Identification of Tom5 and Tom6 in the preprotein translocase complex of human mitochondrial outer membrane

Biochem Biophys Res Commun. 2008 May 9;369(3):958-63. doi: 10.1016/j.bbrc.2008.02.150. Epub 2008 Mar 10.


The fungal preprotein translocase of the mitochondrial outer membrane (TOM complex) comprises import receptors Tom70, Tom20, and Tom22, import channel Tom40, and small Tom proteins Tom5, Tom6, and Tom7, which regulate TOM complex assembly. These components are conserved in mammals; unlike the other components, however, Tom5 and Tom6 remain unidentified in mammals. We immuno-isolated the TOM complex from HeLa cells expressing hTom22-FLAG and identified the human counterparts of Tom5 and Tom6, together with the other components including Tom7. These small Tom proteins are associated with Tom40 in the TOM complex. Knockdown of Tom7, but not Tom5 and Tom6, strongly compromised stability of the TOM complex. Conversely, knockdown of hTom40 decreased the level of all small Tom proteins. Matrix import of preprotein was affected by double knockdown of any combination of small Tom proteins. These results indicate that human small Tom proteins maintain the structural integrity of the TOM complex.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Carrier Proteins / antagonists & inhibitors
  • Carrier Proteins / chemistry
  • Carrier Proteins / metabolism*
  • HeLa Cells
  • Humans
  • Membrane Proteins / antagonists & inhibitors
  • Membrane Proteins / genetics
  • Membrane Proteins / metabolism
  • Membrane Transport Proteins / genetics
  • Membrane Transport Proteins / isolation & purification
  • Membrane Transport Proteins / metabolism
  • Mitochondrial Membranes / enzymology*
  • Mitochondrial Precursor Protein Import Complex Proteins
  • Mitochondrial Proteins / antagonists & inhibitors
  • Mitochondrial Proteins / genetics
  • Mitochondrial Proteins / isolation & purification
  • Mitochondrial Proteins / metabolism*
  • Protein Transport / drug effects
  • Protein Transport / genetics
  • RNA Interference
  • Saccharomyces cerevisiae / enzymology


  • Carrier Proteins
  • Membrane Proteins
  • Membrane Transport Proteins
  • Mitochondrial Precursor Protein Import Complex Proteins
  • Mitochondrial Proteins
  • TOMM7 protein, human