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. [Table; see text]