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An insertion in the human thyrotropin receptor critical for high affinity hormone binding
H L Wadsworth1, G D Chazenbalk, Y Nagayama
1Department of Medicine, Veterans Administration Medical Center, San Francisco, CA 94121.
Science (New York, N.Y.)
|September 21, 1990
Summary
A specific eight-amino acid region in the thyrotropin (TSH) receptor is crucial for TSH and thyroid-stimulating immunoglobulin (TSI) binding and activity. A larger 50-amino acid insertion has no significant impact.
Area of Science:
- Endocrinology
- Molecular Biology
- Receptor Binding Studies
Background:
- Thyrotropin (TSH), luteinizing hormone (LH), and chorionic gonadotropin (CG) are structurally related glycoprotein hormones.
- These hormones bind to receptors with high sequence similarity, but the TSH receptor possesses unique extracellular domain insertions.
- The functional relevance of these insertions in the TSH receptor is not fully understood.
Purpose of the Study:
- To investigate the functional significance of two unique amino acid insertions in the extracellular domain of the TSH receptor.
- To determine the role of these insertions in the binding and biological activity of TSH and thyroid-stimulating immunoglobulin (TSI).
Main Methods:
- Site-directed mutagenesis was employed to create TSH receptor variants with deleted or substituted amino acid insertions.
- TSH binding assays were performed to assess the effect of mutations on hormone interaction.
- Biological activity assays were conducted using TSH and TSI to evaluate receptor function post-mutation.
Main Results:
- Deletion of a 50-amino acid tract (residues 317-366) in the TSH receptor did not affect TSH binding or biological activity.
- Deletion or substitution of an eight-amino acid region (residues 38-45) near the amino terminus abolished TSH and TSI binding and activity.
- The eight-amino acid tract is identified as a critical interaction site for TSH and TSI.
Conclusions:
- The eight-amino acid region (residues 38-45) of the TSH receptor is essential for mediating the biological effects of TSH and TSI.
- The 50-amino acid insertion (residues 317-366) is functionally insignificant for TSH and TSI interactions.
- This study elucidates a key functional domain within the TSH receptor involved in thyroid hormone regulation and autoimmune thyroid disease pathogenesis.