title: Evidence supporting the 19 β-strand model for Tom40 from cysteine scanning and protease site accessibility studies.
abstract: 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.
authors.affiliation: From the Department of Biological Sciences, University of Alberta, Edmonton, Alberta T6G 2E9, Canada.
authors.forename: Sebastian W K
authors.initials: SW
authors.lastname: Lackey
authors.affiliation: From the Department of Biological Sciences, University of Alberta, Edmonton, Alberta T6G 2E9, Canada.
authors.forename: Rebecca D
authors.initials: RD
authors.lastname: Taylor
authors.affiliation: From the Department of Biological Sciences, University of Alberta, Edmonton, Alberta T6G 2E9, Canada.
authors.forename: Nancy E
authors.initials: NE
authors.lastname: Go
authors.affiliation: From the Department of Biological Sciences, University of Alberta, Edmonton, Alberta T6G 2E9, Canada.
authors.forename: Annie
authors.initials: A
authors.lastname: Wong
authors.affiliation: From the Department of Biological Sciences, University of Alberta, Edmonton, Alberta T6G 2E9, Canada.
authors.forename: E Laura
authors.initials: EL
authors.lastname: Sherman
authors.affiliation: From the Department of Biological Sciences, University of Alberta, Edmonton, Alberta T6G 2E9, Canada frank.nargang@ualberta.ca.
authors.forename: Frank E
authors.initials: FE
authors.lastname: Nargang
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D003545:Cysteine / Q000378:metabolism*; D005656:Fungal Proteins / Q000737:chemistry / Q000378:metabolism*; D033681:Mitochondrial Membrane Transport Proteins / Q000737:chemistry / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009492:Neurospora crassa / Q000378:metabolism*; D010447:Peptide Hydrolases / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid
chemical_list: D005656:Fungal Proteins; D033681:Mitochondrial Membrane Transport Proteins; D010447:Peptide Hydrolases; D003545:Cysteine
keywords: Membrane Protein; Mitochondria; Neurospora; Protein Structure; SCAM; Tom40; Transmembrane Domain; β-Barrel Protein