FIGURE 10.

Aromatic-aromatic interactions. A, axes and definition of polar coordinates (r, φ, and θ) as originally defined by Burley and Petsko (44). Ψ provides the dihedral angle between the two planes formed by each of the aromatic rings. The two interacting aromatic rings are shown in red. B, interacting pairs of aromatic rings at the dimer interface of WT insulin and the 3-I-Tyr^B26 analog. Upper panel, Phe^B24/Tyr^B26, Phe^B24/Phe^B24′, Phe^B24/Tyr^B26, and Tyr^B26/Tyr^B16′; primed residue numbers indicate the dimer-related residue A representative WT structure (green) is overlaid in comparison with the side chains of the 3-[iodo-Tyr^B26,Nle^B29]insulin structure (cyan). Lower panel, Phe^B25/Phe^B25 interaction pair and its three possible conformations. Images of representative Phe^B25 side chains from the crystal structure of 3-I-Tyr^B26; the side chains of [Nle^B29]insulin are not shown due to dynamic disorder. WT coordinates were obtained from PDB code 1ZNJ.