To Fold or To Fibrillate? Serendipity in Stability Studies

Abstract: Proteins are complex structures and years of research have been spent on attempts to understand their complexity. The non-covalent interactions involved in protein folding are: hydrophobic effect, electrostatic interactions, van der Waals interactions and hydrogen bonding. It has been of great interest to address the importance of each of those interactions in proteins. While hydrophobic effect is believed to play the major role in protein folding, Coulombic interactions are of importance in for example protein function, specificity, kinetics and avoidance of unspecific association. Proteins, which are usually folded under native conditions, may also enter other conformations, for example amyloid structures, upon changes in the intrinsic and extrinsic factors. The general objective of this thesis was to study the interplay of the non-covalent interactions in protein folding, assembly and aggregation processes. We found a correlation between stability and assembly of mutants of monellin which implies that the same non-covalent interactions govern the two processes. We also found that the net charge of monellin is important in order to bind to its receptor. In order to stabilize the protein PGB1, we used the split GFP method and selected mutants with elevated melting temperatures by as much as 12?C. Another series of monellin mutants revealed a correlation between stability and aggregation lag time. In the same study a correlation between predicted aggregation propensity and aggregation lag time was found. We also investigated how terminal extensions of the amino acid sequence affected the aggregation properties of Alzheimer´s ?-peptide (A?) and found that addition of non-aggregating sequence decreases the aggregation rate of this peptide.