Nitroxide spin-probe study of amphotericin B-ergosterol interaction in egg phosphatidylcholine multilayers

Area of Science:

• Biochemistry
• Membrane Biophysics
• Pharmacology

Background:

• Polyene macrolide antibiotics like amphotericin B are crucial antifungal agents.
• Ergosterol is a key component of fungal cell membranes, making it a target for amphotericin B.
• Understanding the precise interaction mechanism is vital for developing more effective antifungal therapies.

Purpose of the Study:

• To elucidate the molecular interactions between amphotericin B and ergosterol within phosphatidylcholine multilayers.
• To determine the stoichiometry and structural changes associated with amphotericin B-ergosterol complex formation.
• To investigate the role of ergosterol concentration on complex formation.

Main Methods:

• Utilized spin-labelled phosphatidylcholine probes to monitor interactions at the head group and acyl chain levels.
• Employed egg phosphatidylcholine multilayers as a model membrane system.
• Varied the concentrations of amphotericin B and ergosterol to observe binding dynamics.

Main Results:

• Amphotericin B initially accumulates near the phosphatidylcholine head group region at ergosterol concentrations below 15 mol%.
• A distinct amphotericin B:ergosterol complex forms with a ratio of approximately 0.7, followed by acyl chain disordering at a 1:1 ratio.
• Dicetyl phosphate enabled higher ergosterol solubility, revealing a postulated 2:1 ergosterol:amphotericin B complex at supra-physiological ergosterol levels.

Conclusions:

• The study demonstrates a concentration-dependent, multi-step interaction model between amphotericin B and ergosterol.
• Complex formation involves distinct structural arrangements influencing membrane properties.
• Findings provide insights into the molecular basis of amphotericin B's antifungal activity and potential resistance mechanisms.