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Related Experiment Videos

Rapid cellular removal of a membrane-inserted foreign polypeptide

J O Moskaug1, K Prydz, S Olsnes

  • 1Institute for Cancer Research, Norwegian Radium Hospital, Montebello, Oslo.

The Biochemical Journal
|April 15, 1993
PubMed
Summary

Researchers studied how diphtheria toxin B-fragment enters and degrades in Vero cells after membrane insertion. Findings reveal rapid degradation via endocytosis and lysosomal pathways, crucial for understanding toxin fate.

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Area of Science:

  • Cell Biology
  • Molecular Biology
  • Toxicology

Background:

  • Diphtheria toxin is a bacterial protein capable of inserting into eukaryotic plasma membranes.
  • Understanding the cellular fate of such membrane-inserted proteins is crucial for cell biology and toxicology.

Purpose of the Study:

  • To investigate the endocytic uptake and degradation pathway of the diphtheria toxin B-fragment after its insertion into the plasma membrane.
  • To elucidate the cellular mechanisms governing the degradation of membrane-inserted foreign polypeptides.

Main Methods:

  • Utilized a system to study foreign polypeptide fate in plasma membranes.
  • Applied acidification to induce membrane insertion of diphtheria toxin B-fragment.
  • Assessed degradation rates, inhibition by protease treatment, ATP depletion, low temperatures, cytosol acidification, and NH4Cl treatment in Vero cells.

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Main Results:

  • Diphtheria toxin B-fragment undergoes rapid degradation (t1/2 = 6 min) following membrane insertion and extracellular cleavage.
  • Degradation is an energy-dependent process, sensitive to temperature (inhibited below 18°C) and ATP levels.
  • Endocytosis, particularly from clathrin-coated pits, and lysosomal/late endosomal transport are critical for degradation, as indicated by inhibition studies.

Conclusions:

  • The inserted and cleaved diphtheria toxin B-fragment is rapidly degraded through an endocytic pathway.
  • Degradation involves transport to late endosomes or lysosomes, requiring cellular energy and specific membrane trafficking events.
  • This study provides insights into the cellular processing of membrane-inserted bacterial toxins.