Sequestration and autophagy of mitochondria do not cut proteins across the board

Mitochondria that acquire deleterious DNA mutations or sustain chemical damage to proteins are sequestered and cleared by autophagy, purportedly to maintain the fidelity of the remaining organelles. In PNAS, Vincow et al. demonstrate that two proteins, phosphatase and tensin homolog-induced putative kinase 1 (PINK1) and Parkin, which are mutated in forms of familial parkinsonism, promote mitochondrial autophagy (mitophagy) in vivo in Drosophila raised in a normal laboratory environment (1). Thus, mitophagy appears to be a routine and necessary housekeeping activity that may be essential for survival of certain neurons and muscle cells that die in PINK1 and Parkin mutant flies. The work also uncovers a mystery that some mitochondrial respiratory chain (RC) proteins appear to be selectively routed for autophagosomal degradation, a process generally thought to remove entire mitochondria and indiscriminately eliminate RC components. PINK1 and Parkin in Drosophila are known to act in the same pathway to prevent dopaminergic neuron loss, flight muscle degeneration, and accumulation of swollen and dysfunctional mitochondria (2⇓–4). Mammalian cell culture studies also illustrate that PINK1 and Parkin work together to induce autophagy of chemically or genetically impaired mitochondria (5⇓⇓⇓⇓–10). Diverse mitochondrial insults generate the same stress signal: a loss of membrane potential diverts PINK1 from constitutive degradation following …