High prevalence of 2-mono- and 2,6-di-substituted manol-terminating sequences among O-glycans released from brain glycopeptides by reductive alkaline hydrolysis

Abstract

Di- to heptasaccharides isolated from total nondialyzable brain glycopeptides after release by alkaline borohydride treatment have been subjected to mass spectrometric and nuclear magnetic resonance spectroscopic analyses supplemented by TLC-MS analyses of derived neoglycolipids. A family of Manol-terminating oligosaccharides has been revealed which includes novel sequences with a 2,6-disubstituted Manol: GlcNAcβ1-2Manol; Galβ1- 4GlcNAcβ1-2Manol; Galβ1-4GlcNAcβ1-2Manol; | 1,3; Fucα; NeuAcα2-3Galβ1- 4GlcNAcβ1-2Manol; Galβ1-4GlcNAcβ1-6 Manol; NeuAcα2-3Gal β1-4GlcNAcβ1-2 Manol; NeuAcα2-3Galβ1-4GlcNAcβ1-6 Manol; Galβ1-4GlcNAcβ1-2 Manol; NeuAα2c-3Galβ1-4GlcNAcβ1-6 Manol; NeuAcα2-3Galβ1-4GlcNAcβ1-2 Manol. In contrast to the Manol-terminating HNK-1 antigen-positive chains described previously that occur as a minor population [Yuen, C.-T., Chai, W., Loveless, R.W., Lawson, A.M., Margolis, R.U. and Feizi, T. (1997) J. Biol. Chem. 272, 8924-8931], the above oligosaccharides are abundant. The ratio of these compounds to the classical N-acetylgalactosaminitol-terminating oligosaccharides is about 1:3. Thus, there appears to be in higher eukaryotes a major alternative pathway related to the yeast-type protein O- mannosylation, the enzymatic basis and functional importance of which now require investigation.