Shiga toxin

Ribbon diagram of Shiga toxin (Stx) from S. dysenteriae. From PDB: 1R4Q​.

Shiga-like toxin beta subunit
Identifiers
Symbol	SLT_beta
Pfam	PF02258
InterPro	IPR003189
SCOP2	2bos / SCOPe / SUPFAM
TCDB	1.C.54
Available protein structures: Pfam   structures / ECOD   PDB RCSB PDB; PDBe; PDBj PDBsum structure summary

Shiga-like toxin subunit A
Identifiers
Symbol	Shiga-like_toxin_subunit_A
InterPro	IPR016331
SCOP2	1r4q / SCOPe / SUPFAM

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.^[1] The toxins are named after Kiyoshi Shiga, who first described the bacterial origin of dysentery caused by Shigella dysenteriae.^[2] Shiga-like toxin (SLT) is a historical term for similar or identical toxins produced by Escherichia coli.^[3] The most common sources for Shiga toxin are the bacteria S. dysenteriae and some serotypes of Escherichia coli (shigatoxigenic or STEC), which include serotypes O157:H7, and O104:H4.^[4][5]

Nomenclature

Microbiologists use many terms to describe Shiga toxin and differentiate more than one unique form. Many of these terms are used interchangeably.

1. Shiga toxin type 1 and type 2 (Stx-1 and 2) are the Shiga toxins produced by some E. coli strains. Stx-1 is identical to Stx of Shigella spp. or differs by only one amino acid.^[6] Stx-2 shares 55% amino acid homology with Stx-1.^[7]
2. Cytotoxins – an archaic denotation for Stx – is used in a broad sense.
3. Verocytotoxins/verotoxins – a seldom-used term for Stx – is from the hypersensitivity of Vero cells to Stx.^[8][9][10]
4. The term Shiga-like toxins is another antiquated term which arose prior to the understanding that Shiga and Shiga-like toxins were identical.^[11]

History

The toxin is named after Kiyoshi Shiga, who discovered S. dysenteriae in 1897.^[2] In 1977, researchers in Ottawa, Ontario discovered the Shiga toxin normally produced by Shigella dysenteriae in a line of E. coli.^[12] The E. coli version of the toxin was named "verotoxin" because of its ability to kill Vero cells (African green monkey kidney cells) in culture. Shortly after, the verotoxin was referred to as Shiga-like toxin because of its similarities to Shiga toxin.

It has been suggested by some researchers that the gene coding for Shiga-like toxin comes from a toxin-converting lambdoid bacteriophage, such as H-19B or 933W, inserted into the bacteria's chromosome via transduction.^[13] Phylogenetic studies of the diversity of E. coli suggest that it may have been relatively easy for Shiga toxin to transduce into certain strains of E. coli, because Shigella is itself a subgenus of Escherichia; in fact, some strains traditionally considered E. coli (including those that produce this toxin) in fact belong to this lineage. Being closer relatives of Shigella dysenteriae than of the typical E. coli, it is not at all unusual that toxins similar to that of S. dysenteriae are produced by these strains. As microbiology advances, the historical variation in nomenclature (which arose because of gradually advancing science in multiple places) is increasingly giving way to recognizing all of these molecules as "versions of the same toxin" rather than "different toxins".^{[14]: 2–3}

Transmission

The toxin requires highly specific receptors on the cells' surface in order to attach and enter the cell; species such as cattle, swine, and deer which do not carry these receptors may harbor toxigenic bacteria without any ill effect, shedding them in their feces, from where they may be spread to humans.^[15]

Clinical significance

Symptoms of Shiga toxin ingestion include abdominal pain as well as watery diarrhea. Severe life-threatening cases are characterized by hemorrhagic colitis (HC).^[16]

The toxin is associated with hemolytic-uremic syndrome. In contrast, Shigella species may also produce shigella enterotoxins, which are the cause of dysentery.

The toxin is effective against small blood vessels, such as found in the digestive tract, the kidney, and lungs, but not against large vessels such as the arteries or major veins. A specific target for the toxin appears to be the vascular endothelium of the glomerulus. This is the filtering structure that is a key to the function of the kidney. Destroying these structures leads to kidney failure and the development of the often deadly and frequently debilitating hemolytic uremic syndrome. Food poisoning with Shiga toxin often also has effects on the lungs and the nervous system.

