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

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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.