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Structure of the third deadly anthrax protein
Edward R. Winstead


Scientists have determined the structure of a key protein involved in causing anthrax. It is one of three proteins that together comprise the toxin secreted by the bacterium Bacillus anthracis.

The first protein allows anthrax bacteria to enter cells, while the second inhibits an immune response by host cells. The structures of these toxins were published last year.

Bacillus anthracis. View larger

The third protein, oedema factor, or EF, binds to an important signaling molecule in host cells and triggers a series of events that leads to a buildup of fluid in the body. The new study reports the structure of EF in two different states—alone and bound to the signaling molecular in host cells, calmodulin.

The researchers also identified a structural 'pocket' in the protein that may be a potential drug target. Andrew Bohm, of the Boston Medical Research Institute, Massachusetts, and Wei-Jen Tang, of the University of Chicago, Illinois, led the study.

"The structure shows how EF hijacks one of the key intracellular proteins involved in calcium-triggered signalling pathways, at once disabling the protein and using it to stimulate its own catalytic activity," writes Robert C. Liddington, of The Burnham Institute in La Jolla, California, in a commentary accompanying the paper in Nature. "This activity inhibits the immune response against the bacterium, allowing infection to proceed."

Liddington led the team that reported the structure of the anthrax toxin, called lethal factor, in October 2001.

See related GNN article
»Structures and targets of the anthrax bacterium

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Drum, C.L. et al. Structural basis for the activation of anthrax adenylyl cyclase exotoxin by calmodulin. Nature 415, 396-402 (January 24, 2002).
Liddington, R.C. Anthrax: A molecular full nelson. Nature 415, 373-374 (January 24, 2002).

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