All-or-none N-glycosylation in primate follicle-stimulating hormone beta-subunits.
ABSTRACT Human FSH exists as two major glycoforms designated, tetra-glycosylated and di-glycosylated hFSH. The former possesses both alpha- and beta-subunit carbohydrates while the latter possesses only alpha-subunit carbohydrate. Western blotting differentiated the glycosylated, 24,000 M(r) hFSHbeta band from the non-glycosylated 21,000 M(r) FSHbeta band. Postmenopausal urinary hFSH preparations possessed 75-95% 24,000 M(r) hFSHbeta, while pituitary hFSH immunopurified from 21- to 43-year-old females and 21-43-year-old males possessed only 35-40% 24,000 M(r) hFSHbeta. The pituitary hFSH from a postmenopausal woman on estrogen replacement was 75% 21,000 M(r) hFSHbeta. Other immunopurified postmenopausal pituitary hFSH preparations possessed 50-60% 21,000 M(r) hFSHbeta. Gel filtration removed predominantly 21,000 M(r) free hFSHbeta and reduced its abundance to 13-22% in postmenopausal pituitary hFSH heterodimer preparations. A major regulatory mechanism for FSH glycosylation involves control of beta-subunit N-glycosylation, possibly by inhibition of oligosaccharyl transferase. Two primate species exhibited the same all-or-none pattern of pituitary FSHbeta glycosylation.
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ABSTRACT: The effects of glycosylation beyond the Asn-linked GlcNAc residues on the stability of the α subunit of human chorionic gonadotropin are investigated, using enzymatic deglycosylation and NMR spectroscopy. Comparison of thermal denaturation profiles of both the intact α subunit and the α subunit carrying only GlcNAc monomers at both Asn52 and Asn78 established a small but significant decrease in thermal stability of the deglycosylated form. Since there is no secondary structure around Asn52 in the free subunit these results demonstrate that glycosylation beyond the Asn78-linked GlcNAc residue enhances the thermal stability of the α subunit of hCG. This feature has implications for understanding the effect of glycosylation on protein stabilization in general.Biochemical and Biophysical Research Communications 01/1997; 232(1):117-120. · 2.41 Impact Factor
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ABSTRACT: Lentil lectin-bound, fucose-enriched hTSH was reported to stimulate both cAMP and inositol phosphate (IP) intracellular signalling pathways, whereas fucose-depleted hTSH stimulated only the cAMP pathway. Gonadotropins activate the cAMP pathway and in several studies higher concentrations activate the IP pathway. Since only the 10% of α subunit Asn56 oligosaccharides (Asn52 in humans) are fucosylated, the higher glycoprotein hormone concentrations required for IP pathway activation might be related to the abundance of competent hormone isoforms. Lentil lectin-fractionated equine (e)LHα and eFSHα preparations were combined with a truncated, des(121–149)eLHβ preparation. All four hybrid hormone preparations induced IP accumulation in porcine theca cells, suggesting that activation of the IP pathway was not dependent on fucosylation at α subunit Asn56. However, the presence of Asn56 carbohydrate was necessary for increased IP accumulation. Intact, rather than Asn56-deglycosylated eLH preparations provoked a biphasic steroidogenic response by rat testis Leydig cells, suggesting that Gαi stimulation was also sensitive to loss of Asn56 carbohydrate. While rat granulosa cells responded to human FSH preparations in a biphasic manner, a classical sigmoidal response was obtained to eFSH and Asn56-deglycosylated eFSH, suggesting that the equine preparations did not activate Gαi. Purified oLHα Asn56 oligosaccharides inhibited FSH-stimulated steroidogenesis in rat granulosa cell cultures indicating a direct role for carbohydrate in FSH action. The same carbohydrate preparation inhibited hCG-stimulated fluorescence energy transfer suggesting oligosaccharide involvement in activated LH receptor self-association.Molecular and Cellular Endocrinology - MOL CELL ENDOCRINOL. 01/2003; 199(1):73-86.
- Endocrinology 01/1973; 92(6):1660-1666. · 4.72 Impact Factor