(La Jolla, CA). A team of researchers led by The Burnham Institute's Robert C. Liddington has determined the crystal structure of the binding complex between anthrax toxin and one of its host receptors. Inhalation anthrax, unless diagnosed at a very early stage, is fatal: there is no existing antidote once the toxin is blood borne. The studies published by Liddington and colleagues on-line in the July 4th issue of Nature offer new leads for the discovery of anthrax antitoxins that could be used in conjunction with antibiotics to treat late-stage anthrax. In a surprising twist, the new information will also help in the design of anthrax toxin as an anti-tumor agent for treatment of cancer.
Anthrax toxin is comprised of three proteins: protective antigen (PA), lethal factor (LF), and edema factor (EF). To gain entry into host cells, PA must recognize a receptor on the surface of the target cell. Once PA has bound to the cell, it then enables EF and LF to bind and form a pore through which PA forces EF and LF into the cell in a syringe-like action.
Liddington's laboratory, together with Stephen Leppla at the National Institute of Allergy and Infectious Diseases, studied the interaction of PA with the two known receptors for anthrax: TEM8 and CMG2. PA binds tightly to both receptors and can use either to transfer toxicity into the cell. They were able to determine the crystal structure of the PA-CMG2 binding complex at atomic resolution, which makes it possible to design small molecules that will interact with PA and prevent the binding complex from forming. Soluble forms of the receptors have indeed acted as decoys, distracting PA from binding both receptors.
The two receptors are similar in how they mediate entry into the cells, but differ in important ways: The CMG2 receptor is present in most tissues, whereas the TEM8 receptor is mostly found on the
Contact: Nancy Beddingfield