Structure of Dunaliella Photosystem II reveals conformational flexibility of stacked and unstacked supercomplexes
Photosystem II (PSII) generates an oxidant whose redox potential is high enough to enable water oxidation (Shen 2015; McEvoy and Brudvig 2006), a substrate so abundant that it assures a practically unlimited electron source for life on earth (Barber 2004). Our knowledge on the mechanism of water photooxidation was greatly advanced by high-resolution structures of prokaryotic PSII (Umena et al. 2011; Suga et al. 2019; Kato et al. 2021). Here we show high-resolution cryo-EM structures of eukaryotic PSII from the green alga Dunaliella salina at two distinct conformations. The conformers are also present in stacked PSII, exhibiting flexibility that may relevant to the grana formation in chloroplasts of the green lineage. CP29, one of PSII associated light-harvesting antennae, plays a major role in distinguishing the two conformations of the supercomplex. We also show that the stacked PSII dimer, a form suggested to support the organization of thylakoid membranes (Garab and Mustárdy 2000; Kirchhoff et al. 2007), can appear in many different orientations providing a flexible stacking mechanism for the arrangement of grana stacks in thylakoids. Our findings provide a structural basis for the heterogenous nature of the eukaryotic PSII on multiple levels.
Data availability: The atomic coordinates have been deposited in the Protein Data Bank, with accession code 7PI0 (C2S2 COMP ), 7PI5 (C2S2 STR), 7PNK (C2S), 7PIN (stacked C2S2 COMP ) and 7PIW (stacked C2S2 STR ). The cryo-EM maps have been deposited in the Electron Microscopy Data Bank, with accession codes EMD-13429 (C2S2 COMP ), EMD-13430 (C2S2 STR ), EMD-13548 (C2S), EMD-13444 (stacked C2S2 COMP ) and EMD-13455 (stacked C2S2 STR ).
Unstacked compact Dunaliella PSIIEMDB, EMD-13429.
Unstacked stretched Dunaliella PSIIEMDB, EMD-13430.
Unstacked compact Dunaliella PSIIEMDB, EMD-13548.
Stacked compact Dunaliella PSIIEMDB, EMD-13444.
Stacked stretched Dunaliella PSIIEMDB, EMD-13455.
Article and author information
Israel Science Foundation (569/17)
- Nathan Nelson
Israel Science Foundation (199/21)
- Nathan Nelson
German-Israeli Foundation for Scientific Research and Development (G-1483-207/2018)
- Nathan Nelson
National Science Foundation (2034021)
- Yuval Mazor
The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.
- David M Kramer, Michigan State University, United States
- Preprint posted: November 30, 2021 (view preprint)
- Received: June 16, 2022
- Accepted: February 16, 2023
- Accepted Manuscript published: February 17, 2023 (version 1)
- Version of Record published: February 23, 2023 (version 2)
© 2023, Caspy et al.
This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.
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