Structural insights into the interaction of the nuclear exosome helicase Mtr4 with the preribosomal protein Nop53

NMR studies of RNA and Nop53 binding. (A) NMR chemical shift perturbations (CSPs) for KOW domain titration with Nop53 peptide (orange), dsRNA (yellow), and both ligands simultaneously (blue). Note that in the presence of both ligands, CSPs correspond to the sum of the single ligand titrations. The secondary structure elements of the KOW domain are shown on top with α-helices indicated by an ellipse and β-strands by a rectangle. The dashed horizontal lines indicate 1 SD unit of the shift for all residues. Only residues with a shift greater than 1 SD deviation are highlighted in B and C. (B) CSPs for Nop53 peptide titration plotted (in orange) onto the Mtr4–Nop53 crystal structure. (C) CSPs for dsRNA titration plotted (in yellow) onto the Mtr4–Nop53 crystal structure. Two residues previously shown to affect RNA-binding when mutated (K700N and P731S [Li et al. 2016]) are highlighted. (D) Zoomed view of ¹H,¹⁵N-HSQC spectra of free KOW (black) and with either (orange and yellow) or both ligands (blue). The chemical shifts appear additive with respect to the two individual ligand titration.