Two-Dimensional Structure of β-Amyloid(10−35) Fibrils

Abstract

β-Amyloid (Aβ) peptides are the main protein component of the pathognomonic plaques found in the brains of patients with Alzheimer's disease. These heterogeneous peptides adopt a highly organized fibril structure both in vivo and in vitro. Here we use solid-state NMR on stable, homogeneous fibrils of Aβ_(10-35). Specific interpeptide distance constraints are determined with dipolar recoupling NMR on fibrils prepared from a series of singly labeled peptides containing ¹³C-carbonyl-enriched amino acids, and skipping no more that three residues in the sequence. From these studies, we demonstrate that the peptide adopts the structure of an extended parallel β-sheet in-register at pH 7.4. Analysis of DRAWS data indicates interstrand distances of 5.3 ± 0.3 Å (mean ± standard deviation) throughout the entire length of the peptide, which is compatible only with a parallel β-strand in-register. Intrastrand NMR constraints, obtained from peptides containing labels at two adjacent amino acids, confirm the secondary structural findings obtained using DRAWS. Using peptides with ¹³C incorporated at the carbonyl position of adjacent amino acids, structural transitions from α-helix to β-sheet were observed at residues 19 and 20, but using similar techniques, no evidence for a turn could be found in the putative turn region comprising residues 25−29. Implications of this extended parallel organization for Aβ_(10-35) for overall fibril formation, stability, and morphology based upon specific amino acid contacts are discussed.