Inquiry Basket
Loading ......
Staphylococcus aureus (S. aureus) is an important type of food-borne pathogenic bacteria that causes food contamination and food poisoning. It is also a symbiont of human skin and mucous membranes. About 20% to 30% of healthy individuals carry Staphylococcus aureus. Animal foods are susceptible to Staphylococcus aureus infection, such as milk, butter, cured ham, etc. Food poisoning incidents caused by Staphylococcus aureus have been frequently reported, and more than 95% of them are caused by enterotoxin. It is reported that the proportion of food poisoning incidents caused by enterotoxins (SEs) in the United States and Canada is 33% and 45%, respectively. Epidemiological studies have shown that Staphylococcus aureus enterotoxin A (There are about 23 serotypes including SEA), Staphylococcus aureus enterotoxin B (SEB), Staphylococcus aureus enterotoxin C1 (SEC1), Staphylococcus aureus enterotoxin D (SED), which have similar structures and functions. properties, molecular weight is 27.5~30kDa. Among the above types of SEs, SEB is one of the most common biotoxins reported so far and is also a typical biotoxin causing food poisoning.
Staphylococcus aureus enterotoxin B (SEB) is a monomeric protein with a molecular mass of 28366 Da and an isoelectric point pI of 8.6. The amino acid number of Staphylococcus aureus enterotoxin B is 238.
Figure 1. 3D models S. aureus enterotoxin type B - SEB and B subunit of the type II heat-labile enterotoxin of E. coli monomer. (Kaliniak S, et al., 2024)
Through X-ray crystallography, the three-dimensional structure of a molecule of SEB contains two regions, which are connected by a loop extending by 6 residues; the first region (30-120) and the second region (127-239). A long a-helix spans the center of the molecule between two regions. The first region contains a β-cylinder (containing β1, β2, β3, β4, β5 strands) and three helices (a2, a3, and a5). Through different β turns, β1 is connected to β2 strands and β2 to 3. Two cysteine residues (cysteine 93 and cysteine 113) form a disulfide bond above the β cylinder. The sequence between two cysteine residues forms a mobile, soluble LOOP.
The second region of SEB is different from the superantigens of other microorganisms. It contains antiparallel β sheets (β6-β12) and a central a-helix. β6 is antiparallel to β7, and β7 is parallel to β12; β9 is antiparallel to β12 and β10. Recently, it was reported that the second region may bind to p85 protein. The N-terminal tail (residues 1 to 20) is on the surface of domain II. Residues 14 to 17 form a 310-helical turn at the top of domain II (labeled as the a1 helix). SEB binds MHCII with high affinity, and it binds to mouse T cell Vβ3, 7, 8.1, 8.1, 8.3, and 17. According to SEB topoisomerism and mutational studies, the T-cell receptor binding site is surrounded by a shallow groove formed by SEB regions 1 and 2. The a5 helix in the SEB molecule faces the adjacent site that binds the MHCII molecule.
SEB is a heat-stable protein. Due to excessive initial heating, SEB activity will be weakened under high temperature conditions. When the toxin is heated at pH 7.3 at 100°C for 5 minutes, its activity loss is less than 50%. Thermal fusion reactions at 70°C-80°C will cause serious loss of their activity. However, heating to 100°C can restore 35%-40% of the immune activity, which is due to the dissociation of the polymer under high temperature conditions. Therefore, the loss of immune activity of SEB is more severe when heated to 70C-80°C than when heated to 90 -100°C. Some toxins that have been inactivated by heating will have their activity restored if they are incubated at 25°C.
SEB is resistant to the denaturing effects of denaturants such as urea and guanidine hydrochloride. Mild denaturant experimental results show that in 9M urea or 6M guanidine hydrochloride solvent, it takes a longer time for the structure of the SEB protein to open and reach an equilibrium state. The denatured toxin is diluted by the denaturant, and it only takes a few minutes or hours to return to the native state of the protein through refolding. This shows that the opening of the toxin protein requires a very large activation energy, while its refolding requires only a small activation energy. The structure of SEB protein is stable because of the disulfide ring. It covalently locks two β-sheets in a stable, antiparallel structure. However, below pH 3.5, SEB will denature rapidly, and this process is irreversible. Because SEB is a basic protein, low pH results in protonation of the carboxylate groups that maintain the native SEB structure. This protonation results in a change in the native structure of SEB such that the local electrostatic cations generated from the protonation of the carboxylate group are reduced. It is difficult to characterize SEB due to its microscopic heterogeneous effect. Depending on the form of SEB, different processing and purification methods are available. It is generally believed that the Staphylococcus aureus strain synthesizes only one component. Hydrolysis of the unstable amide group of glutamine and astonamide residues gives SEB its strong base properties. Therefore, a series of isomers of SEB defined by serum have different pIs.
Staphylococcus aureus SEB is a superantigen that does not require APC processing. It uses a complete protein molecule to directly bind to the a1 domain of MHC class II molecules and the β-chain V region of TCR, thereby stimulating T cell activation and proliferation and releasing a large amount of cytokines.
Staphylococcus aureus SEB has different affinities to different leukocyte antigen molecules (HLA), and the order of affinity is HLA-DR>DQ>DP. The complex formed between SEB and MHC class II molecules (HLA-DR1) occurs between the a1 domain of MHC class II molecules and the N-terminal domain of SEB molecules, binding with low affinity (0.4~0.7μ mol/L). The main interaction between SEB and HLA-DR1 is the salt bridge formed between glutamic acid (Glu) 67 of SEB and lysine (Lys) 39 of HLA-DR1. The side chain of the hydrophobic end of SEB interacts with HLA -Interaction of the non-polarized region between the α1 helix and β-sheet of DR1.
The two main routes of SEB poisoning are oral and respiratory. Ingestion of 3.5ugSEB through oral route will cause vomiting. Inhaled SEB is also highly toxic, with as little as 30ng causing fever, respiratory discomfort (eg, cough, dyspnea, retrosternal discomfort and chest pain), and gastrointestinal symptoms. Severe poisoning can lead to pulmonary edema, adult distress respiratory syndrome (ARDS) and death.
Reference
| Target | Cat. No. | Product Name | Expression System | Tag/Conjugate | Application | |
| SEB | DAG-WT627 | Recombinant Staphylococcus aureus Enterotoxin B (SEB) | E. coli | His | ELISA | Inquiry |
| DAGB111 | S. aureus Enterotoxin Type B Toxoid | S. aureus | Unconjugated | ELISA | Inquiry |
Loading ......
