The mitochondrial outer membrane harbors two protein translocases that are essential for cell viability: the translocase of the outer mitochondrial membrane (TOM) and the sorting and assembly machinery (SAM). The precursors of β-barrel proteins use both translocases - TOM for import to the intermembrane space and SAM for export into the outer membrane. It is unknown if the translocases cooperate and where the β-barrel of newly imported proteins is formed. We established a position-specific assay for monitoring β-barrel formation in vivo and in organello and demonstrated that the β-barrel was formed and membrane inserted while the precursor was bound to SAM. β-barrel formation was inhibited by SAM mutants and, unexpectedly, by mutants of the central import receptor, Tom22. We show that the cytosolic domain of Tom22 links TOM and SAM into a supercomplex, facilitating precursor transfer on the intermembrane space side. Our study reveals receptor-mediated coupling of import and export translocases as a means of precursor channeling. PaperFlick © 2013 Elsevier Inc.
Qiu, J., Wenz, L. S., Zerbes, R. M., Oeljeklaus, S., Bohnert, M., Stroud, D. A., … Becker, T. (2013). Coupling of mitochondrial import and export translocases by receptor-mediated supercomplex formation. Cell, 154(3), 596–608. https://doi.org/10.1016/j.cell.2013.06.033