Equine follicle-stimulating hormone: Molecular cloning of β subunit and biological role of the asparagine-linked oligosaccharide at asparagine56 of α subunit

Equine FSH (eFSH) and eCG are members of the glycoprotein hormone family. These proteins are heterodimeric, composed of noncovalently associated α and β subunits. We have previously reported that recombinant eCG has potent LH- and FSH-like activities and that the oligosaccharide at Asn¹⁶ of the α subunit plays an indispensable role in expressing LH- but not FSH-like activity. In the present study, we cloned eFSH β subunit cDNA and expressed wild-type recombinant eFSH and a partially deglycosylated mutant FSH (eFSH α56/β) to investigate the biological role of the oligosaccharide at Asn¹⁶ in FSH activity. The wild-type eFSH and eCG stimulated estradiol production in a dose-dependent manner in the primary cultures of rat granulosa cells, indicating that these equine gonadotropins have FSH activity. Partially deglycosylated eCG (eCG α56/β) also stimulated estradiol production, confirming that the FSH-like activity of eCG is resistant to the removal of the N-linked oligosaccharide. Partially deglycosylated eFSH (eFSH α56/β), however, did not show any FSH activity, indicating that the oligosaccharide at Asn⁵⁶ was necessary for eFSH. Thus, FSH-like activities of two gonadotropins, eCG and eFSH, are evoked through the distinct molecular mechanisms regarding the biological role of oligosaccharide at Asn⁵⁶ of the αsubunit.