Department of Chemical and Biomolecular Engineering, University of Maryland, College Park, Maryland; Engineering Physics Division, National Institute of Standards and Technology, Gaithersburg, Maryland.
Engineering Physics Division, National Institute of Standards and Technology, Gaithersburg, Maryland.
Biophys J. 2018 Nov 6;115(9):1720-1730. doi: 10.1016/j.bpj.2018.09.009. Epub 2018 Sep 18.
Molecular dynamics simulations were performed to describe the function of the ion-channel-forming toxin α-hemolysin (αHL) in lipid membranes that were composed of either 1,2-diphytanoyl-sn-glycero-3-phospho-choline or 1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-choline. The simulations highlight the importance of lipid type in maintaining αHL structure and function, enabling direct comparison to experiments for biosensing applications. We determined that although the two lipids studied are similar in structure, 1,2-diphytanoyl-sn-glycero-3-phospho-choline membranes better match the hydrophobic thickness of αHL compared to 1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-choline membranes. This hydrophobic match is essential to maintaining proper alignment of β-sheet loops at the trans entrance of αHL, which, when disrupted, creates an additional constriction to ion flow that decreases the channel current below experimental values and creates greater variability in channel conductance. Agreement with experiments was further improved with sufficient lipid membrane equilibration and allowed the discrimination of subtle αHL conduction states with lipid type. Finally, we explore the effects of truncating the extramembrane cap of αHL and its role in maintaining proper alignment of αHL in the membrane and channel conductance. Our results demonstrate the essential role of lipid type and lipid-protein interactions in simulations of αHL and will considerably improve the interpretation of experimental data.
采用分子动力学模拟的方法，研究了由 1,2-二植烷酰基-sn-甘油-3-磷酸胆碱或 1-棕榈酰基-2-油酰基-sn-甘油-3-磷酸胆碱组成的脂质膜中离子通道形成毒素 α-溶血素（αHL）的功能。模拟结果突出了脂质类型在维持αHL 结构和功能方面的重要性，使我们能够直接将模拟结果与用于生物传感应用的实验进行比较。我们确定，尽管所研究的两种脂质在结构上相似，但与 1-棕榈酰基-2-油酰基-sn-甘油-3-磷酸胆碱膜相比，1,2-二植烷酰基-sn-甘油-3-磷酸胆碱膜更能匹配αHL 的疏水性厚度。这种疏水性匹配对于维持αHL 跨膜入口处β-折叠环的正确排列至关重要，因为这种排列的破坏会在离子流中产生额外的限制，从而使通道电流降低到实验值以下，并使通道电导的变化更大。通过足够的脂质膜平衡，模拟结果与实验进一步吻合，允许根据脂质类型区分细微的αHL 传导状态。最后，我们探讨了截断αHL 跨膜帽的影响及其在维持αHL 在膜中的正确排列和通道电导方面的作用。我们的结果表明，在αHL 的模拟中，脂质类型和脂质-蛋白相互作用起着至关重要的作用，这将极大地改善对实验数据的解释。
