Preprotein translocase of the outer mitochondrial membrane: molecular dissection and assembly of the general import pore complex

Mol Cell Biol. 1998 Nov;18(11):6515-24. doi: 10.1128/MCB.18.11.6515.


The preprotein translocase of the outer mitochondrial membrane (Tom) is a multisubunit machinery containing receptors and a general import pore (GIP). We have analyzed the molecular architecture of the Tom machinery. The receptor Tom22 stably associates with Tom40, the main component of the GIP, in a complex with a molecular weight of approximately 400,000 ( approximately 400K), while the other receptors, Tom20 and Tom70, are more loosely associated with this GIP complex and can be found in distinct subcomplexes. A yeast mutant lacking both Tom20 and Tom70 can still form the GIP complex when sufficient amounts of Tom22 are synthesized. Besides the essential proteins Tom22 and Tom40, the GIP complex contains three small subunits, Tom5, Tom6, and Tom7. In mutant mitochondria lacking Tom6, the interaction between Tom22 and Tom40 is destabilized, leading to the dissociation of Tom22 and the generation of a subcomplex of approximately 100K containing Tom40, Tom7, and Tom5. Tom6 is required to promote but not to maintain a stable association between Tom22 and Tom40. The following conclusions are suggested. (i) The GIP complex, containing Tom40, Tom22, and three small Tom proteins, forms the central unit of the outer membrane import machinery. (ii) Tom20 and Tom70 are not essential for the generation of the GIP complex. (iii) Tom6 functions as an assembly factor for Tom22, promoting its stable association with Tom40.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adenosine Triphosphatases / chemistry*
  • Bacterial Proteins / chemistry*
  • Carrier Proteins / metabolism
  • Escherichia coli Proteins*
  • Fungal Proteins / chemistry
  • Fungal Proteins / metabolism
  • Membrane Proteins / chemistry*
  • Membrane Proteins / metabolism
  • Membrane Transport Proteins*
  • Mitochondria / physiology*
  • Mitochondrial Membrane Transport Proteins*
  • Mitochondrial Precursor Protein Import Complex Proteins
  • Receptors, Cell Surface*
  • SEC Translocation Channels
  • Saccharomyces cerevisiae / physiology*
  • Saccharomyces cerevisiae Proteins*
  • SecA Proteins


  • Bacterial Proteins
  • Carrier Proteins
  • Escherichia coli Proteins
  • Fungal Proteins
  • Membrane Proteins
  • Membrane Transport Proteins
  • Mitochondrial Membrane Transport Proteins
  • Mitochondrial Precursor Protein Import Complex Proteins
  • Receptors, Cell Surface
  • SEC Translocation Channels
  • Saccharomyces cerevisiae Proteins
  • TOM22 protein, S cerevisiae
  • TOM5 protein, S cerevisiae
  • TOM7 protein, S cerevisiae
  • Tom40 protein, S cerevisiae
  • Adenosine Triphosphatases
  • SecA Proteins