The N-terminal domain of Tob55 has a receptor-like function in the biogenesis of mitochondrial beta-barrel proteins

J Cell Biol. 2007 Jan 1;176(1):77-88. doi: 10.1083/jcb.200602050. Epub 2006 Dec 26.


beta-Barrel proteins constitute a distinct class of mitochondrial outer membrane proteins. For import into mitochondria, their precursor forms engage the TOM complex. They are then relayed to the TOB complex, which mediates their insertion into the outer membrane. We studied the structure-function relationships of the core component of the TOB complex, Tob55. Tob55 precursors with deletions in the N-terminal domain were not affected in their targeting to and insertion into the mitochondrial outer membrane. Replacement of wild-type Tob55 by these deletion variants resulted in reduced growth of cells, and mitochondria isolated from such cells were impaired in their capacity to import beta-barrel precursors. The purified N-terminal domain was able to bind beta-barrel precursors in a specific manner. Collectively, these results demonstrate that the N-terminal domain of Tob55 recognizes precursors of beta-barrel proteins. This recognition may contribute to the coupling of the translocation of beta-barrel precursors across the TOM complex to their interaction with the TOB complex.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Mitochondria / metabolism
  • Mitochondrial Membranes / metabolism
  • Mitochondrial Proteins / biosynthesis*
  • Mitochondrial Proteins / chemistry
  • Mitochondrial Proteins / metabolism
  • Multiprotein Complexes / metabolism
  • Mutant Proteins / metabolism
  • Phenotype
  • Porins / metabolism
  • Protein Binding
  • Protein Folding
  • Protein Precursors / metabolism
  • Protein Structure, Secondary
  • Protein Structure, Tertiary
  • Protein Transport
  • Receptors, Cell Surface / metabolism*
  • Saccharomyces cerevisiae / cytology
  • Saccharomyces cerevisiae / growth & development
  • Saccharomyces cerevisiae / metabolism*
  • Saccharomyces cerevisiae Proteins / biosynthesis
  • Saccharomyces cerevisiae Proteins / chemistry*
  • Saccharomyces cerevisiae Proteins / metabolism*
  • Sequence Deletion
  • Structure-Activity Relationship


  • Mitochondrial Proteins
  • Multiprotein Complexes
  • Mutant Proteins
  • Porins
  • Protein Precursors
  • Receptors, Cell Surface
  • Saccharomyces cerevisiae Proteins
  • Sam50 protein, S cerevisiae