FIGURE 2.

SAXS data for the VCI-II aptamer in the presence of different ions in the absence and presence of glycine. VCI-II SAXS profiles in the presence of 2 M Na⁺ (A), 2 M K⁺ (B), 20 mM Ca²⁺ (C), 20 mM Mn²⁺ (D), 20 mM Sr²⁺ (E), 20 mM Ba²⁺ (F), and 20 mM Zn²⁺ (G), in the absence (green, solid lines) and presence (red, solid lines) of 20 mM glycine. For comparison, profiles in 50 mM Na-MOPS buffer only (blue, dashed lines), in the presence of 20 mM Mg²⁺ (green, dashed lines), and in the presence of 20 mM Mg²⁺ and 20 mM glycine (red, dashed lines) are shown. Data are shown in Kratky representation (q^2.I as a function of q, where I is the scattering intensity and q is defined as q = 4π sin(θ)/λ, with λ being the X-ray wavelength and 2θ the total scattering angle), which is particularly sensitive to conformational changes (Lipfert et al. 2009). The lower signal-to-noise at high q (which is emphasized by the Kratky representation) noticeable in the profiles for 2 M Na⁺ and K⁺ is due to X-ray absorption and reduced scattering contrast at the high salt concentrations.