Synthesis of soluble myelin-associated glycoprotein in insect and mammalian cells.

The myelin-associated glycoprotein (MAG) has an extracellular domain containing five sequences which are homologous to the immunoglobulin-fold motif. Adhesive interactions mediated by the MAG extracellular domain are involved in the development of the myelin sheath. The MAG cDNA has been modified to introduce a stop codon immediately before the transmembrane domain. Expression of the modified cDNA in insect cells and murine NIH-3T3 cells resulted in secretion of the soluble MAG extracellular domain. Treatment of soluble MAG with glycopeptidase F and endoglycosidase H showed significant differences in glycosylation for the insect and mammalian cell-expression systems. The soluble form of MAG has been purified from insect-cell supernatants by adsorption to a lentil-lectin support. The soluble MAG will provide a powerful new approach for studies of MAG-adhesive interactions during brain development.