Site-specific and complete enzymic deglycosylation of the native human chorionic gonadotropin α-subunit

Abstract

Numerous studies have shown that glycosylation of the alpha-subunit of human chorionic gonadotropin (αCG) is essential for the biological activity of this hormone. To obtain detailed insight into the function of N-glycosylation, the availability of site-specifically and fully deglycosylated alpha-subunits obtained under non-denaturing conditions is a prerequisite. NMR spectroscopy in combination with FAB-mapping demonstrates that only Asn52 of the α-subunit is accessible to digestion by peptide-N4-(N -acetyl-β-glucos-aminyl)asparagine amidase F under native conditions. Treatment of native αhCG with endo-β-N -acetylglucosaminidase B results in full deglycosylation yielding αhCG with one GlcNAc residue at both Asn52 and Asn78.