Novel heterocyst-specific flavodiiron proteins in Anabaena sp. PCC 7120

Flavodiiron proteins present in many prokaryotic and some eukaryotic organisms have a capacity to protect cells against nitrosative or oxidative stress. In Anabaena sp. PCC 7120, Flv1 and Flv3 proteins are encoded by families of two genes. We demonstrate here that flv1A and flv3A genes are up-regulated in vegetative cells in low CO2 and high light conditions. In contrast, flv1B and flv3B genes are expressed in N2-fixing conditions and corresponding proteins are located exclusively in heterocysts. It is suggested that Flv1B and Flv3B protect enzymes of N2-fixation in heterocysts of Anabaena 7120 by reducing molecular oxygen directly to water.

► We show expression patterns of genes encoding Flv proteins in Anabaena 7120.
► Four flv genes are expressed in a manner similar to homologues in Synechocystis.
► Two “extra” genes are expressed during N2-fixation and exclusively in heterocysts.