Distinct types of intramitochondrial protein aggregates protect mitochondria against proteotoxic stress - Data Set2: PIM1 AP-MS

Mitochondria consist of hundreds of proteins, most of which are long-lived and inaccessible to the proteasomal quality control system of the cytosol. How cells stabilize the mitochondrial proteome during challenging conditions is poorly understood. Here we show that mitochondria form spatially defined protein aggregates as a stress-protecting mechanism. Thereby different types of intramitochondrial protein aggregates can be distinguished. The mitoribosomal protein Var1 (uS3m) undergoes a stress-induced transition from a soluble, chaperone-stabilized protein that is prevalent under benign conditions to an insoluble aggregated form upon acute stress. The formation of Var1 bodies stabilizes mitochondrial proteostasis presumably by sequestration of aggregation-prone proteins. The AAA chaperone Hsp78 associates with a different type of intramitochondrial aggregate. These Hsp78-bound aggregates sequester non-native matrix proteins to promote their subsequent folding or Pim1-mediated degradation. Our study shows that mitochondrial proteins actively control the formation of different types of intramitochondrial protein aggregates which actively cooperate to stabilize the mitochondrial proteome during proteotoxic stress conditions.