Mitochondrial fusion, illustration. Mitochondrial fusion can help mitigate the effects of stress by fusing a partially damaged mitochondrion with an undamaged mitochondrion. This is known as complementation, where each original mitochondrion compensates for the other and carries out any functions that the other cannot perform. Therefore, fusion restores the full functionality of the mitochondria. At the beginning of mitochondrial fusion, the two outer mitochondrial membranes are tethered by mitofusin (green). This comprises Mfn1 and Mfn2 - membrane-anchored dynamin family proteins.