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Plant Physiol. 2018 Feb;176(2):1433-1451. doi: 10.1104/pp.17.01022. Epub 2017 Nov 29.

Molecular Mechanisms of Photoadaptation of Photosystem I Supercomplex from an Evolutionary Cyanobacterial/Algal Intermediate.

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Solar Fuels Laboratory, Center of New Technologies, University of Warsaw, 02-097 Warsaw, Poland.
Faculty of Biology, University of Warsaw, 02-096 Warsaw, Poland.
Centre of the Region Haná for Biotechnological and Agricultural Research, Department of Biophysics, Faculty of Science, Palacký University, 783 71 Olomouc, Czech Republic.
Leibniz Institute on Aging-Fritz Lipmann Institute, 07745 Jena, Germany.
Botany Department, Faculty of Science, Kafrelsheikh University, 33516, Kafr El-Sheikh, Egypt.
Plant Biochemistry, Faculty of Biology and Biotechnology, Ruhr University, D-44780 Bochum, Germany.
Solar Fuels Laboratory, Center of New Technologies, University of Warsaw, 02-097 Warsaw, Poland


The monomeric photosystem I-light-harvesting antenna complex I (PSI-LHCI) supercomplex from the extremophilic red alga Cyanidioschyzon merolae represents an intermediate evolutionary link between the cyanobacterial PSI reaction center and its green algal/higher plant counterpart. We show that the C. merolae PSI-LHCI supercomplex is characterized by robustness in various extreme conditions. By a combination of biochemical, spectroscopic, mass spectrometry, and electron microscopy/single particle analyses, we dissected three molecular mechanisms underlying the inherent robustness of the C. merolae PSI-LHCI supercomplex: (1) the accumulation of photoprotective zeaxanthin in the LHCI antenna and the PSI reaction center; (2) structural remodeling of the LHCI antenna and adjustment of the effective absorption cross section; and (3) dynamic readjustment of the stoichiometry of the two PSI-LHCI isomers and changes in the oligomeric state of the PSI-LHCI supercomplex, accompanied by dissociation of the PsaK core subunit. We show that the largest low light-treated C. merolae PSI-LHCI supercomplex can bind up to eight Lhcr antenna subunits, which are organized as two rows on the PsaF/PsaJ side of the core complex. Under our experimental conditions, we found no evidence of functional coupling of the phycobilisomes with the PSI-LHCI supercomplex purified from various light conditions, suggesting that the putative association of this antenna with the PSI supercomplex is absent or may be lost during the purification procedure.

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