| Popis: |
The amyloid-β peptide is an amphiphilic peptide that exhibits self-aggregating properties, forming the amyloid fibrils that can be found in the brains of Alzheimer patients. Today it is believed that it is the soluble Aβ oligomers rather than the mature fibrils that are the main neurotoxic species. These small peptide assemblies are known to associate with lipid membranes and form pores that can transport Ca2+ into the cell, which in part could be responsible for their neurotoxic properties. However, most biophysical methods that have been developed to study Aβ target either the monomer or the mature fibrils, and not the low abundance and polydisperse oligomers. In this work, a soft ionization mass spectrometry method that retains non-covalent oligomer interactions in the gas phase has been developed. Using this method, monomeric and oligomeric Aβ (1-40) from dimers up to octamers, except heptamers, were detected in vitro. It was also possible to detect and study the effects of peptide modifications such as methionine-35 oxidation. As mass spectrometry is a non-averaging technique the aggregation kinetics for reduced and oxidized peptides are followed simultaneously, and the results showed that the oxidized form of Aβ(1-40) aggregates slower and forms lower amounts of soluble oligomers than the reduced form. Additionally, Aβ(1-40) interactions with zwitterionic SB3-14 detergent micelles were studied in the gas phase, and it was demonstrated that Aβ-micelle complexes can survive in the mass spectrometer and be identified. Detergent head group charges seem to be essential for peptide-micelle interaction, both in the gas phase and in solution as no structure induction is observed upon addition of the non-ionic detergent DDM. Overall gas phase and solution properties agree well, which is encouraging for future gas phase studies of Aβ interactions with membrane mimetics. |
