Although the A29C RDCs are generally in good agreement with the WT RDCs, variations are observed for a number of residues (U26, A27, A31) that indicate differences in conformation and/or dynamic behavior ( Figure 4C ). Though an order tensor analysis of 13 RDCs shows best agreement with an A-form structure, the quality of the fit is not as good as that observed for WT (Q-factor = 8.77%, Figure 4D ). The S zz direction measured for A29C when assuming an A-form structure deviates substantially from that predicted using PALES ($11 , Supplementary Figure S9 ). These data suggest that A29C deviates from an idealized A-form structure as compared to WT. These deviations may reflect static and/or dynamic bending about the C29 pivot point, possibly arising from looping out of this residue from the helical stack. Such a conformation is observed in the REMD simulations of A29C $1% but not in WT (data not shown).