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, Gal beta(1—3)[GlcNAc beta(1—6)] GalNAc alpha(1—3)GalNAc(-ol), and of chain termination, [Gal alpha(1—4)]0-1[Gal beta(1—4)]2GlcNAc beta(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 beta(1----3)[GlcNAc beta(1----6)]GalNAc alpha(1----3)GalNAc-ol. Moreover, the (1----6)-linked branch consisted of an unusual di- or trigalactosyl sequence, [Gal alpha(1----4)0-1Gal beta(1----4)Gal beta (1----4)GlcNAc beta(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.