Quenched hydrogen/deuterium exchange NMR characterization of amyloid-β peptide aggregates formed in the presence of Cu2+ or Zn2+

Alzheimer's disease, a neurodegenerative disorder causing synaptic impairment and neuronal cell death, is strongly correlated with aggregation of the amyloid-beta peptide (A beta). Divalent metal ions such as Cu2+ and Zn2+ are known to significantly affect the rate of aggregation and morphology of Ab assemblies in vitro and are also found at elevated levels within cerebral plaques in vivo. The present investigation characterized the architecture of the aggregated forms of A beta(1-40) and A beta(1-42) in the presence or absence of either Cu2+ or Zn2+ using quenched hydrogen/deuterium exchange combined with solution NMR spectroscopy. The NMR analyses provide a quantitative and residue-specific structural characterization of metal-induced A beta aggregates, showing that both the peptide sequence and the type of metal ion exert an impact on the final architecture. Common features among the metal-complexed peptide aggregates are two solvent-protected regions with an intervening minimum centered at Asn27, and a solvent-accessible N-terminal region, Asp1-Lys16. Our results suggest that Ab in complex with either Cu2+ or Zn2+ can attain an aggregation-prone beta-strand-turn-beta-strand motif, similar to the motif found in fibrils, but where the metal binding to the N-terminal region guides the peptide into an assembly distinctly different from the fibril form.