Cryo-EM structures of the Synechocystis sp. PCC 6803 cytochrome b6f complex with and without the regulatory PetP subunit

Proctor, Matthew S., Malone, Lorna A., Farmer, David A., Swainsbury, David J. K., Hawkings, Frederick R., Pastorelli, Federica, Emrich-Mills, Thomas Z., Siebert, C. Alistair, Hunter, C. Neil, Johnson, Matthew P. and Hitchcock, Andrew (2022) Cryo-EM structures of the Synechocystis sp. PCC 6803 cytochrome b6f complex with and without the regulatory PetP subunit. Biochemical Journal, 479 (13). pp. 1487-1503. ISSN 0264-6021

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In oxygenic photosynthesis, the cytochrome b6f (cytb6f) complex links the linear electron transfer (LET) reactions occurring at photosystems I and II and generates a transmembrane proton gradient via the Q-cycle. In addition to this central role in LET, cytb6f also participates in a range of processes including cyclic electron transfer (CET), state transitions and photosynthetic control. Many of the regulatory roles of cytb6f are facilitated by auxiliary proteins that differ depending upon the species, yet because of their weak and transient nature the structural details of these interactions remain unknown. An apparent key player in the regulatory balance between LET and CET in cyanobacteria is PetP, a ∼10 kDa protein that is also found in red algae but not in green algae and plants. Here, we used cryogenic electron microscopy to determine the structure of the Synechocystis sp. PCC 6803 cytb6f complex in the presence and absence of PetP. Our structures show that PetP interacts with the cytoplasmic side of cytb6f, displacing the C-terminus of the PetG subunit and shielding the C-terminus of cytochrome b6, which binds the heme cn cofactor that is suggested to mediate CET. The structures also highlight key differences in the mode of plastoquinone binding between cyanobacterial and plant cytb6f complexes, which we suggest may reflect the unique combination of photosynthetic and respiratory electron transfer in cyanobacterial thylakoid membranes. The structure of cytb6f from a model cyanobacterial species amenable to genetic engineering will enhance future site-directed mutagenesis studies of structure-function relationships in this crucial ET complex.

Item Type: Article
Additional Information: Funding Information: M.S.P acknowledges funding from the Leverhulme Trust (Grant RPG-2019-045). L.A.M., F.P. and T.E.M. were supported by PhD studentships from the Biotechnology and Biological Sciences Research Council (BBSRC) White Rose Doctoral Training Partnership in Mechanistic Biology. D.A.F and A.C.S. acknowledge Diamond Light Source for access and support of the cryo-EM facilities at the UK’s national Electron Bio-Imaging Centre (eBIC) under proposals nt21004 and nr21005, funded by the Wellcome Trust, Medical Research Council and BBRSC. F. R.H. was supported by a Diamond Light Source PhD studentship (number STU0355) jointly funded by the University of Sheffield. C.N.H acknowledges support from the European Research Council (Synergy Award 854126). M.P.J. acknowledges support from the BBSRC (award number BB/V006630/1) and the Leverhulme Trust (Grant RPG-2019-045). A.H. is a Royal Society University Research Fellow (award number URF\R1 \191548).
Uncontrolled Keywords: biochemistry,molecular biology,cell biology ,/dk/atira/pure/subjectarea/asjc/1300/1303
Faculty \ School: Faculty of Science > School of Biological Sciences
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Depositing User: LivePure Connector
Date Deposited: 17 Aug 2022 13:30
Last Modified: 22 Oct 2022 07:54
DOI: 10.1042/BCJ20220124

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