Department of Chemistry, National Tsing Hua University, Hsinchu 300-044, Taiwan.
Department of Chemistry, National Chung Hsing University, Taichung 402-002, Taiwan.
Langmuir. 2022 Dec 13;38(49):15372-15383. doi: 10.1021/acs.langmuir.2c02596. Epub 2022 Dec 1.
Nanodiscs are broadly used for characterization of membrane proteins as they are generally assumed to provide a near-native environment. In fact, it is an open question whether the physical properties of lipids in nanodiscs and membrane vesicles of the same lipid composition are identical. Here, we investigate the properties of lipids (1,2-dipalmitoyl--glycero-3-phosphocholine, 1,2-dilauroyl--glycero-3-phosphocholine, and their mixtures) in two different sample types, nanodiscs and multilamellar vesicles, by means of spin-label electron spin resonance techniques. Our results provide a quantitative description of lipid dynamics and ordering, elucidating the molecular details of how lipids in the two sample types behave differently in response to temperature and lipid composition. We show that the properties of lipids are altered in nanodiscs such that the dissimilarity of the fluid and gel lipid phases is reduced, and the first-order phase transitions are largely abolished in nanodiscs. We unveil that the ensemble of lipids in the middle of a nanodisc bilayer, as probed by the end-chain spin-label 16-PC, is promoted to a state close to a miscibility critical point, thereby rendering the phase transitions continuous. Critical phenomena have recently been proposed to explain features of the heterogeneity in native cell membranes. Our results lay the groundwork for how to establish a near-native environment in nanodiscs with simple organization of lipid components.
纳米盘被广泛用于膜蛋白的特性研究，因为它们通常被认为提供了一种接近天然的环境。事实上，纳米盘中的脂质的物理性质与具有相同脂质组成的膜泡中的脂质是否相同，这仍然是一个悬而未决的问题。在这里，我们通过自旋标记电子顺磁共振技术研究了两种不同样品类型（纳米盘和多层囊泡）中脂质（1,2-二棕榈酰基-sn-甘油-3-磷酸胆碱、1,2-二月桂酰基-sn-甘油-3-磷酸胆碱及其混合物）的性质。我们的结果提供了对脂质动力学和有序性的定量描述，阐明了脂质在两种样品类型中如何因温度和脂质组成而表现出不同行为的分子细节。我们表明，纳米盘中的脂质性质发生了变化，从而降低了流体和凝胶脂质相的不相似性，并在纳米盘中基本消除了一级相变。我们揭示了纳米盘双层中间的脂质集合体，如通过末端链自旋标记 16-PC 探测到的那样，被促进到接近混溶性临界点的状态，从而使相变连续进行。最近有人提出临界现象来解释天然细胞膜异质性的特征。我们的结果为如何在具有简单脂质成分组织的纳米盘中建立接近天然的环境奠定了基础。
