IMMUNOCHEMICAL CHARACTERIZATION OF 2 THYROID-STIMULATING HORMONE BETA-SUBUNIT EPITOPES

The epitopes of human thyroid-stimulating hormone (hTSH) recognized by two murine monoclonal antibodies (MAbs), designated MAb 279 and MAb 2 99, have been characterized. These MAbs are highly specific for the be ta-subunit of TSH. The epitope recognized by MAb 279 appears to be com pletely conserved between bovine and human TSH and partially conserved in the porcine species, The TSH beta-subunit epitope recognized by MA b 299 is only partially conserved between the human, bovine and porcin e species. Both MAbs are capable of inhibiting the binding of TSH to i ts receptor in a TSH radioreceptor assay, indicating that the epitopes either coincide or are located close to the TSH beta-subunit receptor -binding sites. The carbohydrate moieties of the TSH beta-subunit appe ar to play little or no role in the epitope recognition by MAb 279 or MAb 299 while the integrity of the disulphide bonds are essential. The epitopic recognition may also involve lysine residues, as determined by the immunoreactivity with both MAbs following citraconylation of TS H. In addition, the amino acid sequence region between residues bTSH b eta 34-44 could be excised by trypsin digestion of bovine TSH beta (bT SH beta) without eliminating epitopic recognition by either MAb. These results provide further insight into the relationship between the str ucture of the TSH beta-subunit epitopes and location of the receptor-b inding sites.