Preprotein transport machineries of yeast mitochondrial outer membrane are not required for Bax-induced release of intermembrane space proteins

J Mol Biol. 2007 Apr 20;368(1):44-54. doi: 10.1016/j.jmb.2007.01.016. Epub 2007 Jan 12.


The mitochondrial outer membrane contains protein import machineries, the translocase of the outer membrane (TOM) and the sorting and assembly machinery (SAM). It has been speculated that TOM or SAM are required for Bax-induced release of intermembrane space (IMS) proteins; however, experimental evidence has been scarce. We used isolated yeast mitochondria as a model system and report that Bax promoted an efficient release of soluble IMS proteins while preproteins were still imported, excluding an unspecific damage of mitochondria. Removal of import receptors by protease treatment did not inhibit the release of IMS proteins by Bax. Yeast mutants of each Tom receptor and the Tom40 channel were not impaired in Bax-induced protein release. We analyzed a large collection of mutants of mitochondrial outer membrane proteins, including SAM, fusion and fission components, but none of these components was required for Bax-induced protein release. The released proteins included complexes up to a size of 230 kDa. We conclude that Bax promotes efficient release of IMS proteins through the outer membrane of yeast mitochondria while the inner membrane remains intact. Inactivation of the known protein import and sorting machineries of the outer membrane does not impair the function of Bax at the mitochondria.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Carrier Proteins / metabolism
  • Carrier Proteins / physiology
  • Cytochromes c / metabolism
  • Fungal Proteins / drug effects
  • Fungal Proteins / physiology*
  • Membrane Proteins / drug effects
  • Membrane Proteins / physiology*
  • Mitochondria / drug effects
  • Mitochondria / physiology
  • Mitochondrial Membranes / drug effects*
  • Mitochondrial Proteins / metabolism*
  • Protein Transport / drug effects
  • Saccharomyces cerevisiae / drug effects
  • Saccharomyces cerevisiae / metabolism
  • Saccharomyces cerevisiae / physiology
  • bcl-2-Associated X Protein / pharmacology*


  • Carrier Proteins
  • Fungal Proteins
  • Membrane Proteins
  • Mitochondrial Proteins
  • TOM translocase
  • bcl-2-Associated X Protein
  • Cytochromes c