BRAIN CONTAINS HNK-1 IMMUNOREACTIVE O-GLYCANS OF THE SULFOGLUCURONYL LACTOSAMINE SERIES THAT TERMINATE IN 2-LINKED OR 2,6-LINKED HEXOSE (MANNOSE)

The monoclonal antibody HNK-1 originally raised to an antigenic marker of natural killer cells also binds to selected regions in nervous tis sue. The antigen is a carbohydrate that has attracted much interest as its expression is developmentally regulated in nervous tissue, and it is found, and proposed to be a ligand, on several of the adhesive gly coproteins of the nervous system. It is also expressed on glycolipids and proteoglycans, and is the target of monoclonal auto-antibodies tha t give rise to a demyelinating disease. The epitope, as characterized on glycolipids isolated from the nervous system, is expressed on 3-sul fated glucuronic acid joined by beta 1-3-linkage to a neolacto backbon e. Here we exploit the neoglycolipid technology, in conjunction with i mmunodetection and in situ liquid secondary ion mass spectrometry, to characterize HNK-1-positive oligosaccharide chains derived by reductiv e alkaline release from total brain glycopeptides. The immunoreactive oligosaccharides detected are tetra- to octasaccharides that are very minor components among a heterogeneous population, each representing l ess than 0.1% of the starting material. Their peripheral and backbone sequences resemble those of the HNK-1-positive glycolipids. An unexpec ted finding is that they terminate not with N-acetylgalactosaminitol b ut with hexitol (2-substituted and 2,6-disubstituted). In a tetrasacch aride investigated in the greatest detail, the hexitol is identified a s a substituted mannitol.