SUMOylation of MFF is required for stress-induced mitochondrial fission

Mitochondrial fission regulates mitochondrial morphology, function, mitophagy and apoptosis. Fission is mediated by the GTPase dynamin related protein-1 (DRP1) and its recruitment to the outer mitochondrial membrane by DRP1 receptors. Mitochondrial fission factor (MFF) is considered the major pro-fission receptor, whereas the mitochondrial dynamics proteins (MiD49/51) sequester inactive DRP1 and facilitate the MFF-DRP1 interaction by forming a trimeric DRP1-MiD-MFF complex. Here, we identify MFF as a target of poly-SUMOylation at a single residue (Lys151). Following bioenergetic stress, AMPK phosphorylates MFF to promote its SUMOylation, a critical step in stress-induced fragmentation. MFF SUMOylation is not required for DRP1 recruitment from the cytosol but causes a rearrangement of the trimeric fission complex to displace MiD proteins. This alleviates MiD inhibition of DRP1 to facilitate formation of a fission-competent complex. Thus, our data demonstrate that MFF SUMOylation fine-tunes the ratio of MiD to DRP1 for the dynamic control of stress-induced mitochondrial fragmentation.