Intermediate States of Aggregation-Prone Polypeptides

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In the past decade, protein folding has gained wider recognition and acceptance as an important field of biomedical research due, in part, to the growing number of examples of protein misfolding that have been linked to human diseases. In most cases, the misfolding event results in the formation of intermolecular aggregates and higher-ordered structures, often leading to the characteristic plaques known as amyloid. One aim of this research is to monitor the changes in protein conformation that precede aggregation in a unique environment where intermolecular interactions are prohibited. This will be achieved by encapsulating aggregation-prone polypeptides in the pores of a silica glass matrix by the sol-gel technique. Once encapsulated, solvent conditions will be altered to mimic those conditions that favor aggregation in solution. Circular dichroism spectroscopy will be used to detect intermediate states that differ in conformation from both the native and aggregated states of each protein and to screen for drug candidates or solutes that destabilize the intermediate conformation. Lysozyme, alpha-synuclein, a peptide fragment from the yeast prion Sup35, and a disease-associated variant of CuZn-superoxide dismutase will be among the first polypeptides studied by this approach. A second major aim of this research is to determine whether unfavorable backbone hydration serves as a dominant force in aggregation of misfolded proteins. This goal involves the testing of a new thermodynamic framework, developed by this laboratory, that accounts for the participation of bulk water in aqueous equilibria. A combination of density measurements and calorimetry techniques will be used to calculate the free energy of the bulk aqueous phase in the presence of specific solutes. Calorimetry studies will be followed by solubility measurements of model amide-containing compounds to elucidate the magnitude of backbone solvation energetics in protein folding and aggregation. This project aims to further our understanding of factors that promote protein aggregation. This research could lead to new strategies for therapeutic intervention of diseases caused by misfolding of proteins, including Alzheimer's, Parkinson's, and Huntington's diseases.