Related Research Articles
An exotoxin is a toxin secreted by bacteria. An exotoxin can cause damage to the host by destroying cells or disrupting normal cellular metabolism. They are highly potent and can cause major damage to the host. Exotoxins may be secreted, or, similar to endotoxins, may be released during lysis of the cell. Gram negative pathogens may secrete outer membrane vesicles containing lipopolysaccharide endotoxin and some virulence proteins in the bounding membrane along with some other toxins as intra-vesicular contents, thus adding a previously unforeseen dimension to the well-known eukaryote process of membrane vesicle trafficking, which is quite active at the host–pathogen interface.
An enterotoxin is a protein exotoxin released by a microorganism that targets the intestines. They can be chromosomally or plasmid encoded. They are heat labile (>60⁰), 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, secreted by bacteria, that assemble to form pores in cell membranes. This causes the cells to die.
Diphtheria toxin is an exotoxin secreted mainly by Corynebacterium diphtheriae but also by Corynebacterium ulcerans and Corynebacterium pseudotuberculosis. the pathogenic bacterium that causes diphtheria. The toxin gene is encoded by a prophage called corynephage β. The toxin causes the disease in humans by gaining entry into the cell cytoplasm and inhibiting protein synthesis.
Adenylate cyclase toxin is a virulence factor produced by some members of the genus Bordetella. Together with the pertussis toxin it is the most important virulence factor of the causative agent of whooping cough, Bordetella pertussis. Bordetella bronchiseptica and Bordetella parapertussis, also able to cause pertussis-like symptoms, also produce adenylate cyclase toxin. It is a toxin secreted by the bacteria to influence the host immune system.
Cytolysin refers to the substance secreted by microorganisms, plants or animals that is specifically toxic to individual cells, in many cases causing their dissolution through lysis. Cytolysins that have a specific action for certain cells are named accordingly. For instance, the cytolysins responsible for the destruction of red blood cells, thereby liberating hemoglobins, are named hemolysins, and so on. Cytolysins may be involved in immunity as well as in venoms.
Pore-forming proteins are usually produced by bacteria, and include a number of protein exotoxins but may also be produced by other organisms such as apple snails that produce perivitellin-2 or earthworms, who produce lysenin. They are frequently cytotoxic, as they create unregulated pores in the membrane of targeted cells.
The AB5 toxins are six-component protein complexes secreted by certain pathogenic bacteria known to cause human diseases such as cholera, dysentery, and hemolytic–uremic syndrome. One component is known as the A subunit, and the remaining five components are B subunits. All of these toxins share a similar structure and mechanism for entering targeted host cells. The B subunit is responsible for binding to receptors to open up a pathway for the A subunit to enter the cell. The A subunit is then able to use its catalytic machinery to take over the host cell's regular functions.
Clostridium septicum is a gram positive, spore forming, obligate anaerobic bacterium.
Streptolysins are two hemolytic exotoxins from Streptococcus. Types include streptolysin O, which is oxygen-labile, and streptolysin S, which is oxygen-stable.
Clostridium difficile toxin B is a cytotoxin produced by the bacteria Clostridioides difficile, formerly known as Clostridium difficile. It is one of two major kinds of toxins produced by C. difficile, the other being an related enterotoxin. Both are very potent and lethal.
Clostridium difficile toxin A (TcdA) is a toxin generated by Clostridioides difficile, formerly known as Clostridium difficile. It is similar to Clostridium difficile Toxin B. The toxins are the main virulence factors produced by the gram positive, anaerobic, Clostridioides difficile bacteria. The toxins function by damaging the intestinal mucosa and cause the symptoms of C. difficile infection, including pseudomembranous colitis.
The AB toxins are two-component protein complexes secreted by a number of pathogenic bacteria, though there is a pore-forming AB toxin found the eggs of a snail. They can be classified as Type III toxins because they interfere with internal cell function. They are named AB toxins due to their components: the "A" component is usually the "active" portion, and the "B" component is usually the "binding" portion. The "A" subunit possesses enzyme activity, and is transferred to the host cell following a conformational change in the membrane-bound transport "B" subunit. These proteins consist of two independent polypeptides, which correspond to the A/B subunit moieties. The enzyme component (A) enters the cell through endosomes produced by the oligomeric binding/translocation protein (B), and prevents actin polymerisation through ADP-ribosylation of monomeric G-actin.
Microbial toxins are toxins produced by micro-organisms, including bacteria, fungi, protozoa, dinoflagellates, and viruses. Many microbial toxins promote infection and disease by directly damaging host tissues and by disabling the immune system. Endotoxins most commonly refer to the lipopolysaccharide (LPS) or lipooligosaccharide (LOS) that are in the outer plasma membrane of Gram-negative bacteria. The botulinum toxin, which is primarily produced by Clostridium botulinum and less frequently by other Clostridium species, is the most toxic substance known in the world. However, microbial toxins also have important uses in medical science and research. Currently, new methods of detecting bacterial toxins are being developed to better isolate and understand these toxin. Potential applications of toxin research include combating microbial virulence, the development of novel anticancer drugs and other medicines, and the use of toxins as tools in neurobiology and cellular biology.
Clostridium novyi (oedematiens) a Gram-positive, endospore- forming, obligate anaerobic bacteria of the class Clostridia. It is ubiquitous, being found in the soil and faeces. It is pathogenic, causing a wide variety of diseases in man and animals.
