Conformation of the beta subunit of deglycosylated human chorionic gonadotropin in the interaction at receptor sites.
The present study was performed to evaluate the relationship between the antagonist effect and the conformation of deglycosylated human chorionic gonadotropin (DGhCG) on the Leydig cell lutropin receptors. The maximum binding of [125I]DGhCG to anti-hCG beta antibody was decreased by 50%, while its binding profile to anti-hCG, anti-DGhCG and anti-hCG alpha antibodies remained unchanged, suggesting conformational changes in the beta subunit of DGhCG. However, the association of [125I]DGhCG to the binding sites of the receptors was much faster than that of [125I]hCG, and the ligand reached the binding equilibrium at 4 and 37 degrees C for 3 h and 15-30 min, respectively. Thus, the conformational changes in the beta subunit were not accompanied by loss of its receptor binding ability. The agonist properties of DGhCG which was bound to the receptors was fully restored by the addition of anti-hCG beta subunit antibody, while anti-hCG or anti-DGhCG restored only about 30% of the full agonist activity. This was probably due to a change of the conformation of the beta subunit to make it similar to that of the intact hormone. This restoration caused by anti-hCG beta was partially prevented by anti-hCG alpha. These facts indicate that some conformational change only in the beta subunit, not in the alpha subunit, of the deglycosylated hormone bound to the receptors is essential for the restoration of agonist properties.
Hattori
M
M
Hormone Assay Center, Institute of Endocrinology, Gunma University, Maebashi, Japan.
Hachisu
T
T
Shimohigashi
Y
Y
Wakabayashi
K
K
D000818:Animals; D001666:Binding Sites, Antibody / Q000032:analysis; D006063:Chorionic Gonadotropin / Q000032:analysis* / Q000276:immunology / Q000378:metabolism; D006801:Humans; D007457:Iodine Radioisotopes; D008968:Molecular Conformation; D051381:Rats; D011967:Receptors, Gonadotropin / Q000276:immunology / Q000378:metabolism*
D006063:Chorionic Gonadotropin; C034923:HCG, deglycosylated; D007457:Iodine Radioisotopes; D011967:Receptors, Gonadotropin