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 °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.
| Enterotoxin type B | |||||||
|---|---|---|---|---|---|---|---|
| Identifiers | |||||||
| Organism | |||||||
| Symbol | entB | ||||||
| UniProt | P01552 | ||||||
| |||||||
| Staphylococcal/Streptococcal toxin, N-terminal domain | |||||||||
|---|---|---|---|---|---|---|---|---|---|
 Crystal structure of the superantigen Spe-H (zinc bound) from Streptococcus pyogenes | |||||||||
| Identifiers | |||||||||
| Symbol | Staphylococcal/Streptococcal toxin, N-terminal domain | ||||||||
| Pfam | PF01123 | ||||||||
| Pfam clan | CL0658 | ||||||||
| ECOD | 2.2.1 | ||||||||
| InterPro | IPR006173 | ||||||||
| PROSITE | PDOC00250 | ||||||||
| SCOP2 | 1se3 / SCOPe / SUPFAM | ||||||||
| |||||||||
Additionally, this protein is one of the causative agents of toxic shock syndrome.
Function
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]
Structure
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.
References
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