Probing the molecular structure of water at the interface with the HGB and RG-II polysaccharide

1. 目的和目的我们的目的是在室温和过冷条件下，探测与多糖RG-II（在果胶中发现）和均半乳糖酸HGB（形成RG-II的骨架）界面处的水的分子结构。我们希望这项工作将阐明这些多糖是否具有抑制或促进冰形成的功能。我们在达勒姆大学和利兹大学的实验合作者的初步结果已经表明RG-II是一种潜在的冰再结晶抑制剂。我们希望解决的一个关键问题是，这些分子需要具备什么样的结构特征才能与冰结合。目前，围绕主要的冰结合蛋白和糖蛋白的冰结合机制存在很多争论[1,2]。各种研究发现了不同的机制，从分子与生长中的冰晶的直接氢键，到通过笼形水的排列与冰晶界面融合的间接结合[3,4,5].2。这是一个计算项目，与威克大学以及达勒姆和利兹大学的实验员合作。我们正在使用经典分子动力学（MD）来模拟多糖，并结合改进的采样方法，如基于自由能计算的元动力学[6]。3. 了解冰在生物物质中的形成是进一步研究低温保存技术的关键。在低温保存技术中，防止冰重结晶比增加抗冻性更重要，因为大多数损害发生在生物分子的解冻阶段，细胞外基质中的小冰晶最容易受到再结晶的影响。在我们的工作中，我们将研究多糖作为潜在IRIs的可能性。这是有充分理由的，这些分子没有像它们的蛋白质对应物那样被广泛研究。多糖往往更不易降解和变性，生产成本更低，体积更小。我们预计，我们的工作将进一步深入了解冷冻保存技术，这反过来又对提供下一代医学治疗至关重要，如再生和转化医学。

1. Aims and ObjectivesWe aim to probe the molecular structure of water at the interface with the polysaccharides RG-II (found within pectin) and homogalacturonan, HGB, (which forms the backbone of RG-II) both at room tem- perature and supercooling. We hope this work will shed light on whether these polysaccharides have the functionality to either inhibit or promote the formation of ice. Tentative results from our experimental collaborators at the University of Durham and Leeds have already marked RG-II to be a potential Ice Recrystallisation Inhibitor. One of the key questions we wish to address is what structural features need to be available for these molecules to bind with ice. At present there is much debate surrounding the ice-binding mechanisms of predominantly ice-binding proteins and glycoproteins [1, 2]. Various studies have found different mechanisms which can range from direct hydrogen bonding of a molecule to a growing ice crystal, to indirect binding via the arrangement of clathrate waters which fuse to the ice crystal interface [3, 4, 5].2. MethodologyThis is a computational project, in collaboration with experimentalists both at the University of War- wick as well as Durham and Leeds. We are using classical molecular dynamics (MD) to simulate the polysaccharides, in conjunction with enhanced sampling methods such a metadynamics based on free-energy calculations [6]. 3. ContextUnderstanding the formation of ice in biological matter is key to furthering cryopreservation technologies. Preventing ice recrystallisation over increasing freezing resistance is particularly preferable in cryopreservation techniques, as most damage arises during the thawing stages of the biomolecules where the small ice crystals in the extracellular matrix are most susceptible to recrystallisation [7]. In our work we will look at the possibility of polysaccharides acting as potential IRIs. There is good reason for this, these molecules have not been as widely studied as their protein counterparts. Polysaccharides tend to be more resistant to degradation and denaturation, cheaper to produce as well as being smaller. We anticipate that our work will add further insights to the cryopreservation techniques which in turn are essential to deliver the next generation of medical treatments such a regenerative and translational medicine.