PEPTIDE-MAPPING OF INTERSUBUNIT AND RECEPTOR INTERACTIONS OF HUMAN CHORIO-GONADOTROPIN

Seven peptides covering the entire sequence of human choriogonadotropin (hCG) α-subunit, eight peptides covering the hCG β-subunit sequence and two peptides, one of human β-lutropin and one of β-thyrotropin were synthesized. We checked their ability to prevent reassociation between hCG α- and β-subunits and between hCG and its receptor. Only the α1-22, α59-92 and β1-16 peptides inhibited the reassociation between the α- and β-subunits of hCG with an ED50 of respectively 2 mM, 2 mM and 4 mM. Using porcine Leydig cells in primary culture, we showed that α33-59, α41-59 and β1-16 peptides decreased both the specific binding to the cell surface and the intemalization of [125I]hCG and [125I]porcine LH with ED50 of 0.3, 0.1 and 0.5 mM, respectively. From these results, the following minimal area may be assigned, (i) to the α-β interaction: α5-16, α52-72 (or α59-70) and β8-16, and (ii) to the hormone-receptor association: α41-45 and β8-16. © 1990.