Exotoxins can be single polypeptides or heteromeric protein complexes that act on different parts of the cells. At the cell surface, they may insert into the membrane to cause damage, bind to receptors to initiate their uptake, or facilitate interactions with other cell types.
A specific bacterial pathogen may produce a single exotoxin or multiple exotoxins. Each exotoxin possesses a unique mechanism of action, which is responsible for the elicitation of a unique pathology.
Exotoxin can be found in both Gram positive and Gram-Negative bacteria. Exotoxins have a significant and sometimes the primary role as the disease-causing virulence factor,
There are three main types of exotoxins and they are often classified by their mode of action on animal cells:
•Type I (membrane acting) toxins bind surface receptors and stimulate transmembrane signals, and include the super-antigenic toxins.
•Type II (membrane damaging) exotoxins that damage host cell membranes
•Type III (intracellular effector) toxins translocate an active enzymatic component into the cell and modify an intracellular target molecule.
The body's major defense against exotoxins is the production of antitoxin antibodies. Once the antibody binds to the exotoxin, the toxin can no longer bind to the receptors on the host cell membrane.
Exotoxin
