Figure 4.

Comparison of μ-SmIIIA native fold and the structure with one disulfide bond opened. (A) Structure of the native peptide (completely oxidized, three disulfide bonds) with 100 conformations of its basic residues (red) superimposed with three residues marked as important for binding activity. The distribution of hydrogen bonds shows a sparse black area which indicates that the region surrounding it is relatively flexible. (B) Structure of the peptide containing one opened disulfide bond (C2–C5) showing (blue) its well-formed α-helix and the dense well-ordered hydrogen bonding illustrated as black cylinders. Higher rigidity inducing an improved structural stability of the peptide in (B) in comparison to the fully oxidized peptide in (A) is apparent from the reference RMSF plot (C). Despite the rigidity of the backbone, the orientations of the basic residues differ from the native structure.