GM1

GM1 (monosialotetrahexosylganglioside) the "prototype" ganglioside, is a member of the ganglio series of gangliosides which contain one sialic acid residue. GM1 has important physiological properties and impacts neuronal plasticity and repair mechanisms, and the release of neurotrophins in the brain. Besides its function in the physiology of the brain, GM1 acts as the site of binding for both Cholera toxin and E. coli heat-labile enterotoxin (Traveller's diarrhea).

Antibodies to GM1 are increased in Guillain-Barré syndrome, dementia and lupus but their function is not clear. There is some evidence to suggest these antibodies are associated with diarrhea in Guillain-Barré syndrome.

GM1 and the cholera toxin
The bacteria Vibrio cholerae produces a multimeric toxin called the cholera toxin. The A1 subunit of this toxin will gain entry to intestinal epithelial cells with the assistance of the B subunit via the GM1 ganglioside receptor. Once inside, the A1 subunit will ADP ribosylate the Gs Alpha subunit which will prevent its GTPase activity. This will lock it in the active state and it will continuously stimulate adenylate cyclase. The sustained adenylate cyclase activity will lead to a sustained increase of cAMP which will cause electrolyte and water loss, causing diarrhea.

Fortunately, the SGLT1 receptor is present in the small intestine. When the cholera patient is given a solution containing water, sodium and glucose, the SGLT1 receptor will reabsorb sodium and glucose, while water will be passively absorbed with the sodium. This will replace the water and electrolyte loss in the cholera induced diarrhea.