Department of biophysics Palacky University

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Molecular mechanisms of photoadaptation of photosystem I supercomplex of in an evolutionary cyanobacterial/algal intermediate.

Autor: Haniewicz P., Abram M., Nosek L., Kirkpatrick J., El-Mohsnawy E., Janna Olmos J.D., Kouřil R., Kargul J.M.Published: Plant Physiology 176(2), 1433-1451Year: 2018

The monomeric PSI-LHCI supercomplex from an extremophilic red alga Cyanidioschyzon merolae represents an intermediate evolutionary link between the cyanobacterial PSI reaction centre 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 combination of biochemical, spectroscopic, mass spectrometry and electron microscopy/single particle analyses we dissected three molecular mechanisms underlying inherent robustness of C. merolae PSI-LHCI supercomplex: (i), the accumulation of a photoprotective zeaxanthin in the LHCI antenna and the PSI reaction centre; (ii), structural remodelling of the LHCI antenna and adjustment of its effective absorption cross-section; and (iii), dynamic re-adjustment 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 8 Lhcr antenna subunits which are organized as 2 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 PSI supercomplex is absent or transient, or may be lost during the purification procedure.

Department of Biophysics

Faculty of Science

Palacký University in Olomouc, Czech Republic

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