Carbohydrate and peptide structure of the α- and β-subunits of human chorionic gonadotropin from normal and aberrant pregnancy and choriocarcinoma

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Abstract
Human chorionic gonadotropin (hCG), purified from the urine of 14 individuals with normal pregnancy, diabetic pregnancy, hydatidiform mole, or choriocarcinoma, plus two hCG standard preparations, was examined for concurrent peptide-sequence and asparagine (N)- and serine (O)-linked carbohydrate heterogeneity. Protein-sequence analysis was used to measure amino-terminal heterogeneity and the “nicking” of internal peptide bonds. The use of high-pH anion-exchange chromatography coupled with the increased sensitivity of pulsed amperometric detection (HPAE/PAD) revealed that distinct proportions of both hCG α- and β-subunits from normal and aberrant pregnancy are hyperglycosylated, and that it is the extent of the specific subunit hyperglycosylation that significantly increases in malignant disease. Peptide-bond nicking was restricted to a single linkage (β47–48) in normal and diabetic pregnancy, but occurred at two sites in standard preparations, at three sites in hydatidiform mole, and at three sites in choriocarcinoma β-subunit. In the carbohydrate moiety, α-subunit from normal pregnancy hCG contained non-fucosylated, mono-and biantennary N-linked structures (49.3 and 36.7%, means); fucosylated biantennary and triantennary oligosaccharides were also identified (7.3 and 6.9%). In choriocarcinoma α-subunit, the level of fucosylated biantennary increased, offset by a parallel decrease in the predominant biantennary structure of normal pregnancy (PN-acetylglucosaminyltransferase IV, in distinct proportions of subunit molecules.

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