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

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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: 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. 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.

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