THE LIMITING BEHAVIOR OF WATER HYDRATING A PHOSPHOLIPID MONOLAYER - A COMPUTER-SIMULATION STUDY
THE LIMITING BEHAVIOR OF WATER HYDRATING A PHOSPHOLIPID MONOLAYER - A COMPUTER-SIMULATION STUDY
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DOI：
10.1063/1.465947
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发表时间：
1993-10-01
影响因子：
4.4
通讯作者：
STOUCH, TR
中科院分区：
文献类型：
--
作者：
ALPER, HE;BASSOLINOKLIMAS, D;STOUCH, TR
我们报道了在消除模拟伪影的条件下，水水合脂质(二肉豆蔻基磷脂酰胆碱)单分子层的分子动力学模拟。这些模拟提供了膜-水界面行为的描述，与最近的实验研究一致。特别是，我们发现水合水的取向是将其偶极的正端贡献给膜内部基本上为正的静电势，这与最近的实验解释是一致的。此外，最近的实验表明，这种水在核磁共振时间尺度上迅速重新定向。我们的结果是一致的，然而相对快速的水运动并不排除我们观察到的优先有序化。该体系的极限行为表现为脂质PC头基周围的三个水化壳层和水与磷酸基团的显著氢键。胆碱组经历不同的环境，第一水合壳的结构明显对应于笼状结构。水合水的运动速度慢于原水，计算的水在脂类中的停留时间(胆碱为20ps，磷酸盐为10ps)与核磁共振实验结果吻合较好。这进一步表明，水在笼状壳层中的停留时间比离子在壳层中的停留时间更长。此外，我们还发现，水合脂质的结构和动力学对长程相互作用的处理非常敏感。特别是，径向结构明显变得尖锐，只有在较大的截止点下才能观察到磷酸盐周围的第三个水合壳，水与脂类的氢键增加了25%。当使用大截止线时，水的移动速度比散装水慢，但当使用小截止线时，水的移动速度比散装水快，而使用大截止线时，脂类周围的水的停留时间是普通水的两倍-五倍。总体而言，人们发现，脂类显著影响水流出到几个水化壳中，而使脂类水合的水的行为与散装水不同。
We report molecular dynamics simulations of water hydrating a lipid (dimyristoylphosphatidylcholine) monolayer under conditions chosen to eliminate simulation artifacts. These simulations provide a description of the behavior of the membrane-water interface that agrees with recent experimental studies. In particular, we find that the hydrating water orients to contribute the positive end of its dipole to the substantially positive electrostatic potential of the membrane interior, consistent with interpretations of recent experiments. In addition, recent experiments show that this water reorients rapidly on the NMR time scale. Our results concur, however the relatively rapid water motion does not preclude the preferential ordering that we observe. The limiting behavior of the system shows three hydration shells about the lipid PC headgroups and significant hydrogen bonding of water to the phosphate groups. The choline group experiences different environments, and the structure of the first hydration shell clearly corresponds to a clathrate. The motion of the hydrating water was found to be slower than that of bulk water, and the computed residence times for water about the lipids (20 ps about choline, 10 ps about phosphate) were in excellent agreement with results of NMR experiments. This further shows that water resides in a clathrate shell longer than in a shell about ions. In addition, we show that the structure and dynamics of water hydrating the lipids are very sensitive to the treatment of the long-range interactions. In particular, the radial structure sharpens considerably, a third hydration shell about the phosphate was observed only with large cutoffs, and hydrogen bonding of water to the lipids increased by 25%. The water moved more slowly than bulk when large cutoffs were employed but moved faster than bulk water when small cutoffs were used and the residence times for water about the lipids were twofold-fivefold larger using large cutoffs. In general it was found that the lipids significantly influence water out to several hydration shells, and that water hydrating the lipids behaves differently than bulk water.