Attenuated endocytosis and toxicity of a mutant cholera toxin with decreased ability to cluster ganglioside GM1 molecules.

Cholera toxin (CT) moves from the plasma membrane (PM) of host cells to the endoplasmic reticulum (ER) by binding to the lipid raft ganglioside GM(1). The homopentomeric B-subunit of the toxin can bind up to five GM(1) molecules at once. Here, we examined the role of polyvalent binding of GM(1) in CT action by producing chimeric CTs that had B-subunits with only one or two normal binding pockets for GM(1).

Gangliosides that associate with lipid rafts mediate transport of cholera and related toxins from the plasma membrane to endoplasmic reticulm.

Cholera toxin (CT) travels from the plasma membrane of intestinal cells to the endoplasmic reticulum (ER) where a portion of the A-subunit, the A1 chain, crosses the membrane into the cytosol to cause disease. A related toxin, LTIIb, binds to intestinal cells but does not cause toxicity. Here, we show that the B-subunit of CT serves as a carrier for the A-subunit to the ER where disassembly occurs.

Uncoupling of the cholera toxin-G(M1) ganglioside receptor complex from endocytosis, retrograde Golgi trafficking, and downstream signal transduction by depletion of membrane cholesterol.

To induce toxicity, cholera toxin (CT) must first bind ganglioside G(M1) at the plasma membrane, enter the cell by endocytosis, and then traffic retrograde into the endoplasmic reticulum. We recently proposed that G(M1) provides the sorting motif necessary for retrograde trafficking into the biosynthetic/secretory pathway of host cells, and that such trafficking depends on association with lipid rafts and lipid raft function. To test this idea, we examined whether CT action in human intestinal T84 cells depends on membrane cholesterol.