Synthetic antimicrobial, oligomers induce a composition-dependent topological transition in membranes
Synthetic antimicrobial, oligomers induce a composition-dependent topological transition in membranes
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DOI：
10.1021/ja072310o
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发表时间：
2007-10-10
影响因子：
15
通讯作者：
Wong, Gerard C. L.
中科院分区：
文献类型：
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作者：
Yang, Lihua;Gordon, Vernita D.;Wong, Gerard C. L.
抗菌肽(AMPs)是一种阳离子两亲性物质，是天然免疫的重要组成部分。合成的AMPS类似物，如苯乙炔抗菌低聚物(AMOS)家族，最近显示出广谱的抗菌活性，但其潜在的分子机制尚不清楚。该家族中的同系物可以是非活性的，可以是针对细菌的特异性活性，也可以是针对细菌和真核细胞的非特异性活性。利用同步辐射小角X射线散射(SAXS)，我们发现观察到的抗菌活性与AMO诱导的小单层囊泡向倒六方相的拓扑转变有关，在该相中形成了由脂质管定义的3：4 nm水通道的六角阵列。偏光显微镜和荧光显微镜显示，经AMO处理的巨大单层囊泡保持完好，而不是重建成块状3D相，但对小于3.4 nm的包裹的大分子具有选择性的渗透性。此外，不同活性谱的AMOS需要不同的最低阈值浓度的磷乙醇胺(PE)脂类来重建膜。使用由DOPG：DOPE：DOPC组成的三元膜囊泡，电荷密度固定在典型的细菌值上，我们发现即使当DOPE完全取代DOPC时，非活性AMO也不能产生反六方相。特定活性AMO的阈值比为DOPE：DOPC 4：1，而非特异性AMO的阈值比为DOPE：DOPC 1.5：1。由于大多数革兰氏阴性细菌膜比真核生物膜含有更多的PE脂类，我们的结果表明，PE等负曲率脂类与有助于选择性抗菌活性的抗菌疏水性有关。
Antimicrobial peptides (AMPs) are cationic amphiphiles that comprise a key component of innate immunity. Synthetic analogues of AMPS, such as the family of phenylene ethynylene antimicrobial oligomers (AMOS), recently demonstrated broad-spectrum antimicrobial activity, but the underlying molecular mechanism is unknown. Homologues in this family can be inactive, specifically active against bacteria, or nonspecifically active against bacteria and eukaryotic cells. Using synchrotron small-angle X-ray scattering (SAXS), we show that observed antibacterial activity correlates with an AMO-induced topological transition of small unilamellar vesicles into an inverted hexagonal phase, in which hexagonal arrays of 3:4-nm water channels defined by lipid tubes are formed. Polarized and fluorescence microscopy show that AMO-treated giant unilamellar vesicles remain intact, instead of reconstructing into a bulk 3D phase, but are selectively permeable to encapsulated macromolecules that are smaller than 3.4 nm. Moreover, AMOS with different activity profiles require different minimum threshold concentrations of phosphoethanolamine (PE) lipids to reconstruct the membrane. Using ternary membrane vesicles composed of DOPG:DOPE:DOPC with a charge density fixed at typical bacterial values, we find that the inactive AMO cannot generate the inverted hexagonal phase even when DOPE completely replaces DOPC. The specifically active AMO requires a threshold ratio of DOPE:DOPC 4:1, and the nonspecifically active AMO requires a drastically lower threshold ratio of DOPE:DOPC 1.5:1. Since most gram-negative bacterial membranes have more PE lipids than do eukaryotic membranes, our results imply that there is a relationship between negative-curvature lipids such as PE and antimicrobial hydrophobicity that contributes to selective antimicrobial activity.