Aβ(M1-40) and Wild-Type Aβ40 Self-Assemble into Oligomers with Distinct Quaternary Structures.

Amyloid-β oligomers (AβOs) self-assemble into polymorphic species with diverse biological activities that are implicated causally to Alzheimer's disease (AD). Synaptotoxicity of AβO species is dependent on their quaternary structure, however, low-abundance and environmental sensitivity of AβOs in vivo have impeded a thorough assessment of structure-function relationships. We developed a simple biochemical assay to quantify the relative abundance and morphology of cross-linked AβOs. We compared oligomers derived from synthetic Aβ40 (wild-type (WT) Aβ40) and a recombinant source, called Aβ(M1-40). Both peptides assemble into oligomers with common sizes and morphology, however, the predominant quaternary structures of Aβ(M1-40) oligomeric states were more diverse in terms of dispersity and morphology. We identified self-assembly conditions that stabilize high-molecular weight oligomers of Aβ(M1-40) with apparent molecular weights greater than 36 kDa. Given that mixtures of AβOs derived from both peptides have been shown to be potent neurotoxins that disrupt long-term potentiation, we anticipate that the diverse quaternary structures reported for Aβ(M1-40) oligomers using the assays reported here will facilitate research efforts aimed at isolating and identifying common toxic species that contribute to synaptic dysfunction.