A common feature of neurodegenerative diseases such as Alzheimer's, Parkinson's or Huntington's disease are deposits of aggregated proteins in the patient's cells that cause damage to cellular functions. Scientists at the Max Planck Institute of Biochemistry and Ludwig-Maximilians-Universität in Munich report that, even in normal cells, aberrant aggregation-prone proteins are continually produced due to partial failure of the respiratory system. Unless they are removed by degradation, aggregates accumulate preferentially in the mitochondria, the cellular power plants, ultimately blocking energy production. In order to get rid of these toxic aggregates, cells have developed an elaborate protein quality control system.