THYROTROPIN AND ITS RECEPTOR

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Although the primary structure of human TSH as well as the structurally similar gonadotropins LH, FSH, and hCG, has been determined, the three dimensional structure of the hormone and the details of its structure-function relationships remain unknown. Current evidence suggests that several hormone sites are involved in the interaction of TSH with its receptor and that the sites involve both the TSH specific beta-subunit as well as the alpha-subunit that is common to all four hormones. Our recent studies, using a synthetic peptide approach, identified two regions within the common alpha-subunit and four regions of beta-TSH that possess binding activity for TSH receptors. The synthetic peptides representing these sequences were not hormone agonists, but proved to be antagonists of the intact hormones in bioassay and also inhibited the bioactivity of the thyroid stimulating immunoglobulins (TSI) that are the cause of the hyperthyroidism observed in patients with Graves' disease. In the current application I propose: 1) to study the structure-function relationships of the hTSH alpha-subunit and to identify further the specific residues of the subunit that thyroid specific binding and perhaps bioactivity using a synthetic peptide strategy; 2) to develop specific inhibitors of TSH by substitution, deletion, and/or chemical modification of the above identified active amino acid residues; 3) to use a similar synthetic peptide approach in the study of the recently cloned human TSH receptor (hTSHr) in order to identify the specific regions of the receptor that are involved in hormone binding; and 4) to identify the epitope for the auto-antibodies directed against the hTSHr found in patients with Graves' disease using the synthetic receptor peptides generated for the above aim (3). Both the development of inhibitors of TSH, and the identification of the auto-epitope of the receptor by the synthetic peptide should be considered important first steps in the direction of specific immune therapy of autoimmune thyroid disease.