title: Cyanobacterial flv4-2 Operon-Encoded Proteins Optimize Light Harvesting and Charge Separation in Photosystem II.
abstract: Photosystem II (PSII) complexes drive the water-splitting reaction necessary to transform sunlight into chemical energy. However, too much light can damage and disrupt PSII. In cyanobacteria, the flv4-2 operon encodes three proteins (Flv2, Flv4, and Sll0218), which safeguard PSII activity under air-level CO2 and in high light conditions. However, the exact mechanism of action of these proteins has not been clarified yet. We demonstrate that the PSII electron transfer properties are influenced by the flv4-2 operon-encoded proteins. Accelerated secondary charge separation kinetics was observed upon expression/overexpression of the flv4-2 operon. This is likely induced by docking of the Flv2/Flv4 heterodimer in the vicinity of the QB pocket of PSII, which, in turn, increases the QB redox potential and consequently stabilizes forward electron transfer. The alternative electron transfer route constituted by Flv2/Flv4 sequesters electrons from QB(-) guaranteeing the dissipation of excess excitation energy in PSII under stressful conditions. In addition, we demonstrate that in the absence of the flv4-2 operon-encoded proteins, about 20% of the phycobilisome antenna becomes detached from the reaction centers, thus decreasing light harvesting. Phycobilisome detachment is a consequence of a decreased relative content of PSII dimers, a feature observed in the absence of the Sll0218 protein.
authors.affiliation: Laboratory of Biophysics, Wageningen University, P.O. Box 8128, 6700 ET Wageningen, The Netherlands; MicroSpectroscopy Centre, Wageningen University, 6703HA Wageningen, The Netherlands; BioSolarCells, P.O. Box 98, 6700AB Wageningen, The Netherlands.
authors.forename: Volha
authors.initials: V
authors.lastname: Chukhutsina
authors.affiliation: Department of Biochemistry, Molecular Plant Biology, University of Turku, FI-20014 Turku, Finland.
authors.forename: Luca
authors.initials: L
authors.lastname: Bersanini
authors.affiliation: Department of Biochemistry, Molecular Plant Biology, University of Turku, FI-20014 Turku, Finland.
authors.forename: Eva-Mari
authors.initials: EM
authors.lastname: Aro
authors.affiliation: Laboratory of Biophysics, Wageningen University, P.O. Box 8128, 6700 ET Wageningen, The Netherlands; MicroSpectroscopy Centre, Wageningen University, 6703HA Wageningen, The Netherlands; BioSolarCells, P.O. Box 98, 6700AB Wageningen, The Netherlands. Electronic address: herbert.vanamerongen@wur.nl.
authors.forename: Herbert
authors.initials: H
authors.lastname: van Amerongen
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D004579:Electron Transport; D008027:Light; D009876:Operon; D010788:Photosynthesis / Q000528:radiation effects; D045332:Photosystem II Protein Complex / Q000235:genetics / Q000378:metabolism*; D046939:Synechocystis / Q000235:genetics / Q000378:metabolism* / Q000528:radiation effects
chemical_list: D001426:Bacterial Proteins; D045332:Photosystem II Protein Complex
keywords: electron transfer; flavodiiron proteins; light harvesting; photoprotection; photosystem II