The epitopes of human thyroid-stimulating hormone (hTSH) recognized by two murine monoclonal antibodies (MAbs), designated MAb 279 and MAb 299, have been characterized. These MAbs are highly specific for the β-subunit of TSH. The epitope recognized by MAb 279 appears to be completely conserved between bovine and human TSH and partially conserved in the porcine species, The TSH β-subunit epitope recognized by MAb 299 is only partially conserved between the human, bovine and porcine species. Both MAbs are capable of inhibiting the binding of TSH to its receptor in a TSH radioreceptor assay, indicating that the epitopes either coincide or are located close to the TSH β-subunit receptor-binding sites. The carbohydrate moieties of the TSH β-subunit appear 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 TSH. In addition, the amino acid sequence region between residues bTSH β34-44 could be excised by trypsin digestion of bovine TSH β (bTSHβ) without eliminating epitopic recognition by either MAb. These results provide further insight into the relationship between the structure of the TSH β-subunit epitopes and location of the receptor-binding sites.
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|Published - 1995