title: Operon flv4-flv2 provides cyanobacterial photosystem II with flexibility of electron transfer.
abstract: Synechocystis sp PCC 6803 has four genes encoding flavodiiron proteins (FDPs; Flv1 to Flv4). Here, we investigated the flv4-flv2 operon encoding the Flv4, Sll0218, and Flv2 proteins, which are strongly expressed under low inorganic carbon conditions (i.e., air level of CO(2)) but become repressed at elevated CO(2) conditions. Different from FDP homodimers in anaerobic microbes, Synechocystis Flv2 and Flv4 form a heterodimer. It is located in cytoplasm but also has a high affinity to membrane in the presence of cations. Sll0218, on the contrary, resides in the thylakoid membrane in association with a high molecular mass protein complex. Sll0218 operates partially independently of Flv2/Flv4. It stabilizes the photosystem II (PSII) dimers, and according to biophysical measurements opens up a novel electron transfer pathway to the Flv2/Flv4 heterodimer from PSII. Constructed homology models suggest efficient electron transfer in heterodimeric Flv2/Flv4. It is suggested that Flv2/Flv4 binds to thylakoids in light, mediates electron transfer from PSII, and concomitantly regulates the association of phycobilisomes with PSII. The function of the flv4-flv2 operon provides many β-cyanobacteria with a so far unknown photoprotection mechanism that evolved in parallel with oxygen-evolving PSII.
authors.affiliation: Department of Biochemistry and Food Chemistry, Molecular Plant Biology, University of Turku, 20520 Turku, Finland.
authors.forename: Pengpeng
authors.initials: P
authors.lastname: Zhang
authors.forename: Marion
authors.initials: M
authors.lastname: Eisenhut
authors.forename: Anna-Maria
authors.initials: AM
authors.lastname: Brandt
authors.forename: Dalton
authors.initials: D
authors.lastname: Carmel
authors.forename: Henna M
authors.initials: HM
authors.lastname: Silén
authors.forename: Imre
authors.initials: I
authors.lastname: Vass
authors.forename: Yagut
authors.initials: Y
authors.lastname: Allahverdiyeva
authors.forename: Tiina A
authors.initials: TA
authors.lastname: Salminen
authors.forename: Eva-Mari
authors.initials: EM
authors.lastname: Aro
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D000458:Cyanobacteria / Q000235:genetics / Q000378:metabolism*; D004579:Electron Transport / Q000235:genetics / Q000502:physiology*; D009876:Operon / Q000235:genetics / Q000502:physiology*; D045332:Photosystem II Protein Complex / Q000235:genetics / Q000378:metabolism*; D046939:Synechocystis
chemical_list: D001426:Bacterial Proteins; D045332:Photosystem II Protein Complex