Figure 3 - full size

Figure 3.
Details of the stabilizing interactions of the loop at the C terminus of the engineered helix in the mutant L20/R63A in the presence of guanidinium (A), methylguanidinium (B), and ethylguanidi-nium (C). The superimposed F[o]-F[c] difference maps contoured at 3[sigma] (red) define the position of the ligands. The resolution of the maps is 1.45 A, 1.7 A, and 1.8 A, respectively. The methylated and ethylated ligands adopt alternative conformations as shown. (D) Interactions made by Arg63 in the lysozyme (Molecule B, PDB code 262L). Similar interactions are made by Arg52 in wild-type lysozyme.