Colitis X, equine colitis X or peracute toxemic colitis is a catchall term for various fatal forms of acute or peracute colitis found in horses, but particularly a fulminant colitis where clinical signs include sudden onset of severe diarrhea, abdominal pain, shock, and dehydration. Death is common, with 90% to 100% mortality, usually in less than 24 hours. The causative factor may be Clostridium difficile, but it also may be caused by other intestinal pathogens. Horses under stress appear to be more susceptible to developing colitis X, and like the condition pseudomembranous colitis in humans, an association with prior antibiotic use also exists. Immediate and aggressive treatment can sometimes save the horse, but even in such cases, 75% mortality is considered a best-case scenario.
The RTX toxin superfamily is a group of cytolysins and cytotoxins produced by bacteria. There are over 1000 known members with a variety of functions. The RTX family is defined by two common features: characteristic repeats in the toxin protein sequences, and extracellular secretion by the type I secretion systems (T1SS). The name RTX refers to the glycine and aspartate-rich repeats located at the C-terminus of the toxin proteins, which facilitate export by a dedicated T1SS encoded within the rtx operon.
Clostridium perfringens beta toxin is one of the four major lethal protein toxins produced by Clostridium perfringens Type B and Type C strains. It is a necrotizing agent and it induces hypertension by release of catecholamine. It has been shown to cause necrotic enteritis in mammals and induces necrotizing intestinal lesions in the rabbit ileal loop model. C. perfringens beta toxin is susceptible to breakdown by proteolytic enzymes, particularly trypsin. Beta toxin is therefore highly lethal to infant mammals because of trypsin inhibitors present in the colostrum.
The thiol-activated Cholesterol-dependent Cytolysin(CDC) family is a member of the MACPF superfamily. Cholesterol dependent cytolysins are a family of β-barrel pore-forming exotoxins that are secreted by gram-positive bacteria. CDCs are secreted as water-soluble monomers of 50-70 kDa, that when bound to the target cell, form a circular homo-oligomeric complex containing as many as 40 monomers. Through multiple conformational changes, the β-barrel transmembrane structure is formed and inserted into the target cell membrane. The presence of cholesterol in the target membrane is required for pore formation, though the presence of cholesterol is not required by all CDCs for binding. For example, intermedilysin secreted by Streptococcus intermedius will bind only to target membranes containing a specific protein receptor, independent of the presence of cholesterol, but cholesterol is required by intermedilysin for pore formation. While the lipid environment of cholesterol in the membrane can affect toxin binding, the exact molecular mechanism that cholesterol regulates the cytolytic activity of the CDC is not fully understood.
Clostridioides difficile is a bacterium that is well known for causing serious diarrheal infections, and may also cause colon cancer. It is known also as C. difficile, or C. diff, and is a Gram-positive species of spore-forming bacteria. Clostridioides spp. are anaerobic, motile bacteria, ubiquitous in nature and especially prevalent in soil. Its vegetative cells are rod-shaped, pleomorphic, and occur in pairs or short chains. Under the microscope, they appear as long, irregular cells with a bulge at their terminal ends. Under Gram staining, C. difficile cells are Gram-positive and show optimum growth on blood agar at human body temperatures in the absence of oxygen. C. difficile is catalase- and superoxide dismutase-negative, and produces up to three types of toxins: enterotoxin A, cytotoxin B and Clostridioides difficile transferase (CDT). Under stress conditions, the bacteria produce spores that are able to tolerate extreme conditions that the active bacteria cannot tolerate.
The Clostridium difficile TcdE Holin Family is a group of transporters belonging to the Holin Superfamily IV. A representative list of its members can be found in the Transporter Classification Database.
References
- 1 2 Saier, MH Jr. "1.C.57 The Clostridial Cytotoxin (CCT) Family". Transporter Classification Database. Saier Lab Bioinformatics Group / SDSC.
- ↑ Pruitt RN, Chambers MG, Ng KK, Ohi MD, Lacy DB (July 2010). "Structural organization of the functional domains of Clostridium difficile toxins A and B". Proceedings of the National Academy of Sciences of the United States of America. 107 (30): 13467–72. Bibcode:2010PNAS..10713467P. doi: 10.1073/pnas.1002199107 . PMC 2922184 . PMID 20624955.
- ↑ Yu, Zhonghua; Caldera, Patricia; McPhee, Fiona; Voss, James J. De; Jones, Patrick R.; Burlingame, Alma L.; Kuntz, Irwin D.; Craik, Charles S.; Montellano, Paul R. Ortiz de (1996-06-26). "Irreversible Inhibition of the HIV-1 Protease: Targeting Alkylating Agents to the Catalytic Aspartate Groups". Journal of the American Chemical Society. 118 (25): 5846–5856. doi:10.1021/ja954069w.
- ↑ Reineke J, Tenzer S, Rupnik M, Koschinski A, Hasselmayer O, Schrattenholz A, Schild H, von Eichel-Streiber C (March 2007). "Autocatalytic cleavage of Clostridium difficile toxin B". Nature. 446 (7134): 415–9. Bibcode:2007Natur.446..415R. doi:10.1038/nature05622. PMID 17334356. S2CID 4392083.
- 1 2 Zhang Z, Park M, Tam J, Auger A, Beilhartz GL, Lacy DB, Melnyk RA (March 2014). "Translocation domain mutations affecting cellular toxicity identify the Clostridium difficile toxin B pore". Proceedings of the National Academy of Sciences of the United States of America. 111 (10): 3721–6. Bibcode:2014PNAS..111.3721Z. doi: 10.1073/pnas.1400680111 . PMC 3956163 . PMID 24567384.
- ↑ Voth DE, Ballard JD (April 2005). "Clostridium difficile toxins: mechanism of action and role in disease". Clinical Microbiology Reviews. 18 (2): 247–63. doi:10.1128/CMR.18.2.247-263.2005. PMC 1082799 . PMID 15831824.