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

Abstract

Sialic acids are prominent termini of mammalian glycoconjugates and are key binding determinants for cell-cell recog-nition lectins. Binding of the sialic acid-dependent lectin, myelin-associated glycoprotein (MAG), to nerve cells is implicated in the inhibition of nerve regeneration after injury. Therefore, blocking MAG binding to nerve cell sialoglycoconjugates might enhance nerve regeneration. Previously, we reported that certain sialoglycoconjugates bearing N-acetylneuraminic acid (NeuAc) but not N-glycolylneuraminic acid (NeuGc) support MAG binding (Collins et al., 1997a). We now report highly efficient conversion of sialic acids on living neural cells from exclusively NeuAc to predominantly NeuGc using a novel synthetic metabolic precursor, N-glycolylmannosamine pentaacetate (Man-NGc-PA). When NG108-15 neuroblastoma-glioma hybrid cells, which normally express only NeuAc (and bind to MAG), were cultured in the presence of 1 mM ManNGcPA, they expressed 80-90% of 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 result, treatment of NG108-15 cells with ManNGcPA resulted in nearly complete abrogation of MAG binding. These results demonstrate that ManNGcPA treatment efficiently alters the sialic acid structures on living cells, with a commensurate change in recognition by a physiologically important lectin.

Evolution of human-chimpanzee differences in malaria susceptibility: Relationship to human genetic loss of N -glycolylneuraminic acid

“…After 24 h in 3 mM Neu5Gc, the cells were similar to chimpanzee erythrocytes with regard to Sia content [Ϸ75% of total Sias in the form of Neu5Gc (data not shown)]. A separate incubation with a metabolic precursor of Neu5Gc (N-glycolylmannosamine, per-Oacetylated form) gave a lower expression of Neu5Gc (only Ϸ10%) (42). The pathways by which such metabolic incorporation occurs are known (41,42).…”

“…Some cells were incubated with 3 mM free Neu5Gc for 24 h to cause high expression of Neu5Gc on the cell surface (41). Other loading experiments were performed by incubation for 3 days in 100 M of the per-O-acetylated precursor N-glycolylmannosamine (41,42), resulting in a lower expression of Neu5Gc on the cell surface.…”

“…A separate incubation with a metabolic precursor of Neu5Gc (N-glycolylmannosamine, per-Oacetylated form) gave a lower expression of Neu5Gc (only Ϸ10%) (42). The pathways by which such metabolic incorporation occurs are known (41,42). With both approaches, the resulting cell-surface Neu5Gc appears exactly as if it had been originally synthesized by the human cell.…”

Tissue-based metabolic labeling of polysialic acids in living primary hippocampal neurons

“…PSA-NCAMs occasionally remain until adulthood in the brain regions that exhibit plasticity, including hippocampus, and they are reported to be involved in glia-neuron interactions, regulation of circadian rhythms, and learning and memory (10). Other than these roles, PSA is closely related to the tumor progression of malignant neuroblastoma (11,12). However, despite the widespread occurrence of PSAs and their biological complexity in the nerve systems, the PSA-mediated modulation of neuronal functions is not fully understood.…”

Metabolic incorporation of unnatural sialic acids into Haemophilus ducreyi lipooligosaccharides

“…A variety of mannosamine derivatives successfully navigate this biosynthetic process, including analogs with extended N-acyl groups (11) and analogs modified at the N-acyl position with reactive electrophiles (12)(13)(14). Cells bearing modified sialic acids have shown altered profiles of virus binding (15) and altered responses to adhesion molecules and growth factors (16,17), effects that implicate sialic acid as a determinant of each process. These examples prompted us to consider whether bacterial sialylation pathways are amenable to biosynthetic modulation.…”