Medical Definition of Toxin, anthrax

  • Medical Author:
    William C. Shiel Jr., MD, FACP, FACR

    Dr. Shiel received a Bachelor of Science degree with honors from the University of Notre Dame. There he was involved in research in radiation biology and received the Huisking Scholarship. After graduating from St. Louis University School of Medicine, he completed his Internal Medicine residency and Rheumatology fellowship at the University of California, Irvine. He is board-certified in Internal Medicine and Rheumatology.

Reviewed on 12/11/2018

Toxin, anthrax: The toxic substance secreted by the bacterium Bacillus anthracis, the causative agent of the disease anthrax.

Anthrax toxin is made up of three proteins. One is protective antigen and two are enzymes that are called edema factor and lethal factor. The protective antigen binds to surface receptors on the host's cell membranes. After being cleaved by a protease, protective antigen binds to the two toxic enzymes -- edema factor and lethal factor -- and mediates their transportation into the cytosol (the soluble portion of the cytoplasm) where they exert their pathogenic (disease-causing) effects. Lethal factor is the crucial pathogenic enzyme. It is the killer in the toxin.

Anthrax toxin is not yet fully fathomed. The receptor for protective antigen, named anthrax toxin receptor, has been discovered to be a type I membrane protein with an extracellular Von Willebrand factor A domain that binds directly to protective antigen. And lethal factor has been found to cleave members of what is called the MAPKK (mitogen-activated protein kinase kinase) family and to disrupt cellular signalling.

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Reviewed on 12/11/2018