Figure 7.

Solid-state NMR on fibrils. (a) Doubled cross-peak patterns of a single labeled Gln in fibrils prepared from [U-¹³C, ¹⁵N-Q10] K₂Q₁₁PGQ₁₁D₂ reproduce the Gln peaks in fibrils (b) from [U-¹³C, ¹⁵N-Q6] K₂Q₃₀K₂ peptide that lacks β-hairpin encouraging motifs ¹⁵. Red and blue lines mark peaks of the two distinct conformers. Asterisks mark spinning side bands. Spectra were obtained at 600MHz (for ¹H), using 10 kHz MAS and 8ms or 25ms DARR mixing, respectively. (c) For the >10,000 Gln in the Biomolecular NMR database (bar graphs) the Gln Cβ (light bars) and Cγ shifts (dark bars) are generally well-separated. In each of the two polyQ conformers ‘form a’ (red bracket) and ‘form b’ (blue) there is instead small shift difference between Cβ and Cγ. The Cβ shift of ‘form a’ is highly unusual, and the Cβ and Cγ shifts of ‘form b’ are both atypical. (d) The average shifts of the few BMRB Gln that feature Cβ/Cγ shifts very close together (within 1 ppm). The particular shifts of conformer a (red) or b (blue) are seen in 0.5% and 0.4% of all Gln, respectively.