Hybrid Materials Interfaces Group, Faculty Production Engineering, Bremen Center for Computational Materials Science, University of Bremen, Am Fallturm 1, 28359 Bremen, Germany.
Phys Chem Chem Phys. 2018 Jul 25;20(29):19595-19605. doi: 10.1039/c8cp03747g.
The force spectra of proteins detaching from oxide surfaces measured by atomic force microscopy (AFM) often present complex patterns of peaks, which are difficult to correlate with individual bond-breaking events at the atomic scale. In this work we rationalize experimental AFM force spectra of hen-egg-white lysozyme detaching from silica by means of all-atom steered molecular dynamics (SMD) simulations. In particular, we demonstrate that the native tertiary structure of lysozyme is preserved if, and only if, its four intramolecular disulfide bridges are intact. Otherwise, the protein pulled off the surface undergoes severe unfolding, which is well captured by SMD simulations in explicit solvent. Implicit solvent simulations, on the contrary, wrongly predict protein unfolding even in the presence of S-S bridges, due to the lack of additional structural stabilization provided by the water's hydrogen-bond network within and surrounding the protein. On the basis of our combined experimental and theoretical findings, we infer that the rugged force spectra characteristic of lysozyme/silica interfaces are not due to the successive breaking of internal disulfide bonds leading to partial unfolding events. Rather, they reflect the detachment of several molecules bound to the same AFM tip, each anchored to the surface via multiple hydrogen and ionic bonds.
原子力显微镜（AFM）测量的蛋白质从氧化物表面脱离的力谱通常呈现出复杂的峰型模式，难以与原子尺度上的单个键断裂事件相关联。在这项工作中，我们通过全原子导向分子动力学（SMD）模拟，对从二氧化硅上脱离的鸡卵清溶菌酶的实验 AFM 力谱进行了合理化解释。具体来说，如果且仅如果溶菌酶的四个分子内二硫键完整，那么其天然三级结构就可以得到保留。否则，从表面拉起的蛋白质会经历严重的展开，这在明确溶剂中的 SMD 模拟中得到了很好的捕捉。相反，由于缺乏蛋白质内部和周围水分子氢键网络提供的额外结构稳定性，隐式溶剂模拟甚至在存在 S-S 键的情况下也会错误地预测蛋白质展开。基于我们的实验和理论综合研究结果，我们推断溶菌酶/二氧化硅界面的崎岖力谱特征不是由于连续打破内部二硫键导致部分展开事件。相反，它们反映了多个分子与同一 AFM 尖端的脱离，每个分子通过多个氢键和离子键固定在表面上。
