Sensitivity-Enhanced Solid-State NMR Detection of Structural Differences and Unique Polymorphs in Pico- to Nanomolar Amounts of Brain-Derived and Synthetic 42-Residue Amyloid-β Fibrils

Amyloid-beta (A beta) fibrils in neuritic plaques are a hallmark of Alzheimer's disease (AD). Since the 42-residue A beta (A beta 42) fibril is the most pathogenic among different A beta species, its structural characterization is crucial to our understanding of AD. While several polymorphs have been reported for A beta 40, previous studies of A beta 42 fibrils prepared at neutral pH detected essentially only one structure, with an S-shaped beta-sheet arrangement (e.g., Xiao et al. Nat. Struct. Mol. Biol. 2015, 22, 499). Herein, we demonstrate the feasibility of characterizing the structure of trace amounts of brain-derived and synthetic amyloid fibrils by sensitivity-enhanced H-1-detected solid-state NMR (SSNMR) under ultrafast magic angle spinning. By taking advantage of the high sensitivity of this technique, we first demonstrate its applicability for the high-throughput screening of trace amounts of selectively C-13- and N-15-labeled A beta 42 fibril prepared with similar to 0.01% patient-derived amyloid (ca. 4 pmol) as a seed. The comparison of 2D C-13/H-1 SSNMR data revealed marked structural differences between AD-derived A beta 42 (similar to 40 nmol or similar to 200 mu g) and synthetic fibrils in less than 10 min, confirming the feasibility of assessing the fibril structure from similar to 1 pmol of brain amyloid seed in similar to 2.5 h. We also present the first structural characterization of synthetic fully protonated A beta 42 fibril by H-1-detected 3D and 4D SSNMR. With procedures assisted by automated assignments, main-chain resonance assignments were completed for trace amounts (similar to 42 nmol) of a fully protonated amyloid fibril in the H-1-detection approach. The results suggest that this A beta 42 fibril exhibits a novel fold or polymorph structure.