Amphotericin B Assembles into Seven-Molecule Ion Channels in Membrane Domain

Abstract

Amphotericin B, a long-used antifungal drug, forms fungicidal ion-permeable channels across cell membranes. Using solid-state nuclear magnetic resonance spectroscopy and molecular dynamics simulations, we experimentally elucidated the three-dimensional structure of the molecular assemblies formed by this drug in membranes in the presence of the fungal sterol, ergosterol. A stable assembly of seven drug molecules was observed to form an ion conductive channel. The structure somewhat resembled the upper half of the barrel-stave model proposed in the 1970s but different substantially in the number of molecules and their arrangement. Based on the structure obtained, the aggregation of the channel assemblies in membranes was investigated and a mechanism was proposed in which complexation with ergosterol stabilizes the drug’s assemblies, leading to their aggregation, and in turn enhancing channel activity. The high-resolution structure is consistent with many previous findings, including structure-activity relationships of the drug, and the channel aggregation provides a more reasonable explanation for the selective toxicity of this drug to fungi.

Deciphering the Biological Activities of Antifungal Agents with Chemical Probes

“…Most recent evidence in favor of the barrel-stave model was provided by the Murata group, who employed a set of 19 F-and 13 C-labeled AmB derivatives to structurally characterize the AmB-ergosterol channel assembly by solidstate NMR and molecular dynamics calculations. [30,31,[39][40][41] Analysis of the assembly of 14-F-AmB using the Centerband-Only Detection of Exchange (CODEX) NMR method to study slow molecular dynamics revealed that an average of seven AmB molecules were present in each assembly. Structural information was gained from crystallographic data and Rotational Echo Double Resonance (REDOR) NMR experiments designed to measure the distance between two selected labeled heteronuclei.…”

A Fluorescent Probe for C24 Fatty Acids to Report the Deep Interior of Lipid Bilayers

“…Recently, some examples have been reported in which interdigitation has a pronounced impact on the association state of membrane-bound molecules such as peptides 26 or drugs. 27 To assess interdigitation, selective measurement of the depth-dependent chain ordering of the bilayer would be a promising approach. TCTEA could also be introduced into lysosphingomyelin to serve as a lipid-mimicking fluorescent probe similar in structure to the VLCFA-bearing SM.…”