25 maggio 2015
articolo postato il: 2015-05-24 23:24:17
J Am Chem Soc. 2015 May 22.
High Resolution Structural Characterization of Aβ42 Amyloid Fibrils by MAS NMR.
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 Aβ1-40 and Aβ1-42, respectively. While there have been numerous reports that structurally characterize fibrils of Aβ1-40, very little is known about the structure of amyloid fibrils of Aβ1-42, which are considered the more toxic alloform involved in AD. We have prepared isotopically 13C/15N labeled AβM01-42 fibrils in vitro from recombinant protein, and examined their 13C-13C and 13C-15N 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 AβM01-42 fibrils utilizing 13C and 15N shift assignments of 38 of the 43 residues, including the backbone and sidechains, obtained through a series of cross polarization based 2D and 3D 13C-13C, 13C-15N 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.