Figure 4.

¹⁵N^H and ¹³C^α chemical shifts for the disordered arch region indicate that only some of the residues are sampling helical conformations. Bar graphs indicate the magnitude of the difference of experimental (δ_e) and sequence-corrected random coil chemical shifts (δ_r) for (A) ¹⁵N^H and (B) ¹³C^α for the indicated regions. Differences less than one (dotted line) suggest disorder. The anti-correlated nature of ¹⁵N^H and ¹³C^α is used to suggest which segments of the disordered region populate either helical or extended peptide backbone angles. Positive and negative ¹⁵N^H and ¹³C^α chemical shift differences, respectively, imply extended backbone angles, whereas negative and positive ¹⁵N^H and ¹³C^α chemical shift differences, respectively, suggest sampling α-helical backbone angles (53). (C) Agadir helical percentage predictions for the indicated residues assessed at 114 mM ionic strength, pH 7.5 and 25°C (NMR conditions) (54). Black bars indicate the residues for which NMR data is available to validate the prediction, whereas open bars indicate an absence of NMR assignments. A secondary structure map is illustrated below as described in Figure 2D.