Mitochondrial protein quality control (proteostasis) is essential to correct mitochondrial function, including the regulated turnover of misfolded proteins by proteases. YME1 is an AAA protease complex localised to the inner mitochondrial membrane (IMM), which mediates such degradation. Depletion of Yme1, the core subunit of the YME1 complex, results in altered mitochondrial morphology and respiratory defects. In this study (Kumar et al., 2023), Patrick D’Silva and colleagues use yeast cells to demonstrate a genetic link between YME1 and the TIM22 system, a translocase complex that mediates the import of proteins to the IMM. Components of the TIM22 pathway have previously been shown to be cargo for YME1. Here, the authors show that impairment of the TIM22 complex (by depletion of the subunit Tim18) rescues mitochondrial defects of cells lacking Yme1. Furthermore, Yme1 is found to be essential for TIM22 complex stability and, in turn, regulates the proteostasis of TIM22 pathway substrates. The authors propose that excessive levels of TIM22 pathway substrates in the absence of Yme1 might be responsible for respiratory growth defects, and thus loss of TIM22 activity can compensate for this imbalance in protein levels. Together, these findings suggest a functional crosstalk between mitochondrial protein import and turnover, via the YME1 and TIM22 complexes, in mitochondrial proteostasis.
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