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Two-subunit structure of the human thyrotropin receptor
H Loosfelt1, C Pichon, A Jolivet
1Institut National de la Santé et de la Recherche Médicale, Hôpital de Bicêtre, Le Kremlin Bicêtre, France.
Summary
Researchers characterized the human thyrotropin receptor, finding it comprises two disulfide-linked subunits. These subunits, alpha (hormone binding) and beta (membrane-spanning), are derived from a single precursor and located on the basolateral cell membrane.
Area of Science:
- Molecular Endocrinology
- Receptor Biology
- Protein Biochemistry
Background:
- The human thyrotropin receptor (TSHR) mediates the effects of thyrotropin (TSH) in the thyroid gland.
- Understanding TSHR structure is crucial for comprehending thyroid hormone regulation and related pathologies.
Purpose of the Study:
- To characterize the subunit composition and structural properties of the human thyrotropin receptor.
- To generate specific antibodies for TSHR subunit identification and localization.
Main Methods:
- Expression of extracellular and intracellular TSHR domains in Escherichia coli.
- Production of monoclonal anti-receptor antibodies.
- Immunoblot analysis and immunoaffinity purification.
- Deglycosylation using N-glycosidase F.
- Immunocytochemistry on human thyroid tissue.
Main Results:
- The TSHR is a disulfide-linked heterodimer, likely arising from proteolytic cleavage of a 90-kDa precursor.
- The extracellular alpha subunit (53 kDa, 35 kDa deglycosylated) binds TSH.
- The membrane-spanning beta subunit exhibits heterogeneity (33-42 kDa).
- Human thyroid membranes show a 2.5-3 fold excess of beta subunits over alpha subunits.
- Both subunits are present in follicular thyroid cells, localized to the basolateral membrane.
Conclusions:
- The human TSHR exists as a heterodimer composed of alpha and beta subunits.
- Subunit stoichiometry and localization provide insights into TSHR function and regulation.
- The generated antibodies are valuable tools for studying TSHR structure and function.