Electron paramagnetic resonance spectroscopy analysis of 19 spin-labeled derivatives of the Alzheimer's amyloid β (Aβ) peptide was used to reveal structural features of amyloid fibril formation. In the fibril, extensive regions of the peptide show an in-register, parallel arrangement. Based on the parallel arrangement and side chain mobility analysis we find the amyloid structure to be mostly ordered and specific, but we also identify more dynamic regions (N and C termini) and likely turn or bend regions (around residues 23-26). Despite their different aggregation properties and roles in disease, the two peptides, Aβ40 and Aβ42, homogeneously co-mix in amyloid fibrils suggesting that they possess the same structural architecture.
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