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. Here, the outer membranes of two mitochondria have fused (through mitofusin tethering), and their inner membranes are now tethered using a dynamin-like protein, OPA1 (orange).