Structural insight into the SAM-mediated assembly of the mitochondrial TOM core complex

Barrels that build barrels Cells produce specialized machinery to produce functional β-barrel proteins that are involved in cross-membrane transport and membrane protein biogenesis in eukaryotic organelles and some bacteria. Wang et al . studied one of these systems that is itself a β-barrel, the mitochondrial sorting and assembly machinery (SAM), in complex with one of its client proteins, translocase of the outer membrane (TOM). TOM subunits can be added one at a time while the protein is bound to SAM. Compared with the full TOM core complex, the final TOM core subunit clashes with SAM and suggests that release of TOM may be driven by its association. —MAF