Carbohydrate-dependent epitope mapping of human thyrotropin

Area of Science:

• Endocrinology
• Glycobiology
• Immunochemistry

Background:

• Human thyroid-stimulating hormone (hTSH) is a glycoprotein hormone essential for thyroid function.
• Carbohydrate chains on glycoprotein hormones play roles in their conformation and biological activity.
• Understanding the role of glycosylation in hTSH structure and antigenicity is important for diagnostics and therapeutics.

Purpose of the Study:

• To investigate the impact of glycosylation on the antigenic properties of hTSH.
• To determine which subunits and epitopes are affected by deglycosylation.
• To differentiate between glycosylation-dependent and independent epitopes on hTSH.

Main Methods:

• Preparation of radiolabeled native, partially deglycosylated, and fully deglycosylated hTSH.
• Screening of monoclonal antibodies for binding to intact and deglycosylated hTSH and its subunits.
• Solid-phase and competitive binding assays using monoclonal and polyclonal antibodies.

Main Results:

• Partially deglycosylated hTSH showed identical binding to monoclonal antibodies as native hTSH.
• Fully deglycosylated hTSH exhibited significantly reduced binding to antibodies targeting the hormone and the beta-subunit, but preserved binding to anti-alpha antibodies.
• Deglycosylation of individual subunits did not alter antibody recognition, indicating the effect is on the dimer.
• Polyclonal antisera showed reduced binding to deglycosylated hTSH, suggesting glycosylation-independent epitopes on the beta-subunit.

Conclusions:

• Most epitopes involved in subunit association and on the beta-subunit of hTSH are dependent on glycosylation.
• The alpha-subunit possesses glycosylation-independent epitopes.
• Carbohydrate chains significantly influence the conformation and antigenicity of the hTSH dimer.