A Novel Drp1 Interface Specifically Governs Mff Interactions

Abstract

In eukaryotic cells, mitochondria comprise a dynamic network of organelles that undergo cycles of fission and fusion. Among many other functions, these opposing processes allow for the quality control of the cellular mitochondria pool by allowing for the rescue and/or disposal of dysfunctional mitochondria. Therefore, mitochondrial fission is an essential cellular process. The dynamin family GTPase, dynamin-related protein 1 (Drp1), initiates fission by translocating from the cytosol to the mitochondrial outer membrane (MOM), where it forms a helical polymer circumscribing the mitochondria. This initial recruitment of Drp1 to the mitochondria is a highly regulated process that requires interaction with one or more MOM-anchored partner proteins including mitochondrial fission 1 protein (Fis1), mitochondrial fission factor (Mff), and the mitochondrial dynamics proteins of 49/51 kDa (MiD49/51). In metazoans, Mff is a key partner protein for Drp1, so understanding the nature of Drp1 interaction with Mff may yield significant insight to the mechanisms underlying mitochondrial fission in higher eukaryotes. Given the absence of Mff in lower eukaryotes, we compared regions of low sequence conservation between human and yeast Drp1 homologues to identify putative Drp1-Mff interaction interfaces. Using biochemical and structural studies, we identified one region in particular where mutations ablate Mff-stimulated Drp1 activities. Importantly, no effect on intrinsic Drp1 behaviors including GTPase activity, cardiolipin interaction, and several modes of self-assembly were observed. Identification of this region provides a novel tool to selectively interrogate the role of Drp1-Mff interactions in diverse cellular functions.