A membrane-anchored form but not the secretory form of human chorionic gonadotropin-alpha chain acquires polylactosaminoglycan.
Large polylactosaminoglycans have only been observed linked to membrane proteins. To determine if membrane anchoring of a secretory protein might lead to the addition of polylactosaminoglycan, we have examined the carbohydrate structure on a membrane-anchored form of human chorionic gonadotropin-alpha subunit. This protein was generated by fusing the DNA encoding the human chorionic gonadotropin-alpha subunit to the DNA encoding the membrane-spanning and cytoplasmic domains of the vesicular stomatitis virus glycoprotein. DNAs encoding this hybrid form and the secretory form of human chorionic gonadotropin-alpha were expressed in monkey COS-1 cells using an SV40-based vector. We show here that the parent secretory glycoprotein contains typical Asn-linked complex-type oligosaccharides while the membrane-bound form contains large, heterogenous polylactosaminoglycans. We conclude that membrane anchoring increases the accessibility of the N-linked glycans to the enzymes involved in polylactosamine addition. The inhibitor 1-deoxymannojirimycin blocks addition of the polylactosaminoglycan.
D017485:1-Deoxynojirimycin; D000606:Amino Sugars / Q000378:metabolism*; D000818:Animals; D002460:Cell Line; D002850:Chromatography, Gel; D005944:Glucosamine / Q000031:analogs & derivatives / Q000378:metabolism / Q000494:pharmacology; D015292:Glycoprotein Hormones, alpha Subunit; D006031:Glycosylation; D000882:Haplorhini; D006801:Humans; D008715:Methionine / Q000378:metabolism; D008970:Molecular Weight; D010908:Pituitary Hormones, Anterior / Q000378:metabolism*; D011108:Polymers; D011134:Polysaccharides / Q000378:metabolism*
D000606:Amino Sugars; D015292:Glycoprotein Hormones, alpha Subunit; D010908:Pituitary Hormones, Anterior; D011108:Polymers; D011134:Polysaccharides; C039448:lactosaminoglycan; D017485:1-Deoxynojirimycin; D008715:Methionine; D005944:Glucosamine