Distance to backbone Looking at the methyl group order parameters for all residues, there is a very clear correlation between mobility and distance to the backbone as shown in Fig. 3c. Methyl groups separated by two torsion angles (Cδ1 and Cδ2, depending on χ1 and χ2) have a mean order parameter of only 0.25 compared to 0.52 for those separated by only one torsion angle (Cγ1 and Cγ2, depending only on χ1). As seen above, the alanines Cβ have much higher order parameters with a mean value of 1.