EXPRESSION OF FUNCTIONAL LUTROPIN CHORIOGONADOTROPIN RECEPTOR IN THE BACULOVIRUS SYSTEM

The LH/CG receptor (LH/CG-R) is a G protein-coupled receptor with a re latively large glycosylated extracellular domain. The complete 674 ami no acid residue rat receptor was expressed in Sf9 insect cells using t he baculovirus expression system. Optimal expression under the control of the polyhedrin promoter was obtained at 72 h post-infection and a multiplicity of infection of 0.1. The recombinant LH/CG-R was expresse d on the cell surface (ca. 4500 receptors/cell) and exhibited saturabl e, high affinity binding of human CG (hCG) with a K-d of 0.4 nM. There was no evidence of intracellular trapping of the receptor. The intrac ellular concentration of cAMP was increased in response to hCG binding . In contrast, baculovirus-expressed recombinant hCG only weakly stimu lated intracellular cAMP levels at relatively high doses. Two forms of the receptor (similar to 75 and similar to 200 kDa) were detected by Western blot analysis, These results demonstrate that the full length LH/CG-R expressed in insect cells is functional in that it binds hormo ne with high affinity and is able to couple to adenylate cylase.