Cornell Caitlin E, McCarthy Nicola L C, Levental Kandice R, Levental Ilya, Brooks Nicholas J, Keller Sarah L
University of Washington, Department of Chemistry, Seattle, Washington.
Department of Chemistry, Imperial College London, London, United Kingdom.
Biophys J. 2017 Sep 19;113(6):1200-1211. doi: 10.1016/j.bpj.2017.06.066. Epub 2017 Aug 9.
A persistent challenge in membrane biophysics has been to quantitatively predict how membrane physical properties change upon addition of new amphiphiles (e.g., lipids, alcohols, peptides, or proteins) in order to assess whether the changes are large enough to plausibly result in biological ramifications. Because of their roles as general anesthetics, n-alcohols are perhaps the best-studied amphiphiles of this class. When n-alcohols are added to model and cell membranes, changes in membrane parameters tend to be modest. One striking exception is found in the large decrease in liquid-liquid miscibility transition temperatures (T) observed when short-chain n-alcohols are incorporated into giant plasma membrane vesicles (GPMVs). Coexisting liquid-ordered and liquid-disordered phases are observed at temperatures below T in GPMVs as well as in giant unilamellar vesicles (GUVs) composed of ternary mixtures of a lipid with a low melting temperature, a lipid with a high melting temperature, and cholesterol. Here, we find that when GUVs of canonical ternary mixtures are formed in aqueous solutions of short-chain n-alcohols (n ≤ 10), T increases relative to GUVs in water. This shift is in the opposite direction from that reported for cell-derived GPMVs. The increase in T is robust across GUVs of several types of lipids, ratios of lipids, types of short-chain n-alcohols, and concentrations of n-alcohols. However, as chain lengths of n-alcohols increase, nonmonotonic shifts in T are observed. Alcohols with chain lengths of 10-14 carbons decrease T in ternary GUVs of dioleoyl-PC/dipalmitoyl-PC/cholesterol, whereas 16 carbons increase T again. Gray et al. observed a similar influence of the length of n-alcohols on the direction of the shift in T. These results are consistent with a scenario in which the relative partitioning of n-alcohols between liquid-ordered and liquid-disordered phases evolves as the chain length of the n-alcohol increases.
膜生物物理学中一个长期存在的挑战是定量预测添加新的两亲分子（如脂质、醇类、肽或蛋白质）后膜的物理性质如何变化，以便评估这些变化是否足够大，从而可能产生生物学影响。由于其作为全身麻醉剂的作用，正醇类可能是此类中研究最深入的两亲分子。当将正醇类添加到模型膜和细胞膜中时，膜参数的变化往往较小。一个显著的例外是，当短链正醇类掺入巨型质膜囊泡（GPMV）中时，观察到液 - 液混溶转变温度（T）大幅下降。在低于T的温度下，在GPMV以及由低熔点脂质、高熔点脂质和胆固醇的三元混合物组成的巨型单层囊泡（GUV）中观察到共存的液相有序和液相无序相。在这里，我们发现当在短链正醇类（n≤10）的水溶液中形成典型三元混合物的GUV时，相对于水中的GUV，T升高。这种变化方向与细胞来源的GPMV报道的方向相反。T的升高在几种类型脂质的GUV、脂质比例、短链正醇类类型和正醇类浓度范围内都很显著。然而，随着正醇类链长的增加，观察到T的非单调变化。碳链长度为10 - 14的醇类会降低二油酰磷脂酰胆碱/二棕榈酰磷脂酰胆碱/胆固醇三元GUV中的T，而碳链长度为16的醇类又会使T升高。格雷等人观察到正醇类链长对T变化方向有类似影响。这些结果与随着正醇类链长增加，正醇类在液相有序和液相无序相之间的相对分配发生变化的情况一致。
