Figure 3.

Effect of 3′-UMP and 5′-AMP ligand binding on functionally distinct RNases. Compounded chemical shift perturbations (Δδ_obs at the highest ligand concentration) relative to the apo form upon binding of two mononucleotides 3′-UMP (A–E) and 5′-AMP (F–J) for bovine RNase A (A,F) and human RNases 2 (B,G), 3 (C–H), 4 (D,I), and 5 (E,J) are plotted as function of consensus sequence. Active-site residues (His12, Lys41, His119, RNase A numbering) are highlighted using green lines. Chemical shift perturbations were calculated by comparing the shifts at the largest enzyme:ligand molar ratios relative to the apo state for each enzyme. Δδ_obs are shown using the putty representation on the 3D structures to the right of the plots. Secondary structure of bovine RNase A is traced on top of the sequence alignment using blocks, arrows and dashed lines to represent α-helix, β-strand and loop regions, respectively. The 3′-UMP and 5′-AMP ligand positions, depicted on the structures of RNase A (A,F), were obtained from PDB entries 1O0N and 1Z6S, respectively.