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 motif present in immunoglobulin-binding domains, ubiquitin, 2Fe-2 S ferredoxin and translation initiation factor 3 as identified by the SCOP database. Clostridium difficile Clostridium perfringens (Clostridium enterotoxin) Vibrio cholerae (Cholera toxin) Staphylococcus aureus (Staphylococcal enterotoxin B) Yersinia enterocolitica Shigella dysenteriae (Shiga toxin) Viral Viruses in the families Reoviridae, Caliciviridae, and Astroviridae are responsible for a huge percentage of gastrointestinal disease worldwide. Rotaviruses (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. However, when NSP4 from group A Rotaviruses was purified (4 alleles tested), concentrated, and injected into a mouse model, diarrheal disease mimicking that caused by Rotavirus infection commenced. A putative mode of toxicity is that NSP4 activates a signal transduction pathway that ultimately results in an increased cellular concentration of calcium and subsequent chloride secretion from the cell. Secretion of ions from villi lining the gut alter normal osmotic pressures and prevent uptake of water, eventually causing diarrhea. Rotavirus (NSP4) See also Endotoxin Exotoxin References External links Toxins by organ system affected Peripheral membrane proteins Protein families