Beta-subunits of equine chorionic gonadotropin and lutenizing hormone with an identical amino acid sequence have different asparagine-linked oligosaccharide chains.

The article investigates how the glycoprotein hormones equine chorionic gonadotropin (eCG) and lutenizing hormone (eLH) with identical beta-subunit amino acid sequences have different Asn-linked oligosaccharide chains.

Research Objectives and Strategy

• The chief objective of this research is to explore the differences in the Asn-linked oligosaccharide chains of the beta-subunits of eCG and eLH, despite their identical amino acid sequence.
• Researchers were able to liberate the oligosaccharide chains as tritium-labeled oligosaccharides from eCG beta and eLH beta. This was achieved by using a chemical method known as hydrazinolysis followed by N-acetylation and NaB3H4-reduction.

Analytical Methods and Findings

• Paper electrophoresis, in combination with sialidase digestion and solvolytic desulfation, was utilized to analyze the liberated oligosaccharides.
• Results showed that eCG beta contained neutral and sialylated oligosaccharides, while eLH beta contained neutral, sialylated, sulfated, and both sialylated and sulfated oligosaccharides.
• This variation in oligosaccharides suggests a difference in the Asn-linked oligosaccharide chains of the two glycoproteins, despite their identical amino acid sequences.

Further Verification and Conclusions

• To further validate their findings, researchers compared the elution profiles of the neutralized oligosaccharide mixtures from eCG beta and eLH beta on a Bio-Gel P-4 column.
• The elution profiles were different, reinforcing the idea that the molecular masses of oligosaccharides in the two glycoproteins are different.
• The research concludes that even with identical amino acid sequences, the structures of the Asn-linked oligosaccharide chains of eCG beta and eLH beta are different.