The common α subunit of bovine glycoprotein hormones: Limited formation of native structure by the totally nonglycosylated polypeptide chain
✍ Scribed by Thomas W. Strickland; Arlen R. Thomason; John H. Nilson; John G. Pierce
- Publisher
- John Wiley and Sons
- Year
- 1985
- Tongue
- English
- Weight
- 736 KB
- Volume
- 29
- Category
- Article
- ISSN
- 0730-2312
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✦ Synopsis
The folding of the bovine glycoprotein hormone a subunit, synthesized in bacteria following insertion of the nucleotide sequence coding for this polypeptide, has been studied to determine the effect that a complete lack of carbohydrate has on this process. The bacterially derived a polypeptide (bac-a), extracted from E. coli in the presence of reductant and denaturant, had an estimated 0.2% native structure as determined by a conformationally sensitive radioimmunoassay . Upon reduction of disulfide bonds and reoxidation in air, the amount of native structure increased about 18-fold. Approximately 2 % of the refolded bac-a preparation combines with the (3 subunit of human chorionic gonadotropin (hCGP) to form a complex that binds to the gonadotropin receptor and elicits a biological response. Since the correct folding (by immunological criteria) of bac-a (ca 3 % ) is significantly greater than expected from a random formation of disulfide bonds (0.1 %), it appears that correct folding of a subunit can occur in the complete absence of carbohydrate, though in very low yield. Native bovine lutropin a subunit (LHa) and chemically deglycosylated L H a (which retains two asparagine-linked N-acetyl glucosamine residues per a oligosaccharide) were subjected to the same reduction/ reoxidation regimen as the bacterially produced a subunit. As has been reported previously [Giudice LC, Pierce, JG, J Biol Chem 251: 6392, 19761 intact LHa fully regained its native structure. The partially deglycosylated LHa also refolds to a native-like structure in high yield as assessed by immunological assays and by its ability to combine with HGC(3 to form a biologically active complex.