Design and Characterization of Chemically Stabilized Aβ42 Oligomers

A popular working hypothesis of Alzheimer's disease causation is amyloid beta-protein oligomers are the key neuro-pathogenetic agents. Rigorously elucidating the role of oligomers requires the production of stable oligomers of each size. We previously used zero-length photochemical cross-linking to allow stabilization, isolation, and determination of structure-activity relationships of pure populations of A beta 40 dimers, trimers, and tetramers. We also attempted to study A beta 42 but found that A beta 42 oligomers subjected to the same procedures were not completely stable. On the basis of the fact that Tyr is a critical residue in cross-linking chemistry, we reasoned that the chemical accessibility of Tyr10 in A beta 42 must differ from that in A beta 40. We thus chemically synthesized four singly substituted Tyr variants that placed the Tyr in different positions across the A beta 42 sequence. We then studied the stability of the resulting cross-linked oligomers as well as procedures for fractionating the oligomers to obtain pure populations of different sizes. We found that [Phe(10), Tyr(42)]A beta 42 produced stable oligomers yielding highly pure populations of dimers through heptamers. This provides the means to establish formal structure-activity relationships of these important A beta 42, assemblies. In addition, we were able to analyze the dissociation patterns of non-cross-linked oligomers to produce a model for oligomer formation. This work is relevant to the determination of structure-activity relationships that have the potential to provide mechanistic insights into disease pathogenesis.