Structural Basis for Monomer–Dimer Transition of Dri1 Upon Heme Binding

Domain related to iron (DRI) contains approximately 90 residues and is involved in iron and heme metabolism. Recent discoveries have annotated Dri1, a DRI-only protein from the cyanobacterium Synechocystis, as a regulator of succinate dehydrogenase in a b-type heme-dependent manner or as a c-type heme oxygenase. Here, we report high-resolution structures of Dri1 in complex with b-type and c-type hemes, respectively. Bis-His-ligated heme is located in the middle of the dimeric Dri1 complex with heme b, as well as in the complex of monomeric Dri1 with c-type heme, but distinct heme binding modes are revealed. Structural analyses suggest that Dri1 may participate in the succinate dehydrogenase activity and/or the metabolism of cytochromes.