Hypo-glycosylated hFSH21/18 (possesses FSHβ21 and FSH18 bands) was isolated from hLH preparations by immunoaffinity chromatography followed by gel filtration. Fully-glycosylated hFSH24 was prepared by combining the fully-glycosylated FSHβ24 variant with hCGα and isolating the heterodimer. The hFSH21/18 glycoform preparation was significantly smaller than the hFSH24 preparation and possessed 60% oligomannose glycans, which is unusual for hFSH. Hypo-glycosylated hFSH21/18 was 9- to 26-fold more active than fully-glycosylated hFSH24 in FSH radioligand assays. Significantly greater binding of 125I-hFSH21/18 tracer than hFSH24 tracer was observed in all competitive binding assays. In addition, higher binding of hFSH21/18 was noted in association and saturation binding assays, in which twice as much hFSH21/18 was bound as hFSH24. This suggests that more ligand binding sites are available to hFSH21/18 in FSHR than to hFSH24. Hypo-glycosylated hFSH21/18 also bound rat FSHRs more rapidly, exhibiting almost no lag in binding, whereas hFSH24 specific binding proceeded very slowly for almost the first hour of incubation.
Follicle stimulating hormone (FSH) is one of the important hormones that regulate gonadal functions. This hormone is glycosylated, and the glycans greatly influence the biological properties. In the present study the negatively charged glycopeptides of equine and human pituitary follicle stimulating hormone (eFSH and hFSH) have been characterized in a glycosylation site-specific manner using FT-ICR-MS and Edman sequencing. The characteristic pattern of glycan distribution at each glycosylation site has been deduced and compared between horse and human FSH preparations. The data suggest that site-specific differences exist between glycoforms of human and equine FSH. For instance, except for one site in the beta subunit (Asn7) of hFSH all other sites in both species have sulfated glycoforms. Also, glycoforms at Asn52 of hFSH are all complex type, whereas in eFSH, both complex and hybrid structures exist at this site. There is also a higher percentage of sulfated glycans in the latter site compared to the former. This is the first study that characterizes the glycans from this hormone in a glycosylation site-specific manner, and these data can be used to begin correlative studies between glycosylation structure and hormone function.
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