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Updated: Sep 21, 2026
Detection of Toxin Translocation into the Host Cytosol by Surface Plasmon Resonance
Published on: January 3, 2012
Demonstration of diphtheria toxin receptors on surface membranes from both toxin-sensitive and toxin-resistant
Abstract:
A detailed binding study of 125I-labeled diphtheria toxin to isolated cell surface membrane-enriched fractions is reported. The study was undertaken to determine if toxin-resistant species exhibit a defet in either the binding step or the transport step of the intoxication process. Surface membrane fractions were obtained from liver and mammary glands of toxin-sensitive species, rabbit and giunea pig, and toxin-resistant species, rat mouse. All membrane fractions exhibited reversible binding of 125I-toxin which was competitively inhibited by unlabeled toxin. Toxin receptors from liver co-purified with plasma membranes and the plasma membrane marker 5'-nucleotidase. One-half saturation of all receptors occurred between 5 x 10(-8) and 1.8 x 10(-7) M. Scatchard plots were nonlinear and concave upwards. Total receptor sites ranged from 3.4 to 16 pmol/mg of membrane protein, tissue differences being more pronounced than difference between sensitive and nonsensitive species. Over 95% of the toxin specific binding was inhibited by removal of divalent cation from the medium or by the inclusion of 1 mM ATP, procedures which have been shown to protect sensitive cells from intoxication by diphtheria toxin. We conclude that the rat and mouse have surface membrane receptors for diphtheria toxin and that the toxin insensitivity of these species results from a defect in or a lack of the transport process.
Insights
Toxin-resistant species like rats and mice possess diphtheria toxin receptors on their cell membranes. However, their resistance stems from a defect in the toxin transport process, not binding.
Area of Science:
- Toxicology
- Cell Biology
- Molecular Biology
Background:
- Diphtheria toxin causes cell damage by binding to surface receptors and entering cells.
- Understanding the molecular basis of toxin resistance is crucial for developing effective treatments and vaccines.
Purpose of the Study:
- To investigate whether toxin-resistant species have defects in diphtheria toxin binding or transport.
- To characterize diphtheria toxin receptors in sensitive and resistant animal models.
Main Methods:
- Isolated cell surface membrane-enriched fractions from liver and mammary glands of sensitive (rabbit, guinea pig) and resistant (rat, mouse) species were used.
- Binding studies with 125I-labeled diphtheria toxin were performed, assessing reversible binding, competitive inhibition, and receptor site density.
- The effect of divalent cations and ATP on toxin binding was evaluated.
Main Results:
- All tested membrane fractions showed reversible binding of diphtheria toxin, inhibited by unlabeled toxin.
- Diphtheria toxin receptors co-purified with plasma membranes and 5'-nucleotidase in liver fractions.
- Receptor site densities varied by tissue but were similar between sensitive and resistant species.
- Divalent cations and ATP significantly inhibited toxin binding, consistent with protection mechanisms in sensitive cells.
Conclusions:
- Rats and mice possess functional diphtheria toxin receptors on their cell surface membranes.
- The insensitivity of rats and mice to diphtheria toxin is due to a defect in the intracellular transport process, not impaired receptor binding.
