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Differences in the interaction of the polyene antibiotic amphotericin B with cholesterol- or ergosterol-containing
Abstract:
The selective toxicity of the polyene antibiotic amphotericin B between pathogenic eukaryotic organisms and animal cells has often been said to originate in the presence of ergosterol in fungal membranes instead of cholesterol, found in membranes of animal cells. We have tested this hypothesis by measuring the proton efflux induced by amphotericin B in egg yolk phosphatidylcholine small unilamellar vesicles. By measuring circular dichroism under the same conditions, we monitored the interaction of the antibiotic and its conformational changes. Sterol-free vesicles are sensitive to amphotericin B, but the sensitivity of sterol-containing vesicles is always greater and increasingly so with increasing sterol concentration. Ergosterol-containing vesicles are more sensitive than cholesterol-containing vesicles. On the other hand, numerous amphotericin B conformers can be detected in sterol-containing vesicles, depending upon both the concentration of sterol and the amphotericin B sterol ratio. It appears that one conformer, or maybe two at high amphotericin B concentration, is responsible for the induced permeability. From their circular dichroism spectra, these two conformers are the same in the presence of ergosterol or cholesterol. The concentration of amphotericin B necessary to obtain the two conformers is higher with cholesterol than with ergosterol, which agrees with the permeability results.
Insights
The polyene antibiotic amphotericin B shows selective toxicity due to differences in cell membrane sterols. Ergosterol in fungal membranes enhances amphotericin B
Area of Science:
- Biochemistry
- Molecular Biology
- Pharmacology
Background:
- The selective toxicity of amphotericin B is often attributed to ergosterol in fungal membranes versus cholesterol in animal cells.
- Understanding this interaction is crucial for developing targeted antifungal therapies.
Purpose of the Study:
- To investigate the role of ergosterol versus cholesterol in amphotericin B-induced membrane permeability.
- To analyze the conformational changes of amphotericin B in response to different sterols.
Main Methods:
- Proton efflux measurements in egg yolk phosphatidylcholine small unilamellar vesicles.
- Circular dichroism spectroscopy to monitor amphotericin B-sterol interactions and conformational changes.
Main Results:
- Amphotericin B induced proton efflux in sterol-free vesicles, with increased sensitivity in sterol-containing vesicles.
- Ergosterol-containing vesicles showed greater sensitivity to amphotericin B than cholesterol-containing vesicles.
- Specific amphotericin B conformers, detected via circular dichroism, were associated with induced permeability, and their formation was sterol-dependent.
Conclusions:
- The differential sensitivity of fungal versus animal cells to amphotericin B is supported by the greater interaction and permeability induced by ergosterol compared to cholesterol.
- The study elucidates the molecular basis for amphotericin B's selective toxicity, highlighting the critical role of membrane sterol composition.