Expression of a recombinant bifunctional protein from a chimera of human lutropin receptor and human chorionic gonadotropin β-subunit

Human lutropin (hLH) and human chorionic gonadotropin (hCG) are structurally and functionally similar and play important roles in reproduction via a common gonadal receptor (LH-R). However, hormone specific hCG-β subunit contains 24 additional amino acid carboxyl terminal peptide (CTP), which produce specific antibodies to hCG-β with little cross-reaction with LH. A chimeric protein containing both hLH-R and hCG-β would provide a unique bifunctional antigen for immunocontraception. In this study is described the synthesis of a chimeric DNA construct of full-length of hLH-receptor and hCG-β and its expression in Sf9 cells to produce a bifunctional protein. Recombinant protein was recognized by antibodies to LH-R as well as anti-hCG-β in Western Blots, thus indicating the preservation of immunological epitopes for both hLH-R and hCG-β in the chimera. Specific ligand binding of recombinant hLH-R component was demonstrated by the displacement of bound labeled hCG at increasing concentrations of unlabeled hCG, indicating that, the presence of hCG-β component of the chimera did not interfere with the binding of hCG to LH-R. hCG-β was also present in the recombinant chimeric protein as shown by a specific hCG-β chemiluminescence assay. Treatment of transfected Sf9 cells with hCG induced dose-dependent increase in the stimulation of intracellular cAMP production, which showed that the ligand binding had functional activity. These results demonstrate that the chimeric DNA construct of hLHR-hCG-β expressed a bifunctional protein containing both hLH-R and hCG-β activities, which could provide a unique potential antigen for immunocontraception in vertebrates.