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164  structures 9  species 0  interactions 44  sequences 1  architecture

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
OrganismStaphylococcus aureus
Staphylococcal/Streptococcal toxin, N-terminal domain
PDB 1eu4 EBI.jpg
Crystal structure of the superantigen Spe-H (zinc bound) from Streptococcus pyogenes
SymbolStaphylococcal/Streptococcal toxin, N-terminal domain
Staphylococcal/Streptococcal toxin, beta-grasp domain

In the field of molecular biology, enterotoxin type B, also known as Staphylococcal enterotoxin B (SEB), 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 Â°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.

Additionally, this protein is one of the causative agents 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 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.
  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

This entry represents an OB-fold domain found in enterotoxins.

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

External database links

This tab holds annotation information from the InterPro database.

InterPro entry IPR006173

Streptococcus pyogenes (group A streptococcus) cause a wide range of human infections, in a range from acute illness in an initial exposure such as pharyngitis or impetigo to serious and life-threatening infections in humans like toxic shock syndrome (TSS) with or without necrotizing fasciitis and myositis. This pathogen is also associated with development of autoimmune diseases, namely rheumatic fever, acute glomerulonephritis, and guttate psoriasis. Staphylococcus aureus is another major human pathogen that can cause a wide variety of infections, ranging from relatively benign furuncles and soft tissue abscesses to others that are life-threatening, such as infective endocarditis, necrotizing (hemorrhagic) pneumonia, sepsis, and toxic shock syndrome (TSS). The ability of these two pathogens to cause serious infections relays on the production of cell surface and secreted virulence factors, known altogether as superantigens exotoxins which overstimulates many immune processes. Among the cell surface factors, large families of microbial surface components recognising adhesive matrix molecules (MSCRAMMs) and immunoglobulin Fc-binding proteins are included, which are important for host colonisation and interfere with local host immune responses. The secreted virulence factors include multiple cytolysins, proteases, nucleases, and lipases. A hallmark of superantigens is a conserved overall structure containing two major protein domains: an amino-terminal oligosaccharide/oligonucleotide binding (O/B) fold, comprised of a beta-barrel, and a carboxy-terminal beta-grasp domain made of antiparallel beta-strands, with domains connected by a central, diagonal alpha-helix [ PUBMED:23824366 , PUBMED:26433203 ].

This entry represents the O/B fold domain present in streptococcal and staphylococcal exotoxins. This entry also includes exotoxins found in Streptococcus phage.

Gene Ontology

The mapping between Pfam and Gene Ontology is provided by InterPro. If you use this data please cite InterPro.

Domain organisation

Below is a listing of the unique domain organisations or architectures in which this domain is found. More...

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Pfam Clan

This family is a member of clan OB_enterotoxin (CL0658), which has the following description:

This superfamily contains OB-fold domains found within bacterial enterotoxins. According to the SCOP and ECOD databases these domains are distinct from Clan:CL0021.

The clan contains the following 9 members:

Enterotoxin_b PatG_C PatG_D Pertus-S4-tox Pertus-S5-tox Pertussis_S2S3 SLT_beta SSL_OB Stap_Strp_toxin


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Seed source: Prosite
Previous IDs: none
Type: Domain
Sequence Ontology: SO:0000417
Author: Finn RD , Bateman A , Griffiths-Jones SR
Number in seed: 9
Number in full: 44
Average length of the domain: 85.50 aa
Average identity of full alignment: 31 %
Average coverage of the sequence by the domain: 34.60 %

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HMM build commands:
build method: hmmbuild -o /dev/null HMM SEED
search method: hmmsearch -Z 57096847 -E 1000 --cpu 4 HMM pfamseq
Model details:
Parameter Sequence Domain
Gathering cut-off 23.0 23.0
Trusted cut-off 23.2 23.2
Noise cut-off 21.1 20.0
Model length: 87
Family (HMM) version: 22
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Species distribution

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Archea Archea Eukaryota Eukaryota
Bacteria Bacteria Other sequences Other sequences
Viruses Viruses Unclassified Unclassified
Viroids Viroids Unclassified sequence Unclassified sequence


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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 164 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 sequence.

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AlphaFold Structure Predictions

The list of proteins below match this family and have AlphaFold predicted structures. Click on the protein accession to view the predicted structure.

Protein Predicted structure External Information
Q2FXX5 View 3D Structure Click here