Life science
Drug discovery, Medical & healthcare

Elucidating the ion channel structure of the antibiotic
amphotericin B, solving a 50-year-old mystery
Department of Chemistry, Graduate School of Science (currently, Office of Management and Planning)
Assistant Professor (currently, Chief Research Administrator)

Yuichi Umegawa					https://researchmap.jp/yuichi_umegawa?lang=en

Department of Chemistry, Graduate School of Science
Professor Michio Murata			https://researchmap.jp/quay?lang=en

Life science

Abstract
Fungal infections are highly lethal, as in the case of mucormycosis (see below). The mechanism of action of selective toxicity
of drugs against fungi is quite different from that of bacteria, making the development of therapeutic agents difficult. Amphotericin
B (AmB, Fig. 1) is an antibiotic that can be used to treat serious
systemic infections, and the ion channels formed by AmB, together with ergosterol (Erg, Fig. 1) in the fungal cell membrane, areresponsible for its fungicidal action. Since the 1970s, the detailed
structure of this ion channel has remained unknown. The authors
turned to solid-state nuclear magnetic resonance (Fig. 2) to solvethis conundrum, and succeeded in measuring the number of molecules and the distances between the isotope-labeled sites of AmB.
Based on this information, and with the help of molecular dynamics
simulations, the authors were able to elucidate the entire ion channel structure (Fig. 2).

▍ Background & Results

Figure 1. Chemical structure of AmB and Erg. AmB molecules form ion channels
only in fungal biomembranes containing Erg. On the other hand, AmB also interacts with Cho in human cell membranes, causing side effects.

The ion channel structure elucidated in this study allows us torationally explain the pharmacological effects and serious side effects of AmB. In other words, it may serve as key information for thedevelopment of AmB derivatives with reduced side effects and new
antifungal drugs. The approach used in this study also provides
important clues to the remaining difficult questions concerning themechanism of action of pharmacologically active substances.

▍ Significance of the research and Future perspective
AmB has long been used as a reliable therapeutic agent because of its excellent antifungal activity against a wide spectrum ofpathogenic fungi and yeasts. For example, persons infected withnovel coronaviruses with compromised immune functions often
become infected with environmental fungi. In particular, a fungal infection called mucormycosis is highly lethal and has become a major problem in India. AmB is widely used for its treatment and has
saved many lives. On the other hand, AmB has serious side effects
such as nephrotoxicity, which has been a major clinical problem.
The mechanism of pharmacological action and side effects of AmB
must be elucidated to overcome the adverse effects.
The results of this research have clarified the structure of ionchannels, the main entity responsible for the pharmacologicaleffect of AmB. It is expected that the development of AmB derivatives with reduced side effects will be possible in the future basedon the channel structure. It has first been disclosed that the lifetimeof molecular aggregates required for further assembly of the channel aggregates and stable expression of pharmacological activity
differs between the two sterol membranes is a key point to improve
the selective toxicity of AmB (Fig. 3). The combination of experiments and calculations used in this study and the ideas for themechanism of activity expression are expected to provide insight
into the remaining difficult questions regarding the mechanism ofdrug action.

Figure 2. 3D molecular configuration information was obtained using a solid-state NMR
system (left), and the structure was assembled to satisfy these requirements (right).

Figure 3: Hypothesized mechanism by which ergosterol and cholesterol produce
different pharmacological effects and side effects of AmB, respectively. In fungal
Erg-containing cell membranes, the ion-permeable AmB-Erg aggregates are sufficiently stable and can migrate through the membrane to form large aggregates(the body of pharmacological action, far right). On the other hand, in human
Cho-containing cell membranes, the stability of AmB-Cho aggregates is insufficient, and AmB aggregates irregularly before forming large aggregates, which do
not show effective ion permeability.

P a t e n t
Umegawa, Yuichi; Yamamoto, Tomoya; Dixit, Mayank et al. Amphotericin B assembles into seven-molecule ion channels: An NMR and moleculardynamics study. Science Advances 2022, 8(24), eabo2658. doi: 10.1126/sciadv.abo2658
Yamamoto, Tomoya; Umegawa, Yuichi; Yamagami, Masaki et al. The perpendicular orientation of amphotericin B methyl ester in lipid bilayers elucidatedby 2H and 19F solid-state NMR supports the barrel-stave model. Biochemistry 2019, 58 (17), 2282-2291. doi: 10.1021/acs.biochem.9b00180
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L https://www.science.org/doi/10.1126/sciadv.abo2658
K e y w o r d antibiotics, lipid bilayer, solid-state NMR, molecular dynamic simulationTr e a t i s e