Opioid receptor, delta 1 (DRD4) is a G-protein coupled receptor that functions as receptor for endogenous enkephalins and for a subset of other opioids. Ligand binding causes a conformation change that triggers signaling via guanine nucleotide-binding proteins (G proteins) and modulates the activity of down-stream effectors, such as adenylate cyclase and signaling leads to the inhibition of adenylate cyclase activity. DRD4 inhibits neurotransmitter release by reducing calcium ion currents and increasing potassium ion conductance. DRD4 plays a role in the perception of pain and in opiate-mediated analgesia and in developing analgesic tolerance to morphine. References: The UniProt Consortium. Nucleic Acids Res. 47: D506-515 (2019); Nucleic Acids Res. 2016 Jan 4;44(D1):D733-45, PMID:26553804