Structural features of mammalian gonadotropins

Area of Science:

• Endocrinology
• Molecular Biology
• Protein Chemistry

Background:

• Pituitary and placental gonadotropins from humans and horses are available for study.
• Equine gonadotropins present exceptions to established structure-function principles of mammalian gonadotropins.
• Differences in glycosylation and gene expression distinguish equine from human gonadotropins.

Purpose of the Study:

• To investigate the role of glycosylation in the differential receptor binding affinities of equine luteinizing hormone (eLH) and equine chorionic gonadotropin (eCG).
• To evaluate the contribution of N-linked oligosaccharides on the alpha subunit to the biological activities of equine gonadotropins.
• To explore the influence of the equine alpha subunit on heterodimer potency and receptor binding.

Main Methods:

• Selective removal of oligosaccharides using peptide-N-glycanase digestion.
• Analysis of oligosaccharide patterns on native equine alpha-subunit preparations.
• Construction and activity assessment of hybrid hormones and chimeric subunits.

Main Results:

• Oligosaccharide moieties significantly affect receptor binding affinity, with eCG showing lower affinity than eLH.
• Removal of alpha Asn56 N-linked oligosaccharides enhanced subunit association and receptor binding.
• The equine alpha-subunit N-terminal domain appears to enhance LH receptor binding activity.
• Equine FSH exhibits higher FSH receptor binding activity, attributed to the alpha subunit and beta subunit charge.

Conclusions:

• Glycosylation patterns on equine gonadotropins critically influence their biological activity and receptor interactions.
• The equine alpha subunit plays a key role in promoting receptor binding and potentially determining heterodimer potency.
• Structural variations in equine gonadotropins provide valuable insights into conserved and divergent mechanisms of hormone-receptor recognition.