High Resolution Structural Characterization of A?42 Amyloid Fibrils by MAS NMR.
 

High Resolution Structural Characterization of A?42 Amyloid Fibrils by MAS NMR.

High Resolution Structural Characterization of A?42 Amyloid Fibrils by MAS NMR.

J Am Chem Soc. 2015 May 22;

Authors: Colvin MT, Silvers R, Frohm B, Su Y, Linse S, Griffin RG

Abstract
The presence of amyloid plaques composed of amyloid beta (A?) fibrils is a hallmark of Alzheimer's disease (AD). The A? peptide is present as several length variants with two common alloforms consisting of 40 and 42 amino acids, denoted A?1-40 and A?1-42, respectively. While there have been numerous reports that structurally characterize fibrils of A?1-40, very little is known about the structure of amyloid fibrils of A?1-42, which are considered the more toxic alloform involved in AD. We have prepared isotopically 13C/15N labeled A?M01-42 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 A? 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 A?M01-42 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 ? and ? dihedral angles from the chemical shift assignments indicate that 4 ?-strands are present in the fibril's secondary structure.


PMID: 26001057 [PubMed - as supplied by publisher]



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