Axial Hydrogen at C7 Position and Bumpy Tetracyclic Core Markedly Reduce Sterol’s Affinity to Amphotericin B in Membrane

Cu(II)-Triggered Ion Channel Properties of a 2,2'-Bipyridine-Modified Amphotericin B

The development of stimuli-responsive synthetic channels that open and close in response to physical and chemical changes in the surrounding environment has attracted attention because of their potential bioapplications such as sensing, drug release, antibiotics, and molecular manipulation tools to control membrane transport in cells. Metal coordination is ideal as a stimulus for stimuli-responsive channels because it allows for reversible gating behavior through the addition and removal of metal ions and fine-tuning of channel structure through coordination geometry defined by the type of the metal ion and ligand. We have previously reported on transition metal-ion dependent ion permeability control of Amphotericin B (AmB) modified with a metal coordination site, 2,2'-bipyridine ligand (bpy-AmB). AmB is one of the polyene macrolide antibiotics, and it is known that the interaction between AmB and ergosterol molecules is required for AmB channel formation. In contrast, the Cu²⁺ coordination to the bpy moiety of bpy-AmB induces formation of Ca²⁺ ion-permeable channels in the ergosterol-free POPC membrane. However, the details of bpy-AmB properties such as channel stability, ion selectivity, pore size, and the effect of ergosterol on channel formation remain unclear. Here, we investigate bpy-AmB channels triggered by transition metal coordination in POPC or ergosterol-containing POPC liposomes using an HPTS assay, electrophysiological measurements, and time-resolved UV-vis spectral measurements. These analyses reveal that bpy-AmB channels triggered by Cu²⁺ ions are more stable and have larger pore sizes than the original AmB channels and enable efficient permeation of various cations. We believe that our channel design will lead to the construction of metal coordination-triggered synthetic ion channels.

Amphotericin B assembles into seven-molecule ion channels: An NMR and molecular dynamics study

Amphotericin B, an antifungal drug with a long history of use, 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 consisting of seven drug molecules was observed to form an ion conductive channel. The structure is somewhat similar to the upper half of the barrel-stave model proposed in the 1970s but substantially different in the number of molecules and in their arrangement. The present structure explains many previous findings, including structure-activity relationships of the drug, which will be useful for improving drug efficacy and reducing adverse effects.

Design, Synthesis, and Antifungal Activity of 16,17-Dihydroheronamide C and ent-Heronamide C

16,17-Dihydroheronamide C (8) and ent-heronamide C (ent-1) were designed as probes for the mode-of-action analysis of heronamide C (1). These molecules were synthesized by utilizing a highly modular strategy developed in the preceding paper. The evaluation of the antifungal activity of these compounds revealed the exceptional importance of the C16-C17 double bond for the antifungal activity of heronamide C and the existence of chiral recognition between heronamide C (1) and cell membrane components.

pH-Dependent ion permeability control of a modified amphotericin B channel through metal complexation

Amphotericin B incorporating 2,2'-bipyridine (bpy-AmB) forms a membrane channel exhibiting pH-dependent Ca2+ ion permeability with a selective response to Cu2+ ions. The coordination structure at bpy sites depends on the pH and metal ions can control the association state of bpy-AmB in the membrane.

Development of Amphotericin B Micellar Formulations Based on Copolymers of Poly(ethylene glycol) and Poly(ε-caprolactone) Conjugated with Retinol

Amphotericin B (AmB) is a broad spectrum of antifungal drug used to treat antifungal diseases. However, due to the high toxicity of AmB, treated patients may suffer the risk of side effects, such as renal failure. Nanoencapsulation strategies have been reported to elicit low toxicity, albeit most of them possess low encapsulation efficiency. The aim of this research is to develop micellar delivery systems for AmB with reduced toxicity while maintaining its affectivity by employing retinol (RET)-conjugated amphiphilic block copolymers (ABCs) as precursors. Copolymers composed of poly(ε-caprolactone) (A) and polyethylenglycol (B) of types AB and ABA were synthesized by ring opening polymerization and subsequently conjugated with RET by Steglich esterification. 1H-NMR spectroscopy was used to corroborate the structure of copolymers and their conjugates and determine their molecular weights. Analysis by gel permeation chromatography also found that the materials have narrow distributions. The resulting copolymers were used as precursors for delivery systems of AmB, thus reducing its aggregation and consequently causing a low haemolytic effect. Upon conjugation with RET, the encapsulation capacity was enhanced from approximately 2 wt % for AB and ABA copolymers to 10 wt %. AmB encapsulated in polymer micelles presented improved antifungal efficiency against Candida albicans and Candida auris strains compared with Fungizone®, as deduced from the low minimum inhibitory concentration.

