Figure 1.

A simplified scheme of mitochondrial fission and fusion in mammalian cells. (A) Schematic representation of fusion. The outer membranes of two adjacent mitochondria are tethered by the interaction in trans of the HR2 domains of Mfns. GTP binding and hydrolysis cause Mfns conformational change leading to OMM fusion. Following OMM fusion, OPA1 drives IMM fission. (B) Schematic representation of fission. Fission is initiated by ER-mediated constriction and marks the site for further constriction by Drp1 and its binding partners. Drp1 is recruited from the cytosol to the fission site via its receptors (MFF, MiD49 and MiD51) and forms multimeric contractile rings at the fission site. GTP hydrolysis powers Drp1 multimers to make conformational changes that constrict and divide the organelle.