Shiga toxin
| Shiga toxin, subunit A ( Shigella dysenteriae ) | ||
|---|---|---|
|
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| Surface model from A + 5B to PDB 1DM0 | ||
| Mass / length primary structure | 293 amino acids | |
| Secondary to quaternary structure | Monomer | |
| Identifier | ||
| Gene name (s) | stxA | |
| External IDs | ||
| Enzyme classification | ||
| EC, category | 3.2.2.22 , glycosidase | |
| Response type | hydrolysis | |
| Substrate | N-glycoside of an adenine in 28S rRNA | |
| Products | defective 28S rRNA | |
Shiga toxins are cytotoxic proteins named after the Japanese bacteriologist Kiyoshi Shiga , produced by Shigella dysenteriae , the causative agent of the shigellosis or bacterial dysentery , and closely related proteins that are produced by Escherichia coli ( enterohemorrhagic Escherichia coli ) ( Vero toxins ).
The entire Shiga toxin has a molar mass of around 70,000 Daltons ; the protein consists of two different subunits that are linked by disulfide bridges . The B subunit (7.6 kDa ) is present five times and ensures that it binds to the cell surface and that the A subunit (about 30 kDa) is channeled into the interior of the cell, where it supports protein synthesis by cleaving the 28s rRNA which inhibits ribosomes . It has a pronounced neuro tropism .
Shiga toxins are lectins . They are not enterotoxins and are not responsible for diarrhea in bacterial dysentery, but - like the similar Vero toxins - for their hemolytic course.
| Shiga toxin | ||
|---|---|---|
|
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| Binding of adenine to Stx2, the Shiga toxin 2 from Escherichia coli O157: H7 according to PDB 2ga4 | ||
| Mass / length primary structure | 315 + 89 amino acids (A + B) | |
| Secondary to quaternary structure | Heterodimer | |
| Enzyme classification | ||
| EC, category | 3.2.2.22 , N-glycosylase | |
| Response type | Hydrolysis of an N-glycosyl bond | |
| Substrate | rRNA (60S) + H 2 O | |
| Products | defective rRNA (60S) | |
| Occurrence | ||
| Parent taxon | Escherichia coli | |
The lectins Vero-Toxin 1 and Vero-Toxin 2 from Escherichia coli are also called Shiga-like-toxin I / II (SLT I / II) or Shiga-Toxin 1/2 (Stx1 / Stx2) due to their similarity to Shiga-Toxin . It affects the eukaryotic protein synthesis by the 60S subunit of the ribosome to catalytic inactivate way. The elongation of the peptide chain is impaired by the fact that the binding of aminoacyl- tRNA to the ribosomes is prevented.
In terms of their structure and mode of action, vero toxins and Shiga toxins belong to the same group of toxins as the lectins ricin and abrin . Like these, they have two chains or subunits. It is striking that their respective subunit exactly at the same place as ricin A cleavage of the N-glycosidic bond of adenine in the 28S rRNA caused. These toxins act as specific RNA-N-glycosidases which inactivate ribosomes.
Individual evidence
- ↑ a b Entry on Shiga toxin. In: Römpp Online . Georg Thieme Verlag, accessed on May 28, 2011.