The Role of Sugars for Protein Stabilization

Abstract: The understanding of biomolecular interactions with water and co-solutes can lead to greater knowledge regarding the mechanisms behind biomolecular stabilization. This is highly important for developing technologies aimed to preserve biological materials. Such techniques include cryopreservation of pharmaceuticals or human organ transplants, for example. For these purposes, the disaccharide trehalose has been shown to be an outstanding biomolecular stabilizing agent during cryostorage or storage of desiccated materials. In this thesis, the questions regarding the stabilizing role of trehalose is addressed from several different angles. Structural properties of trehalose in water are studied and are compared to those of a similar sugar molecule, namely sucrose. From these studies it was concluded that there were surprisingly small differences between the interactions of trehalose or sucrose with water. The thermodynamic properties of trehalose--water--protein systems were investigated using DSC, where it was indirectly found that the protein hydration shell was not substituted by trehalose, and that the protein stability did not necessarily couple to the glass transition temperature of the trehalose--protein--water-matrix. The structure and dynamics of such a ternary trehalose--water--protein system was also investigated using neutron diffraction combined with EPSR, and QENS combined with an MD simulation. In these studies, it was primarily found that the trehalose molecules were preferentially excluded from the protein surface, and that the local motions of the protein residues were slowed down via a reduction in the motion of the water molecules at the protein surface. Furthermore, the temperature dependences of relaxation dynamics in this system were measured using dielectric spectroscopy. This study showed that the presence of protein hinder certain local trehalose motions, and that the relatively slow dynamics of the trehalose solvent governs the conformational motions of the protein. The presented results elucidates some fundamental properties of how proteins and trehalose behave and interact, which may benefit the development of new biomolecular protective co-solutes.