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The labile interactions of cyclic electron flow effector proteins.

ABSTRACT: The supramolecular organization of membrane proteins (MPs) is sensitive to environmental changes in photosynthetic organisms. Isolation of MP supercomplexes from the green algae Chlamydomonas reinhardtii, which are believed to contribute to cyclic electron flow (CEF) between the cytochrome b 6 f complex (Cyt-b 6 f) and photosystem I (PSI), proved difficult. We were unable to isolate a supercomplex containing both Cyt-b 6 f and PSI because in our hands, most of Cyt-b 6 f did not comigrate in sucrose density gradients, even upon using chemical cross-linkers or amphipol substitution of detergents. Assisted by independent affinity purification and MS approaches, we utilized disintegrating MP assemblies and demonstrated that the algae-specific CEF effector proteins PETO and ANR1 are bona fide Cyt-b 6 f interactors, with ANR1 requiring the presence of an additional, presently unknown, protein. We narrowed down the Cyt-b 6 f interface, where PETO is loosely attached to cytochrome f and to a stromal region of subunit IV, which also contains phosphorylation sites for the STT7 kinase.

SUBMITTER: Buchert F

PROVIDER: S-EPMC6231120 | biostudies-literature | 2018 Nov

REPOSITORIES: biostudies-literature

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The labile interactions of cyclic electron flow effector proteins.

Buchert Felix F Hamon Marion M Gäbelein Philipp P Scholz Martin M Hippler Michael M Wollman Francis-André FA

The Journal of biological chemistry 20180918 45

The supramolecular organization of membrane proteins (MPs) is sensitive to environmental changes in photosynthetic organisms. Isolation of MP supercomplexes from the green algae Chlamydomonas reinhardtii, which are believed to contribute to cyclic electron flow (CEF) between the cytochrome b6f complex (Cyt-b6f) and photosystem I (PSI), proved difficult. We were unable to isolate a supercomplex containing both Cyt-b6f</ ...[more]

PMID: 30228184

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Project description:The Antarctic green alga Chlamydomonas sp. UWO241 (UWO241) survives in the deep photoc zone of the permanently ice-covered Lake Bonney in the McMurdo Dry Valleys. The extreme habitat in its natural environment has given way to unique adaptive mechanisms in this halotolerant psychrophile. One of the most striking phenotype of UWO241 is the constitutive upregulation of cyclic electron flow (CEF) around Photosystem I (PSI). This CEF is associated with the formation of a PSI-cytochrome b6f supercomplex that is stable under conditions of high salinity, corresponding to its natural habitat. Although studies have been done to understand the changes in the photosynthetic apparatus associated with increased CEF, not much is known about the purpose of constitutive CEF in UWO241. In this study, we examined the changes in the metabolism associated with increased in CEF and PSI-supercomplex formation in UWO241 under high salinity. Using Electrochomic Shift (ECS) based spectroscopy we identified a higher NPQ and proton motif flux through ATP synthase associated with UWO241 under high salinity. This higher proton flux was associated with high alternative electron transport when plotted against linear electron flow. We also identified several proteins associated with PSI-cytb6f supercomplex in UWO241 that have not been shown before. A Bestrophin-like protein was identified in the whole cell proteome of UWO241 suggesting high capacity for NPQ. Using comparative shotgun proteomics we identified a total of 98 proteins that were significantly affected under high CEF phenotype in UWO241. Out of the 98 proteins, 46 were upregulated and belonged to Calvin cycle, secondary metabolism and translational machinery. Several enzymes in the secondary metabolic Shikimate pathway were upregulated under high CEF phenotype, with one protein involved in downstream indole acetic acid (IAA) biosynthesis upregulated. Metabolomics revealed upregulation of compatible solutes and downregulation of tryptophan in UWO241 under high salinity. We suggest that UWO241 maintains constitutively high CEF with associated PSI-cytb6f supercomplex under native high salinity conditions to rewire its downstream metabolism towards higher carbon fixation capacity and that fixed carbon is utilized to make secondary metabolites necessary for adaptation in its extreme habitat.

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The labile interactions of cyclic electron flow effector proteins.

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The labile interactions of cyclic electron flow effector proteins.

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