Lipids spontaneously form bilayered structures when brought into an aqueous environment. This is the foundation in the architecture of biological cell membranes. However, lipid bilayers do not lend themselves easily to common biophysical studies; be it of the bilayer itself or of embedded membrane proteins. Detergents, on the other hand, form small aggregates known as micelles that readily solubilize membrane proteins and are well-suited for numerous biophysical methods. However, they are not excellent models of biological membranes as they may denature the structure of a protein and the curvature of the micelle may impose a non-native protein folding. When lipid and detergent meet in an aqueous environment, entities with wholly different properties are formed: lipid bicelles. Bicelles are made of patches of lipid bilayers that are either encircled or perforated by detergent ‘rims’. They combine the advantages of both components alone (micelle and lipid bilayer), namely being good models for a biological membrane and having advantageous properties for biophysical experiments. An additional advantage of certain bicelle preparations is their tendency to macroscopically align when brought into a magnetic field. This fact has been exploited not only in the highresolution structural and dynamics studies of membrane proteins, but also for globular proteins using nuclear magnetic resonance (NMR) experiments. Fig. 1 gives a graphical introduction to the two types of bicellar phases most commonly employed. At a high detergent concentration and low temperatures, isotropically tumbling disk-like aggregates are formed, the so-called isotropic bicelles (Fig. 1B). At a high lipid concentration and in certain temperature ranges, extended bilayered lamellae are formed that are perforated or delimited by detergent, and have the potential for magnetic alignment (Fig. 1D). Cryo-transmission electron microscopy (TEM) micrographs (A, C) of bicelles taken from the literature [1] are also included in Fig. 1. Fig. 1 Lipid bicelles are supramolecular aggregates that are formed when appropriate amounts of lipids and detergents are mixed in an aqueous environment. The size and phase of bicellar aggregates depend on the [lipid]:[detergent] ratio as well as on the temperature. ... Since their first description in 1988, the great potential of bicelles in the study of membrane proteins and proteins in general has been realized. A steady stream of remarkable insights and applications has emerged that is still growing in size. In the present contribution, we will give an introduction to the properties of lipid bicelle phases with an emphasis on NMR experimental measurements. In addition, we will discuss some of the most exciting recent applications of bicelles in the structural and dynamic studies of membrane proteins.

中文翻译：

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当洗涤剂遇到双层：脂质双细胞的诞生和时代

当进入水性环境时，脂质会自发地形成双层结构。这是生物细胞膜结构的基础。然而，脂质双层不容易用于常见的生物物理研究。无论是双层本身还是嵌入的膜蛋白。另一方面，洗涤剂会形成称为胶束的小聚集体，可轻松溶解膜蛋白，非常适合多种生物物理方法。然而，它们不是生物膜的优秀模型，因为它们可能使蛋白质的结构变性，胶束的曲率可能会导致非天然蛋白质折叠。当脂质和洗涤剂在水性环境中相遇时，会形成具有完全不同特性的实体：脂质双细胞。Bicelles 由脂质双层补丁制成，这些脂质双层被洗涤剂“边缘”包围或穿孔。它们结合了单独两种组分（胶束和脂质双层）的优点，即是生物膜的良好模型，并具有用于生物物理实验的有利特性。某些 bicelle 制剂的另一个优点是当它们进入磁场时，它们倾向于宏观对齐。这一事实不仅被用于膜蛋白的高分辨率结构和动力学研究，还被用于使用核磁共振 (NMR) 实验的球状蛋白。图 1 以图形方式介绍了最常用的两种双晶相。在高洗涤剂浓度和低温下，形成各向同性翻滚的盘状聚集体，所谓的各向同性双细胞（图 1B）。在高脂质浓度和特定温度范围内，会形成延伸的双层薄片，这些薄片被洗涤剂穿孔或定界，并具有磁性排列的潜力（图 1D）。取自文献 [1] 的双胞胎的冷冻透射电子显微镜 (TEM) 显微照片 (A, C) 也包含在图 1 中。 图 1 脂质双胞胎是超分子聚集体，当加入适量的脂质和去污剂时形成在水性环境中混合。双胞胎聚集体的大小和相取决于 [脂质]: [洗涤剂] 比率以及温度。... 自 1988 年首次描述以来，bicelles 在膜蛋白和一般蛋白质研究中的巨大潜力已被实现。已经出现了源源不断的非凡见解和应用程序，其规模仍在增长。在目前的贡献中，我们将介绍脂质双细胞相的特性，重点是 NMR 实验测量。此外，我们将讨论 bicelles 在膜蛋白的结构和动态研究中的一些最新应用。