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Purified Bacillus Anthracis Lethal Toxin Complex Formed In Vitro and During Infection Exhibits Functional and Biological Activity



Rekha Panchal, Kelly Halverson, Wilson Ribot, Douglas Lane, Tara Kenny, Teresa G. Abshire, John W. Ezzell, Timothy A. Hoover, Bradford Powell, Stephen Little, John J. Kasianowicz, Sina Bavari


Anthrax protective antigen (PA, 83 kDa), a pore-forming protein upon protease activation to 63 kDa (PA63), translocates lethal factor (LF) and edema factor (EF) from endosomes into the cytosol of the cell. The relatively small size of the heptameric PA63 pore (12 ') raises questions as to how large molecules like LF and EF can move through the pore. In addition, the reported high binding affinity between PA and EF/LF suggests that EF/LF may not dissociate but remain complexed with activated PA63. In this study, we found that purified (PA63)7:LF complex exhibited biological and functional activities similar to the free LF. Purified LF complexed with PA63 heptamer was able to cleave both a synthetic peptide substrate and endogenous mitogen-activated protein kinase kinase substrates and kill susceptible macrophage cells. Electrophysiological studies of the complex showed strong rectification of the ionic current at positive voltages, an effect similar to that observed if LF is added to the channels formed by heptameric PA63 pore. Complexes of (PA63)7:LF found in the plasma of infected animals showed functional activity. Identifying active complex in the blood of infected animals has important implications for therapeutic design, especially those directed against PA and LF. Our studies suggest that the individual toxin components and the complex must be considered as critical targets for anthrax therapeutics.
Journal of Biological Chemistry


anthrax, protective antigen, PA63 ion channel, lethal factor, therapeutics, bacterial toxins


Panchal, R. , Halverson, K. , Ribot, W. , Lane, D. , Kenny, T. , Abshire, T. , Ezzell, J. , Hoover, T. , Powell, B. , Little, S. , Kasianowicz, J. and Bavari, S. (2005), Purified Bacillus Anthracis Lethal Toxin Complex Formed In Vitro and During Infection Exhibits Functional and Biological Activity, Journal of Biological Chemistry, [online], (Accessed July 23, 2024)


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Created March 17, 2005, Updated October 12, 2021