The extracellular matrix (the so-called jelly coat) surrounding amphibian eggs mainly comprises highly O-glycosylated proteins. These oviducal mucins have an important role in the fertilization process, and their carbohydrate chains are remarkably species-specific. Alkaline reductive treatment of the jelly-coat material of the frog Rana clamitans led to the release of oligosaccharide alditols. The neutral oligosaccharide alditols were fractionated and purified by successive chromatographic techniques. The structures of 27 of them, ranging from three to sixteen monosaccharides, were established by a combination of NMR spectroscopy, methylation analyses and matrix-assisted laser-desorption ionization—time of flight MS. Typically, some of the neutral compounds appeared to possess the core structure: Gal(β1–3)[GlcNAc(β1–6)]Gal(β1–3)[GlcNAc(β1–6)]GalNAc-ol (where GalNAc-ol represents N-acetylgalactosaminitol). Moreover, a novel type of chain termination, characterized by an unusual sequence {Fuc(α1–2)Gal(α1–3)Gal(α1–4)Gal(β1–3/4)} was observed. Indeed, the most complex representative structure of this series was found to be: Fuc(α1–2)Gal(α1–3)Gal(α1–4)Gal(β1–3)[Fuc(α1–2)Gal(α1–3)Gal(α1–4)Gal(β1–4)GlcNAc(β1–6)]Gal(β1–3)[Fuc(α1–2)Gal(α1–3)Gal(α1–4)Gal(β1–4)GlcNAc(β1–6)]GalNAc-ol.
Species specificity of O-linked carbohydrate chains of the oviducal mucins in amphibians: structural analysis of neutral oligosaccharide alditols released by reductive β-elimination from the egg-jelly coats of Rana clamitans
