Stx1aencoded

Stx1aencoded refers to the genetic element that encodes the A subunit of Shiga toxin type 1 (Stx1), typically the stx1A gene found in certain Escherichia coli and Shigella strains. The toxin is an AB5 toxin, consisting of one A subunit (Stx1a) and a pentamer of B subunits (Stx1B). The stx1A and stx1B genes are commonly carried together on a lambdoid phage integrated into the bacterial chromosome, and their presence can vary between strains due to horizontal gene transfer.

Genetic and expression context: The stx1A and stx1B genes are part of a phage-encoded toxin cassette. Expression of the toxin is linked to phage induction, often triggered by the bacterial SOS response. This means toxin production can increase when the bacterial cell experiences DNA damage or stress, leading to phage-mediated lysis and release of the toxin.

Mechanism of action: The Stx1a A subunit is an N-glycosidase that cleaves a specific adenine residue from 28S rRNA, inhibiting protein synthesis and potentially causing cell death. The Stx1B subunits form a binding pentamer that attaches the toxin to Gb3 receptors on the surface of susceptible cells, facilitating entry.

Clinical relevance: Stx1a-encoded toxins contribute to diseases associated with Shiga toxin–producing bacteria, including hemorrhagic colitis and hemolytic uremic syndrome (HUS). The presence and expression of stx1A (often alongside other stx genes) influence disease severity and epidemiology in outbreaks involving strains such as certain E. coli serotypes.

See also: Shiga toxin, Stx1, stx1A, stx1B, phage-encoded toxins.