Figure 3.

Two views of the structure of HH21. (A) ΔPhe side chains from two shape-complement helices stack one against the other resulting in a core with extended phenyl embrace arrangement. The thin dotted lines represent additional weak interactions such as C—H—O, N—H—π responsible for helix–helix association and turn stabilization and thick dotted (colored white) line represents the 4→1 N—H—O hydrogen bond at the type I β-turn region. Thin lines (green) with the corresponding values (4.62 Å, 4.96 Å) are the distances between the C_α atoms of the two ΔPhe residues stacking one above the other and belong to the two shape-complement helices. These distances highlight the extent of intercalation of the side chains belonging to two shape-complement helices. (B) Another view of the molecule.