P4‐316: Stabilization of neurotoxic Alzheimer amyloid‐beta oligomers by protein engineering

Abstract

Soluble oligomeric aggregates of the amyloid-ß peptide (Aß) have been implicated in the pathogenesis of Alzheimer's disease (AD). The biochemical instability of neurotoxic aggregates in vitro is a problem for research on the molecular biology of AD. While the conformation adopted by Aß within these aggregates is not known, a ß-hairpin conformation is known to be accessible to monomeric Aß. The ß-hairpin is for instance observed in a complex with Affibody binding protein. To test the hypothesis that the ß-hairpin is a building block of toxic oligomers, we have engineered a double-cysteine mutant of Aß (called AßCC) in which the ß-hairpin conformation is stabilized by an intramolecular disulfide bond. AßCC oligomers were characterized to determine if they represent a stable model of wild type neurotoxic aggregates. Aß40CC and Aß42CC form stable protofibrils, but are unable to convert into amyloid fibrils. Biochemical and biophysical experiments and assays with conformation-specific antibodies used to detect Aß aggregates in vivo indicate that the wild-type oligomer structure is preserved and stabilized in AßCC oligomers. Stable oligomers are potent inducers of neuronal apoptosis. Stable neurotoxic AßCC oligomers/protofibrils might facilitate studies of their structure and role in the pathogenesis of AD. Stable protofibril preparations might potentially also be used for therapy development based on active or passive immunization.