Fluorescence Studies Of Biophysical Properties Of Polyun

神经元和视网膜组织的膜富含含有一个或两个长链多不饱和酰基链的磷脂。二十二碳六烯酸（简称DHA或22:6n-3）是这些组织中主要的多不饱和酰基链。本研究旨在确定多不饱和磷脂（特别是含有22:6n-3酰基链的磷脂）调节G蛋白偶联受体信号的分子基础。研究还集中在这些磷脂对急性暴露于乙醇的反应。荧光能量转移（FRET）研究表明，在含有di16:0PC和di22:6 PC加胆固醇的双分子层中，横向结构域的形成依赖于胆固醇和视紫红质的存在。通过开发一种新的技术来确定胆固醇在各种脂质双分子层中的分配系数，阐明了胆固醇的作用。结果表明，胆固醇在含有DHA侧链的脂质中分配系数最低，在饱和酰基链脂质中分配系数最高。因此，横向结构域的形成可能是由胆固醇与di16:0PC酰基链的相互作用以及视紫红质与di22:6PC的优先相互作用驱动的。分配研究的一个有趣的结果是，胆固醇在更大程度上分裂成含有反式脂肪酸的脂质双层，而不是顺式脂肪酸。反式脂肪酸在血管内皮膜脂中的掺入会导致胆固醇水平升高，这可能有助于动脉粥样硬化斑块的形成。在对照大鼠和n-3缺陷大鼠的棒外段盘膜的研究中，我们已经证明了磷脂酰基链填充特性的差异，这是由n-6酰基链DPA （22:5n-6）取代n-3 DHA酰基链造成的。这两个侧链只有一个单双键的区别，但这种取代被发现对G蛋白偶联信号在视觉转导途径中的功效有显著的功能影响。在这里进行的研究对于理解脂质组成，特别是22:6n-3酰基链在结构域形成、膜蛋白功能的调节、细胞膜中胆固醇的不均匀分布以及与多不饱和脂肪酸和反式脂肪酸相关的健康益处和缺陷的作用具有重要意义。

The membranes of neuronal and retinal tissue are high in phospholipids containing one or two long chain polyunsaturated acyl chains. Docosahexaenoic acid (abbreviated DHA or 22:6n-3) is the major polyunsaturated acyl chain in these tissues. This study is directed towards determining a molecular basis for the modulation of G protein-coupled receptor signaling by polyunsaturated phospholipids, in particular those containing 22:6n-3 acyl chains. Studies are also focused on the response of these phospholipids to the acute exposure to ethanol. Fluorescence Energy Transfer (FRET) studies have demonstrated lateral domain formation in bilayers containing di16:0PC and di22:6 PC plus cholesterol, which was dependent on the presence of both cholesterol and rhodopsin. The role of cholesterol was clarified by developing a new technique to determine the partition coefficient for cholesterol in various lipid bilayers. The results demonstrate that cholesterol has the lowest partition coefficient in lipids containing DHA side chains and the highest partitioning in saturated acyl chain lipids. Therefore, lateral domain formation is likely driven by the interaction of cholesterol with the di16:0PC acyl chains and the preferential interaction of rhodopsin with the di22:6PC. An interesting result of the partitioning studies is that cholesterol partitions to a much greater degree into lipid bilayers containing trans fatty acids than cis fatty acids. Incorporation of trans fatty acids in the membrane lipids of the endothelial lining of blood vessels would result in higher cholesterol levels, which may well contribute to the formation of atherosclerotic plaques. In studies of the rod outer segment disk membrane derived from control and n-3 deficient rats, we have demonstrated differences in the phospholipid acyl chain packing properties that result from the substitution of DPA, 22:5n-6, an n-6 acyl chain for the n-3 DHA acyl chain. These two side chains differ by only a single double bond, yet the substitution was found to have marked functional consequences for the efficacy of G protein-coupled signaling in the visual transduction pathway. The studies carried out here are important in developing an understanding the role lipid composition in general and 22:6n-3 acyl chains in particular, in domain formation, the modulation of membrane protein function, the heterogeneous distribution of cholesterol in cell membranes, and the health benefits and deficits associated with polyunsaturated fatty acids and trans fatty acids, respectively.