Real-Time Monitoring of Heat Induced Unfolding and Aggregation of β-lactoglobulin in the Presence of Chaperones Using High Resolution Ultrasonic Spectroscopy

Abstract

Fluorescence Resonance Energy Transfer (FRET) was used to study protein structures within soluble oligomer intermediates of amyloid and non-amyloid aggregates. Three protein aggregation systems were studied using fluorescence donor and acceptor near the N and C terminus:(1) Alzheimer's Ab 1-40 peptide.(2) 20-residue polyglutamine K 2 Q 16 K 2 .(3) 20-residue polyglutamic acid E 20 . (non-amyloid) The aggregation of each peptide showed different conformational changes: Ab 1-40 partially compacted into a structure consistent with solid-state NMR structures, K 2 Q 16 K 2 extended to form b-sheets, and E 20 compacted heavily into b-hairpins. However, based on donor-acceptor distances, soluble oligomers conformations of all three peptides show a remarkable degree of similarity to their monomeric precursors, albeit with a slightly expanded conformation for Ab 1-40 and E 20 . These findings support assembly models of small soluble oligomers which largely consist of monomer-like structures, with some increase in a-helical content for Ab 1-40 . These donor-acceptor distances are used to directly assess the accuracy of different molecular dynamics force fields in the study of these soluble oligomers.