The outer membrane (OM) of Gram-negative bacteria is a complex asymmetric bilayer containing lipids, lipopolysaccharides (LPS) and proteins. While it is a mechanical and chemical barrier, it is also the primary surface of bacterial recognition processes that involve infection by and of the bacterium. Uncovering the mechanisms of these biological functions has been hampered by the lack of suitable model systems. Here we report the step-by-step assembly of a synthetic OM model from its fundamental components. To enable the efficient formation of a supported lipid bilayer at room temperature, dimyristoyl-phosphocholine (DMPC) was used as the lipid component to which we progressively added LPS and OM proteins. The assembled system enabled us to explore the contribution of the molecular components to the topographical structure and stability of the OM. We found that LPS prefers solid-state membrane regions and forms stable vesicles in the presence of divalent cations. LPS can gradually separate from DMPC membranes to form independent vesicles, pointing at the dynamic nature of the lipid-LPS system. The addition of OM proteins from E. coli and saturating levels of LPS to DMPC liposomes resulted in a thicker and more stable bilayer the surface of which displayed a nanoscale texture formed of parallel, curved, long (>500 nm) stripes spaced apart with a 15 nm periodicity. The synthetic membrane may facilitate the investigation of binding and recognition processes on the surface of Gram-negative bacteria.

中文翻译：

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合成大肠杆菌外膜模型的开发、结构和力学

革兰氏阴性菌的外膜 (OM) 是一个复杂的不对称双层，含有脂质、脂多糖 (LPS) 和蛋白质。虽然它是一种机械和化学屏障，但它也是涉及细菌感染和细菌感染的细菌识别过程的主要表面。缺乏合适的模型系统阻碍了揭示这些生物学功能的机制。在这里，我们报告了从其基本组件逐步组装合成 OM 模型。为了能够在室温下有效地形成支持的脂质双层，二肉豆蔻酰磷酸胆碱 (DMPC) 被用作我们逐渐添加 LPS 和 OM 蛋白的脂质成分。组装的系统使我们能够探索分子成分对 OM 的拓扑结构和稳定性的贡献。我们发现 LPS 更喜欢固态膜区域并在存在二价阳离子的情况下形成稳定的囊泡。LPS 可以逐渐从 DMPC 膜中分离出来，形成独立的囊泡，这表明了脂质-LPS 系统的动态特性。添加 OM 蛋白大肠杆菌和饱和水平的 LPS 对 DMPC 脂质体产生更厚和更稳定的双层，其表面显示出由平行、弯曲、长 (>500 nm) 条纹形成的纳米级纹理，以 15 nm 的周期性间隔。合成膜可能有助于研究革兰氏阴性菌表面的结合和识别过程。