The Amphotericin B-Ergosterol Complex Spans a Lipid Bilayer as a Single-Length Assembly

Area of Science:

• Biophysics
• Membrane Biology
• Antimicrobial Drug Action

Background:

• Amphotericin B (AmB) is a crucial antifungal polyene macrolide antibiotic.
• AmB targets fungal membranes by complexing with ergosterol (Erg), forming ion channels.
• The precise mechanism of lipid bilayer spanning by AmB-Erg complexes remains poorly understood due to limited direct observation methods.

Purpose of the Study:

• To elucidate the mode of lipid bilayer spanning by Amphotericin B-Ergosterol complexes.
• To determine the length and orientation of AmB-Erg complexes within a lipid bilayer.
• To provide experimental evidence for the structural organization of AmB-induced fungal membrane pores.

Main Methods:

• Solid-state nuclear magnetic resonance (NMR) experiments utilizing paramagnetic relaxation enhancement with Mn²⁺.
• Depth-dependent analysis of ¹³C NMR signal decay for individual AmB carbon atoms.
• Molecular dynamics (MD) simulations to confirm complex stabilization and membrane interaction.

Main Results:

• Solid-state NMR experiments demonstrated that the AmB-Erg complex spans a palmitoyloleoylphosphatidylcholine (POPC) bilayer with a single-molecule length.
• Paramagnetic relaxation enhancement indicated that the terminal segments of AmB (41-COOH and C38-C40 methyl groups) interact with the bilayer surface.
• MD simulations corroborated the stabilization of the AmB-Erg complex as a single-length spanning structure within the membrane.

Conclusions:

• The AmB-Erg complex integrates into lipid bilayers as a single-molecule length spanning structure.
• This finding clarifies the structural basis of AmB's antifungal activity at the membrane level.
• The study provides critical experimental validation for the proposed AmB-Erg channel architecture in model fungal membranes.