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Bacteria - Exotoxins

Bacteria - Exotoxins

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Exotoxins
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.

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