Heat-labile enterotoxin family

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Heat-labile enterotoxin alpha chain
PDB 1s5e EBI.jpg
cholera holotoxin, crystal form 1
Identifiers
SymbolEnterotoxin_a
Pfam PF01375
Pfam clan CL0084
InterPro IPR001144
SCOP2 1lts / SCOPe / SUPFAM
Available protein structures:
Pfam   structures / ECOD  
PDB RCSB PDB; PDBe; PDBj
PDBsum structure summary
Heat-labile enterotoxin beta chain
PDB 1eei EBI.jpg
cholera toxin b-pentamer complexed with metanitrophenyl-alpha-d-galactose
Identifiers
SymbolEnterotoxin_b
Pfam PF01376
InterPro IPR001835
SCOP2 1lts / SCOPe / SUPFAM
Available protein structures:
Pfam   structures / ECOD  
PDB RCSB PDB; PDBe; PDBj
PDBsum structure summary
Type II heat-labile enterotoxin , B subunit (LT-IIB)
PDB 1qb5 EBI.jpg
escherichia coli heat labile enterotoxin type iib b-pentamer
Identifiers
SymbolLT-IIB
Pfam PF06453
InterPro IPR010503
SCOP2 1tii / SCOPe / SUPFAM
Available protein structures:
Pfam   structures / ECOD  
PDB RCSB PDB; PDBe; PDBj
PDBsum structure summary

In molecular biology, the heat-labile enterotoxin family includes Escherichia coli heat-labile enterotoxin (Elt or LT) and cholera toxin (Ctx) secreted by Vibrio cholerae .

Contents

lt is so named because it is inactivated at high temperatures. [1]

Mechanism

The A subunits are transported inside by the pentameric B subunits. It then acts by raising cAMP levels through ADP-ribosylation of the alpha-subunit of a Gs protein leading to the constitutive activation of adenylate cyclase. Elevated cAMP levels stimulate the activation of the CFTR channel thus stimulating secretion of chloride ions and water from the enterocyte into the gut lumen. This ionic imbalance causes watery diarrhea.

In addition to its effects on chloride secretion, which involve the same steps as the effects of cholera toxin, Elt binds additional substrates: lipopolysaccharide on the surface of E. coli cells and A-type blood antigens. [2] The importance of these binding events is not yet known.

Structure

These toxins consist of an AB5 multimer structure, in which a pentamer of B chains has a membrane-binding function and an A chain is needed for enzymatic activity. [3] The B subunits are arranged as a doughnut-shaped pentamer, each subunit participating in ~30 hydrogen bonds and 6 salt bridges with its two neighbours. [3]

The A subunit has a less well-defined secondary structure. It predominantly interacts with the pentamer via the C-terminal A2 fragment, which runs through the charged central pore of the B subunits. A putative catalytic residue in the A1 fragment (Glu112) lies close to a hydrophobic region, which packs two loops together. It is thought that this region might be important for catalysis and membrane translocation. [3]

The structural arrangement of E. coli type I and type II heat-labile enterotoxins are very similar, although they are antigenically distinct. [4]

Origin

The cholera toxin is carried by the CTXφ bacteriophage and may be isolated from plasmids. The E. coli LT (elt) is similarly associated with mobile elements, in this case Ent plasmids that can carry LT, ST, or both. Partial insertion sequences (ISs) flanking the elt genes provide extra transmission capabilities by homologous recombination at their inverted repeats. [5] Οβ phage-induced conversion in E. coli has been described as well. [6]

Applications

The B subunits of toxins in this family is relatively harmless on its own. CtxB is routinely used as a neuronal tracer. [7] Elt-IB has been looked into as an adjuvant in transdermal vaccines. [8] [1]

Related Research Articles

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Escherichia coli ( ESH-ə-RIK-ee-ə KOH-lye) is a gram-negative, facultative anaerobic, rod-shaped, coliform bacterium of the genus Escherichia that is commonly found in the lower intestine of warm-blooded organisms. Most E. coli strains are harmless, but some serotypes such as EPEC, and ETEC are pathogenic and can cause serious food poisoning in their hosts, and are occasionally responsible for food contamination incidents that prompt product recalls. Most strains are part of the normal microbiota of the gut and are harmless or even beneficial to humans (although these strains tend to be less studied than the pathogenic ones). For example, some strains of E. coli benefit their hosts by producing vitamin K2 or by preventing the colonization of the intestine by pathogenic bacteria. These mutually beneficial relationships between E. coli and humans are a type of mutualistic biological relationship — where both the humans and the E. coli are benefitting each other. E. coli is expelled into the environment within fecal matter. The bacterium grows massively in fresh fecal matter under aerobic conditions for three days, but its numbers decline slowly afterwards.

<span class="mw-page-title-main">Shiga toxin</span> Family of related toxins

Shiga toxins are a family of related toxins with two major groups, Stx1 and Stx2, expressed by genes considered to be part of the genome of lambdoid prophages. The toxins are named after Kiyoshi Shiga, who first described the bacterial origin of dysentery caused by Shigella dysenteriae. Shiga-like toxin (SLT) is a historical term for similar or identical toxins produced by Escherichia coli. The most common sources for Shiga toxin are the bacteria S. dysenteriae and some serotypes of Escherichia coli, which include serotypes O157:H7, and O104:H4.

<span class="mw-page-title-main">Exotoxin</span> Toxin from bacteria that destroys or disrupts cells

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.

