Enhanced Seeding Efficacy of Reverse Micelle‐Propagated Aβ ₄₀ Oligomers Arises From Local Conformational Dynamics

ABSTRACT

Soluble amyloid‐β (Aβ) oligomers are widely regarded as the principal pathogenic species in Alzheimer's disease. Different oligomeric assemblies exhibit markedly different abilities to seed amyloid fibril formation, yet the molecular features that govern this seeding efficacy remain poorly understood. Here, we developed a serial propagation strategy in reverse micelles to generate Aβ ₄₀ oligomers with progressively enhanced seeding activity. Successive propagation produced oligomers whose ability to accelerate Aβ ₄₀ aggregation approached that of mature Aβ ₄₀ fibrils. This enhancement was preserved when propagation was initiated in the presence of brain homogenate, despite the intrinsic inhibitory effect of the homogenate on Aβ ₄₀ aggregation. Solid‐state NMR spectroscopy revealed that the propagated oligomers retained the characteristic β‐loop‐β molecular architecture previously observed for reverse‐micelle‐derived Aβ ₄₀ oligomers, with only localized chemical‐shift perturbations. In contrast, comparison of ¹³ C– ¹³ C dipolar correlation intensities demonstrated a selective increase in conformational dynamics within the C‐terminal β ₂ region. The propagated oligomers also exhibited increased cytotoxicity relative to oligomers prepared by a single incubation cycle. These results indicate that the remarkable enhancement in seeding efficacy is not accompanied by a major structural rearrangement but instead is associated with localized dynamic modulation of the β ₂ region. Our findings suggest that efficient Aβ ₄₀ templating requires an optimal balance between structural order and local conformational flexibility, providing new insight into the molecular basis of amyloid propagation.