Dynamic molecular structure of DPPC-DLPC-cholesterol ternary lipid system by spin-label electron spin resonance
Dynamic molecular structure of DPPC-DLPC-cholesterol ternary lipid system by spin-label electron spin resonance
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DOI：
10.1529/biophysj.104.044438
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发表时间：
2004-10-01
影响因子：
3.4
通讯作者：
Freed, JH
中科院分区：
文献类型：
--
作者：
Chiang, YW;Shimoyama, Y;Freed, JH
二棕榈酰-PC/二月桂酰-PC/胆固醇（DPPC/DLPC/Chol）的水合三元层状脂质混合物已通过电子自旋共振（ESR）进行了研究，以揭示在几乎整个组合物范围内存在并共存的不同相的分子水平上的动态结构。通过非线性最小二乘拟合分析了100多种不同组分在室温下的光谱，以提供末端链标记的磷脂16-PC的旋转扩散速率和有序参数。尽管各个相通常彼此之间存在相当小的差异，但ESR谱随组成的变化而表现出显着的变化。L-alpha和L-beta相被清楚地区分开，前者表现出明显较低的有序性和较大的运动速率，而定义明确的L-o相表现出最大的有序性和相对较快的运动速率。通常，较小的变化发生在给定的相位内。ESR谱分析也产生相边界和共存区，这被认为是与以前的结果从荧光方法，虽然发现新的功能。相共存区在某些情况下，证实了通过观察存在的等吸光点的吸收模式ESR谱从相。富含DPPC的L-β相和富含DLPC的L-α相在其两相共存区域内的动态结构性质不随组成沿沿着联络线变化，但两相的比例遵循符合热力学原理的杠杆规则。分析表明，16-PC自旋标记物在L-alpha和L-beta相之间几乎相等，使其成为研究这种共存相的有用探针。两相共存区的广泛研究需要确定的联络线，这是近似在这项研究中。然而，建议的方法，以准确地确定连接线的ESR。
The hydrated ternary lamellar lipid mixture of dipalmitoyl-PC/dilauroyl-PC/cholesterol (DPPC/DLPC/Chol) has been studied by electron spin resonance (ESR) to reveal the dynamic structure on a molecular level of the different phases that exist and coexist over virtually the full range of composition. The spectra for more than 100 different compositions at room temperature were analyzed by nonlinear least-squares fitting to provide the rotational diffusion rates and order parameters of the end-chain labeled phospholipid 16-PC. The ESR spectra exhibit substantial variation as a function of composition, even though the respective phases generally differ rather modestly from each other. The L-alpha and L-beta phases are clearly distinguished, with the former exhibiting substantially lower ordering and greater motional rates, whereas the well-defined L-o phase exhibits the greatest ordering and relatively fast motional rates. Typically, smaller variations occur within a given phase. The ESR spectral analysis also yields phase boundaries and coexistence regions which are found to be consistent with previous results from fluorescence methods, although new features are found. Phase coexistence regions were in some cases confirmed by observing the existence of isosbestic points in the absorption mode ESR spectra from the phases. The dynamic structural properties of the DPPC-rich L-beta and DLPC-rich L-alpha phases, within their two-phase coexistence region do not change with composition along a tie-line, but the ratio of the two phases follows the lever rule in accordance with thermodynamic principles. The analysis shows that 16-PC spin-label partitions nearly equally between the L-alpha and L-beta phases, making it a useful probe for studying such coexisting phases. Extensive study of two-phase coexistence regions requires the determination of tie-lines, which were approximated in this study. However, a method is suggested to accurately determine the tie-lines by ESR.