Coupling of mitochondrial import and export translocases by receptor-mediated supercomplex formation

Cell. 2013 Aug 1;154(3):596-608. doi: 10.1016/j.cell.2013.06.033.


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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Mitochondria / metabolism*
  • Mitochondrial Membrane Transport Proteins / genetics
  • Mitochondrial Membrane Transport Proteins / metabolism*
  • Mitochondrial Proteins / chemistry
  • Mitochondrial Proteins / metabolism*
  • Mutation
  • Porins / chemistry
  • Porins / metabolism
  • Protein Folding
  • Protein Structure, Secondary
  • Protein Transport*
  • Saccharomyces cerevisiae / metabolism*
  • Saccharomyces cerevisiae Proteins / chemistry
  • Saccharomyces cerevisiae Proteins / genetics
  • Saccharomyces cerevisiae Proteins / metabolism*


  • Mitochondrial Membrane Transport Proteins
  • Mitochondrial Proteins
  • Por1 protein, S cerevisiae
  • Porins
  • Saccharomyces cerevisiae Proteins
  • Sam50 protein, S cerevisiae
  • TOM22 protein, S cerevisiae
  • Tom40 protein, S cerevisiae