Shiga toxins (named for Kiyoshi Shiga, who first described the bacterial origin of dysentery caused by Shigella dysenteriae) are a family of related toxins with two major groups, Stx1 and Stx2, whose genes are considered to be part of the genome of lambdoid prophages. The most common sources for Shiga toxin are the bacteria Shigella dysenteriae and the Shigatoxigenic group of Escherichia coli (STEC), which includes serotype O157:H7 and other enterohemorrhagic E. coli.

Shiga toxins act to inhibit protein synthesis within target cells in a similar mechanism to ricin toxin produced by Ricinus communis. After entering a cell, the protein functions as an N-glycosidase, cleaving several nucleobases from the RNA that comprises the ribosome, thereby halting protein synthesis.

The toxin has 2 subunits, A and B. The B subunit is a pentamer that binds to specific glycolipids on the host cell, specifically globotriaosylceramide (Gb3). Following this the A subunit is internalised and cleaved into 2 parts. The A1 component then binds to the ribosome disrupting protein synthesis.

Shiga-Toxin