Studies of the Ligand Binding to Cholera Toxin, I. The Lipophilic Moiety of Sialoglycolipids

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Abstract
The fixation of cholera toxin ([CT] to mammalian cells) by ganglioside GGtet1 is dependent on the nature of the carbohydrate and lipid moieties of the glycolipid. The role of the lipid in binding to the toxin was investigated with synthetic ganglioside analogues (gangliosidoides). The interaction between glycolipid and toxin was followed by precipitate formation, by inhibition of toxicity and in polyacrylamide gel electrophoresis. For specific precipitation, an aliphatic hydrocarbon chain at least 14 C-atoms in length is required. Some of the gangliosidoides form high molecular weight complexes with CT at lower molar ratios of ligand to protein than the natural compound. None of the synthetic gangliosidoides equalled natural ganglioside in its ability to inhibit the effects of the toxin in vivo, but some did show considerable inhibitory activity in the vascular permeability test. Reaction of CT with monosialo-gangliotetraose or corresponding sialo-glycolipids prevents the easy degradation of the B-protein of CT into protein subunits by sodium dodecyl sulfate.