The third extracellular loop of the human delta-opioid receptor (hDOR) is known to play an important role in the binding of delta-selective ligands. In particular, mutation of three amino acids (Trp(284), Val(296), and Val(297)) to alanine significantly diminished delta-opioid receptor affinity for delta-selective ligands. To assess the changes in conformation accompanying binding of the endoge...
