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KMID : 0900920020260030299
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Korean journal of Animal Reproduction
2002 Volume.26 No. 3 p.299 ~ p.308
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On the Biological Functions of Equine Chorionic Gonadotropin
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Min Kwan-Sik
Yun Jong-Taek
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Abstract
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In horse, a single gene encodes both eCG and eLH beta subunits. The difference between eCG and eLH lies in the structure of their glycoresidues, which are both sialylated and sulfated in LH and sialylated in CG eCG consists of highly glycosyiated alpha- and beta-subunits and is an unique member of the gonadotropin family because it elicits response characteristics of both FSH and LH in other species than the horse. This dual activity of eCG in heterologous species is of fundamental interest to the study of gonadotropin structure-function relationships and the understanding of the molecular bases of the specific interactions of these hormones with their receptors. Thus, eCG is a dintinct molecule from the view points of its biological function and glycoresidue structures. The oligosaccharide at Asn 56 of the alpha-subunit plays an indispensable role, whereas the carboxyl-terminal extension of the eCG beta-subunit with its associated O-linked oligosaccharides is not improtant for, the in vitro LH-like activity of eCG. In contrast, both N- and O-linked oligosaccharides play important roles for FSH-like activity and increase FSH-like activity by removal of N- and O-linked oligosaccharides. Therefore, the dual LH- and FSH-like activities of eCG can be clearly separated by removal of either the N-linked oligosaccharide on the alpha-subunit or CTP-associated O-linked oligosaccharides from its beta-subunit. The glycoresidues seem to play crucial roles fer biological activities. The tethered-eCG was effciently secreted and showed similar LH-like activity to the dimeric eCG alpha/ beta and native eCG. FSH-like activity of the tethered-eCG was also shown similarly in comparison with the native and wild type eCG alpha/ beta. Our data for the first time suggest that the tethered-eCG can be expressed efficiently and the produced product by the CHO-Kl cells is fully LH- and FSH-like activities in rat in vitro bioassay system. Our results also suggest that this molecular can imply particular models ot FSH-like activity not LH-like activity in the eCG. Taken together, these data indicate that the constructs of tethered molecule will be useful in the study of mutants that affect subunit association and/or secretion.
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KEYWORD
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Equine chorionic gonadotropin, Biological activity, rec-eCG
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