1H detection and dynamic nuclear polarization-enhanced NMR of Aβ1-42 fibrils

Several publications describing high-resolution structures of amyloid-beta (A beta) and other fibrils have demonstrated that magicangle spinning (MAS) NMR spectroscopy is an ideal tool for studying amyloids at atomic resolution. Nonetheless, MAS NMR suffers from low sensitivity, requiring relatively large amounts of samples and extensive signal acquisition periods, which in turn limits the questions that can be addressed by atomic-level spectroscopic studies. Here, we show that these drawbacks are removed by utilizing two relatively recent additions to the repertoire of MAS NMR experiments-namely, H-1 detection and dynamic nuclear polarization (DNP). We show resolved and sensitive two-dimensional (2D) and three-dimensional (3D) correlations obtained on C-13, N-15-enriched, and fully protonated samples of M(0)A beta(1-42) fibrils by high-field H-1-detected NMR at 23.4 T and 18.8 T, and C-13-detected DNP MAS NMR at 18.8 T. These spectra enable nearly complete resonance assignment of the core of M(0)A beta(1-42) (K16-A42) using submilligram sample quantities, as well as the detection of numerous unambiguous internuclear proximities defining both the structure of the core and the arrangement of the different monomers. An estimate of the sensitivity of the two approaches indicates that the DNP experiments are currently similar to 6.5 times more sensitive than H-1 detection. These results suggest that H-1 detection and DNP may be the spectroscopic approaches of choice for future studies of A beta and other amyloid systems.

Automated summary

Magic-angle spinning (MAS) NMR spectroscopy has been widely used to study the high-resolution structures of amyloid-beta (A beta) and other fibrils, but it suffers from low sensitivity. In this study, the drawbacks of MAS NMR were overcome by using two relatively recent techniques: H-1 detection and dynamic nuclear polarization (DNP). The results showed improved sensitivity and allowed for nearly complete resonance assignment and structural analysis of A beta fibrils.