Tissue Receptor for Cholera Exotoxin: Postulated Structure from Studies with G M1 Ganglioside and Related Glycolipids

Abstract

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 G M1 but not by any of the related glycolipids G M3 , G M2 , G M1 -GlcNAc, G D1a , G D1b , G T1 , globoside, G A1 , and tetrahexoside-GlcNAc. Twenty-five nanograms of G M1 was enough to give a precipitation line with 1.2 μg of toxin, whereas about 50 ng was required with this amount of toxoid. G M1 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 G M1 could inactivate 5 ng (about 50 blueing doses) of isolated toxin. G M1 inactivated crude toxin (culture fil rate) with the same efficiency as isolated toxin, and the inactivating capacity of G M1 was unaffected by mixing with other gangliosides, indicating the specificity in the reaction between G M1 and toxin. The other glycolipids tested did not inactivate toxin except G D1a and G A1 which did so with approximately 1,000 times less efficiency than G M1 . This identified the portion Gal → GalNAc [Formula: see text] as the critical region in G M1 for toxin fixation, and it is postulated that this may be the tissue receptor structure for the cholera toxin.