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152  structures 4262  species 8  interactions 24787  sequences 2  architectures

Family: Stap_Strp_toxin (PF01123)

Summary: Staphylococcal/Streptococcal toxin, OB-fold domain

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This is the Wikipedia entry entitled "Enterotoxin type B". More...

Enterotoxin type B Edit Wikipedia article

Enterotoxin type B
Organism Staphylococcus aureus
Symbol entB
UniProt P01552
Other data
Staphylococcal/Streptococcal toxin, N-terminal domain
PDB 1eu4 EBI.jpg
Crystal structure of the superantigen Spe-H (zinc bound) from Streptococcus pyogenes
Symbol Staphylococcal/Streptococcal toxin, N-terminal domain
Pfam PF01123
InterPro IPR006173
SCOP 1se3
Staphylococcal/Streptococcal toxin, beta-grasp domain
Symbol Stap_Strp_tox_C
Pfam PF02876
InterPro IPR006123
SCOP 1se3

In the field of molecular biology, enterotoxin type B, also known as Staphylococcal enterotoxin B (SEB), this is an enterotoxin produced by the gram-positive bacteria Staphylococcus aureus. It is a common cause of food poisoning, with severe diarrhea, nausea and intestinal cramping often starting within a few hours of ingestion.[1] Being quite stable,[2] the toxin may remain active even after the contaminating bacteria are killed. It can withstand boiling at 100°C for a few minutes.[1] Gastroenteritis occurs because SEB is a superantigen, causing the immune system to release a large amount of cytokines that lead to significant inflammation.

The protein domain found in this bacteria causes infections due to its multiple antibiotic resistant nature.[3] Additionally, this protein is the causative agent of toxic shock syndrome.


The function of this protein is to facilitate the infection of the host organism. It is a virulence factor designed to induce pathogenesis.[3] One of the major virulence exotoxins is the toxic shock syndrome toxin (TSST), which is secreted by the organism upon successful invasion. It causes a major inflammatory response in the host via superantigenic properties, and is the causative agent of toxic shock syndrome. It functions as a superantigen through activation of a significant fraction of T-cells (up to 20%) by cross-linking MHC class II molecules with T-cell receptors. TSST is a multisystem illness with several symptoms such as high fever, hypotension, dizziness, rash and peeling skin.[3]


All of these toxins share a similar two-domain fold (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 motif at the C-terminal domain. Each superantigen possesses slightly different binding mode(s) when it interacts with MHC class II molecules or the T-cell receptor.[4]

N-terminal domain

The N-terminal domain is also referred to as OB-fold, or in other words the oligonuclucleotide binding fold. This region contains a low-affinity major histocompatibility complex class II (MHC II) site which causes an inflammatory response.[5]

The N-terminal domain contains regions involved in Major Histocompatibility Complex class II association. It is a five stranded beta barrel that forms an OB fold.[6][7][8]

C-terminal domain

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.


  1. ^ a b "eMedicine - CBRNE - Staphylococcal Enterotoxin B". eMedicine. Retrieved 2011-02-06. 
  2. ^ Nema V, Agrawal R, Kamboj DV, Goel AK, Singh L (June 2007). "Isolation and characterization of heat resistant enterotoxigenic Staphylococcus aureus from a food poisoning outbreak in Indian subcontinent". Int. J. Food Microbiol. 117 (1): 29–35. doi:10.1016/j.ijfoodmicro.2007.01.015. PMID 17477998. 
  3. ^ a b c Blomster-Hautamaa DA, Kreiswirth BN, Kornblum JS, Novick RP, Schlievert PM (November 1986). "The nucleotide and partial amino acid sequence of toxic shock syndrome toxin-1". J. Biol. Chem. 261 (33): 15783–6. PMID 3782090.  Cite error: Invalid <ref> tag; name "pmid3782090" defined multiple times with different content (see the help page). Cite error: Invalid <ref> tag; name "pmid3782090" defined multiple times with different content (see the help page).
  4. ^ Acharya KR, Papageorgiou AC, Tranter HS (1998). "Crystal structure of microbial superantigen staphylococcal enterotoxin B at 1.5 A resolution: implications for superantigen recognition by MHC class II molecules and T-cell receptors". J. Mol. Biol. 277 (1): 61–79. doi:10.1006/jmbi.1997.1577. PMID 9514739. 
  5. ^ Brosnahan AJ, Schlievert PM (December 2011). "Gram-positive bacterial superantigen outside-in signaling causes toxic shock syndrome". FEBS J. 278 (23): 4649–67. doi:10.1111/j.1742-4658.2011.08151.x. PMC 3165073. PMID 21535475. 
  6. ^ Prasad GS, Earhart CA, Murray DL, Novick RP, Schlievert PM, Ohlendorf DH (December 1993). "Structure of toxic shock syndrome toxin 1". Biochemistry 32 (50): 13761–6. doi:10.1021/bi00213a001. PMID 8268150. 
  7. ^ Acharya KR, Passalacqua EF, Jones EY, Harlos K, Stuart DI, Brehm RD, Tranter HS (January 1994). "Structural basis of superantigen action inferred from crystal structure of toxic-shock syndrome toxin-1". Nature 367 (6458): 94–7. doi:10.1038/367094a0. PMID 8107781. 
  8. ^ Prasad GS, Radhakrishnan R, Mitchell DT, Earhart CA, Dinges MM, Cook WJ, Schlievert PM, Ohlendorf DH (June 1997). "Refined structures of three crystal forms of toxic shock syndrome toxin-1 and of a tetramutant with reduced activity". Protein Sci. 6 (6): 1220–7. doi:10.1002/pro.5560060610. PMC 2143723. PMID 9194182. 

