Housing Aquaporins in Nanostructured Glass

Abstract: Proteins are a group of biomolecules that perform versatile tasks, which in many cases are essential for life. The magnitude of their importance is perhaps expressed by the word protein itself, coined by the Swedish chemist Jöns Jacob Berzelius in the summer of 1838. It is derived from the Greek word πρωτείος which means ‘primary’ or ‘of the highest importance’. By adding a different ending, Berzelius shaped the word protein which means ‘the most important building block in a thin thread’. The proteins of importance to this PhD thesis are aquaporins, whose primary function in nature is to sustain the osmotic balance across the cell membrane by transporting water. This transportation is highly energy efficient and selective compared to artificial processes, which renders aquaporins interesting from a water purification point of view. Many proteins, including aquaporins, are however not stable in non-native environments, which often results in protein degradation or aggregation upon use in synthetic environments. This is particularly prominent for membrane proteins, which need to be housed in an amphiphilic environment to function properly. This thesis explores aquaporin stabilization through different kinds of interactions with glass. Human Aquaporin 4 was either intercalated with a mesoporous silica substrate or covered in a thin layer of silica. In both cases, aquaporins were stabilized by a lipid bilayer that mimics its native cell membrane surroundings. This thesis also includes work on the first structural and functional characterization of Climbing Perch Aquaporin 1 and a synthesis method for producing uniform silica nanoparticles with accessible mesopores. Detailed characterization provided valuable information on different kinds of aquaporin-silica interactions. Aquaporins were, for instance, shown to extend into a porous silica substrate underneath a supported lipid bilayer. Furthermore, aquaporin secondary structure was preserved when stabilized by a silica shell. The findings in this thesis show that silica may be used as a biocompatible stabilization option for aquaporins, potentially paving the way for better aquaporin utilization in applications such as water purification.