Topographic antigenic determinants recognized by monoclonal antibodies on human choriogonadotropin beta-subunit

• Published in: The Journal of biological chemistry 1987-06, Vol.262 (18), p.8551-8556
• Main Authors: Bidart, J M, Troalen, F, Salesse, R, Bousfield, G R, Bohuon, C J, Bellet, D H
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Analytical, structural and metabolic biochemistry; Antibodies, Monoclonal; Antigen-Antibody Complex; Biological and medical sciences; Chorionic Gonadotropin - immunology; Chorionic Gonadotropin, beta Subunit, Human; Epitopes - analysis; Fundamental and applied biological sciences. Psychology; Glycoproteins; Iodine Radioisotopes; Kinetics; Peptide Fragments - immunology; Proteins
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1016/S0021-9258(18)47449-2

We describe a first attempt to study the antibody-combining sites recognized by monoclonal antibodies raised against the beta-subunit of human choriogonadotropin (hCG). Two groups of antibodies were first defined by their ability to recognize only the free beta-subunit or the free and combined subunit. Antibodies FBT-11 and FBT-11-L bind only to hCG beta-subunit but not to hCG, whereas antibodies FBT-10 and D1E8 bind to both the beta-subunit and the hormone. In both cases, the antigenic determinants were localized to the core of the protein (residues 1-112), indicating the weak immunogenicity of the specific carboxyl-terminal extension of hCG-beta. Nine synthetic peptides spanning different regions of hCG-beta and lutropin-beta were assessed for their capacity to inhibit antibody binding. A synthetic peptide inclusive of the NH2-terminal region (residues 1-7) of the hCG beta-subunit was found to inhibit binding to the radiolabeled subunit of a monoclonal antibody specific for free hCG-beta (FBT-11). Further delineation of the antigenic site recognized by this antibody provided evidence for the involvement of fragment 82-92. Moreover, monoclonal antibody FBT-11 inhibited the recombination of hCG-beta to hCG-alpha, indicating that its antigenic determinant might be located nearby or in the hCG-beta portion interacting with the alpha-subunit. Binding of monoclonal antibody FBT-10, corresponding to the second antigenic determinant, was weakly inhibited by fragment 82-105 and did not impair the recombination of the hCG beta-subunit to the hCG alpha-subunit. Its combining site appeared to be located in a region of the intact native choriogonadotropin present at the surface of the hormone-receptor complex.