Structure and mechanism

SLT2 from Escherichia coli O157:H7. A-subunit is shown above (viridian), with B-subunit pentamer below (multicolored). From PDB: 1R4P​.

Mechanism

The B subunits of the toxin bind to a component of the cell membrane known as glycolipid globotriaosylceramide (Gb3). Binding of the subunit B to Gb3 causes induction of narrow tubular membrane invaginations, which drives formation of inward membrane tubules for toxin-receptor complex^[17] uptake into the cell. These tubules are essential for uptake into the host cell.^[18] The Shiga toxin (a non-pore forming toxin) is transferred to the cytosol via Golgi network and endoplasmic reticulum (ER). From the Golgi toxin is trafficked to the ER. It is then processed through cleavage by a furin-like protease to separate the A1 subunit. Some toxin-receptor complexes reportedly bypass these steps and are transported to the nucleus rather than the cytosol, with unknown effects.^[17]

Shiga toxins act to inhibit protein synthesis within target cells by a mechanism similar to that of the infamous plant toxin ricin.^[19][20] After entering a cell via a macropinosome,^[21] the payload (A subunit) cleaves a specific adenine nucleobase from the 28S RNA of the 60S subunit of the ribosome, thereby halting protein synthesis.^[22] As they mainly act on the lining of the blood vessels, the vascular endothelium, a breakdown of the lining and hemorrhage eventually occurs.^{[clarification needed]} The first response is commonly a bloody diarrhea. This is because Shiga toxin is usually taken in with contaminated food or water.

The bacterial Shiga toxin can be used for targeted therapy of gastric cancer, because this tumor entity expresses the receptor of the Shiga toxin. For this purpose an unspecific chemotherapeutical is conjugated to the B-subunit to make it specific. In this way only the tumor cells, but not healthy cells, are destroyed during therapy.^[23]

Structure

The toxin has two subunits—designated A (mol. wt. 32000 Da) and B (mol. wt. 7700 Da)—and is one of the AB₅ toxins. The B subunit is a pentamer that binds to specific glycolipids on the host cell, specifically globotriaosylceramide (Gb3).^[24][25] Following this, the A subunit is internalised and cleaved into two parts. The A1 component then binds to the ribosome, disrupting protein synthesis. Stx-2 has been found to be about 400 times more toxic (as quantified by LD₅₀ in mice) than Stx-1.

Gb3 is, for unknown reasons, present in greater amounts in renal epithelial tissues, to which the renal toxicity of Shiga toxin may be attributed. Gb3 is also found in central nervous system neurons and endothelium, which may lead to neurotoxicity.^[26] Stx-2 is also known to increase the expression of its receptor GB3 and cause neuronal dysfunctions.^[27]

