Figure 1
From: Anti-sense DNA d(GGCCCC)n expansions in C9ORF72 form i-motifs and protonated hairpins
CD and NMR spectra indicate the presence of protonated structures.
(a) CD spectra of d(G2C4) (black), d(G2C4)2 (green), d(G2C4)4 (blue) and d(G2C4)8 (purple) immediately after dilution in H2O (dashed line) and after incubation (full line). Positive and negative peaks, at 285 and 265 nm, respectively, are associated with the formation of i-motifs. (b) Comparison of CD spectra of d(G2C4)4 in water (dashed lines) and under molecular crowding conditions in 40% w/v PEG8000 (full lines) at pH 6.5 (purple), 7.0 (green), 7.2 (blue). Peaks characteristic for i-motifs persist up to pH 7.0 in 40% w/v PEG8000. All spectra were acquired at 37 °C. (c) Imino region of 1H NMR spectra of d(G2C4), d(G2C4)2, d(G2C4)4, and d(G2C4)8 after incubation in H2O at pH 6.0 and 5 °C. Signals between δ 12.5 and 13.5 ppm are indicative of Watson-Crick hydrogen bonding, while signals between δ 16.0 and 17.0 ppm correspond to imino protons from hemi-protonated C+-C base pairs.
