High-efficiency expression of mammalian beta-adrenergic receptors in baculovirus-infected insect cells.

Infection of a clonal isolate of Spodoptera frugiperda cells (Sf9) with a baculovirus expression vector harboring the cDNA encoding the beta-adrenergic receptor resulted in a high efficiency expression. At 48 hr post-infection, the level of expression of beta-adrenergic receptors was approximately 12 million/cell. Specific activities of crude lysates of infected Sf9 cells were approximately 30 pmol/mg of protein, 5-fold greater than those of membranes of high-expressor Chinese hamster ovary cells stably transfected with an SV-40 expression vector. One liter of infected Sf9 cells expresses 20-40 nmol of receptor. Autoradiography of membranes incubated with the beta-adrenergic antagonist [125I]iodoazidobenzylpindolol, photolyzed, and subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed 46,000- (presumably unglycosylated) and 48,000-Mr peptides for Sf9 cells as compared to approximately 65,000-Mr for Chinese hamster ovary cells. The baculovirus Sf9 system provides high-efficiency expression of receptor sufficient to permit physicochemical analyses.

Identification of a novel Mr = 76-kDa form of beta-adrenergic receptors.

The structure of the human beta-adrenergic receptor in purified basal membranes of human placental syncytiotrophoblast was probed using photoaffinity labeling. Basal membranes display a high specific activity of receptors (4-5 pmol/mg protein) and possess both beta 1- and beta 2-adrenergic receptors subtypes. Autoradiography of membranes that were incubated with the beta-adrenergic antagonist [125I]iodoazidobenzylpindolol, photolyzed and then subjected to sodium dodecylsulfate-polyacrylamide gel electrophoresis, identified four radiolabeled peptides, Mr = 65-kDa, 54-kDa, 43-kDa and a novel higher molecular weight 76-kDa form of the receptor. Photoaffinity labeling of each of these four peptides displayed the pharmacological properties expected for true beta-adrenergic receptors. The 76-kDa photoaffinity labeled receptor peptide observed in human placenta basal membranes has not been reported elsewhere. Competition studies with the beta1-selective ligand CGP-20712A demonstrate that the photoaffinity labeled receptor peptides are composed of both beta 1- and beta 2-adrenergic receptor subtypes.