Polypeptides secreted by both gram-positive and gram-negative bacteria.
Many are dimeric in structure, with A and B subunits.
The A subunit is the toxic active Portion; the B subunit is the Binding portion that attaches to the host cell.
Highly toxic, even in small quantities.
Directly kill or alter host cell functions.
Mechanisms & Consequences:
ADP-ribosylation adds ADP-ribose to proteins in the host cell.
Diptheria toxin inhibits protein synthesis, leading to cell death; other toxins that act via ADP-ribosylation can hyperactivate protein synthesis.
Increase Cyclic AMP
In the case of heat-labile enterotoxin, this results in fluid and electrolyte loss into the lumen of the gastrointestinal tract, which causes watery diarrhea.
Proteases
Botulinum toxin is a neurotoxin that blocks acetylcholine release, producing paralysis.
Super antigens
For example,
Toxic Shock Syndrome toxin overstimulates
T cells, triggering cytokine storms.