STRUCTURAL STUDIES ON FETAL MUCINS FROM HUMAN AMNIOTIC-FLUID - CORE TYPING OF SHORT-CHAIN O-LINKED GLYCANS

Mucins in human amniotic fluid are represented by two distinct molecular species, FM-1 and FM-2, with apparent molecular masses of 700 and 570 kDa, respectively, in SDS/polyacrylamide gradient gels. FM-1 and FM-2 were isolated by preparative SDS/PAGE to apparent homogeneity and subjected to structural studies on their carbohydrate portions. The carbohydrate compositions of the mucin species differed only marginally and exhibited significant amounts of mannose. O-linked core-region glycans on human amniotic mucin-derived pronase-stable glycopeptides were analyzed after reductive beta-elimination and purification on HPLC by a combination of methylation analysis, electron-impact mass spectrometry of permethylated oligosaccharide alditols and fast-atom-bombardment mass spectrometry of acetylated or methylated alditols (positive-ion mode) or alditol-derived neoglycolipids (negative-ion TLC-MS). The primary structures of major monosaccharides to tetrasaccharides have been established which exhibit at their reducing termini core 1, core 2 and core 3 sequences, as follows. GalNAc-ol (N1) Gal-beta(1-3)GalNAc-ol (N3) Fuc-alpha(1-2)Gal-beta(1-3)GalNAc-ol (N4) Gal-beta(1-3)GlcNAc-beta(1-3)GalNAc-ol (N5) Gal-beta(1-4)GlcNAc-beta(1-3)GalNAc-ol (N5) Gal-beta(1-3)[GlcNAc-beta(1-6)]GalNAc-ol (N6) Gal-beta(1-4)[Fuc-alpha(1-3)]GlcNAc-beta(1-3)GalNAc-ol (N7) Gal-beta(1-3)[Gal-beta(1-4)GlcNAc-beta(1-6)]GalNAc-ol (N9)