Cholera toxin

Cholera Toxin is an enzyme secreted by the cholera causing bacterium Vibrio cholerae. It ribosylates the alpha subunit of a G-protein associated with an intestinal epithelial cell, preventing the hydrolysis of GTP bound to the same G-protein. This locks the G-protein in an active state, leading to the indefinite stimulation of adenylyl cyclase, causing a rise in cAMP concentration. This then causes water and Cl^- to leave the cell and enter the intestinal lumen, leading to the severe diarrhoea and dehydration associated with cholera.