Arabidopsis cytosolic Nbp35 homodimer can assemble both [2Fe–2S] and [4Fe–4S] clusters in two distinct domains

Iron–sulfur proteins play physiologically important roles in a variety of metabolic processes in eukaryotes. In plants, iron–sulfur cluster biosynthesis is known to take place both in mitochondria and chloroplasts. However no components that mediate iron–sulfur cluster delivery in the plant cell cytosol have been identified so far. Here we report identification and characterization of a cytosolic Nbp35 homolog named AtNbp35 from Arabidopsis thaliana. AtNbp35-deficient Arabidopsis mutants were seedling lethal. Unlike the previously characterized yeast ScNbp35 which forms a heterotetramer with ScCfd1, AtNbp35 forms a homodimer in the cytosol and can harbor both [4Fe–4S] and [2Fe–2S] clusters on its amino- and carboxyl-terminal domains, respectively. Taken together, our data suggest that Nbp35 plays a pivotal role in iron–sulfur cluster assembly and delivery in the plant cell cytosol as a bifunctional molecular scaffold.