Zhu Qing, Vaughn Mark W
Department of Chemical Engineering, P.O. Box 43121, Texas Tech University, Lubbock, Texas 79409-3121, USA.
J Phys Chem B. 2005 Oct 20;109(41):19474-83. doi: 10.1021/jp051419k.
The effect of surface tension on the lipid bilayer membrane is a question that has drawn considerable research effort. This interest has been driven both by the desire to determine the surface tension effects on the lipid bilayer and from the suggestion that adding finite surface tension to a small membrane system may provide more realistic lipid properties in molecular dynamics simulations. Here, the effect of surface tension on a palmitololelylphosphatidylcholine (POPC) bilayer membrane containing a four-helix transmembrane alamethicin peptide bundle is investigated. Simulations of 10 ns were undertaken for two different ensembles, NPT and NP(z)gammaT with a surface tension, gamma, of 20 mN m(-1) per interface, which is near the pore-forming region. The significance of differences between the tension-free and surface tension simulations was determined using nonparametric statistical analysis on replicate simulations with different initial conditions. The results suggest that, when the membrane is under surface tension, the peptide helical structure is perturbed from that in the tension-free state but that the bundle conformation is more stable than that in the tension-free state, with hydrogen bonding playing an important stabilizing role. Surface tension counteracts the influence of the transmembrane helix bundle on nearby lipid order, making the lipid order more uniform throughout the membrane in the tension state. Conversely, the lipid mobility was less uniform in the tension state, with lipids far from the bundle being significantly more mobile than those near the bundle. One general implication of the results is that surface tension can affect the membrane nonuniformly, in that the properties of lipids near the peptide are different from those further away.
表面张力对脂质双分子层膜的影响是一个吸引了大量研究精力的问题。这种兴趣既源于确定表面张力对脂质双分子层影响的愿望，也源于这样一种观点，即在分子动力学模拟中给小的膜系统添加有限的表面张力可能会提供更现实的脂质特性。在此，研究了表面张力对含有四螺旋跨膜丙甲菌素肽束的棕榈油酰磷脂酰胆碱（POPC）双分子层膜的影响。针对两种不同的系综进行了10纳秒的模拟，即NPT和NP(z)γT，每个界面的表面张力γ为20 mN m⁻¹，这接近成孔区域。使用对具有不同初始条件的重复模拟进行的非参数统计分析来确定无张力模拟和表面张力模拟之间差异的显著性。结果表明，当膜处于表面张力作用下时，肽的螺旋结构相对于无张力状态会受到扰动，但束状构象比无张力状态下更稳定，氢键起着重要的稳定作用。表面张力抵消了跨膜螺旋束对附近脂质有序性的影响，使得在张力状态下整个膜中的脂质有序性更加均匀。相反，在张力状态下脂质流动性不太均匀，远离束的脂质比靠近束的脂质流动性明显更高。这些结果的一个普遍含义是，表面张力可以非均匀地影响膜，因为肽附近的脂质性质与较远区域的脂质性质不同。
