Structures of acidic O-linked polylactosaminoglycans on human skim milk mucins

Abstract

O-Linked glycans were isolated from human skim milk mucins or mucin-derived high-molecular weight glycopeptides and fractionated by anion exchange chromatography into neutral and acidic alditols. Major oligosaccharides contained in the acidic fraction were purified by high performance liquid chromatography and structurally characterized by a combination of fast atom bombardment mass spectrometry, methylation analysis and 500 MHz¹H-nuclear magnetic resonance spectroscopy. The structural aspects exhibited by these major species in the acidic fraction resemble those established previously for the neutral oligosaccharides from human skim milk mucins: the size of the alditols varies from tri- to decasaccharides the core structure is of the ubiquitous type 2 the backbone sequences are of the poly-N-acetyllactosamine type with a particular preponderance of linearly extended GlcNAcβ(1–3)Gal (major) or GlcNAcβ(1–6)Gal units (minor). N-Acetylneuraminic acid on monosialylated (mucin- or glycopeptide-derived) and disialylated glycans (glycopeptide derived) is linked predominantly to position C-3 of galactose.