Conversion of cellular sialic acid expression from N-acetyl- to N-glycolylneuraminic acid using a synthetic precursor, N-glycolylmannosamine pentaacetate: inhibition of myelin-associated glycoprotein binding to neural cells

Sialic acids are prominent termini of mammalian glycoconjugates and are key binding determinants for cell-cell recognition lectins, Binding of the sia lic acid-dependent lectin, myelin-associated glycoprotein (MAG), to nerve c ells is implicated in the inhibition of nerve regeneration after injury. Th erefore, blocking MAG binding to nerve cell sialoglycoconjugates might enha nce nerve regeneration. Previously, we reported that certain sialoglycoconj ugates bearing N-acetylneuraminic acid (NeuAc) but not N-glycolylneuraminic acid (NeuGc) support MAG binding (Collins et at, 1997a), We now report hig hly efficient conversion of sialic acids on living neural cells from exclus ively NeuAc to predominantly NeuGc using a novel synthetic metabolic precur sor, N-glycolylmannosamine pentaacetate (ManNGcPA). When NG108-15 neuroblas toma-glioma hybrid cells, which normally express only NeuAc (and bind to MA G), mere cultured in the presence of 1 mM ManNGcPA, they expressed 80-90% o f their sialic acid precursor pool as NeuGc within 24 h, Within 5 days, 80% of their ganglioside-associated sialic acids and 70% of their glycoprotein -associated sialic acids were converted to NeuGc. Consistent with this resu lt, treatment of NG108-15 cells with ManNGcPA resulted in nearly complete a brogation of MAG binding. These results demonstrate that ManNGcPA treatment efficiently alters the sialic acid structures on living cells, with a comm ensurate change in recognition by a physiologically important lectin.