The morphology proteins Mdm12/Mmm1 function in the major beta-barrel assembly pathway of mitochondria

EMBO J. 2007 May 2;26(9):2229-39. doi: 10.1038/sj.emboj.7601673. Epub 2007 Apr 5.


The beta-barrel proteins of mitochondria are synthesized on cytosolic ribosomes. The proteins are imported by the translocase of the outer membrane (TOM) and the sorting and assembly machinery (SAM). It has been assumed that the SAM(core) complex with the subunits Sam35, Sam37 and Sam50 represents the last import stage common to all beta-barrel proteins, followed by splitting in a Tom40-specific route and a route for other beta-barrel proteins. We have identified new components of the beta-barrel assembly machinery and show that the major beta-barrel pathway extends beyond SAM(core). Mdm12/Mmm1 function after SAM(core) yet before splitting of the major pathway. Mdm12/Mmm1 have been known for their role in maintenance of mitochondrial morphology but we reveal assembly of beta-barrel proteins as their primary function. Moreover, Mdm10, which functions in the Tom40-specific route, can associate with SAM(core) as well as Mdm12/Mmm1 to form distinct assembly complexes, indicating a dynamic exchange between the machineries governing mitochondrial beta-barrel assembly. We conclude that assembly of mitochondrial beta-barrel proteins represents a major function of the morphology proteins Mdm12/Mmm1.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

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


  • MDM10 protein, S cerevisiae
  • MMM1 protein, S cerevisiae
  • Membrane Proteins
  • Membrane Transport Proteins
  • Mitochondrial Membrane Transport Proteins
  • Saccharomyces cerevisiae Proteins
  • Tom40 protein, S cerevisiae