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The glycoprotein hormones: recent studies of structure-function relationships
R J Ryan1, M C Charlesworth, D J McCormick
1Department of Biochemistry and Molecular Biology, Mayo Medical School, Rochester, Minnesota 55905.
Summary
Glycoprotein hormones like LH and hCG bind to receptors via specific sites on their alpha and beta subunits. Carbohydrates are crucial for biological responses, not receptor binding.
Area of Science:
- Endocrinology
- Molecular Biology
- Biochemistry
Background:
- Heterodimeric glycoprotein hormones (LH, FSH, TSH, hCG) play critical roles in endocrine signaling.
- Carbohydrate chains influence hormone function, but their role in receptor binding versus biological response requires clarification.
Purpose of the Study:
- To investigate the structural regions of glycoprotein hormones responsible for receptor binding and biological activity.
- To elucidate the role of specific peptide sequences and carbohydrate moieties in hormone-receptor interactions.
Main Methods:
- Review of existing structural data on glycoprotein hormones.
- Analysis of studies using synthetic peptides to replicate regions of alpha and beta subunits.
- Assessment of hormone binding to membrane receptors and biological responses.
Main Results:
- Removal of carbohydrate chains reduced biological responses but not receptor binding.
- Specific regions on the alpha subunit (residues 26-46 and 75-92) are involved in LH, hCG, and TSH receptor binding.
- Synthetic peptides from the hCG beta subunit (38-57 and 93-100) blocked hCG receptor binding.
- The beta 38-57 peptide stimulated testosterone production.
Conclusions:
- Glycoprotein hormone receptor binding involves a discontinuous site spanning both alpha and beta subunits.
- Alpha subunit binding sites are conserved across LH, hCG, and TSH.
- Carbohydrates are essential for mediating biological responses, not initial receptor recognition.