Studies of Aggregation Pathways for Amyloidogenic Peptides by Dielectric Relaxation Spectroscopy

• Main Author: Barry, Donald
• Other Authors: Izabela Stroe, Advisor
• Format: Others
• Published: Digital WPI 2013
• Subjects: dielectric spectroscopy; amyloids
• Online Access: https://digitalcommons.wpi.edu/etd-dissertations/143; https://digitalcommons.wpi.edu/cgi/viewcontent.cgi?article=1142&context=etd-dissertations

Diseases associated with amyloid aggregation have been a growing focus of medical research in recent years. Altered conformations of amyloidogenic peptides assemble to form soluble aggregates that deposit into the brain and spleen causing disorders such as Alzheimer's disease and Type II diabetes. Emergent theories predict that fibrils may not be the toxic form of amyloidogenic structures and that smaller oligomer and protofibril aggregates may be the primary source of cellular function damage. Studies show that these amyloidogenic aggregates are characterized by an increased number of poorly dehydrated hydrogen backbones and large surface densities of patches of bulk like water which favor protein association. When proteins aggregate to form larger structures, there is a redistribution of water surrounding these proteins. The water dynamics of amyloidogenic aggregation is different than the monomeric form and has a decrease in the number of patches occupied by molecules with bulk-like water behavior. We demonstrate that the redistribution of water during amyloid aggregation is reflected in a change in the dielectric relaxation signal of protein-solvent mixtures. We use dielectric relaxation spectroscopy (DRS) as a tool for studying the dynamics of amyloidogenic peptides--amyloid beta (Ab 1-42) and human islet amyloid polypeptide (hIAPP)--during self-assembly and aggregation. Non-amyloidogenic analogs-- scrambled (Ab 42-1) and rat islet amyloid polypeptide (rIAPP)--were used as controls. We first present studies of amyloidogenic peptides in a deionized water buffer at room temperature as a function of concentration and incubation time. From this we were able to determine differences in amyloidogenic and non-amyloidogenic peptides through the dielectric modulus. We next present the same analytes in a deionized water-glycerol buffer to facilitate the study of the dielectric permittivity at sub-freezing temperatures and model the kinetics of the alpha- and beta- relaxation processes. We conclude our work by studying the peptides in a bovine serum albumin (BSA) and glycerol buffer to demonstrate dielectric spectroscopy as a sensitive tool for measuring amyloidogenic peptides in an in vivo- like condition.