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How does the TOM complex mediate insertion of precursor proteins into the mitochondrial outer membrane?

Rapaport D - J. Cell Biol. (2005)

Bottom Line: A multisubunit translocase of the outer mitochondrial membrane (TOM complex) mediates both the import of mitochondrial precursor proteins into the internal compartments of the organelle and the insertion of proteins residing in the mitochondrial outer membrane.The proposed beta-barrel structure of Tom40, the pore-forming component of the translocase, raises the question of how the apparent uninterrupted beta-barrel topology can be compatible with a role of Tom40 in releasing membrane proteins into the lipid core of the bilayer.In this review, I discuss insertion mechanisms of proteins into the outer membrane and present alternative models based on the opening of a multisubunit beta-barrel TOM structure or on the interaction of outer membrane precursors with the outer face of the Tom40 beta-barrel structure.

View Article: PubMed Central - PubMed

Affiliation: Institute for Physiological Chemistry, Ludwig-Maximilians University, 81377 Munich, Germany. rapaport@med.uni-muenchen.de

ABSTRACT
A multisubunit translocase of the outer mitochondrial membrane (TOM complex) mediates both the import of mitochondrial precursor proteins into the internal compartments of the organelle and the insertion of proteins residing in the mitochondrial outer membrane. The proposed beta-barrel structure of Tom40, the pore-forming component of the translocase, raises the question of how the apparent uninterrupted beta-barrel topology can be compatible with a role of Tom40 in releasing membrane proteins into the lipid core of the bilayer. In this review, I discuss insertion mechanisms of proteins into the outer membrane and present alternative models based on the opening of a multisubunit beta-barrel TOM structure or on the interaction of outer membrane precursors with the outer face of the Tom40 beta-barrel structure.

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The TOM complex. The TOM complex mediates the translocation of mitochondrial precursor proteins. After crossing the outer membrane (OM), presequence-containing precursor proteins are engaged by the Tim23 complex in the inner membrane (IM), whereas polytopic inner membrane proteins are inserted by the Tim22 complex. β-Barrel precursors are crossing the outer membrane through the TOM complex and are then reinserted into the outer membrane via the TOB–SAM complex. The TOM complex contains seven subunits: the primary receptors Tom20 and 70 and the TOM core complex, which consists of Tom5, 6, 7, 22, and 40. The names of the Tom subunits reflect their apparent molecular mass.
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fig1: The TOM complex. The TOM complex mediates the translocation of mitochondrial precursor proteins. After crossing the outer membrane (OM), presequence-containing precursor proteins are engaged by the Tim23 complex in the inner membrane (IM), whereas polytopic inner membrane proteins are inserted by the Tim22 complex. β-Barrel precursors are crossing the outer membrane through the TOM complex and are then reinserted into the outer membrane via the TOB–SAM complex. The TOM complex contains seven subunits: the primary receptors Tom20 and 70 and the TOM core complex, which consists of Tom5, 6, 7, 22, and 40. The names of the Tom subunits reflect their apparent molecular mass.

Mentions: Protein import into mitochondria is essential for organelle biogenesis and, thereby, for eukaryotic cell viability. At the surface of mitochondria, precursor proteins are recognized by the translocase of the outer mitochondrial membrane (TOM complex). This complex is composed of at least seven different subunits (Fig. 1). Tom20 and 70 are the primary receptors, whereas the subunits Tom40, 22, 7, 6, and 5 form the stable TOM core complex (Fig. 1; Dekker et al., 1998; Künkele et al., 1998; Ahting et al., 1999). Tom40 forms the protein-conducting channel of the TOM complex, and theoretical predictions and secondary structure determinations suggest that the protein has a β-barrel topology (Mannella et al., 1996; Hill et al., 1998; Ahting et al., 2001).


How does the TOM complex mediate insertion of precursor proteins into the mitochondrial outer membrane?

Rapaport D - J. Cell Biol. (2005)

The TOM complex. The TOM complex mediates the translocation of mitochondrial precursor proteins. After crossing the outer membrane (OM), presequence-containing precursor proteins are engaged by the Tim23 complex in the inner membrane (IM), whereas polytopic inner membrane proteins are inserted by the Tim22 complex. β-Barrel precursors are crossing the outer membrane through the TOM complex and are then reinserted into the outer membrane via the TOB–SAM complex. The TOM complex contains seven subunits: the primary receptors Tom20 and 70 and the TOM core complex, which consists of Tom5, 6, 7, 22, and 40. The names of the Tom subunits reflect their apparent molecular mass.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2171261&req=5

fig1: The TOM complex. The TOM complex mediates the translocation of mitochondrial precursor proteins. After crossing the outer membrane (OM), presequence-containing precursor proteins are engaged by the Tim23 complex in the inner membrane (IM), whereas polytopic inner membrane proteins are inserted by the Tim22 complex. β-Barrel precursors are crossing the outer membrane through the TOM complex and are then reinserted into the outer membrane via the TOB–SAM complex. The TOM complex contains seven subunits: the primary receptors Tom20 and 70 and the TOM core complex, which consists of Tom5, 6, 7, 22, and 40. The names of the Tom subunits reflect their apparent molecular mass.
Mentions: Protein import into mitochondria is essential for organelle biogenesis and, thereby, for eukaryotic cell viability. At the surface of mitochondria, precursor proteins are recognized by the translocase of the outer mitochondrial membrane (TOM complex). This complex is composed of at least seven different subunits (Fig. 1). Tom20 and 70 are the primary receptors, whereas the subunits Tom40, 22, 7, 6, and 5 form the stable TOM core complex (Fig. 1; Dekker et al., 1998; Künkele et al., 1998; Ahting et al., 1999). Tom40 forms the protein-conducting channel of the TOM complex, and theoretical predictions and secondary structure determinations suggest that the protein has a β-barrel topology (Mannella et al., 1996; Hill et al., 1998; Ahting et al., 2001).

Bottom Line: A multisubunit translocase of the outer mitochondrial membrane (TOM complex) mediates both the import of mitochondrial precursor proteins into the internal compartments of the organelle and the insertion of proteins residing in the mitochondrial outer membrane.The proposed beta-barrel structure of Tom40, the pore-forming component of the translocase, raises the question of how the apparent uninterrupted beta-barrel topology can be compatible with a role of Tom40 in releasing membrane proteins into the lipid core of the bilayer.In this review, I discuss insertion mechanisms of proteins into the outer membrane and present alternative models based on the opening of a multisubunit beta-barrel TOM structure or on the interaction of outer membrane precursors with the outer face of the Tom40 beta-barrel structure.

View Article: PubMed Central - PubMed

Affiliation: Institute for Physiological Chemistry, Ludwig-Maximilians University, 81377 Munich, Germany. rapaport@med.uni-muenchen.de

ABSTRACT
A multisubunit translocase of the outer mitochondrial membrane (TOM complex) mediates both the import of mitochondrial precursor proteins into the internal compartments of the organelle and the insertion of proteins residing in the mitochondrial outer membrane. The proposed beta-barrel structure of Tom40, the pore-forming component of the translocase, raises the question of how the apparent uninterrupted beta-barrel topology can be compatible with a role of Tom40 in releasing membrane proteins into the lipid core of the bilayer. In this review, I discuss insertion mechanisms of proteins into the outer membrane and present alternative models based on the opening of a multisubunit beta-barrel TOM structure or on the interaction of outer membrane precursors with the outer face of the Tom40 beta-barrel structure.

Show MeSH
Related in: MedlinePlus