Structural characterization of E22G Aβ_1-42 fibrils via¹H detected MAS NMR

Amyloid fibrils have been implicated in the pathogenesis of several neurodegenerative diseases, the most prevalent example being Alzheimer's disease (AD). Despite the prevalence of AD, relatively little is known about the structure of the associated amyloid fibrils. This has motivated our studies of fibril structures, extended here to the familial Arctic mutant of Aβ_1-42, E22G-Aβ_1-42. We found E22G-Aβ_M0,1-42 is toxic to Escherichia coli, thus we expressed E22G-Aβ_1-42 fused to the self-cleavable tag N^Pro in the form of its EDDIE mutant. Since the high surface activity of E22G-Aβ_1-42 makes it difficult to obtain more than sparse quantities of fibrils, we employed ¹H detected magic angle spinning (MAS) nuclear magnetic resonance (NMR) experiments to characterize the protein. The ¹H detected ¹³C-¹³C methods were first validated by application to fully protonated amyloidogenic nanocrystals of GNNQQNY, and then applied to fibrils of the Arctic mutant of Aβ, E22G-Aβ_1-42. The MAS NMR spectra indicate that the biosynthetic samples of E22G-Aβ_1-42 fibrils comprise a single conformation with ¹³C chemical shifts extracted from hCH, hNH, and hCCH spectra that are very similar to those of wild type Aβ_1-42 fibrils. These results suggest that E22G-Aβ_1-42 fibrils have a structure similar to that of wild type Aβ_1-42.