25 maggio 2015

articolo postato il: 2015-05-24 23:24:17

Verso una descrizione atomica della struttura tridimensionale delle fibre amiloidi attraverso NMR in fase solida: un progresso tecnologico che avrà enormi implicazioni nella progettazione di nuovi farmaci
 

J Am Chem Soc. 2015 May 22.

High Resolution Structural Characterization of Aβ42 Amyloid Fibrils by MAS NMR.

Colvin MTSilvers RFrohm BSu YLinse SGriffin RG.

 

Abstract

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.