Department of Biophysics, Institute of Physics, Maria Curie-Sklodowska University, 20-031, Lublin, Poland.
Department of Physical Chemistry, Gdansk University of Technology, Narutowicza 11/12, 80-233, Gdansk, Poland.
Sci Rep. 2017 Aug 29;7(1):9619. doi: 10.1038/s41598-017-10183-7.
Xanthophylls (polar carotenoids) play diverse biological roles, among which are modulation of the physical properties of lipid membranes and protection of biomembranes against oxidative damage. Molecular mechanisms underlying these functions are intimately related to the localization and orientation of xanthophyll molecules in lipid membranes. In the present work, we address the problem of localization and orientation of two xanthophylls present in the photosynthetic apparatus of plants and in the retina of the human eye, zeaxanthin and lutein, in a single lipid bilayer membrane formed with dimyristoylphosphatidylcholine. By using fluorescence microscopic analysis and Raman imaging of giant unilamellar vesicles, as well as molecular dynamics simulations, we show that lutein and zeaxanthin adopt a very similar transmembrane orientation within a lipid membrane. In experimental and computational approach, the average tilt angle of xanthophylls relative to the membrane normal is independently found to be ~40 deg, and results from hydrophobic mismatch between the membrane thickness and the distance between the terminal hydroxyl groups of the xanthophylls. Consequences of such a localization and orientation for biological activity of xanthophylls are discussed.
叶黄素（极性类胡萝卜素）具有多种生物学功能，包括调节脂质膜的物理性质和保护生物膜免受氧化损伤。这些功能的分子机制与叶黄素分子在脂质膜中的定位和取向密切相关。在本工作中，我们研究了植物光合作用器和人眼视网膜中两种叶黄素（玉米黄质和叶黄素）在由二肉豆蔻酰磷脂酰胆碱形成的单层脂质膜中的定位和取向问题。通过使用荧光显微镜分析和巨单层囊泡的拉曼成像以及分子动力学模拟，我们表明叶黄素和玉米黄质在脂质膜内具有非常相似的跨膜取向。在实验和计算方法中，我们独立地发现叶黄素相对于膜法线的平均倾斜角度约为 40°，这是由膜厚度与叶黄素末端羟基之间的距离不匹配引起的。讨论了这种定位和取向对叶黄素生物活性的影响。
