Structural convergence and membrane interactions of Aβ along the primary nucleation process studied by solid state NMR.

Non-specific disruption of cellular membranes induced by amyloidogenic aggregation of β-amyloid (Aβ) peptides remains a viable cytotoxicity mechanism in Alzheimer's disease (AD). Obtaining structural information about the intermediate states of Aβ-membrane systems and their molecular interactions is challenging due to their heterogeneity and low abundance. Here, we systematically study the molecular interactions of membrane-associated Aβ peptides using solid-state nuclear magnetic resonance (ssNMR) spectroscopy, focusing on the primary nucleation phase of the fibrillation process. Compared to the less pathogenic Aβ peptide, Aβ forms smaller oligomers prior to fibrillation, as evidenced by a higher overall population of lipid-proximity peptides. Aβ also exhibits more pronounced residue-specific contacts with phospholipid headgroups compared to Aβ, with multiple lipid-proximity segments throughout the entire primary sequence. The segments involved in initial inter-strand assembly overlap with those located near the lipid headgroups in Aβ, whereas these two segments are distinct in Aβ. ssNMR spectroscopy with sensitivity enhanced by Dynamic nuclear polarization (DNP) confirmed local secondary structural convergence during the nucleation process of Aβ and the presence of long-range tertiary contacts at early stages of nucleation. Overall, our results provide a molecular-level understanding of the Aβ nucleation process in a membrane-like environment and its membrane-disrupting intermediates. The comparison between Aβ and Aβ explains its higher cytotoxicity from the perspective of membrane disruption.