This article incorporates text from the public domain Pfam and InterPro IPR006123 This article incorporates text from the public domain Pfam and InterPro IPR006173

This page is based on a Wikipedia article. The text is available under the Creative Commons Attribution/Share-Alike License.

This tab holds the annotation information that is stored in the Pfam database. As we move to using Wikipedia as our main source of annotation, the contents of this tab will be gradually replaced by the Wikipedia tab.

Staphylococcal/Streptococcal toxin, OB-fold domain Provide feedback

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Literature references

  1. Swaminathan S, Furey W, Pletcher J, Sax M; , Nature 1992;359:801-806.: Crystal structure of staphylococcal enterotoxin B, a superantigen. PUBMED:1436058 EPMC:1436058

Internal database links

External database links

This tab holds annotation information from the InterPro database.

InterPro entry IPR006173

Staphylococcus aureus is a Gram-positive coccus that grows in clusters or pairs, and is the major cause of nosocomial infections due to its multiple antibiotic resistant nature [PUBMED:3782090]. Patients who are immunocompromised (e.g., those suffering from third degree burns or chronic illness) are at risk from deep staphylococcal infections, such as osteomyelitis and pneumonia. Most skin infections are also caused by this bacterium.

Many virulence mechanisms are employed by Staphylococci to induce pathogenesis: these can include polysaccharide capsules and exotoxins [PUBMED:3782090]. One of the major virulence exotoxins is toxic shock syndrome toxin (TSST), which is secreted by the organism upon successful invasion. It causes a major inflammatory response in the host via superantigenic properties, and is the causative agent of toxic shock syndrome.

The structure of the TSST protein was originally determined to 2.5A by means of X-ray crystallography [PUBMED:8107781]. The N- and C-terminal domains both contain regions involved in MHC class II association; the C-terminal domain is also implicated in binding the T-cell receptor. Overall, the structure resembles that of Staphylococcal enterotoxin B (SEB), but differs in its N terminus and in the degree to which a long central helix is covered by surface loops [PUBMED:8268150]. The region around the carboxyl end of this helix is proposed to govern the superantigenic properties of TSST. An adjacent region along this helix is thought to be critical in the ability of TSST to induce toxic shock syndrome. Most recently, the structures of five mutants of TSST have been determined to 1.95A [PUBMED:9194182]. The mutations are in the central alpha-helix, and allow mapping of portions of TSST involved in superantigenicity and lethality.

Gene Ontology

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Domain organisation

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Seed source: Prosite
Previous IDs: none
Type: Family
Author: Finn RD, Bateman A, Griffiths-Jones SR
Number in seed: 5
Number in full: 24787
Average length of the domain: 85.30 aa
Average identity of full alignment: 30 %
Average coverage of the sequence by the domain: 37.55 %

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HMM build commands:
build method: hmmbuild -o /dev/null HMM SEED
search method: hmmsearch -Z 80369284 -E 1000 --cpu 4 HMM pfamseq
Model details:
Parameter Sequence Domain
Gathering cut-off 20.7 20.7
Trusted cut-off 20.7 20.9
Noise cut-off 20.2 20.6
Model length: 85
Family (HMM) version: 16
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Species distribution

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There are 8 interactions for this family. More...

Stap_Strp_tox_C V-set V-set Stap_Strp_toxin C1-set MHC_II_alpha C1-set Stap_Strp_tox_C


For those sequences which have a structure in the Protein DataBank, we use the mapping between UniProt, PDB and Pfam coordinate systems from the PDBe group, to allow us to map Pfam domains onto UniProt sequences and three-dimensional protein structures. The table below shows the structures on which the Stap_Strp_toxin domain has been found. There are 152 instances of this domain found in the PDB. Note that there may be multiple copies of the domain in a single PDB structure, since many structures contain multiple copies of the same protein seqence.

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