Andreas S. Bommarius, Ph.D. (Georgia Institute of Technology)
Sven H. Behrens, Ph.D. (Georgia Institute of Technology)
Yury O. Chernoff, Ph.D. (Georgia Institute of Technology)
Julie A. Champion, Ph.D. (Georgia Institute of Technology)
M. G. Finn, Ph.D. (Georgia Institute of Technology)
STUDIES ON AMYLOID AGGREGATION AND CROSS-SPECIES PRION TRANSMISSION
Proper folding of protein molecules into their native structure is necessary to maintain function. Misfolding of proteins can reduce functionality as well as result in the formation of amorphous aggregates or ordered aggregates like amyloids. Amorphous aggregate formation during production, transport, and storage of protein-based biologics is a cause of concern in the biopharmaceutical industry as it results in a reduction in the efficacy or activity of the active pharmaceutical ingredient. On the other hand, ordered aggregation of proteins into amyloids (and their transmissible versions, prions) has been shown to result in several neurodegenerative diseases in humans and other mammals. While the effect of co-solutes including ions has been extensively studied in the context of measuring the stability of protein formulations and formation of disordered aggregates, there is limited information available on the effect of ions on the formation of ordered amyloid aggregates. In this thesis, we have investigated in detail the effect of presence of ionic co-solutes on the aggregation of amyloids.
Here, we have studied the efficiency of cross-transmission of the NM fragment of Sup35 protein, from three closely related species of the Saccharomyces sensu stricto group, namely S. cerevisiae, S. bayanus and S. paradoxus, amongst each other. Using ions of the Hofmeister series, we discerned the relative effects of protein sequence, seed conformation, and environment on the cross-species transmission of this protein. Further, investigation of the fibrillation of Amyloid beta-42 (Aβ42) and Sup35NM in the presence of anions of the Hofmeister series at pH above and below their isoelectric points uncovered interesting differences in their aggregation behavior pointing to key differences in the aggregation mechanism and the biophysical/biochemical properties of these proteins. Lastly, we developed a computational model for amyloid aggregation kinetics and used it for global fitting of Sup35NM amyloid aggregation data. In all, this thesis expands the current knowledge of ion-specific effects on aggregation of amyloid proteins as well as the mechanisms of amyloid aggregation.