See also

• 2011 German E. coli outbreak
• Cholera toxin
• Enterotoxin
• Pertussis toxin

References

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2. Trofa, Andrew F.; Ueno-Olsen, Hannah; Oiwa, Ruiko; Yoshikawa, Masanosuke (1999-11-01). "Dr. Kiyoshi Shiga: Discoverer of the Dysentery Bacillus". Clinical Infectious Diseases. 29 (5): 1303–1306. doi:10.1086/313437. ISSN 1058-4838. PMID 10524979.
3. Zhu Q; Li L; Guo Z; Yang R (June 2002). "Identification of Shiga-like toxin Escherichia coli isolated from children with diarrhea by polymerase chain reaction". Chin. Med. J. 115 (6): 815–8. PMID 12123543.
4. Beutin L (2006). "Emerging enterohaemorrhagic Escherichia coli, causes and effects of the rise of a human pathogen". Journal of Veterinary Medicine, Series B. 53 (7): 299–305. doi:10.1111/j.1439-0450.2006.00968.x. PMID 16930272.
5. Spears KJ, Roe AJ, Gally DL (2006). "A comparison of enteropathogenic and enterohaemorragic Escherichia coli pathogenesis". FEMS Microbiology Letters. 255 (2): 187–202. doi:10.1111/j.1574-6968.2006.00119.x. PMID 16448495.
6. Kaper JB, O'Brien AD (2014). Sperandio V, Hovde CJ (eds.). "Overview and Historical Perspectives". Microbiology Spectrum. 2 (6). doi:10.1128/microbiolspec.EHEC-0028-2014. PMC 4290666. PMID 25590020.
7. Kaper, James B.; Nataro, James P.; Mobley, Harry L. T. (February 2004). "Pathogenic Escherichia coli". Nature Reviews Microbiology. 2 (2): 123–140. doi:10.1038/nrmicro818. PMID 15040260.
8. Beutin L; Geier D; Steinrück H; Zimmermann S; Scheutz F (September 1993). "Prevalence and some properties of verotoxin (Shiga-like toxin)-producing Escherichia coli in seven different species of healthy domestic animals". Journal of Clinical Microbiology. 31 (9): 2483–8. doi:10.1128/JCM.31.9.2483-2488.1993. PMC 265781. PMID 8408571.
9. Bitzan M; Richardson S; Huang C; Boyd B; Petric M; Karmali MA (August 1994). "Evidence that verotoxins (Shiga-like toxins) from Escherichia coli bind to P blood group antigens of human erythrocytes in vitro". Infection and Immunity. 62 (8): 3337–47. doi:10.1128/IAI.62.8.3337-3347.1994. PMC 302964. PMID 8039905.
10. Giraldi R; Guth BE; Trabulsi LR (June 1990). "Production of Shiga-like toxin among Escherichia coli strains and other bacteria isolated from diarrhea in São Paulo, Brazil". Journal of Clinical Microbiology. 28 (6): 1460–2. doi:10.1128/JCM.28.6.1460-1462.1990. PMC 267957. PMID 2199511.
11. Scheutz F, Teel LD, Beutin L, Piérard D, Buvens G, Karch H, Mellmann A, Caprioli A, Tozzoli R, Morabito S, Strockbine NA, Melton-Celsa AR, Sanchez M, Persson S, O'Brien AD (September 2012). "Multicenter evaluation of a sequence-based protocol for subtyping Shiga toxins and standardizing Stx nomenclature". Journal of Clinical Microbiology. 50 (9): 2951–63. doi:10.1128/JCM.00860-12. PMC 3421821. PMID 22760050.
12. Konowalchuk J, Speirs JI, Stavric S (December 1977). "Vero response to a cytotoxin of Escherichia coli". Infection and Immunity. 18 (3): 775–9. doi:10.1128/IAI.18.3.775-779.1977. PMC 421302. PMID 338490.
13. Mizutani S, Nakazono N, Sugino Y (April 1999). "The so-called chromosomal verotoxin genes are actually carried by defective prophages". DNA Research. 6 (2): 141–3. doi:10.1093/dnares/6.2.141. PMID 10382973.
14. Silva CJ, Brandon DL, Skinner CB, He X, et al. (2017), "Chapter 3: Structure of Shiga toxins and other AB5 toxins", Shiga toxins: A Review of Structure, Mechanism, and Detection, Springer, ISBN 978-3319505800.
15. Asakura, H.; Makino, S-I.; Kobori, H.; Watarai, M.; Shirahata, T.; Ikeda, T.; Takeshi, K. (April 2001). "Phylogenetic diversity and similarity of active sites of Shiga toxin (Stx) in Shiga toxin-producing Escherichia coli (STEC) isolates from humans and animals". Epidemiology and Infection. 127 (1): 27–36. doi:10.1017/s0950268801005635. PMC 2869726. PMID 11561972.
