Images depict the molecular structure of edema factor, a component of the anthrax toxin. The X-ray diffraction models show the molecule before it enters a cell (top left) and once inside (top right). The two bottom images show the opposite side of the molecule in each form. The twisted form inside cells interacts with a substance called calmodulin (not shown). Thus activated, edema factor spurs fluid overproduction, or edema, says researcher Andrew Bohm of the Boston Biomedical Research Institute in Watertown, Mass. Knowing the structure, described in the Jan. 24 Nature, may help scientists neutralize edema factor.