Reconstitution of the solubilized μ-opioid receptor coupled to a GTP-binding protein

A μ-opioid receptor-GTP binding protein (μ-opioid receptor-G-protein) complex from the 7315c cell was solubilized with CHAPS (3-[(3-cholamidopropyl)dimethylammonio]-1-propane sulfonate) and reconstituted into phospholipid vesicles. Pretreatment of the tissue with either [ 3H]etorphine or morphine greatly improved recovery of the receptor and maintained it in a GTP-sensitive state. GTP sensitivity was consistent with the hypothesis that a receptor-G-protein complex had been obtained. Other evidence consistent with this hypothesis was that recovery of the solubilized, prelabelled receptor was decreased by approximately 70% by pretreatment of 7315c cells with pertussis toxin. The reconstituted receptor was μ-selective: DAGO (Tyr-D-Ala-Gly-Met-Phe-NH(CH 2) 2OH), but not ICI 174864 or U50488-H, displaced [ 3H]etorphine binding with high affinity. The affinity of the reconstituted receptor for [ 3H]etorphine (1.25 ± 0.20 nM) was similar to that observed for the membrane-associated receptor (0.53 ± 0.25 nM). GTPγS decreased this affinity 3-fold without changing the number of binding sites. The potencies of GTPγS and GTP in diminishing [ 3H]etorphine binding were similar in the membrane and vesicle preparations, but were 10-fold lower than the potencies observed in diminishing binding to the solubilized receptor. The ability to reconstitute a functional μ-opioid receptor-G-protein complex will facilitate further study of the structure and function of the receptor and the specific identification of the associated GTP-binding protein(s).