- Opioid Receptor Functional Interaction: Insight Using Receptor-G Protein Fusions

Fusion proteins between a receptor and a pertussis toxin-insensitive Gi subunit were used to gain insight into the mo-lecular interactions that take place upon and opioid recep-tor heterodimerization. When opioid receptor-Gi1 fusions were coexpressed with nonfused opioid receptors in human embryonic kidney 293 cells, or vice versa, receptor het-erodimers were detected by coimmunoprecipitation. In per-tussis toxin-treated cells, receptor coexpression decreased the amount of guanosine 5-O-(3-[35S]thio)triphosphate ([35S]GTPS) incorporated in the fused G protein after the addition of agonists specific for the receptor-Gi1 fusion. In addition, activation of the G protein occurred in heterodimers upon addition of an agonist specific for the nonfused receptor. It remained unaffected by an inverse agonist specific for th