Membrane Sterols Modulate the Binding Mode of Amphotericin B without Affecting Its Affinity for a Lipid Bilayer
Membrane Sterols Modulate the Binding Mode of Amphotericin B without Affecting Its Affinity for a Lipid Bilayer
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DOI：
10.1021/acs.langmuir.5b04433
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发表时间：
2016-04-12
期刊：
影响因子：
3.9
通讯作者：
Czub, Jacek
中科院分区：
文献类型：
--
作者：
Neumann, Anna;Wieczor, Milosz;Czub, Jacek
已知膜活性抗生素可根据细胞膜特性（例如流动性、脂质排序和相行为）选择性地针对某些病原体。这些反过来又受到脂质双层的组成，特别是膜甾醇的存在和类型的调节。两性霉素 B (AmB) 是抗真菌治疗的黄金标准，对富含麦角甾醇的真菌膜表现出更高的活性，这使得它能够用于治疗系统性真菌病；然而，对真菌膜的选择性远不能令人满意，导致严重的副作用。尽管进行了数十年的研究，但关于 AmB 对真菌细胞的特异性起源及其在分子水平上的实际作用模式尚未达成共识。此前，有人提出AmB的特异作用与其对不同组成的膜的亲和力差异有关。在这项工作中，我们通过采用分子动力学模拟来比较 AmB 插入三种类型的膜的自由能来研究这种关系：纯 DMPC 双层和含有 30% 胆固醇或麦角甾醇的 DMPC 双层。我们分析了双层内 AmB 分子的方向，以便明确地建立它们的膜结合模式，并将方向自由度与脂质堆积的甾醇依赖性紧密度联系起来。我们的结果强烈表明，AmB 的膜插入几乎完全独立于膜类型，因此对真菌膜的较高毒性可能是由于膜中随后的寡聚和单体组装成功能性跨膜孔的差异造成的。特别是，后者可以通过甾醇诱导的 AmB 分子沿着膜法线的排序来促进，这由我们的自由能曲线揭示。此外，与某些说法相反，我们没有发现与膜表面上的 AmB 水平吸附相对应的稳定结合模式。
Membrane-active antibiotics are known to selectively target certain pathogens based on cell membrane properties, such as fluidity, lipid ordering, and phase behavior. These are in turn modulated by the composition of a lipid bilayer and in particular by the presence and type of membrane sterols. Amphotericin B (AmB), the golden standard of antifungal treatment, exhibits higher activity toward ergosterol-rich fungal membranes, which permits its use against systemic mycoses; however, the selectivity for fungal membranes is far from satisfactory leading to severe side effects. Despite decades of research, no consensus has emerged on the origin of AmB specificity for fungal cells and its actual mode of action at the molecular level. Previously, it has been proposed that the specific action of AmB is related to differences in its affinity for membranes of different composition. In this work, we investigate this relationship by employing molecular dynamics simulations to compare the free energy of insertion of AmB into three types of membranes: a pure DMPC bilayer and DMPC bilayers containing 30% of cholesterol or ergosterol. We analyze the orientation of AmB molecules within the bilayer in order to unambiguously establish their membrane binding mode and relate the orientational freedom to the sterol-dependent tightness of lipid packing. Our results strongly indicate that the membrane insertion of AmB proceeds virtually to completion independent of membrane type, and hence the higher toxicity against fungal membranes may rather result from differences in subsequent oligomerization in the membrane and assembly of monomers into functional transmembrane pores. In particular, the latter could be facilitated by sterol-induced ordering of AmB molecules along the membrane normal, revealed by our free energy profiles. Moreover in contrast to certain claims we find no stable binding mode corresponding to the horizontal adsorption of AmB on the membrane surface.