Hydration water dynamics in amyloid-β aggregates using deuterium and oxygen-17 solid-state NMR spectroscopy

The dynamics of water molecules in the hydration shells of solid-like amyloid-β (Aβ) aggregates, key players in neurodegeneration, can play an important role in regulating aggregation and neurotoxicity. This study focuses on identifying the main motional modes of water in Aβ fibrils and oligomers formed from the native Aβ1-40 peptide or the toxic, yet naturally occurring, pyroglutamate-3 (PE) post-translational modification. The oligomers and fibrils were hydrated with either D2O or H217O enriched water for quantitative analysis of the dynamics of protein-bound and remote layers, using 2H and 17O solid-state NMR spectroscopy in the 300-170 K temperature range. Line shape and relaxation measurements, spanning laboratory and rotating frame relaxation, provide complementary assessment of motions in the protein-bound and remote layers, sensing different amplitudes and time scales. The comparison of the water dynamics between all of the Aβ species and a previously characterized globular protein indicates distinct differences. In particular, the general trend is the enhancement of water dynamics in the oligomers compared to fibrils, with the PE oligomer in the lead.