Atomic-resolution three-dimensional structure of amyloid β fibrils bearing the Osaka mutation

Abstract

Despite its central importance for understanding the molecular basis of Alzheimer's disease (AD), high-resolution structural information on amyloid β-peptide (Aβ) fibrils, which are intimately linked with AD, is scarce. We report an atomic-resolution fibril structure of the Aβ1-40 peptide with the Osaka mutation (E22Δ), associated with early-onset AD. The structure, which differs substantially from all previously proposed models, is based on a large number of unambiguous intra- and intermolecular solid-state NMR distance restraints.

Keywords: Alzheimer's disease; amyloids; solid-state NMR spectroscopy; structure elucidation.

Figure 1

NMR and STEM data establish the basic amyloid architecture. a) Negative-stain TEM image of Aβ1-40 E22Δ fibrils. b) STEM image of unstained, freeze-dried fibrils. Regions that used MPL measurements are marked in red. c) MPL measurement. d,e) The comparison of NCO (d) and NCA (e) NMR spectra of uniformly [¹⁵N,¹³C]-labeled fibrils (black contours) with mixed [¹⁵N,¹³C]-labeled fibrils (orange contours) establishes an in-register parallel β-sheet architecture. f,g) Traces taken at the Gln15 Nε2-resonance.

Figure 2

Extracts of NMR spectra that distinguish intra- from intermolecular contacts. a,b) Overlay of PAR spectra recorded on a uniformly [¹³C]-labeled sample (black contours) and on a sample of 20 % uniformly [¹⁵N,¹³C]-labeled protein and 80 % unlabeled material (green contours). Details are given in Figure S5. c) Intensity ratios of crosspeaks in dilutely and uniformly labeled samples. Inter- and intramolecular correlations, expected to be attenuated to 20 % and not attenuated, are shown as red and black bars, respectively. The full statistics are shown in Figure S5. d) Trace extracted at the Ile32 Cδ1-resonance from PAR spectra of uniformly (black) and dilutely labeled (green) samples. All cross peaks of this resonance are intramolecular.

Figure 3

a) Backbone structure of Aβ1-40 E22Δ calculated on the basis of unambiguous distance restraints (solid red and black lines). Blue dashed contacts are discussed in the text but were not used in the calculation. b) Register hydrogen bonds between β-strands entered into the calculation (green lettering). Blue: additional residues with TALOS+ predictions used in the structure calculation.

Figure 4

Representation of the 3D structure of Aβ1-40 E22Δ calculated from NMR-derived distance and torsion-angle restraints. The structure is deposited in the Protein Data Base with accession number 2mvx. a) Schematic view of the lowest-energy conformer of a Aβ1-40 E22Δ bi-decamer (2×10 monomers). The symmetry axis (arrow) coincides with the long axis of the fibril. b) NMR bundle of the middle layer only. c) Cross section of the fibril hydrophobic residues are colored white, negatively charged residues red, positively charged residues blue, and polar ones (and Gly) green.