Periodate-Modified Gangliosides Enhance Surface Binding of Tetanus Toxin to PC 12 Pheochromocytoma Cells

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Abstract
The interaction of 125I-labeled tetanus toxin with PC12 pheochromocytoma cells in monolayer cultures has been examined. Under regular growth conditions, the PC12 cells bind 125I-tetanus toxin to a limited degree compared with dissociated cerebral neuron cultures. After exposure to nerve growth factor for 2 days in low serum-containing media with growth factor supplements, binding of toxin increases over twofold compared with untreated PC12 cells. Binding can also be enhanced (> 2.5-fold) after treatment of cells with 2 mM sodium metaperiodate for 20 min. Dissociated cerebral neurons but not fibroblasts in cell culture bind more toxin after periodate treatment. The effect of periodate can be abolished by 5 mM sodium borohydride. A ganglioside isolated from periodate-treated PC12 cells and tentatively identified as GT1b [(N-acetylneuraminyl)galactosyl-N-acetyl-galactosaminyl(N-acetylneuraminyl-N-acetylneuraminyl)-galactosyl-glucosylceramide] binds 125I-tetanus toxin on silica gel chromatoplates and on nitrocellulose paper. There are no indications to suggest binding to a polypeptide from treated cells after polyacrylamide gel electrophoresis. Cells artificially supplemented with GT1b and subsequently treated with periodate effectively bind the toxin. The data suggest that modified sialyl groups linked to gangliosides, and not to proteins, are preferential targets for tetanus toxin.