CARBOHYDRATE MOIETIES OF MYELIN-ASSOCIATED GLYCOPROTEIN, MAJOR GLYCOPROTEIN OF THE PERIPHERAL NERVOUS-SYSTEM MYELIN AND OTHER MYELIN GLYCOPROTEINS POTENTIALLY INVOLVED IN CELL-ADHESION

The myelin-associated glycoprotein (MAG) and the major glycoprotein of the peripheral nervous system myelin (PO) are two members of the family of cell adhesion molecules (CAMs). A role in cell adhesion of the carbohydrate moiety of these molecules has been attributed to the presence of N-glycans bearing the HNK-1 carbohydrate epitope. On the other hand, it has been suggested that these glycoproteins could be ligands of an endogenous mannose-binding lectin present in myelin, the cerebellar soluble lectin (CSL). In order to further document the heterogeneity of the glycans of these two CAMs, we have used several probes: an anti-carbohydrate antibody of the HNK-1 type, called Elec-39, the plant lectin concanavalin A (ConA), and the endogenous lectin CSL involved in myelin compaction. This study shows that CSL binds to a small proportion of the polypeptide chains of MAG found in adult CNS of rats and man and the polypeptide chains of PO molecules from adult human and rat sciatic nerve. For MAG from adult rat brain, the binding of CSL is restricted to glycans of polypeptide chains which could be separated from the others according to their solubility properties. These MAG molecular entities react also with the Elec-39 antibody and with ConA. These results confirm that PO and MAG are heterogeneous in their carbohydrate moieties. They show that, in the CNS of adult rats, the MAG molecules potentially involved in cell adhesion as ligands of the endogenous lectin CSL possess polypeptide chains physicochemically different from the others, but endowed with similar porperties to those of other CSL ligands, unrelated to MAG, present in myelin preparations.