High Resolution Structural Characterization of Aβ(42) Amyloid Fibrils by Magic Angle Spinning NMR

[Image: see text] The presence of amyloid plaques composed of amyloid beta (Aβ) fibrils is a hallmark of Alzheimer’s disease (AD). The Aβ peptide is present as several length variants with two common alloforms consisting of 40 and 42 amino acids, denoted Aβ(1–40) and Aβ(1–42), respectively. While there have been numerous reports that structurally characterize fibrils of Aβ(1–40), very little is known about the structure of amyloid fibrils of Aβ(1–42), which are considered the more toxic alloform involved in AD. We have prepared isotopically (13)C/(15)N labeled Aβ(M01–42) fibrils in vitro from recombinant protein and examined their (13)C–(13)C and (13)C–(15)N magic angle spinning (MAS) NMR spectra. In contrast to several other studies of Aβ fibrils, we observe spectra with excellent resolution and a single set of chemical shifts, suggesting the presence of a single fibril morphology. We report the initial structural characterization of Aβ(M01–42) fibrils utilizing (13)C and (15)N shift assignments of 38 of the 43 residues, including the backbone and side chains, obtained through a series of cross-polarization based 2D and 3D (13)C–(13)C, (13)C–(15)N MAS NMR experiments for rigid residues along with J-based 2D TOBSY experiments for dynamic residues. We find that the first ∼5 residues are dynamic and most efficiently detected in a J-based TOBSY spectrum. In contrast, residues 16–42 are easily observed in cross-polarization experiments and most likely form the amyloid core. Calculation of ψ and φ dihedral angles from the chemical shift assignments indicate that 4 β-strands are present in the fibril’s secondary structure.