Anthrax toxins

Though its lethal effects were ascribed to an exotoxin almost half a century ago, the pathogenesis of anthrax has yet to be satisfactorily explained. Subsequent work has led to the molecular identification and enzymatic characterization of three proteins that constitute two anthrax toxins. Protective antigen binds an as yet unknown cell receptor and mediates the entry of the other two components to the cytoplasm via the endosomal pathway. Edema factor, so named for its ability to induce edema, is a Ca²⁺/calmodulin-dependent adenylate cyclase. Lethal factor, the dominant virulence factor associated with the toxin, proteolytically inactivates mitogen-activated protein kinase kinases, key players in signal transduction. We describe the fascinating work that has led to these discoveries and discuss their relevance to our understanding of the pathogenesis of anthrax. Received 6 January 1999; received after revision 8 March 1999; accepted 9 March 1999