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

Abstract

The interaction of amphotericin B (AmB) with fungal ergosterol (Erg) is stronger than its interaction with mammalian cholesterol (Cho), and this property of AmB as an antifungal drug is thought to be responsible for its selective toxicity toward fungi. However, the mechanism by which AmB recognizes the structural differences between sterols, particularly minor difference in the sterol alicyclic portion, is largely unknown. Thus, to investigate the mode of interaction between AmB and the sterol core, we assessed the affinity of AmB to various sterols with different alicyclic structures. Ion flux assays and UV spectral measurements clearly revealed the importance of the Δ7-double bond of the sterol B-ring for interaction with the drug. AmB showed lower affinity for triene sterols, which have double bonds at the Δ5, Δ7, and Δ9 positions. Intermolecular distance measurements by (13)C{(19)F} rotational echo double resonance (REDOR) revealed that the AmB macrolide ring is in closer contact with the steroid core of Erg than it is with the Cho core in the membrane. Conformational analysis suggested that an axial hydrogen atom at C7 of Δ5-sterol (2, 6) and the protruded A-ring of Δ5,7,9-sterol (4, 8) sterically hampered face-to-face contact between the van der Waals surface of the sterol core and the macrolide of AmB. These results further suggest that the α-face of sterol alicycle interacts with the flat macrolide structure of AmB.

Mechanism and kinetics of the oxidative damage to ergosterol induced by peroxyl radicals in lipid media: a theoretical quantum chemistry study

“…Ergosterol has been proposed as a target molecule in the medical treatment of fungal infections, following mainly two routes: (i) the inhibition of the biosynthesis of ergosterol, as in the case of ketoconazole and clotrimazole drugs action, and (ii) direct interaction, as in the case of amphotericin B, where two reaction mechanisms have been proposed . The first mechanism proposed for direct interaction of ergosterol with amphotericin B has been widely studied.…”

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

“…35,36 As shown in Figure S17, this absorption was observed only for the AmB/ergosterol membrane while the 4/ergosterol preparation showed the peak not at 415 but at 408 nm; the spectra implied that 4 has lower affinity to ergosterol, and thus its channel assembly is probably less stable than that of AmB. 8,36,37 Another possible explanation is that the extended conformation enhances the stability of large aggregates in water (Fig. S16), which prevent the analog to bind to membrane.…”

“…Recently, we have reported the SAR results of various sterol analogs, and found that the AmB-ergosterol interaction is probably stabilized by face-face VDW interaction. 7,8 Thus, the gauche-containing conformation induced by 7a-OH-AmB may prevent the VDW contact between the AmB macrolide and sterol, consequently altering the sterol selectivity of 3 ( Fig. 3f/g).…”

“…In addition, detailed SAR studies on sterols were conducted to evaluate their hydrophobic interactions. 7,8 For the mycosamine moiety, chemical modification of the C3 0 -amine group revealed that the positive charge of the amine was necessary for its activity. 9 More recent SAR studies disclosed that the C2 0 -OH group affects the sterol selectivity.…”

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

“…Based on these distance data as well as our previous structure-activity relation study [148], a geometry search for AmB and Erg complexes was performed and the most likely geometries for the AmB-Erg complex were obtained for the parallel and antiparallel orientations (Fig. 14] [147].…”