Tissue Receptor for Cholera Exotoxin: Postulated Structure from Studies with GM1 Ganglioside and Related Glycolipids

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By a double-diffusion precipitation-in-gel technique, isolated cholera toxin as well as its natural toxoid were shown to be fixed and precipitated by the ganglioside GM1 but not by any of the related glycolipids GM3, GM2, GM1-GlcNAc, GD1a, GD1b, GT1, globoside, GA1, and tetrahexoside-GlcNAc. Twenty-five nanograms of GM1 was enough to give a precipitation line with 1.2 μg of toxin, whereas about 50 ng was required with this amount of toxoid. GM1 also inactivated the toxin in the ileal loop as well as in the intradermal models in rabbits. A 1: 1 molar ratio of ganglioside to toxin was found limiting, e.g., 100 pg of GM1 could inactivate 5 ng (about 50 blueing doses) of isolated toxin. GM1 inactivated crude toxin (culture fil rate) with the same efficiency as isolated toxin, and the inactivating capacity of GM1 was unaffected by mixing with other gangliosides, indicating the specificity in the reaction between GM1 and toxin. The other glycolipids tested did not inactivate toxin except GD1a and GA1 which did so with approximately 1,000 times less efficiency than GM1. This identified the portion Gal → GalNAc [Formula: see text] as the critical region in GM1 for toxin fixation, and it is postulated that this may be the tissue receptor structure for the cholera toxin.

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