Fig. 3. Deviation of amide ¹H (A, C), ¹⁵N (B, D) chemical shifts from wild-type values. (A and B) Comparison of chemical shift changes between R249S and H168R/R249S. Residues that show recovery of wild-type chemical shifts upon the H168R mutation are indicated in (A) and (B) and colour coded red in Figure 4A. (C and D) Comparison of chemical shift changes between R249S/H168R and R249S/H168R/T123A. Residues with large chemical shift changes upon the third T123A mutation are indicated in (C) and (D) and colour coded red in Figure 4B. The chemical shifts for some residues were not determined (shown as gaps between data points) due to cross-peak overlapping or insufficient sensitivity in NMR experiments.