Investigation of domain formation in sphingomyelin/cholesterol/POPC mixtures by fluorescence resonance energy transfer and Monte Carlo simulations.
Investigation of domain formation in sphingomyelin/cholesterol/POPC mixtures by fluorescence resonance energy transfer and Monte Carlo simulations.
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DOI：
10.1529/biophysj.106.100107
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发表时间：
2007-04-01
影响因子：
3.4
通讯作者：
Almeida, Paulo F F
中科院分区：
文献类型：
--
作者：
Frazier, Monica L;Wright, Jenny R;Pokorny, Antje;Almeida, Paulo F F
我们最近根据两亲性多肽δ-Lysin诱导的羧基荧光素外流动力学，提出了猪脑鞘磷脂、胆固醇和1-棕榈酰基-2-油酰磷脂酰胆碱混合物的相图。尽管这项研究表明了微区的存在，但在荧光显微镜下，BSM/Chol/POPC混合物中并没有观察到微米级的相分离，尽管对于其他一些鞘磷脂(SM)来说，它们已经发生了相分离。在这里，我们通过结合荧光共振能量转移(FRET)和蒙特卡罗模拟来研究相同的BSM/CHOL/POPC体系。结果清楚地表明，在该体系中形成了微区。FRET实验数据与计算机模拟的比较允许估计SM/Chol、SM/POPC和Chol/POPC之间的脂-脂相互作用吉布斯能。后两种相互作用是弱排斥的，但SM和CHOL之间的相互作用是有利的。此外，这三个不同的脂类相互作用参数在三个可能的脂类对之间足以在三元相图中存在一个闭合环，而不需要涉及多体相互作用。计算还表明，最大的POPC结构域包含数千种脂类，对应于数百纳米量级的线性尺寸。
We have recently proposed a phase diagram for mixtures of porcine brain sphingomyelin (BSM), cholesterol (Chol), and 1-palmitoyl-2-oleoyl-phosphatidylcholine (POPC) on the basis of kinetics of carboxyfluorescein efflux induced by the amphipathic peptide δ-lysin. Although that study indicated the existence of domains, phase separations in the micrometer scale have not been observed by fluorescence microscopy in BSM/Chol/POPC mixtures, though they have for some other sphingomyelins (SM). Here we examine the same BSM/Chol/POPC system by a combination of fluorescence resonance energy transfer (FRET) and Monte Carlo simulations. The results clearly demonstrate that domains are formed in this system. Comparison of the FRET experimental data with the computer simulations allows the estimate of lipid-lipid interaction Gibbs energies between SM/Chol, SM/POPC, and Chol/POPC. The latter two interactions are weakly repulsive, but the interaction between SM and Chol is favorable. Furthermore, those three unlike lipid interaction parameters between the three possible lipid pairs are sufficient for the existence of a closed loop in the ternary phase diagram, without the need to involve multibody interactions. The calculations also indicate that the largest POPC domains contain several thousand lipids, corresponding to linear sizes of the order of a few hundred nanometers.