Regulated interactions of mtHsp70 with Tim44 at the translocon in the mitochondrial inner membrane

Nat Struct Mol Biol. 2004 Nov;11(11):1084-91. doi: 10.1038/nsmb846. Epub 2004 Oct 17.


Preproteins synthesized on cytosolic ribosomes, but destined for the mitochondrial matrix, pass through the presequence translocase of the inner membrane. Translocation is driven by the import motor, having at its core the essential chaperone mtHsp70 (Ssc1 in yeast). MtHsp70 is tethered to the translocon channel at the matrix side of the inner membrane by the peripheral membrane protein Tim44. A key question in mitochondrial import is how the mtHsp70-Tim44 interaction is regulated. Here we report that Tim44 interacts with both the ATPase and peptide-binding domains of mtHsp70. Disruption of these interactions upon binding of polypeptide substrates requires concerted conformational changes involving both domains of mtHsp70. Our results fit a model in which regulated interactions between Tim44 and mtHsp70, controlled by polypeptide binding, are required for efficient translocation across the mitochondrial inner membrane in vivo.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Adenosine Triphosphatases / chemistry
  • Adenosine Triphosphatases / metabolism
  • Adenosine Triphosphate / chemistry
  • Anisotropy
  • Biological Transport
  • Dose-Response Relationship, Drug
  • Escherichia coli / metabolism
  • Gene Library
  • HSP70 Heat-Shock Proteins / metabolism
  • HSP70 Heat-Shock Proteins / physiology*
  • Hydrolysis
  • Immunoprecipitation
  • Intracellular Membranes / metabolism*
  • Mitochondria / metabolism
  • Mitochondrial Membrane Transport Proteins / metabolism*
  • Models, Molecular
  • Mutation
  • Peptides / chemistry
  • Plasmids / metabolism
  • Protein Binding
  • Protein Conformation
  • Protein Structure, Tertiary
  • Protein Transport
  • Saccharomyces cerevisiae / metabolism
  • Saccharomyces cerevisiae Proteins / metabolism*
  • Spectrometry, Fluorescence
  • Time Factors


  • HSP70 Heat-Shock Proteins
  • Mitochondrial Membrane Transport Proteins
  • Peptides
  • Saccharomyces cerevisiae Proteins
  • TIM44 protein, S cerevisiae
  • Adenosine Triphosphate
  • Adenosine Triphosphatases