Shiga Toxin, 1DM0, Biologic Models

Protein Description

Shiga toxins are a family of related bacterial toxins first discovered by Kiyoshi Shiga while researching the origins of dysentery. Two major groups of this toxin are found in the Shigella dysenteriae and the shigatoxigenic serotypes of Escherichia coli bacteria, Stx1 and Stx2.

As the name suggests, this little bugger causes pretty bad dysentery in humans. Shiga-like Toxin is made of 6 primary chains, 5 smaller identical subunits that form a pentamer ring and then the Alpha unit. The two red domains on top are the functionally toxic portions of the protein.

The pentamer is the portion of the compound that binds to surface receptors anchoring the Alpha unit toxin to the membrane. Upon binding, the Alpha unit forces itself into the cytosol. Following this, a predict bile sequence of events occurs that directly inactivates ribosomes halting protein synthesis.

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Shiga Toxin
Shiga Toxin, Molecular Templates, MT-3724
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Pubmed Abstract

Shigella dysenteriae is the pathogen responsible for the severe form of dysentery in humans. It produces Shiga toxin, the prototype of a family of closely related bacterial protein toxins. We have determined the structure of the holotoxin, an AB5 hexamer, by X-ray crystallography. The five B subunits form a pentameric ring, encircling a helix at the carboxy terminus of the A subunit. The A subunit interacts with the B pentamer via this C-terminal helix and a four-stranded mixed beta-sheet. The fold of the rest of the A subunit is similar to that of the A chain of the plant toxin ricin; both are N-glycosidases. However, the active site in the bacterial holotoxin is blocked by a segment of polypeptide chain. These residues of the A subunit would be released as part of the activation mechanism of the toxin.

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