Structure of a PSI–LHCI–cyt b6f supercomplex in Chlamydomonas reinhardtii promoting cyclic electron flow under anaerobic conditions

Steinbeck, Janina and Ross, Ian L. and Rothnagel, Rosalba and Gäbelein, Philipp and Schulze, Stefan and Giles, Nichole and Ali, Rubbiya and Drysdale, Rohan and Sierecki, Emma and Gambin, Yann and Stahlberg, Henning and Takahashi, Yuichiro and Hippler, Michael and Hankamer, Ben. (2018) Structure of a PSI–LHCI–cyt b6f supercomplex in Chlamydomonas reinhardtii promoting cyclic electron flow under anaerobic conditions. Proceedings of the National Academy of Sciences of the United States of America, 115 (41). pp. 10517-10522.

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Official URL: https://edoc.unibas.ch/66343/

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Photosynthetic linear electron flow (LEF) produces ATP and NADPH, while cyclic electron flow (CEF) exclusively drives photophosphorylation to supply extra ATP. The fine-tuning of linear and cyclic electron transport levels allows photosynthetic organisms to balance light energy absorption with cellular energy requirements under constantly changing light conditions. As LEF and CEF share many electron transfer components, a key question is how the same individual structural units contribute to these two different functional modes. Here, we report the structural identification of a photosystem I (PSI)-light harvesting complex I (LHCI)-cytochrome (cyt) b; 6; f supercomplex isolated from the unicellular alga; Chlamydomonas reinhardtii; under anaerobic conditions, which induces CEF. This provides strong evidence for the model that enhanced CEF is induced by the formation of CEF supercomplexes, when stromal electron carriers are reduced, to generate additional ATP. The additional identification of PSI-LHCI-LHCII complexes is consistent with recent findings that both CEF enhancement and state transitions are triggered by similar conditions, but can occur independently from each other. Single molecule fluorescence correlation spectroscopy indicates a physical association between cyt b; 6; f and fluorescent chlorophyll containing PSI-LHCI supercomplexes. Single particle analysis identified top-view projections of the corresponding PSI-LHCI-cyt b; 6; f supercomplex. Based on molecular modeling and mass spectrometry analyses, we propose a model in which dissociation of LHCA2 and LHCA9 from PSI supports the formation of this CEF supercomplex. This is supported by the finding that a; Δlhca2; knockout mutant has constitutively enhanced CEF.
Faculties and Departments:05 Faculty of Science > Departement Biozentrum > Former Organization Units Biozentrum > Structural Biology (Stahlberg)
UniBasel Contributors:Stahlberg, Henning
Item Type:Article, refereed
Article Subtype:Research Article
Note:Publication type according to Uni Basel Research Database: Journal article
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Last Modified:26 Apr 2020 19:36
Deposited On:26 Apr 2020 19:36

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