[Molecular biological study on structure and function of the opioid receptor].

Pharmacological actions of opioid analgesics are mediated by the mu-, delta- and kappa-opioid receptors in the nervous system. To understand the molecular basis of the opioid receptor functions, experiments using molecular biological methods have been performed. Amino acid sequences elucidated by cDNA cloning revealed that the opioid receptor possesses characteristic structural features of the G-protein-coupled receptor family, including the presence of seven transmembrane segments. Furthermore, molecular mechanism for the ligand selectivity of the mu- and delta-opioid receptors was investigated by analyzing chimeric receptors between the mu- and delta-receptors and mutant receptors with one amino acid replacement.