Pan Jianjun, Cheng Xiaolin, Monticelli Luca, Heberle Frederick A, Kučerka Norbert, Tieleman D Peter, Katsaras John
Department of Physics, University of South Florida, Tampa, FL 33620, USA.
Soft Matter. 2014 Jun 7;10(21):3716-25. doi: 10.1039/c4sm00066h. Epub 2014 Feb 18.
Phosphatidylserine (PS) lipids play essential roles in biological processes, including enzyme activation and apoptosis. We report on the molecular structure and atomic scale interactions of a fluid bilayer composed of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylserine (POPS). A scattering density profile model, aided by molecular dynamics (MD) simulations, was developed to jointly refine different contrast small-angle neutron and X-ray scattering data, which yielded a lipid area of 62.7 Å(2) at 25 °C. MD simulations with POPS lipid area constrained at different values were also performed using all-atom and aliphatic united-atom models. The optimal simulated bilayer was obtained using a model-free comparison approach. Examination of the simulated bilayer, which agrees best with the experimental scattering data, reveals a preferential interaction between Na(+) ions and the terminal serine and phosphate moieties. Long-range inter-lipid interactions were identified, primarily between the positively charged ammonium, and the negatively charged carboxylic and phosphate oxygens. The area compressibility modulus KA of the POPS bilayer was derived by quantifying lipid area as a function of surface tension from area-constrained MD simulations. It was found that POPS bilayers possess a much larger KA than that of neutral phosphatidylcholine lipid bilayers. We propose that the unique molecular features of POPS bilayers may play an important role in certain physiological functions.
磷脂酰丝氨酸（PS）脂质在生物过程中发挥着重要作用，包括酶激活和细胞凋亡。我们报道了由1-棕榈酰-2-油酰-sn-甘油-3-磷脂酰丝氨酸（POPS）组成的流体双层的分子结构和原子尺度相互作用。借助分子动力学（MD）模拟，开发了一种散射密度分布模型，以联合优化不同对比度的小角中子和X射线散射数据，在25°C时得到脂质面积为62.7 Ų。还使用全原子模型和脂肪族联合原子模型对POPS脂质面积限制在不同值的MD模拟进行了研究。使用无模型比较方法获得了最佳模拟双层。对与实验散射数据最吻合的模拟双层进行检查，发现Na⁺离子与末端丝氨酸和磷酸基团之间存在优先相互作用。确定了长程脂质间相互作用，主要存在于带正电荷的铵与带负电荷的羧基和磷酸氧之间。通过将脂质面积量化为面积受限MD模拟中表面张力的函数，得出了POPS双层的面积压缩模量KA。发现POPS双层的KA比中性磷脂酰胆碱脂质双层的KA大得多。我们认为POPS双层独特的分子特征可能在某些生理功能中起重要作用。