16. Beutin, Lothar; Miko, Angelika; Krause, Gladys; Pries, Karin; Haby, Sabine; Steege, Katja; Albrecht, Nadine (August 2007). "Identification of Human-Pathogenic Strains of Shiga Toxin-Producing Escherichia coli from Food by a Combination of Serotyping and Molecular Typing of Shiga Toxin Genes". Applied and Environmental Microbiology. 73 (15): 4769–4775. Bibcode:2007ApEnM..73.4769B. doi:10.1128/AEM.00873-07. PMC 1951031. PMID 17557838.
17. Obrig TG (2010). "Escherichia coli Shiga Toxin Mechanisms of Action in Renal Disease". Toxins. 2 (12): 2769–2794. doi:10.3390/toxins2122769. PMC 3032420. PMID 21297888.
18. Römer W, Berland L, Chambon V, Gaus K, Windschiegl B, Tenza D, Aly MR, Fraisier V, Florent JC, Perrais D, Lamaze C, Raposo G, Steinem C, Sens P, Bassereau P, Johannes L (November 2007). "Shiga toxin induces tubular membrane invaginations for its uptake into cells". Nature. 450 (7170): 670–5. Bibcode:2007Natur.450..670R. doi:10.1038/nature05996. PMID 18046403. S2CID 4410673.
19. Sandvig K, van Deurs B (November 2000). "Entry of ricin and Shiga toxin into cells: molecular mechanisms and medical perspectives". The EMBO Journal. 19 (22): 5943–50. doi:10.1093/emboj/19.22.5943. PMC 305844. PMID 11080141.
20. Mercatelli D, Bortolotti M, Giorgi FM (August 2020). "Transcriptional network inference and master regulator analysis of the response to ribosome-inactivating proteins in leukemia cells". Toxicology. 441: 152531. Bibcode:2020Toxgy.44152531M. doi:10.1016/j.tox.2020.152531. PMID 32593706. S2CID 220255474.
21. Lukyanenko V, Malyukova I, Hubbard A, Delannoy M, Boedeker E, Zhu C, Cebotaru L, Kovbasnjuk O (November 2011). "Enterohemorrhagic Escherichia coli infection stimulates Shiga toxin 1 macropinocytosis and transcytosis across intestinal epithelial cells". American Journal of Physiology. Cell Physiology. 301 (5): C1140-9. doi:10.1152/ajpcell.00036.2011. PMC 3213915. PMID 21832249.
22. Donohue-Rolfe A, Acheson DW, Keusch GT (2010). "Shiga toxin: purification, structure, and function". Reviews of Infectious Diseases. 13 Suppl 4 (7): S293-7. doi:10.1016/j.toxicon.2009.11.021. PMID 2047652.
23. Gastric adenocarcinomas express the glycosphingolipid Gb3/CD77: Targeting of gastric cancer cells with Shiga toxin B-subunit
24. Stein PE, Boodhoo A, Tyrrell GJ, Brunton JL, Read RJ (February 1992). "Crystal structure of the cell-binding B oligomer of verotoxin-1 from E. coli". Nature. 355 (6362): 748–50. Bibcode:1992Natur.355..748S. doi:10.1038/355748a0. PMID 1741063. S2CID 4274763.
25. Kaper JB, Nataro JP, Mobley HL (February 2004). "Pathogenic Escherichia coli". Nature Reviews. Microbiology. 2 (2): 123–40. doi:10.1038/nrmicro818. PMID 15040260. S2CID 3343088.
26. Obata F, Tohyama K, Bonev AD, Kolling GL, Keepers TR, Gross LK, Nelson MT, Sato S, Obrig TG (November 2008). "Shiga toxin 2 affects the central nervous system through receptor globotriaosylceramide localized to neurons". The Journal of Infectious Diseases. 198 (9): 1398–406. doi:10.1086/591911. PMC 2684825. PMID 18754742.
27. Tironi-Farinati C, Loidl CF, Boccoli J, Parma Y, Fernandez-Miyakawa ME, Goldstein J (May 2010). "Intracerebroventricular Shiga toxin 2 increases the expression of its receptor globotriaosylceramide and causes dendritic abnormalities". Journal of Neuroimmunology. 222 (1–2): 48–61. doi:10.1016/j.jneuroim.2010.03.001. hdl:11336/16303. PMID 20347160. S2CID 11910897.

External links

• UniprotKB entries: stxA1 Q9FBI2, stxB1 Q7BQ98, stxA2 P09385, stxB2 P09386
• Shiga+toxin at the U.S. National Library of Medicine Medical Subject Headings (MeSH)
• Shiga-Like+Toxin+I at the U.S. National Library of Medicine Medical Subject Headings (MeSH)
• Shiga-Like+Toxin+II at the U.S. National Library of Medicine Medical Subject Headings (MeSH)
• "Shigella" in Todar's Online Textbook of Bacteriology
• Mizutani, S. (1999). "The So-called Chromosomal Verotoxin Genes are Actually Carried by Defective Prophages". DNA Research. 6 (2): 141–143. doi:10.1093/dnares/6.2.141. PMID 10382973.