School of Chemical Sciences, Indian Association for the Cultivation of Science, Jadavpur, Kolkata-700032, India.
Phys Chem Chem Phys. 2019 Sep 21;21(35):19298-19310. doi: 10.1039/c9cp03135a. Epub 2019 Aug 27.
The ice/water interface recognition mechanism of antifreeze proteins (AFPs) is highly contentious. Conventionally, protein adsorption on a solid surface is primarily driven by the polar interactions between the hydrophilic residues of the protein and interfacial water of the solid surface. Ice surface recognition by a type III AFP is surprising in this context where the ice binding surface (IBS) is hydrophobic. The present study provides molecular insight into the unusual interface recognition phenomenon of a type III AFP (QAE isoform) from Macrozoarces americanus. Potential of mean force calculations show that the type III AFP adsorbs on the ice surface mediated through a layer of ordered water. Molecular dynamics simulations at lower than ambient temperature reveal that the flat hydrophobic IBS induces ordering of water. The excellent geometrical synergy between the hydration water structure around the IBS and water arrangements on the pyramidal surface favours adsorption on the pyramidal plane. Mutations that interrupt the hydration shell water ordering essentially lead to less efficient adsorption, which greatly reduces the anti-freezing activity of the AFP. Binding free energy calculations of the wild-type and several mutant AFPs reveal that the binding affinity is linearly correlated with the experimentally observed thermal hysteresis activity. Therefore, binding to a specific ice plane with considerable affinity is the dictating factor of the anti-freeze activity for a type III AFP. Mechanistic insights into the ice binding process of the wild-type and different mutant AFPs obtained from this study pave the way for rational design of type III variants with much improved activity, which possesses ample industrial applicability, particularly in cryo-preservation.
抗冻蛋白（AFPs）的冰/水界面识别机制存在很大争议。传统上，蛋白质在固体表面的吸附主要是由蛋白质的亲水残基与固体表面的界面水之间的极性相互作用驱动的。在这种情况下，III 型 AFP 对冰表面的识别令人惊讶，因为冰结合表面（IBS）是疏水的。本研究提供了分子层面的深入了解，揭示了来自美洲鱒鱼的 III 型 AFP（QAE 同工型）的不寻常界面识别现象。平均力势能计算表明，III 型 AFP 通过一层有序水吸附在冰表面上。低于环境温度的分子动力学模拟表明，平坦的疏水 IBS 诱导水的有序排列。IBS 周围水合结构与金字塔表面上水排列之间的优异几何协同作用有利于在金字塔平面上的吸附。中断水合壳水有序性的突变基本上会导致吸附效率降低，从而大大降低 AFP 的抗冻活性。野生型和几种突变 AFP 的结合自由能计算表明，结合亲和力与实验观察到的热滞活性呈线性相关。因此，与特定冰面具有相当亲和力的结合是 III 型 AFP 抗冻活性的决定因素。本研究获得的关于野生型和不同突变 AFP 冰结合过程的机制见解为具有更高活性的 III 型变体的合理设计铺平了道路，这在低温保存等领域具有广泛的工业应用潜力。
