Site‐Specific and Complete Enzymic Deglycosylation of the Native Human Chorionic Gonadotropin α‐Subunit

Numerous studies have shown that glycosylation of the α‐subunit of human chorionic gonadotropin (αhCG) 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 α‐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.