Protein import defects induce mitophagy without membrane depolarization

Upon mitochondrial dysfunction, mitophagy has been described to be activated by a breakdown of membrane potential leading to PINK1 accumulation on the outer membrane and engulfment of mitochondria for degradation. However, recent findings have indicated that mitophagy may also be triggered in the absence of membrane potential alterations. Here, we report mechanistic details on how inhibition of protein import induces mitophagy independent of mitochondrial membrane depolarization. Carrying out a genome-wide CRISPR/Cas9 screen for regulators of mitophagy, we found that the pre-sequence translocase-associated motor complex PAM controls mitophagy induction. Loss of PAM caused defects in protein import and was sufficient to induce mitophagy without depolarization. Quantitative interaction and aggregation proteomics revealed that PAM was highly sensitive to proteostasis perturbation; upon misfolding conditions, PAM dissociated from the import machinery, sequestered into the insoluble fraction and caused mitophagy despite an intact membrane potential. Our findings extend the current mitophagy model and provide mechanistic insight into how proteostasis perturbation leads to mitophagy induction. They reveal the PAM complex as key folding sensor integrating proteostasis, import and mitophagy.