摘要 : <i>Synechocystis</i> sp. PCC 6803 has four genes encoding flavodiiron proteins (FDPs; Flv1 to Flv4). Here, we investigated the <i>flv4-flv2</i> operon encoding the Flv4, Sll0218, and Flv2 proteins, which are strongly expressed und... 展开 <i>Synechocystis</i> sp. PCC 6803 has four genes encoding flavodiiron proteins (FDPs; Flv1 to Flv4). Here, we investigated the <i>flv4-flv2</i> operon encoding the Flv4, Sll0218, and Flv2 proteins, which are strongly expressed under low inorganic carbon conditions (i.e., air level of CO₂) but become repressed at elevated CO₂ conditions. Different from FDP homodimers in anaerobic microbes, <i>Synechocystis</i> 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 <i>flv4-flv2</i> operon provides many beta -cyanobacteria with a so far unknown photoprotection mechanism that evolved in parallel with oxygen-evolving PSII. 收起