Determination of the glycoforms of human chorionic gonadotropin beta-core fragment by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

TY - JOUR

T1 - Determination of the glycoforms of human chorionic gonadotropin beta-core fragment by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

AU - Jacoby, E S

AU - Kicman, A T

AU - Laidler, P

AU - Iles, R K

PY - 2000

Y1 - 2000

N2 - Background: Metabolism of human chorionic gonadotropin (hCG) in the serum and kidney yields the terminal urinary product hCG beta -core fragment (hCG beta cf), comprising two disulfide-linked peptides (beta6-beta 40 and beta 55-beta 92) of which one (beta6-beta 40) retains truncated N-linked sugars. Hyperglycosylated hCG beta cf may indicate choriocarcinoma or Down syndrome, but the glycosylation profile of hCG beta cf has not been thoroughly evaluated. Methods: hCG beta cf, purified from pregnancy urine, was reduced by "on-target" dithiothreitol (DTT) reduction and analyzed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). The mass ([M+H](+)) of the primary sequence of the glycosylated peptide beta6-beta 40 was subtracted from the m/z values of the discrete peaks observed to give the masses of the carbohydrate moieties. Carbohydrate structure was predicted by sequentially subtracting the masses of the monosaccharide residues corresponding to N-linked carbohydrates of the hCG beta -subunit reported in the literature. Results: Mass spectra of hCG beta cf revealed a broad triple peak at m/z 8700-11300. After reduction, the triple peak was replaced by a discrete set of peaks between m/z 4156 and 6354. A peak at m/z 4156.8 corresponded to the nonglycosylated peptide (beta 55-beta 92). The remaining nine peaks indicated that urinary hCG beta cf comprises a set of glycoforms smaller and larger than the trimannosyl core. Conclusions: hCG beta cf comprises a wider set of glycoforms than reported previously. Peaks of highest mass indicate evidence of hyperglycosylated carbohydrate moieties. The data support previous reports that hCG beta cf oligosaccharides lack sialic acid and galactose residues. No indication was found of a beta 36-beta 40 peptide that was entirely devoid of carbohydrate. (C) 2000 American Association for Clinical Chemistry.

AB - Background: Metabolism of human chorionic gonadotropin (hCG) in the serum and kidney yields the terminal urinary product hCG beta -core fragment (hCG beta cf), comprising two disulfide-linked peptides (beta6-beta 40 and beta 55-beta 92) of which one (beta6-beta 40) retains truncated N-linked sugars. Hyperglycosylated hCG beta cf may indicate choriocarcinoma or Down syndrome, but the glycosylation profile of hCG beta cf has not been thoroughly evaluated. Methods: hCG beta cf, purified from pregnancy urine, was reduced by "on-target" dithiothreitol (DTT) reduction and analyzed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). The mass ([M+H](+)) of the primary sequence of the glycosylated peptide beta6-beta 40 was subtracted from the m/z values of the discrete peaks observed to give the masses of the carbohydrate moieties. Carbohydrate structure was predicted by sequentially subtracting the masses of the monosaccharide residues corresponding to N-linked carbohydrates of the hCG beta -subunit reported in the literature. Results: Mass spectra of hCG beta cf revealed a broad triple peak at m/z 8700-11300. After reduction, the triple peak was replaced by a discrete set of peaks between m/z 4156 and 6354. A peak at m/z 4156.8 corresponded to the nonglycosylated peptide (beta 55-beta 92). The remaining nine peaks indicated that urinary hCG beta cf comprises a set of glycoforms smaller and larger than the trimannosyl core. Conclusions: hCG beta cf comprises a wider set of glycoforms than reported previously. Peaks of highest mass indicate evidence of hyperglycosylated carbohydrate moieties. The data support previous reports that hCG beta cf oligosaccharides lack sialic acid and galactose residues. No indication was found of a beta 36-beta 40 peptide that was entirely devoid of carbohydrate. (C) 2000 American Association for Clinical Chemistry.

M3 - Article

VL - 46

SP - 1796

EP - 1803

JO - Clinical Chemistry

JF - Clinical Chemistry

IS - 11

ER -