids formation of the reactive intermediate semiquinone. The location of a tentatively assigned third PQ molecule is consistent with a transition between the Qp and Qn sites in opposite monomers during the Q cycle. The spinach cytb6 f structure therefore provides new insights into how the complex fulfils its catalytic and regulatory roles in photosynthesis.

Item Type: Article
Additional Information: Funding Information: the Astbury Biostructure Laboratory funded by the University of Leeds (ABSL award) and the Wellcome Trust (108466/Z/15/Z). We thank S. Tzokov, J. Bergeron, J. Wilson and D. Mann for their helpful advice and assistance with the EM and data processing. Funding Information: Acknowledgements M.P.J. acknowledges funding from the Leverhulme Trust grant RPG-2016-161. C.N.H., P.Q., A.H., D.J.K.S. and M.P.J. also acknowledge financial support from the Biotechnology and Biological Sciences Research Council (BBSRC UK) award numbers BB/ M000265/1 and BB/P002005/1. L.A.M. was supported by a White Rose doctoral studentship, G.E.M. was supported by a doctoral studentship from The Grantham Foundation and D.A.F. was supported by a University of Sheffield doctoral scholarship. Cryo-EM data was collected at Publisher Copyright: © 2019, The Author(s), under exclusive licence to Springer Nature Limited.
Uncontrolled Keywords: general ,/dk/atira/pure/subjectarea/asjc/1000
Faculty \ School: Faculty of Science > School of Biological Sciences
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Depositing User: LivePure Connector
Date Deposited: 17 Aug 2022 12:31
Last Modified: 22 Oct 2022 07:54
DOI: 10.1038/s41586-019-1746-6

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