Figure 1.

Core quality-control pathways in mitochondria. Low levels of damaged proteins in mitochondria are cleared at the molecular level by intraorganellar proteases and chaperones such as OMI/HTRA2 and TRAP1 (top left). Enhanced levels of damage probably overwhelm the capacity of the molecular quality-control machinery (middle left), leading to the proposed segregation of damaged mitochondrial components by the fusion/fission machinery. This enables the physical separation of healthy (green) and damaged (orange) daughter mitochondria. Damaged mitochondria are then recycled using the cellular autophagy pathyways. If the levels of damage exceed the capacity of both molecular and organellar quality-control pathways (top right), mitochondria can rupture, leading to the release of apoptosis-promoting factors and cell death.