Extended Data Fig. 5: Analysis of DNAMyc conformers by differential scanning calorimetry (DSC).
From: Structural basis of G-quadruplex unfolding by the DEAH/RHA helicase DHX36
a, DNA constructs used in the analysis. DNAMyc, DNA used for co-crystallization with DHX36-DSM (see Methods). Residues that form a three-tiered G-quadruplex in the complex and those that form propeller loops are boxed and underlined, respectively. 22-nt DNAMyc, DNA used for solution NMR analysis20. Residues that form a three-tiered G-quadruplex and those that form propeller loops in the free DNA are boxed and underlined, respectively. 16-nt DNAMyc, DNA minimized to eliminate 5′ and 3′ single-stranded extensions to the G-quadruplex. 16-nt mutant DNAMyc, variant of the former with two mutations (red) to enforce the three quartets observed in the DHX36-DSM–DNAMyc co-crystal structure. b, Size-exclusion chromatograms (see Methods) of 22-nt DNAMyc, 16-nt DNAMyc and 16-nt mutant DNAMyc in the presence of either 150 mM or 20 mM KCl, demonstrating greater conformational homogeneity of the DNAs at lower KCl concentration. c, DSC thermograms (before buffer correction) for the three DNAs, in 20 mM KCl. Three independent experiments are plotted for each DNA. d, Triplicate nonlinear least-squares analyses of thermograms for the three DNAs. Black and red curves, buffer-corrected DSC data and curve-fits, respectively. Tm (melting temperature) and ΔH (enthalpy change) are reported as mean ± s.d. Each experiment was repeated three times with two sets of identical DNA preparations.
