Figure 3.

Parallel and in-register orientation of β-strands in Aβ42 fibrils. (a) Labeling scheme to test for parallel and in-register orientations of the N- and C-terminal β-strands in Aβ42 fibrils and oligomers using an equimolar mixture of Aβ42-AG1 and Aβ42-AG2 peptides. The red dashed line corresponds to the 4.7 Å distance expected between adjacent Ala21 residues and adjacent Gly37 residues along the fibril axis. (b) Rows through the Ala21 ¹³CO diagonal resonance in DARR NMR spectra of Aβ42 fibrils (red trace) and oligomers (black trace). A distinct Ala21 ¹³CO… Ala21 ¹³Cα cross-peak is observed in the fibril conformation, but not the oligomer conformation. (c) Rows through the Gly37 ¹³CO diagonal resonance in DARR NMR spectra of Aβ42 fibrils (red trace) and oligomers (black trace). A distinct Gly37 ¹³CO… Gly37 ¹³Cα cross-peak is observed in the fibril conformation, but not in the oligomer conformation. Smaller natural abundance (na) cross-peaks are observed in the oligomer samples. Spinning side bands (ssb) due to magic angle spinning are indicated. The data indicate that Aβ42 fibrils have β-strands in a parallel and in-register orientation, but oligomers do not.