Figure 2.

(A) Binding mode of morphiceptin 1. Blue lines indicate π-cation interactions, and purple lines indicate salt bridges. The ligand is represented in brown and the receptor residues are represented in gray. (B) Two-dimensional diagram of the main interactions between morphiceptin and the residues involved in ligand recognition of the μ-opioid receptor (MOR) binding site. Purple lines represent hydrogen bonds, blue-red represent salt bridges, red lines represent π-cation, and green lines represent π-stacking. Hydrophobic residues are colored in green, negatively charged in red, polar in light blue and positively charged in purple.