Expression of N-linked sialyl Le(x) determinants and O-glycans in the carbohydrate moiety of human amniotic fluid transferrin during pregnancy

Transferrin, a glycoprotein involved in iron transport in body fluids, wasisolated from amniotic fluid of a hydramniospatient by sequentialanion-exchange chromatography and gel filtration. The N-glycans of humanamniotic fluid transferrin (hAFT) were enzymatically liberated by PNGase-Fdigestion, isolated by gel filtration and fractionated by (high-pH)anion-exchange chromatography. After alkaline borohydride treatment ofnative hAFT, the released O-glycans were isolated by gel filtration andfractionated by anion-exchange chroma-tography. Structure elucidation of 14N- and 2 O-glycans was performed by 500 or 600 MHz1H-NMR spectroscopy.Besides conventional N-glycans established earlier for human serumtransferrin (hST), new (alpha1-3)-fucosylated N- glycans were found,representing sialyl Le(x) elements. Furthermore, as compared to hST, ahigher degree of (alpha1-6)-fucosylation and an increase in branching fromdi- to triantennary compounds has been detected. The presence of O-glycansis demonstrated for the first time in transferrin.