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<span class="mw-page-title-main">Enterotoxin</span> Toxin from a microorganism affecting the intestines

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.

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Bacterial display is a protein engineering technique used for in vitro protein evolution. Libraries of polypeptides displayed on the surface of bacteria can be screened using flow cytometry or iterative selection procedures (biopanning). This protein engineering technique allows us to link the function of a protein with the gene that encodes it. Bacterial display can be used to find target proteins with desired properties and can be used to make affinity ligands which are cell-specific. This system can be used in many applications including the creation of novel vaccines, the identification of enzyme substrates and finding the affinity of a ligand for its target protein.

<span class="mw-page-title-main">Cholera toxin</span> Protein complex secreted by the bacterium Vibrio cholerae

Cholera toxin is an AB5 multimeric protein complex secreted by the bacterium Vibrio cholerae. CTX is responsible for the massive, watery diarrhea characteristic of cholera infection. It is a member of the heat-labile enterotoxin family.

<span class="mw-page-title-main">GM1</span> Biochemical compound important in the brain and intestines

GM1 (monosialotetrahexosylganglioside) the "prototype" ganglioside, is a member of the ganglio series of gangliosides which contain one sialic acid residue. GM1 has important physiological properties and impacts neuronal plasticity and repair mechanisms, and the release of neurotrophins in the brain. Besides its function in the physiology of the brain, GM1 acts as the site of binding for both cholera toxin and E. coli heat-labile enterotoxin.

P1 is a temperate bacteriophage that infects Escherichia coli and some other bacteria. When undergoing a lysogenic cycle the phage genome exists as a plasmid in the bacterium unlike other phages that integrate into the host DNA. P1 has an icosahedral head containing the DNA attached to a contractile tail with six tail fibers. The P1 phage has gained research interest because it can be used to transfer DNA from one bacterial cell to another in a process known as transduction. As it replicates during its lytic cycle it captures fragments of the host chromosome. If the resulting viral particles are used to infect a different host the captured DNA fragments can be integrated into the new host's genome. This method of in vivo genetic engineering was widely used for many years and is still used today, though to a lesser extent. P1 can also be used to create the P1-derived artificial chromosome cloning vector which can carry relatively large fragments of DNA. P1 encodes a site-specific recombinase, Cre, that is widely used to carry out cell-specific or time-specific DNA recombination by flanking the target DNA with loxP sites.

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<span class="mw-page-title-main">Hok/sok system</span>

The hok/sok system is a postsegregational killing mechanism employed by the R1 plasmid in Escherichia coli. It was the first type I toxin-antitoxin pair to be identified through characterisation of a plasmid-stabilising locus. It is a type I system because the toxin is neutralised by a complementary RNA, rather than a partnered protein.

<span class="mw-page-title-main">Heat-stable enterotoxin</span> Class of bacterial toxins

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<span class="mw-page-title-main">Sambhu Nath De</span>

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References

  1. 1 2 Glenn GM, Flyer DC, Ellingsworth LR, et al. (October 2007). "Transcutaneous immunization with heat-labile enterotoxin: development of a needle-free vaccine patch". Expert Rev Vaccines. 6 (5): 809–19. doi:10.1586/14760584.6.5.809. PMID   17931160. S2CID   38106206.
  2. Mudrak B and Kuehn MJ (2010). "Heat-labile enterotoxin: Beyond GM1 binding". Toxins. 2 (6): 1445–1470. doi: 10.3390/toxins2061445 . PMC   3153253 . PMID   22069646.
  3. 1 2 3 Sixma TK, Kalk KH, van Zanten BA, Dauter Z, Kingma J, Witholt B, Hol WG (April 1993). "Refined structure of Escherichia coli heat-labile enterotoxin, a close relative of cholera toxin". J. Mol. Biol. 230 (3): 890–918. doi:10.1006/jmbi.1993.1209. PMID   8478941.
  4. van den Akker F, Sarfaty S, Twiddy EM, Connell TD, Holmes RK, Hol WG (June 1996). "Crystal structure of a new heat-labile enterotoxin, LT-IIb". Structure. 4 (6): 665–78. doi: 10.1016/s0969-2126(96)00073-1 . PMID   8805549.
  5. Schlor, S.; Riedl, S.; Bla, J.; Reidl, J. (1 January 2000). "Genetic Rearrangements of the Regions Adjacent to Genes Encoding Heat-Labile Enterotoxins (eltAB) of Enterotoxigenic Escherichia coli Strains". Applied and Environmental Microbiology. 66 (1): 352–358. doi:10.1128/AEM.66.1.352-358.2000. PMC   91829 . PMID   10618247.
  6. Takeda, Y; Murphy, JR (January 1978). "Bacteriophage conversion of heat-labile enterotoxin in Escherichia coli". Journal of Bacteriology. 133 (1): 172–7. doi:10.1128/JB.133.1.172-177.1978. PMC   221991 . PMID   338578.
  7. Pierre-Hervé Luppi. "The Discovery of Cholera-Toxin as a Powerful Neuroanatomical Tool" . Retrieved 2011-03-23.
  8. Wagner B, Hufnagl K, Radauer C, et al. (April 2004). "Expression of the B subunit of the heat-labile enterotoxin of Escherichia coli in tobacco mosaic virus-infected Nicotiana benthamiana plants and its characterization as mucosal immunogen and adjuvant". Journal of Immunological Methods. 287 (1–2): 203–15. doi:10.1016/j.jim.2004.02.001. PMID   15099768.
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