Figure 1. Concentration independence and conformational dependence of V_c.

(a, b), Experimental SAXS data plotted on a relative scale for glucose isomerase (cyan), 94-nucleotide SAM-1 riboswitch in the absence of Mg²⁺ (orange) and RAD51AP1, an intrinsically unfolded protein (green). a, Data transformed as the Kratky plot, q²• I(q) vs. q, reveal the parabolic convergence for a folded particle (blue) and divergence for a flexible (orange) or fully unfolded (green) particle. b, Data plotted as q • I(q) vs. q show convergence for both folded and flexible particles. Inset demonstrates convergence for a fully unfolded polymer. c, Concentration independence of V_c for experimental SAXS data. For each of 7 samples, relative difference is calculated as the deviation from the mean normalized to the mean. Concentrations ranged from 0.2 to 3 mg/mL for glucose isomerase (cyan), P4–P6 domain (open red), xylanase (orange), TyMV UUAG TLS RNA (solid black), del8 RNA (open purple), Atu RNase P(open black), SAM-1 riboswitch with Mg²⁺ and ligand (closed purple), SAM-1 riboswitch in the absence of Mg²⁺ (solid green). X-axis (Sample Number) refers to the different concentrations for each sample increasing from left to right. d, Correlated changes in V_c (red) and R_g (cyan) for conformations of SAM-1 riboswitch (PDB 2GIS) simulated from molecular dynamics with CNS²⁸. Horizontal lines demonstrate for R_g or V_c that a single value can map to multiple conformations. Dual specification of both R_g and V_c reduces multiplicity (vertical bars). Relative change represents the difference calculated from the starting model 2GIS. Asterisks denote the time step of the displayed conformation.