New Hypothesis for How Anthrax Toxins Escape Intracellular Endosome

A new hypothesis concerning a crucial step in the anthrax infection process has been advanced by scientists at the National Institute of Standards and Technology (NIST) and the U.S. Army Medical Research Institute for Infectious Diseases (USAMRIID) at Fort Detrick, Maryland. The research teams have explored the behavior of the toxins that rapidly overwhelm the body as the often-fatal disease progresses. Their findings suggest a new possible mechanism by which anthrax bacteria deliver the protein molecules that poison victims. Anthrax is easily weaponized; the findings could help lead to a more effective cure. The results were published online on August 8, 2013 in the Journal of Chemical Physics. Anthrax bacteria kill by releasing three toxins that work in concert to destroy cells. One toxin, called PA, attaches to the cell membrane, where its surface serves as a sort of landing pad for the other two toxins, called LF and EF. Once several molecules of LF and EF have latched onto PA, the cell membrane tries to destroy these unwanted hangers-on by wrapping them up in an "endosome," a small bubble of membrane that gets pinched off and moved into the cell's interior. There, the cell attempts to destroy its contents by a process that includes making the interior of the endosome more acidic. But before the cell can fully carry out its plan, the LF and EF escape from the endosome and wreak havoc in the cell's interior. The question is: how do these toxins escape? "A recent hypothesis is that LF and EF completely unfold and then squeeze through the narrow hole that PA forms in the endosomal membrane," says NIST physical scientist Dr. John Kasianowicz.