DRP1 and MID49 co-diffusion scans mitochondria for fission.

DRP1 is a dynamin-related large GTPase responsible for mitochondrial fission, which ensures proper mitochondrial distribution, morphology and quality control. Despite its relevance, the mechanism of mitochondrial division, especially regarding the dynamic regulation of DRP1, remains elusive. Here we report that DRP1 oligomers diffuse in helical-like trajectories along mitochondria, browsing the organelle surface and stalling at preconstricted fission sites, in what we call 'mito-scanner' motion. Molecular dynamics simulations support a geometry-mediated diffusion mechanism emerging from surface confinement. Perturbation of DRP1 motility results in elongated mitochondria, underscoring the functional importance of DRP1 scanning dynamics in mitochondrial division. We also show that DRP1 dynamics on mitochondria are differentially regulated by interactions with its adaptors, where co-diffusion of MID49/MID51 with DRP1 promotes its motility. Our findings support a model in which receptor-regulated mitochondrial surveillance by DRP1 enables balanced organelle division, with potential implications for targeting this process in disease.