Figure 7. 2D NOESY spectra on WT (a), I79D (b), and L62H (c) showing the proton downfield region.

The cross peaks designated A–C are NOEs from H^ε2/His in a TPLH motif to H^ε1 and H^δ2 of the same histidine residue, and H^α/(His+30) residue (H^α/T207 for H177), respectively. The latter is a supporting evidence of inter-ankyrin repeat hydrogen bond between N^ε2/His and O/(His+29) (e.g. N^ε2/H177 and O/K206). It is clear from the comparisons that L62H mutant retains the TPLH features from AR2 to AR6, while I79D has large perturbation in TPLH of AR3 (H78) and ANK4 (H111), and likely disruption in ⁴²TALH⁴⁵ evidenced by the disappearance of H^ε2/H45 signal.