Chemical diversity and mode of action of natural products targeting lipids in the eukaryotic cell membrane

Covering: up to 2019Nature furnishes bioactive compounds (natural products) with complex chemical structures, yet with simple, sophisticated molecular mechanisms. When natural products exhibit their activities in cells or bodies, they first have to bind or react with a target molecule in/on the cell. The cell membrane is a major target for bioactive compounds. Recently, our understanding of the molecular mechanism of interactions between natural products and membrane lipids progressed with the aid of newly-developed analytical methods. New technology reconnects old compounds with membrane lipids, while new membrane-targeting molecules are being discovered through the screening for antimicrobial potential of natural products. This review article focuses on natural products that bind to eukaryotic membrane lipids, and includes clinically important molecules and key research tools. The chemical diversity of membrane-targeting natural products and the molecular basis of lipid recognition are described. The history of how their mechanism was unveiled, and how these natural products are used in research are also mentioned.

Dynamic membrane interactions of antibacterial and antifungal biomolecules, and amyloid peptides, revealed by solid-state NMR spectroscopy

A variety of biomolecules acting on the cell membrane folds into a biologically active structure in the membrane environment. It is, therefore, important to determine the structures and dynamics of such biomolecules in a membrane environment. While several biophysical techniques are used to obtain low-resolution information, solid-state NMR spectroscopy is one of the most powerful means for determining the structure and dynamics of membrane bound biomolecules such as antibacterial biomolecules and amyloidogenic proteins; unlike X-ray crystallography and solution NMR spectroscopy, applications of solid-state NMR spectroscopy are not limited by non-crystalline, non-soluble nature or molecular size of membrane-associated biomolecules. This review article focuses on the applications of solid-state NMR techniques to study a few selected antibacterial and amyloid peptides. Solid-state NMR studies revealing the membrane inserted bent α-helical structure associated with the hemolytic activity of bee venom melittin and the chemical shift oscillation analysis used to determine the transmembrane structure (with α-helix and 310-helix in the N- and C-termini, respectively) of antibiotic peptide alamethicin are discussed in detail. Oligomerization of an amyloidogenic islet amyloid polypeptide (IAPP, or also known as amylin) resulting from its aggregation in a membrane environment, molecular interactions of the antifungal natural product amphotericin B with ergosterol in lipid bilayers, and the mechanism of lipid raft formation by sphingomyelin studied using solid state NMR methods are also discussed in this review article. This article is part of a Special Issue entitled "Biophysical Exploration of Dynamical Ordering of Biomolecular Systems" edited by Dr. Koichi Kato.

Role of polyol moiety of amphotericin B in ion channel formation and sterol selectivity in bilayer membrane

Amphotericin B (AmB) is a polyene macrolide antibiotic widely used to treat mycotic infections. In this paper, we focus on the role of the polyol moiety of AmB in sterol selectivity using 7-oxo-AmB, 7α-OH-AmB, and 7β-OH-AmB. The 7-OH analogs were prepared from 7-oxo-AmB. Their K(+) flux activity in liposomes showed that introduction of an additional ketone or hydroxy group on the polyol moiety reduces the original activity. Conformational analyses of these derivatives indicated that intramolecular hydrogen-bonding network possibly influenced the conformational rigidity of the macrolactone ring, and stabilized the active conformation in the membrane. Additionally, the flexible polyol leads to destabilization of the whole macrolactone ring conformation, resulting in a loss of sterol selectivity.