Endocrine Abstracts (2004) 7 P195

Analysis of hCG beta core fragment glycosylation in normal and aberrant pregnancy by matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry

S Malatos1, ES Jacoby1, NA Juneja1, SA Butler1, AT Kicman2 & RK Iles1


1The Williamson Laboratory, Queen Mary University of London, London, UK; 2Drug Control Centre, King's College London, London, UK.


Metabolism of the dimeric glycoprotein hormone human chorionic gonadotrophin (hCG) results in the urinary excretion of hCG beta core fragment originating from the beta subunit of hCG (hCGbeta). hCG beta core fragmant retains a certain antigenic shape as well as two metabolically processed N-linked oligosaccharides. Hyperglycosylation of hCGbeta has been used as an indication of aberrant pregnancy especially in malignant disease. We have previously characterised the carbohydrate content of hCG beta core fragment from pooled pregnancy urine with the use of matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI TOF MS). Similar methodology was used to compare the carbohydrate content of hCG beta core fragment from different pregnancy conditions. Urinary hCG beta core fragment from molar, hyperemesis gravidarum, and normal pregnancy states was purified by chromatography, reduced with dithiothreitol, and subjected to previously reported MALDI TOF MS analysis. The major characteristic of the hCG beta core fragment spectrum was a broad peak between 8700 and 10700 Da, which included peaks at 9000, 9200, and 9900 Da. After reduction, the triple peak was replaced by a set of resolved peaks between 4156.8 Da and 5840.6 Da. The peak at 4156.8 Da corresponded to the non-glycosylated peptide of hCG beta core fragment, beta55-92, while the remaining structures represented the glycosylated forms of the peptide beta6-40. Glycoform prediction was achieved by subtraction of the non-glycosylated peptide beta6-40 mass from the observed m/z values. In all cases mono- bi- and triantennary glycosylations were detected. The expected microheterogeneity could be observed within all samples however some similarities were seen between samples obtained from the same type of pregnancy.

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