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

Hiroki Kato1, Katsuyoshi Mihara

  • 1Department of Molecular Biology, Graduate School of Medical Science, Kyushu University, 3-1-1, Maidashi, Higashi-ku, Fukuoka 812-8582, Japan.

Biochemical and Biophysical Research Communications
|March 12, 2008
PubMed

Insights

Human small proteins Tom5, Tom6, and Tom7 are crucial for the mitochondrial outer membrane translocase (TOM) complex stability and function. Their identification and roles in maintaining the TOM complex

Area of Science:

  • Mitochondrial biology
  • Protein import
  • Cellular machinery

Background:

  • The mitochondrial outer membrane translocase (TOM) complex facilitates protein import into mitochondria.
  • Key components include receptors (Tom70, Tom20, Tom22), the channel (Tom40), and small Tom proteins (Tom5, Tom6, Tom7).
  • While conserved in mammals, the mammalian counterparts of small Tom proteins Tom5 and Tom6 were previously unidentified.

Purpose of the Study:

  • To identify the mammalian homologs of fungal small Tom proteins Tom5 and Tom6.
  • To investigate the roles of human small Tom proteins in TOM complex assembly and stability.
  • To elucidate the functional contribution of small Tom proteins to mitochondrial protein import.

Main Methods:

  • Immuno-isolation of the TOM complex from HeLa cells expressing a tagged receptor (hTom22-FLAG).
  • Identification of human TOM complex components using immunoprecipitation.
  • Gene knockdown experiments (Tom7, Tom5, Tom6, hTom40) to assess complex stability and protein import.
  • Analysis of preprotein import into mitochondria following small Tom protein depletion.

Main Results:

  • Human Tom5, Tom6, and Tom7 were identified as components of the TOM complex, associated with Tom40.
  • Tom7 knockdown significantly destabilized the TOM complex.
  • Knockdown of the import channel hTom40 reduced the levels of all small Tom proteins.
  • Combined knockdown of small Tom proteins impaired matrix preprotein import.

Conclusions:

  • Human small Tom proteins (Tom5, Tom6, Tom7) are integral components of the mitochondrial TOM complex.
  • These proteins are essential for maintaining the structural integrity and stability of the TOM complex.
  • The small Tom proteins play a coordinated role in regulating mitochondrial protein import.

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