Hydrogen exchange-mass spectrometry analysis of β-Amyloid peptide structure

beta-Amyloid peptide (Abeta) is the primary protein component of senile plaques in Alzheimer's disease and is believed to be responsible for the neurodegeneration associated with the disease. A has proven to be toxic only when aggregated; however, the structure of the aggregated species associated with toxicity is unknown. In the present study, we use hydrogen-deuterium isotope exchange (HX)-electrospray ionization mass spectrometry (MS) along with enzymatic digestion as a tool to examine at near residue level, the changes in Abeta structure associated with aggregation to a fibril form. Our results show that the structure of Abeta intermediate species formed early in the course of fibrillogenesis is dependent upon solvent conditions. Additionally, the HX-MS data of peptic Abeta fragments suggest that the C-terminal segment of the peptide is approximately 35% protected from exchange in fibril-containing samples, relative to monomeric Abeta species prepared in DMSO/H2O. The N-terminus (residues 1-4) is completely unprotected from exchange, and the fragment containing residues 5-19 is over 50% protected from exchange in the fibril-containing samples. This work contributes to our understanding of Abeta structure associated with aggregation and toxicity and further application of this approach may aid in the design of agents that intervene in the Abeta aggregation processes associated with neurotoxicity.