[NMR paper] High-resolution NMR characterization of low abundance oligomers of amyloid-? without purification.

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High-resolution NMR characterization of low abundance oligomers of amyloid-? without purification.

High-resolution NMR characterization of low abundance oligomers of amyloid-? without purification.

Sci Rep. 2015;5:11811

Authors: Kotler SA, Brender JR, Vivekanandan S, Suzuki Y, Yamamoto K, Monette M, Krishnamoorthy J, Walsh P, Cauble M, Holl MM, Marsh EN, Ramamoorthy A

Abstract
Alzheimer's disease is characterized by the misfolding and self-assembly of the amyloidogenic protein amyloid-? (A?). The aggregation of A? leads to diverse oligomeric states, each of which may be potential targets for intervention. Obtaining insight into A? oligomers at the atomic level has been a major challenge to most techniques. Here, we use magic angle spinning recoupling (1)H-(1)H NMR experiments to overcome many of these limitations. Using (1)H-(1)H dipolar couplings as a NMR spectral filter to remove both high and low molecular weight species, we provide atomic-level characterization of a non-fibrillar aggregation product of the A?1-40 peptide using non-frozen samples without isotopic labeling. Importantly, this spectral filter allows the detection of the specific oligomer signal without a separate purification procedure. In comparison to other solid-state NMR techniques, the experiment is extraordinarily selective and sensitive. A resolved 2D spectra could be acquired of a small population of oligomers (6 micrograms, 7% of the total) amongst a much larger population of monomers and fibers (93% of the total). By coupling real-time (1)H-(1)H NMR experiments with other biophysical measurements, we show that a stable, primarily disordered A?1-40 oligomer 5-15 nm in diameter can form and coexist in parallel with the well-known cross-?-sheet fibrils.


PMID: 26138908 [PubMed - as supplied by publisher]



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