A two-step mitochondrial import pathway couples the disulfide relay with matrix complex I biogenesis

Peker et al. identified a two-step import pathway allowing for dual protein localization to matrix and IMS. Weak targeting signals allow proteins to acquire stabilizing disulfide bonds in the IMS en route to the matrix. This pathway allows the sensing of import activity in two compartments. Mitochondria critically rely on protein import and its tight regulation. Here, we found that the complex I assembly factor NDUFAF8 follows a two-step import pathway linking IMS and matrix import systems. A weak targeting sequence drives TIM23-dependent NDUFAF8 matrix import, and en route, allows exposure to the IMS disulfide relay, which oxidizes NDUFAF8. Import is closely surveyed by proteases: YME1L prevents accumulation of excess NDUFAF8 in the IMS, while CLPP degrades reduced NDUFAF8 in the matrix. Therefore, NDUFAF8 can only fulfil its function in complex I biogenesis if both oxidation in the IMS and subsequent matrix import work efficiently. We propose that the two-step import pathway for NDUFAF8 allows integration of the activity of matrix complex I biogenesis pathways with the activity of the mitochondrial disulfide relay system in the IMS. Such coordination might not be limited to NDUFAF8 as we identified further proteins that can follow such a two-step import pathway.

Automated summary

Peker et al. discovered a two-step import pathway that allows proteins to be localized to both the matrix and IMS. Weak targeting signals enable proteins to form stabilizing disulfide bonds in the IMS before being imported into the matrix. This pathway enables the monitoring of import activity in both compartments. The study found that NDUFAF8, a factor involved in complex I assembly, follows this two-step import pathway, and its import is regulated by proteases to ensure proper function.