Róg Tomasz, Murzyn Krzysztof, Milhaud Jeannine, Karttunen Mikko, Pasenkiewicz-Gierula Marta
Department of Physics, Tampere University of Technology, Tampere, Finland.
J Phys Chem B. 2009 Feb 26;113(8):2378-87. doi: 10.1021/jp8048235.
Physicochemical properties of heavy water (D2O) differ to some extent from those of normal water. Substituting D2O for H2O has been shown to affect the structural and dynamic properties of proteins, but studies of its effects on lipid bilayers are scarce. In this paper, the atomic level molecular dynamics (MD) simulation method was used to determine the effects of this substitution on the properties of a dipalmitoylphosphatidylcholine (DPPC) bilayer and its hydrating water. MD simulations of two DPPC bilayers, one fully hydrated with H2O and the other with D2O, were carried out for over 50 ns. For H2O, the simple point charge (SPC) model was used, and for D2O, the extended SPC-HW model was employed. Analyses of the simulation trajectories indicate that several properties of the membrane core and the membrane/water interface are affected by replacing H2O by D2O. However, the time-averaged properties, such as membrane compactness, acyl chain order, and numbers of PC-water H (D)-bonds and PC-PC water bridges, are much less affected than time-resolved properties. In particular, the lifetimes of these interactions are much longer for D2O molecules than for H2O ones. These longer lifetimes results in a slightly better ordering of the D2O molecules and average self-diffusion, which is 50% slower compared with the H2O molecules. This large isotope effect has been assigned to the repercussions of the longer lived D-bonding to DPPC headgroups insofar as all water molecules sense the presence of the DPPC bilayer.
重水（D₂O）的物理化学性质在一定程度上与普通水不同。用D₂O替代H₂O已被证明会影响蛋白质的结构和动力学性质，但关于其对脂质双层影响的研究却很少。本文采用原子水平的分子动力学（MD）模拟方法来确定这种替代对二棕榈酰磷脂酰胆碱（DPPC）双层及其水化水性质的影响。对两个DPPC双层进行了超过50纳秒的MD模拟，一个用H₂O完全水化，另一个用D₂O完全水化。对于H₂O，使用简单点电荷（SPC）模型，对于D₂O，采用扩展的SPC - HW模型。对模拟轨迹的分析表明，膜核心和膜/水界面的几个性质会受到用D₂O替代H₂O的影响。然而，时间平均性质，如膜的紧密程度、酰基链有序度以及PC - 水H（D）键和PC - PC水桥的数量，受影响程度远小于时间分辨性质。特别是，这些相互作用的寿命对于D₂O分子来说比对H₂O分子长得多。这些更长的寿命导致D₂O分子的有序性略好，平均自扩散速度与H₂O分子相比慢50%。这种大的同位素效应归因于寿命更长的D键与DPPC头部基团的相互作用的影响，因为所有水分子都能感知到DPPC双层的存在。
