Aggregation Dynamics of a 150 kDa Aβ42 Oligomer: Insights from Cryo Electron Microscopy and Multimodal Analysis

I.Protein misfolding is a widespread phenomenon that can result in the formation of protein aggregates, which are markers of various disease states, including Alzheimers disease (AD). In AD, amyloid beta (A{beta}) peptides, particularly A{beta}40 and A{beta}42, are key players in the diseases progression, as they aggregate to form amyloid plaques and contribute to neuronal toxicity. Recent research has shifted attention from solely A{beta} fibrils to also include A{beta} protofibrils and oligomers as potentially critical pathogenic agents. Particularly, oligomers demonstrate greater toxicity compared to other A{beta} specie. Hence, there is an increased interest in studying the correlation between toxicity and their structure and aggregation pathway. The present study investigates the aggregation of a 150 kDa A{beta}42 oligomer that does not lead to fibril formation over time. Using negative stain transmission electron microscopy (TEM), size exclusion chromatography (SEC), dynamic light scattering (DLS), and cryo-electron microscopy (cryo-EM), we demonstrate that 150 kDa A{beta}42 oligomers form higher-order string-like assemblies over time. The strings are unique from the classical A{beta} fibril structures. The significance of our work lies in elucidating molecular behavior of a novel non-fibrillar form of A{beta}42 aggregate.