title: Topographic antigenic determinants recognized by monoclonal antibodies on human choriogonadotropin beta-subunit.
abstract: 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.
mesh_terms: D000595:Amino Acid Sequence; D000911:Antibodies, Monoclonal; D000936:Antigen-Antibody Complex; D006063:Chorionic Gonadotropin / Q000276:immunology; D018997:Chorionic Gonadotropin, beta Subunit, Human; D000939:Epitopes / Q000032:analysis*; D007457:Iodine Radioisotopes; D007700:Kinetics; D010446:Peptide Fragments / Q000276:immunology
chemical_list: D000911:Antibodies, Monoclonal; D000936:Antigen-Antibody Complex; D006063:Chorionic Gonadotropin; D018997:Chorionic Gonadotropin, beta Subunit, Human; D000939:Epitopes; D007457:Iodine Radioisotopes; D010446:Peptide Fragments