Bacterial Toxins

Abstract

This chapter discusses the molecules that have been classically known as bacterial toxins; the last section mentions some recently identified molecules that cause cell intoxication and have many but not all of the properties of classical toxins. A section shows the subunit composition and the spatial organization of toxins whose structures have been solved either by X-ray crystallography or by quick-freeze deep-etch electron microscopy. For simplicity, the toxins have been divided into three main categories: (i) those that exert their powerful toxicity by acting on the surface of eukaryotic cells simply by touching important receptors, by cleaving surface-exposed molecules, or by punching holes in the cell membrane, thus breaking the cell permeability barrier; (ii) those that have an intracellular target and hence need to cross the cell membrane (these toxins need at least two active domains, one to cross the eukaryotic cell membrane and the other to modify the toxin target); and (iii) those that have an intracellular target and are directly delivered by the bacteria into eukaryotic cells. Depending on their target, these toxins can be divided into different groups that act on protein synthesis, signal transduction, actin polymerization, and vesicle trafficking within eukaryotic cells. The toxins that inhibit protein synthesis, causing rapid cell death, at extremely low concentrations are diphtheria toxin (DT), Pseudomonas exotoxin A (ExoA), and Shiga toxin.