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Multistep assembly of the protein import channel of the mitochondrial outer membrane

Nature Structural Biology volume 8, pages 361–370 (2001)Cite this article

Abstract

Proteins targeted to mitochondria are transported into the organelle through a high molecular weight complex called the translocase of the outer mitochondrial membrane (TOM). At the core of this machinery is a multisubunit general import pore (GIP) of 400 kDa. Here we report the assembly of the yeast GIP that involves two successive intermediates of 250 kDa and 100 kDa. The precursor of the channel-lining Tom40 is first targeted to the membrane via the receptor proteins Tom20 and Tom22; it then assembles with Tom5 to form the 250 kDa intermediate exposed to the intermembrane space. The 250 kDa intermediate is followed by the formation of the 100 kDa intermediate that associates with Tom6. Maturation to the 400 kDa complex occurs by association of Tom7 and Tom22. Tom7 functions by promoting both the dissociation of the 400 kDa complex and the transition from the 100 kDa intermediate to the mature complex. These results indicate that the dynamic conversion between the 400 kDa complex and the 100 kDa late intermediate allows integration of new precursor subunits into pre-existing complexes.

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Figure 1: Assembly of the precursors of small Tom proteins and Tom22 into the 400K GIP complex of yeast mitochondria.
Figure 2: Intermediate complexes in the assembly of Tom40 into the 400K GIP complex.
Figure 3: Tom40 within the 250K intermediate is peripherally membrane-associated and exposed to the intermembrane space.
Figure 4: Influence of tom deletion mutants on the formation of GIP assembly complexes.
Figure 5: Mitochondria lacking Tom7 generate Tom40 assembly complexes of larger size.
Figure 6: Association of Tom proteins with Tom40 during assembly.
Figure 7: Tom7 is involved in the assembly of imported Tom6 into the 400K complex.
Figure 8

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Acknowledgements

We thank A. Rietveld and J. Tommassen for discussion and H. Müller for expert technical assistance. This work was supported by the Deutsche Forschungsgemeinschaft, Sonderforschungsbereich 388 Freiburg, the Fonds der Chemischen Industrie/BMBF and a long-term fellowship (to K.N.T.) from the Alexander von Humboldt Foundation.

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  1. Michael T. Ryan

    Present address: Department of Biochemistry, La Trobe University, 3086, Melbourne, Australia

Authors and Affiliations

  1. Institut für Biochemie und Molekularbiologie, Universität Freiburg, Hermann-Herder-Strasse 7, Freiburg, D-79104, Germany

    Kirstin Model, Chris Meisinger, Thorsten Prinz, Nils Wiedemann, Kaye N. Truscott, Nikolaus Pfanner & Michael T. Ryan

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Correspondence to Nikolaus Pfanner.

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Model, K., Meisinger, C., Prinz, T. et al. Multistep assembly of the protein import channel of the mitochondrial outer membrane. Nat Struct Mol Biol 8, 361–370 (2001). https://doi.org/10.1038/86253

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