Institute of Macromolecular Compounds , Russian Academy of Sciences , Bolshoi Prospect V.O. 31 , St. Petersburg 199004 Russia.
J Phys Chem B. 2019 Aug 1;123(30):6505-6514. doi: 10.1021/acs.jpcb.9b05110. Epub 2019 Jul 23.
The interactions of DNA/polycation complexes (polyplexes) with cell membranes are crucial for understanding the molecular mechanisms behind polycation-mediated delivery of nucleic acid therapeutics into the target cells. In this study, we employed both biased and unbiased atomic-scale computer simulations to get an insight into such interactions. To this end, we considered complexes of DNA with linear polyethylenimine (PEI) with various polycation contents, ranging from an almost fully neutralized DNA to a highly overcharged polyplex. Our findings clearly show that the free energy gradually increases when a polyplex approaches the surface of a zwitterionic (neutral) phospholipid membrane from bulk water, implying the lack of attractive polyplex/membrane interactions. Remarkably, overcharging of DNA molecules by polycations enhances the repulsion between the polyplex and the zwitterionic lipid membrane. The observed repulsion is most likely driven by the dehydration of a polyplex upon its partitioning into the zwitterionic lipid membrane as well as by the loss of conformational entropy of PEI chains. We also demonstrate that cationic polymer chains are able to protect DNA from the dehydration as well as from contacts with lipid molecules. Interestingly, the absence of local minima in the free energy profiles does not exclude transient weak adsorption of a polyplex on the zwitterionic membrane surface. We show that such spontaneous adsorption can indeed be initiated by the interactions of loose polycation chains of the polyplex with polar head groups of lipids. Overall, our computational findings contribute considerably to the understanding of the initial stages in polycation-mediated DNA transfection. In particular, we demonstrate that a zwitterionic lipid bilayer represents an energetic barrier for polyplexes, so that a proper model of the cell membrane should account for the anionic surface charge of the membrane (e.g., due to the presence of proteoglycans).
DNA/聚阳离子复合物（多聚物）与细胞膜的相互作用对于理解聚阳离子介导的核酸治疗药物进入靶细胞的分子机制至关重要。在这项研究中，我们采用了有偏见和无偏见的原子尺度计算机模拟来深入了解这些相互作用。为此，我们考虑了具有不同聚阳离子含量的 DNA 与线性聚乙烯亚胺 (PEI) 的复合物，范围从几乎完全中和的 DNA 到高度超荷的多聚物。我们的研究结果清楚地表明，当多聚物从本体水接近带电荷的（中性）磷脂膜表面时，自由能逐渐增加，这意味着多聚物/膜相互作用没有吸引力。值得注意的是，聚阳离子对 DNA 分子的过度荷电增强了多聚物与带电荷的脂质膜之间的排斥。观察到的排斥很可能是由多聚物在分配到带电荷的脂质膜时的脱水以及 PEI 链构象熵的损失所驱动的。我们还证明，阳离子聚合物链能够保护 DNA 免受脱水以及与脂质分子的接触。有趣的是，自由能分布中没有局部最小值并不排除多聚物在带电荷的膜表面上的瞬时弱吸附。我们表明，这种自发吸附确实可以通过多聚物松散的聚阳离子链与脂质的极性头基之间的相互作用来引发。总的来说，我们的计算结果对理解聚阳离子介导的 DNA 转染的初始阶段有很大的贡献。特别是，我们证明了带电荷的脂质双层代表了多聚物的能量障碍，因此细胞膜的适当模型应该考虑到膜的阴离子表面电荷（例如，由于存在糖胺聚糖）。
