P2‐248: Approaches to NMR of mixed Aβ oligomers

Aggregation of beta-amyloid peptides is believed to be critical for the pathogenesis of Alzheimer's Disease. Among the aggregates, recent work has focused on soluble oligomers as neurotoxins. Structural work on oligomers lags behind work on fibrils, however, because oligomers are temporally unstable, and rapidly form insoluble protofibrils and fibrils. In order to learn about the structure of soluble oligomers, we have examined internal fragments of wild type and mutant beta-amyloid peptides, alone and in mixtures doped with the corresponding full length beta-amyloid(1-40) peptides, using several NMR spectroscopy techniques. Among the mutant beta-amyloid peptides examined are the Iowa mutant (D23N) and Japanese mutant (delta-E22) forms of beta-amyloid. As the internal fragments, we have examined a range of peptide chain lengths. The shortest internal fragment peptides consist of the central “core domain” of beta-amyloid, i.e., residues 20-30 of beta-amyloid, which comprise the “bend region” in fibrils. The longest internal fragments peptides extend this region to include portions of the N- and C-terminal beta-sheet domains, i.e., up to beta-amyloid (16-34). The comparison of different chain lengths allows us to determine the minimal oligomer-forming chain length, and the dependency of oligomer number (i.e., number of monomeric units) in these oligomers as a function of peptide chain length. Finally, mixtures of the lowest molecular weight peptides that form oligomers have been doped with full length 15N-and/or 13C-labeled beta-amyloid(1-40) to interrogate the structure of the full-length peptide in these mixed oligomers using NMR. Soluble mixed oligomers containing beta-amyloid core peptides alone, or doped with full length beta-amyloid peptides form oligomers with improved solubility and temporal stability compared to oligomers made purely of the full length beta amyloid peptides. The mixed oligomers are amenable to structural studies by NMR techniques, and these reveal structural differences between wild type and two mutant peptides in their core domains.