Identification of mammalian TOM22 as a subunit of the preprotein translocase of the mitochondrial outer membrane.
A mitochondrial outer membrane protein of approximately 22 kDa (1C9-2) was purified from Vero cells assessing immunoreactivity with a monoclonal antibody, and the cDNA was cloned based on the partial amino acid sequence of the trypsin-digested fragments. 1C9-2 had 19-20% sequence identity to fungal Tom22, a component of the preprotein translocase of the outer membrane (the TOM complex) with receptor and organizer functions. Despite such a low sequence identity, both shared a remarkable structural similarity in the hydrophobicity profile, membrane topology in the Ncyt-Cin orientation through a transmembrane domain in the middle of the molecule, and the abundant acidic amino acid residues in the N-terminal domain. The antibodies against 1C9-2 inhibited the import of a matrix-targeted preprotein into isolated mitochondria. Blue native polyacrylamide gel electrophoresis of digitonin-solubilized outer membranes revealed that 1C9-2 is firmly associated with TOM40 in the approximately 400-kDa complex, with a size and composition similar to those of the fungal TOM core complex. Furthermore, 1C9-2 complemented the defects of growth and mitochondrial protein import in Deltatom22 yeast cells. Taken together, these results demonstrate that 1C9-2 is a functional homologue of fungal Tom22 and functions as a component of the TOM complex.
Saeki
K
K
Institute of Life Science, Kurume University, 2432-3, Aikawa-machi, Kurume 839-0861, Japan.
Suzuki
H
H
Tsuneoka
M
M
Maeda
M
M
Iwamoto
R
R
Hasuwa
H
H
Shida
S
S
Takahashi
T
T
Sakaguchi
M
M
Endo
T
T
Miura
Y
Y
Mekada
E
E
Mihara
K
K
D000251:Adenosine Triphosphatases / Q000737:chemistry*; D000595:Amino Acid Sequence; D000818:Animals; D001426:Bacterial Proteins; D001483:Base Sequence; D015153:Blotting, Western; D002352:Carrier Proteins / Q000737:chemistry*; D002458:Cell Fractionation; D002522:Chlorocebus aethiops; D003001:Cloning, Molecular; D029968:Escherichia coli Proteins; D005455:Fluorescent Antibody Technique; D005656:Fungal Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D005816:Genetic Complementation Test; D006367:HeLa Cells; D006801:Humans; D007425:Intracellular Membranes / Q000201:enzymology* / Q000378:metabolism; D046911:Macromolecular Substances; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D026901:Membrane Transport Proteins; D008928:Mitochondria / Q000201:enzymology* / Q000378:metabolism; D033681:Mitochondrial Membrane Transport Proteins; D000090622:Mitochondrial Precursor Protein Import Complex Proteins; D024101:Mitochondrial Proteins; D008969:Molecular Sequence Data; D008970:Molecular Weight; D021122:Protein Subunits; D021381:Protein Transport; D011956:Receptors, Cell Surface; D000069816:SEC Translocation Channels; D000081416:SecA Proteins; D016415:Sequence Alignment; D014709:Vero Cells; D015003:Yeasts / Q000166:cytology / Q000235:genetics / Q000254:growth & development / Q000378:metabolism
D001426:Bacterial Proteins; D002352:Carrier Proteins; D029968:Escherichia coli Proteins; D005656:Fungal Proteins; D046911:Macromolecular Substances; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D033681:Mitochondrial Membrane Transport Proteins; D000090622:Mitochondrial Precursor Protein Import Complex Proteins; D024101:Mitochondrial Proteins; D021122:Protein Subunits; D011956:Receptors, Cell Surface; D000069816:SEC Translocation Channels; C489971:TOMM22 protein, human; D000251:Adenosine Triphosphatases; D000081416:SecA Proteins