Structure of the monosialyl oligosaccharides derived from salivary gland mucin glycoproteins of the Chinese swiftlet (genus Collocalia). Characterization of novel types of extended core structure, Galβ(1→3)[GlcNAcβ(1→6)]GalNAcα(1→3)GalNAc(-ol), and of chain termination, [Galα(1→4)]0-1[Galβ(1→4)]2GlcNAcβ(1→.)

Abstract

The mucus glycoproteins, the so-called nest-cementing substance, from the salivary gland of Chinese swiftlets (genus Collocalia) are mainly constituted of sialic acid-rich O-glycosylproteins. Alkaline reductive treatment of the crude material led to the release of some neutral and numerous monosialyl and disialyl oligosaccharides. These were fractionated by gel filtration, anion-exchange chromatography, and high- performance liquid chromatography. The structures of the monosialyl oligosaccharides were established by combination of sugar and methylation analysis, fast atom bombardment-mass spectrometry, and electron impact-mass spectrometry after permethylation and 1H NMR spectroscopy (at 500 MHz). Typically, some of the monosialyl oligosaccharides appeared to possess the core structure Gal β(1→3)[GlcNAcβ(1→6)]GalNAcα(1→3)GalNAc-ol. Moreover, the (1→6)-linked branch consisted of an unusual di- or trigalactosyl sequence, [Galα(1→4)0-1Galβ(1→4)Galβ(1→4)GlcNAcβ(1→6). Thus, the most complex representatives of the monosialyl fraction from Collocalia mucin were found to be: (Formula: see text) The other compounds identified are partial structures thereof.