What do the major proteins involved in mitochondrial fission do?

Fis1 acts as an adaptor protein with cytosol-facing protein interaction sites. Drp1 shuttles to the outer mitochondrial membrane during fission events. At fission sites, Drp1 interacts with Fis1, forming a collar around the mitochondrion. This collar tightens, leading to constriction and subsequent cleavage of the outer mitochondrial membrane, resulting in mitochondrial fission of two separate organelles.