Vibrio cholerae exotoxin

Vibrio cholera exotoxin ADP-ribosylates G O, leading to an increase in cAMP and subsequently chloride secretion bom intestinal mucosal cells, causing the diarrhea of cholera. 

Cholera is a condition caused by a protein exotoxin produced by the bacterium vibrio cholerae. This protein toxin consists of six subunits one A subunit and five B subunits. The B subunits are responsible for the binding of the toxin to cAMP-functioning cells in small bowel of the intestines. The A subunit penetrates the cell and has catalytic activity which attaches the ADP portion of naturally occurring NAD (nicotine-adenosine dinucleotide) to the G-protein complex thereby inhibiting its GTPase activity. This deprives the complex of its "off-switch" for cAMP formation. The effect is the uncontrolled... 

As recently as 1980 it was estimated that there were 100 million cases of acute diarrhea in Asia, Africa, and Latin America 3 in 1991 there were four million deaths among children under five years of age.b The causative agents are bacteria and one of the most dangerous is Vibrio cholerae, which multiplies in the small intestine and secretes an exotoxin. Cholera toxin causes such a rapid loss of fluid and salts from the body that death occurs very quickly, even in adults. There is little cellular damage and almost all deaths can be prevented by intravenous administration of water, salts, and the antibiotic tetracycline. Fluids can also be given orally if glucose, which promotes intestinal absorption, is included with the Na+, K+, Cl, and HC03 salts.b... 

A-B Toxins are bacterial toxins composed of two peptide chains one (B) that binds to the invaded cell surface, and the other (A) containing the toxin which is then taken-up into the cell. Some examples of exotoxins secreted by the bacteria into the surrounding medium and highly toxic to certain tissues are pathogens causing botuiism (Clostridium botulinum), tetanus (Clostridium tetani) and diptheria (Corynebacterium diphtheria. An example of an A-B endotoxin is Vibrio cholerae. Botulinum toxin and tetanus toxin have their main toxic actions on neuronal tissues, so are described at NEUROTOXINS. 

The best understood reactions are those catalyzed by ADP-ribosyl transferase components of certain bacterial toxins. These include, for example, toxins produced by Vibrio cholerae (the causative agent of cholera), pertussis toxin (from Bordetella pertussis, which causes whooping cough), diphtheria toxin, exotoxin A from Pseudomonas aeruginosa (an opportunistic pathogen), and toxins from Clostridium botulinum. 

Enterotoxins. Toxic proteins formed by bacteria with molecular masses in the range from 27000 to 30000 which are usually excreted into the medium ( exotoxins). E. can be taken up with contaminated food or be formed by the bacteria colonizing the intestinal walls. Finally, the bacteria can penetrate the intestinal walls and then start to excrete the E. Some E. are thermally very stable and survive when food is boiled. E. from Salmonella and Staphylococcus species are the most frequent causes of food poisoning. Shortly after uptake, the symptoms of nausea, vomiting, diarrhea, and circulatory complaints occur. Deaths are rare and occur only when the subject is already in a weakened state. The sites of attack by E. vary, e.g., at intestinal epithelial cells or in the vegetative nervous system. For the production of antitoxins, E. are obtained by lysis of bacterial cells or from cell-free culture filtrates. E. have been detected, e. g., in the following bacterial species Bacillus cereus, Clostridium perfringens, Escherichia coli. Vibrio cholerae. Staphylococcus aureus, and Streptococcus faecalis. 

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