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J Biol Chem. 2014 Aug 1;289(31):21640-50. doi: 10.1074/jbc.M114.578765. Epub 2014 Jun 19.

Evidence supporting the 19 β-strand model for Tom40 from cysteine scanning and protease site accessibility studies.

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  • 1From the Department of Biological Sciences, University of Alberta, Edmonton, Alberta T6G 2E9, Canada.
  • 2From the Department of Biological Sciences, University of Alberta, Edmonton, Alberta T6G 2E9, Canada


Most proteins found in mitochondria are translated in the cytosol and enter the organelle via the TOM complex (translocase of the outer mitochondrial membrane). Tom40 is the pore forming component of the complex. Although the three-dimensional structure of Tom40 has not been determined, the structure of porin, a related protein, has been shown to be a β-barrel containing 19 membrane spanning β-strands and an N-terminal α-helical region. The evolutionary relationship between the two proteins has allowed modeling of Tom40 into a similar structure by several laboratories. However, it has been suggested that the 19-strand porin structure does not represent the native form of the protein. If true, modeling of Tom40 based on the porin structure would also be invalid. We have used substituted cysteine accessibility mapping to identify several potential β-strands in the Tom40 protein in isolated mitochondria. These data, together with protease accessibility studies, support the 19 β-strand model for Tom40 with the C-terminal end of the protein localized to the intermembrane space.

© 2014 by The American Society for Biochemistry and Molecular Biology, Inc.


Membrane Protein; Mitochondria; Neurospora; Protein Structure; SCAM; Tom40; Transmembrane Domain; β-Barrel Protein

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