Tu K, Tobias D J, Blasie J K, Klein M L
Department of Chemistry, University of Pennsylvania, Philadelphia 19104-6323, USA.
Biophys J. 1996 Feb;70(2):595-608. doi: 10.1016/S0006-3495(96)79623-6.
We report the results of a constant pressure and temperature molecular dynamics simulation of a gel-phase dipalmitoylphosphatidylcholine bilayer with nw = 11.8 water molecules/lipid at 19 degrees C. The results of the simulation were compared in detail with a variety of x-ray and neutron diffraction data. The average positions of specific carbon atoms along the bilayer normal and the interlamellar spacing and electron density profile were in very good agreement with neutron and x-ray diffraction results. The area per lipid and the details of the in-plane hydrocarbon chain structure were in excellent agreement with wide-angle x-ray diffraction results. The only significant deviation is that the chains met in a pleated arrangement at the bilayer center, although they should be parallel. Novel discoveries made in the present work include the observation of a bimodal headgroup orientational distribution. Furthermore, we found that there are a significant number of gauche conformations near the ends of the hydrocarbon chains and, in addition to verifying a previous suggestion that there is partial rotational ordering in the hydrocarbon chains, that the two chains in a given molecule are inequivalent with respect to rotations. Finally, we have investigated the lipid/water interface and found that the water penetrates beneath the headgroups, but not as far as the carbonyl groups, that the phosphates are strongly hydrated almost exclusively at the nonesterified oxygen atoms, and that the hydration of the ammonium groups is more diffuse, with some water molecules concentrated in the grooves between the methyl groups.
我们报告了在19摄氏度下，每脂质含11.8个水分子的凝胶相二棕榈酰磷脂酰胆碱双层的恒压和恒温分子动力学模拟结果。模拟结果与各种X射线和中子衍射数据进行了详细比较。特定碳原子沿双层法线的平均位置、层间距和电子密度分布与中子和X射线衍射结果非常吻合。每个脂质的面积和平面内烃链结构的细节与广角X射线衍射结果高度一致。唯一显著的偏差是，尽管烃链在双层中心应是平行的，但它们以褶皱排列相遇。本工作中的新发现包括观察到双峰头基取向分布。此外，我们发现烃链末端附近有大量的gauche构象，并且除了证实之前关于烃链中存在部分旋转有序的建议外，给定分子中的两条链在旋转方面是不等价的。最后，我们研究了脂质/水界面，发现水渗透到头基下方，但未到达羰基，磷酸盐几乎仅在非酯化氧原子处强烈水合，铵基的水合更分散，一些水分子集中在甲基之间的凹槽中。
