Anthrax toxin is a three-
protein exotoxin secreted by virulent strains of the
bacterium,
Bacillus anthracis—the causative agent of
anthrax. The toxin was first discovered by Harry Smith in 1954. Anthrax toxin is composed of a cell-binding protein, known as protective
antigen (PA), and two enzyme components, called edema factor (EF) and
lethal factor (LF). These three protein components act together to impart their physiological effects. Assembled complexes containing the toxin components are
endocytosed. In the
endosome, the enzymatic components of the toxin
translocate into the
cytoplasm of a target cell. Once in the cytosol, the enzymatic components of the toxin disrupts various immune cell functions, namely cellular signaling and cell migration. The toxin may even induce cell lysis, as is observed for
macrophage cells. Anthrax toxin allows the bacteria to evade the
immune system, proliferate, and ultimately kill the host animal. Research on anthrax toxin also provides insight into the generation of
macromolecular assemblies, and on
protein translocation, pore formation,
endocytosis, and other
biochemical processes.