Cholera toxin is a protein produced by
cholera bacteria. This
protein is responsible for the
disease cholera.
Cholera toxin enters the
epithelial cells that line the walls of the
intestines and then binds to and causes
allosteric change in the alpha subunit of
membrane proteins called
G-proteins. This change in the G protein prevents it from reverting to its inactive state (by preventing it from hydrolyzing
GTP to
GDP). Because G proteins are responsible for regulating the flow of
ions through trans
membrane proteins that span the
cell membrane, the modified, always-active form causes
sodium ions to flow out of the cells. This causes water to flow out of the cells (see
osmosis) and into the intestine. The net result is what the
cell biology text "Essential Cell Biology" (used by students in Physiological Foundations at the
Johns Hopkins University) calls, "
catastrophic diarrhea".