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Related Experiment Videos

Purified presequence binding factor (PBF) forms an import-competent complex with a purified mitochondrial precursor

K Murakami1, M Mori

  • 1Institute for Medical Genetics, Kumamoto University Medical School, Japan.

The EMBO Journal
|October 1, 1990
PubMed
Summary

A novel cytosolic factor, presequence binding factor (PBF), binds to precursor ornithine carbamoyltransferase (OTC) and enhances its mitochondrial import. This process is further aided by heat shock protein 70 (hsp70).

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Area of Science:

  • Mitochondrial biogenesis
  • Protein import
  • Molecular chaperones

Background:

  • Mitochondrial proteins are synthesized in the cytosol and must be imported into mitochondria.
  • The import process requires specific cytosolic factors to facilitate precursor protein translocation.

Purpose of the Study:

  • To identify and characterize cytosolic factors that stimulate mitochondrial import of ornithine carbamoyltransferase (OTC).
  • To elucidate the mechanism by which these factors facilitate protein import.

Main Methods:

  • Purification of presequence binding factor (PBF) using affinity chromatography and HPLC.
  • Biochemical characterization of PBF-OTC complex formation using sucrose gradient centrifugation.
  • In vitro assays to measure PBF and hsp70 stimulated mitochondrial import of pOTC.

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Main Results:

  • A 50 kDa protein, PBF, was purified that specifically binds to the precursor form of OTC (pOTC).
  • PBF forms a 7.1S complex with pOTC, and this interaction is inhibited by presequence peptides.
  • PBF significantly enhances pOTC mitochondrial import, with further stimulation by hsp70.

Conclusions:

  • PBF binds to the presequence of mitochondrial precursor proteins, maintaining them in a transport-competent state.
  • PBF functions in cooperation with hsp70 to promote efficient mitochondrial protein import.