壳聚糖与细菌细胞膜相互作用的分子动力学研究

Molecular Dynamics Simulations of The Interaction Between Chitosan and Bacterial Membranes

目的壳聚糖(chitosan,CS)是一种天然的广谱抗菌活性物质。现有研究表明,壳聚糖与细菌细胞膜的相互作用是其发挥抗菌功能的关键。受限于传统实验技术的表征能力,壳聚糖与细菌细胞膜相互作用的具体机制仍有待研究。本文旨在研究壳聚糖与细菌细胞膜相互作用的分子机制。方法本研究利用全原子分子动力学模拟技术主要探究了完全脱乙酰化的不同聚合度壳聚糖(八聚糖、十二聚糖和十六聚糖)与革兰氏阴性菌外膜(outer membrane,OM)和革兰氏阳性菌质膜(cytoplasmic membrane,CM)相互作用的动态过程。结果壳聚糖主要依靠其氨基、碳6位羟基和碳3位羟基与OM和CM的头部极性区发生快速结合。随后壳聚糖末端糖基单元倾向于插入OM内部,深度约1 nm,并与脂质分子脂肪酸链上的羰基形成稳定的氢键相互作用。与之相比,壳聚糖分子难以稳定地插入CM内部。壳聚糖结合对膜结构性质产生影响,主要表现在降低OM和CM的单分子脂质面积,显著减少OM和CM极性区的Ca2+和Na+数目,破坏阳离子介导的脂质间相互作用。结论本研究证明,壳聚糖带正电的氨基基团是介导其与膜相互作用的关键,并破环脂质间的相互作用,降低细菌膜结构稳定性。这些结果为从原子水平上理解壳聚糖的抗菌机制提供了新的见解。

Objective Chitosan(CS)is a natural broad-spectrum antibacterial active substance.Previous studies revealed that the interaction between chitosan and bacterial cell membrane play a key role in its antibacterial activity.However,Due to the limited characterizing capability of current experimental techniques,the exact mechanism of the interaction between chitosan and bacterial cell membranes remains to be studied.This paper aims to study the molecular mechanism of the interaction between chitosan and bacterial cell membranes.Methods In this study,all-atom molecular dynamics simulations were used to explore the dynamic interaction between totally deacetylated chitosan in different degrees of polymerization(8-,12-,and 16-saccharides)with the outer membrane(OM)of Gram-negative bacteria and the cytoplasmic membrane(CM)of Gram-positive bacteria.Results The amino groups,carbon 6 hydroxyl groups and carbon 3 hydroxyl groups of chitosan play the determinant role in the initial attachment to the polar headgroup regions of the OM and CM.Interestingly,the terminal glycosyl units of chitosan inserted into the OM with an averaged depth of 1 nm where the sugar formed stable hydrogen bonds with the carbonyl groups on the fatty acid tails of the OM lipid A molecules.In contrast,chitosan could not insert into the CM steadily.Further,we found that the binding of chitosan to both OM and CM reduced their area per lipid,displacing the Ca2+and Na+from the headgroup regions of the membranes and thereby attenuating the cation-mediated interactions between membrane lipids.Conclusion Our results demonstrated that the positively charged amino groups of chitosan are essential for the interaction with bacterial membranes,which reduced the interlipid interactions and lead to the structural disorganization of bacterial membranes.These information provides new insights into the antimicrobial mechanism of chitosan at the atomic level.