An enterotoxin is a protein exotoxin released by a microorganism that targets the intestines.[Carlton Gyles, Magdalene So, Stanley Falkow, Journal of Infectious Diseases (1974) 130 (1): 40-49.] They are heat labile (> 60 °C), of low molecular weight and water-soluble. Enterotoxins are frequently cytotoxic and kill cells by altering the apical membrane permeability of the mucosal (epithelial) cells of the intestinal wall. They are mostly pore-forming toxins (mostly chloride pores), secreted by bacteria, that assemble to form pores in cell membranes. This causes the cells to die.
Clinical significance
Enterotoxins have a particularly marked effect upon the gastrointestinal tract, causing traveler's diarrhea and food poisoning. The action of enterotoxins leads to increased
chloride ion permeability of the
apical membrane of intestinal mucosal cells. These membrane pores are activated either by increased cAMP or by increased calcium ion concentration intracellularly. The pore formation has a direct effect on the
osmolarity of the luminal contents of the intestines. Increased chloride permeability leads to leakage into the lumen followed by sodium and water movement. This leads to a secretory diarrhea within a few hours of ingesting enterotoxin. Several microbial organisms contain the necessary enterotoxin to create such an effect, such as
Staphylococcus aureus and
E. coli.
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The drug linaclotide, used to treat some forms of constipation, is based on the mechanism of enterotoxins.
Classification and 3D structures
Bacterial
Enterotoxins can be formed by the bacterial pathogens Staphylococcus aureus and Bacillus cereus and can cause Staphylococcal Food Poisoning and Bacillus cereus diarrheal disease, respectively. Staphylococcal enterotoxins and streptococcal constitute a family of biologically and structurally related pyrogenic .
All of these toxins share a similar two-domain protein folding (N and C-terminal domains) with a long alpha-helix in the middle of the molecule, a characteristic beta-barrel known as the "oligosaccharide/oligonucleotide fold" at the N-terminal domain and a beta-grasp protein motif at the C-terminal domain. An example is staphylococcal enterotoxin B. Each superantigen possesses slightly different binding mode(s) when it interacts with MHC class II molecules or the T-cell receptor.
The beta-grasp domain has some structural similarities to the beta-grasp sequence motif present in immunoglobulin-binding domains, ubiquitin, 2Fe-2 S ferredoxin and translation initiation factor 3 as identified by the SCOP database.
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Clostridioides difficile
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Clostridium perfringens (Clostridium enterotoxin)
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Vibrio cholerae (Cholera toxin)
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Staphylococcus aureus (Staphylococcal enterotoxin B)
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Yersinia enterocolitica
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Shigella dysenteriae (Shiga toxin)
Viral
Viruses in the families Reoviridae, Caliciviridae, and Astroviridae are responsible for a huge percentage of gastrointestinal disease worldwide. (of Reoviridae) have been found to contain an enterotoxin which plays a role in viral pathogenesis. NSP4, is a protein that is made during the intracellular phase of the virion's life cycle and is known to have a primary function in intracellular virion maturation.
See also
External links
