Vácha Robert, Frenkel Daan
National Centre for Biomolecular Research, Faculty of Science and CEITEC - Central European Institute of Technology, Masaryk University , Kamenice 5, 625 00 Brno-Bohunice, Czech Republic.
Langmuir. 2014 Apr 22;30(15):4229-35. doi: 10.1021/la4048159. Epub 2014 Apr 7.
Aqueous mixtures of long-tailed lipids (e.g., dimyristoylphosphatidylcholine - DMPC) and detergents can sometimes form membrane disks called bicelles. Bicelles have found applications as an embedding medium for membrane proteins in the context of NMR studies and protein crystallization. However, the parameters that determine the thermodynamic stability of bicelles are not well understood. Here we report a coarse-grained simulation study of the relationship between lipid-aggregate morphology and the composition and temperature of the surfactant mixture. In agreement with experiments, we find that bicellar mixtures are destabilized at higher temperatures and detergents are present at membrane edges as well as in flat membranes with a strong preference for the edges. In addition, our results suggest that the free-energy difference between bicelles and the perforated lamellar phase is typically very small for molecules without intrinsic curvature and charge. Cone shaped surfactant molecules tend to favor the formation of bicelles; however, none of the systems that we have studied provide unambiguous evidence for the existence of thermodynamically stable bicelles in mixtures of uncharged lipids with long and short tails. We speculate that small changes in the properties of the system (charge, dopants) may make bicelles thermodynamically stable.
长链脂质（如二肉豆蔻酰磷脂酰胆碱 - DMPC）与去污剂的水性混合物有时会形成称为双分子层的膜盘。在核磁共振研究和蛋白质结晶的背景下，双分子层已被用作膜蛋白的嵌入介质。然而，决定双分子层热力学稳定性的参数尚未得到很好的理解。在此，我们报告了一项关于脂质聚集体形态与表面活性剂混合物的组成和温度之间关系的粗粒度模拟研究。与实验一致，我们发现双分子层混合物在较高温度下不稳定，去污剂存在于膜边缘以及扁平膜中，且强烈倾向于边缘。此外，我们的结果表明，对于没有固有曲率和电荷的分子，双分子层与穿孔层状相之间的自由能差通常非常小。锥形表面活性剂分子倾向于促进双分子层的形成；然而，我们所研究的所有体系都没有提供明确的证据证明在具有长短尾的不带电脂质混合物中存在热力学稳定的双分子层。我们推测系统性质（电荷、掺杂剂）的微小变化可能使双分子层具有热力学稳定性。
