Desialylation of extracellular GD1a-neoganglioprotein suggests cell surface orientation of the plasma membrane-bound ganglioside sialidase activity in human neuroblastoma cells

The orientation of the catalytic site of a ganglioside-specific sialidase in the plasma membrane! of SK-N-MC neuroblastoma cells was probed using water-soluble GD1an-coganglioprotein substrate on intact cells and GM1-product detection by cholera toxin B, Desialylation of substrate was readily observed, whereas specific sialidase inhibitors prevented the reaction, and conditioned medium mas inactive. Inhibitors of endocytosis and acidification had no effect on substrate degradation, and lowering temperature to 18 degreesC reduced activity but did not abolish it. We conclude that the ganglioside sialidase activity is cell surface-orientated and displays an in situ specificity that mirrors enzyme preparations in vitro. (C) 2001 Federation of European Biochemical Societies.