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

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: [GRAPHICS] 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. & Feizi, T. (1997) J. Biol. Chern. 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.