2 D ELDOR: LIQUID ORDERED PHASE & LIPID MULTILAMELLAR VESICLE MEMBRANES

该子项目是利用NIH/NCRR资助的中心赠款提供的资源的许多研究子项目之一。子项目和研究者（PI）可能从另一个NIH来源获得了主要资金，因此可以在其他CRISP条目中表示。所列机构为中心，不一定是研究者所在机构。流体镶嵌模型对于理解生物膜的动力学行为具有重要作用。该模型假设膜蛋白在均匀的脂质介质（即二维液体）中扩散和/或波动。然而，最近对生物膜的研究表明，生理功能与脂膜中的异质环境密切相关。当一些物理化学刺激发生时，如与离子，蛋白质和甾醇的相互作用，然后非均相经常出现在生物膜中，产生微区，被称为脂筏。事实上，在脂质和胆固醇（Chol）的模型双层膜中，可以发现液体有序（Lo）相以及液体无序或液晶（Lc）相。我们已经开发了2D-ELDOR测量旋转扩散以及在脂质囊泡膜的平移扩散。我们的研究揭示了纯脂质（Lc）和脂质/胆固醇（Lo）膜中Lo和Lc相的动态结构，其中掺入了链标记的脂质、头基标记的脂质或自旋标记的胆甾烷CSL。在Lc相和Lo相的光谱中分别观察到光谱交叉峰的产生和湮灭。因此，目视检查2D-ELDOR光谱中的交叉峰提供了区分它们的方便方法。在Lo相中，酰基链比在Lc相中经历更快的旋转扩散和更高的有序性。另一方面，胆碱头基在Lo阶段表现出更快的运动和减少的排序相比，Lc阶段。此外，在Lo相中的平移扩散速率在Chol的存在下显著降低。因此，2D-ELDOR被证明是一个强大的方法来研究膜的动态结构。这项工作已经发表，广泛的研究作为胆固醇浓度的函数已经完成。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The fluid mosaic model played an important role for understanding the dynamic behavior in biomembranes. The model postulated that the membranous proteins are diffusing and/or fluctuating in a homogeneous lipid medium, i.e. two-dimensional liquid. However, recent studies on biomembranes have revealed that physiological function is firmly related to the heterogeneous environment in the lipid membranes. When some physico-chemical stimuli occur, such as interactions with ions, proteins, and sterols, then heterogeneous phases frequently appear in biomembranes, yielding microdomains, which have been termed lipid rafts. In fact, in model bilayer membranes of lipids and cholesterol (Chol), one can find liquid ordered (Lo) phases as well as liquid disordered or liquid crystalline (Lc) phases. We have developed 2D-ELDOR for measuring rotational diffusion as well as translational diffusion in lipid vesicle membranes. Our stud ies revealed the dynamic structures of the Lo and Lc phases in membranes of pure lipids (Lc) and lipid/Cholesterol (Lo), in which a chain labeled lipid a headgroup labeled lipid, or a spin labeled cholestane CSL was incorporated. Creation and annihilation of the spectral cross-peaks was observed in the spectra from Lc and from Lo phases respectively. Thus, visual inspection of cross peaks in the 2D-ELDOR spectra provides a convenient way to distinguish them. In the Lo phase, acyl chains undergo a faster rotational diffusion and higher ordering than in the Lc phase. On the other hand, the choline headgroup in the Lo phase exhibits faster motion and reduced ordering as compared to the Lc phase. Also, the translational diffusion rates in the Lo phase are significantly reduced in the presence of Chol. Thus 2D-ELDOR is demonstrated to be a powerful method to study the dynamic structure of membranes. This work has been published and extensive studies as a function of cholesterol concentration have been completed.