January 5, 2015

By: admin

By: Suzanne Canada, Ph.D.
Tanager Medical Writing

 

Three anthrax toxin components—Protective antigen (PA), edema factor (EF) and lethal factor (LF) are available for research purposes from LIST Biological Laboratories, separately at a high level of purification. At least two out of three of these components are necessary to enter a mammalian cell and exert a toxic effect.

With the aim of developing antitoxin therapies, scientists have been investigating the structure of PA, EF, and LF, and the complexes that they form with mammalian cell surface receptors, in hopes of finding the best way to disrupt or block the toxicity. Previously, NIAID-supported scientists have shown that protective antigen can bind edema factor and lethal factor at the same time, forming a greater variety of toxin complexes than were formerly known.¹ They also had produced a three-dimensional molecular structure of the anthrax protective antigen protein bound to one of the receptors (CMG2) it uses to enter cells.² More recently, a group of students in Kansas used Jmol and 3D printing technology to model and Anthrax toxin heterotrimer (PA, EF and LF) which forms a pore in the mammalian cell surface.

In an in vitro disease model, researchers constructed an artificial membrane bilayer using lipid and demonstrated that the blood of animals carrying anthrax infections was able to disrupt this membrane, a model of the cell membrane.  Membrane disruption requires acidification, and therefore the membrane remains intact until the pH is lowered.  When the pH is lowered to the required level for toxin complex binding, the membrane is disrupted by the anthrax toxin already embedded in it.⁴

Anthrax researchers have explored ways to protect healthcare workers and others who may have been exposed or are likely to be infected. One group of scientists has investigated the feasibility of RNA silencing technology (siRNA) to block expression of the anthrax toxin PA receptors on the cell surface, two identified anthrax toxin receptors: tumor endothelial marker 8 (TEM8) and capillary morphogenesis protein 2 (CMG2).  Blocking expression of the receptors was reported to provide almost complete protection against the LF intoxication in mice, and also protected against LF effects in human kidney cells as well as macrophage-like cells.⁵ 

Methods of vaccination have been under investigation for some time, as one of the most likely methods to provide lasting protection against anthrax infection.  In another 2014 publication, researchers at the University of Texas have reported success in vaccinating guinea pigs against anthrax infection using vaccines based on DNA-protein antigen components as well as another based on recombinant protein components.  After immunization, the animals were challenged with a lethal dose of B. cereus G9241 aerosol.  Complete protection against lethal challenge was observed in all guinea pigs that had a detectable pre-challenge serum titer of toxin neutralizing antibodies.⁶

List Biological Laboratories, Inc. offers EF (Product number 167A), LF (176), and PA (171) as well as the antibodies for their detection (773, 769 and 772, and 771, respectively). Refer to the website: https://listlabs.com/product-information/anthrax-toxins/ for more information.

 

References

1. NIAID website: http://www.niaid.nih.gov/topics/anthrax/pages/default.aspx
2. CDC website: http://www.cdc.gov/anthrax/
3. Andrews J, Chick A, Chao T, Chogada V, Douglas A, Florack A, McCormick S, Kessler E, Tuel K, Whalen J and Fisher M (2014) The Anthrax Toxin Heterotrimer: Explorations of the Protective Antigen and Edema and Lethal Factors (LB98). FASEB J 28:LB98 
4. Nablo BJ, Panchal RG, Bavari S, Nguyen TL, Gussio R, Ribot W, Friedlander A, Chabot D, Reiner JE, Robertson JW, Balijepalli A, Halverson KM, Kasianowicz JJ (2013) Anthrax toxin-induced rupture of artificial lipid bilayer membranes J Chem Phys 139(6):065101. PMID: 23947891
5. Arévalo MT, Navarro A, Arico CD, Li J, Alkhatib O, Chen S, Diaz-Arévalo D, Zeng M  (2014) Targeted silencing of anthrax toxin receptors protects against anthrax toxins.  J Biol Chem 289(22):15730-8. PMID: 24742682
6. Palmer J, Bell M, Darko C, Barnewall R, Keane-Myers A. (2014) Protein- and DNA-based anthrax toxin vaccines confer protection in guinea pigs against inhalational challenge with Bacillus cereus G9241. Pathog Dis 72(2):138-42. PMID: 25044336