Peptide mapping of intersubunit and receptor interactions of human choriogonadotropin

Abstract

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 ED 50 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 ED 50 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.