Binding and cell intoxication studies of anthrax lethal toxin |
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Authors: | Email author" target="_blank">Momchilo?VuyisichEmail author Claire?K?Sanders Steven?W?Graves |
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Institution: | Los Alamos National Lab, MS M888, P.O. Box 1663, Los Alamos, NM 87545, USA. vuyisich@lanl.gov |
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Abstract: | Anthrax lethal toxin (LT) is a major virulence factor of Bacillus anthracis. The vast majority of the anthrax toxin-related literature describes the assembly of LT as a cell-dependent process. However,
some reports have provided evidence for the existence of a fully assembled LT, either in vitro or in the bloodstream of anthrax-infected
animals. To follow up on this work, we present studies on fully-assembled LT. We first demonstrate facile and cell-free assembly
and purification of LT. We then show that fully assembled LT binds an anthrax toxin receptor with almost 100-fold higher affinity
than the protective antigen (PA) alone. Quantitative cell intoxication assays were used to determine the LD50 (lethal dose 50) for LT. The cell-binding studies revealed that LT binds mammalian cells using a different mode from PA.
Even when PA-specific receptors were blocked, fully assembled LT was able to bind the cell surface. Our studies support the
existing evidence that LT fully assembles in the blood stream and can bind and intoxicate mammalian cells with very high affinity
and efficacy. More importantly, the data presented here invoke the possibility that LT may bind cells in a receptor-independent
fashion, or recognize receptors that do not interact with PA. Hence, blood borne LT may emerge as a novel therapeutic target
for combating anthrax. |
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