A new laboratory method for quickly detectingactive anthrax proteins within an infected blood sample at extremelylow levels has been developed by researchers at the National Instituteof Standards and Technology (NIST), the U.S. Army Medical ResearchInstitute of Infectious Diseases and the National Cancer Institute.
Current detection methods rely on injecting live animals orcell cultures with samples for analysis and require up to several daysbefore results are available. Described* in an upcoming issue of theJournal of Biological Chemistry, the new method produces unambiguousresults in about an hour. The researchers hope the system willultimately be useful in developing fast, reliable ways to diagnoseanthrax infections or to quickly screen large numbers of drugs aspossible therapies for blocking the bacteria's toxic effects.
The method works by detecting changes in current flow whenanthrax proteins are present in a solution. An anthrax proteinironically called "protective antigen" spontaneously formsnanometer-scale pores that penetrate the surface of an organicmembrane. When a voltage is applied across the membrane, positively andnegatively charged ions flow freely in both directions through thepore. When additional anthrax proteins called lethal factor (LF) oredema factor (EF) are present, however, the proteins bind to theoutside of the pore and shut down the flow of ions in one direction.This change in current flow depends on the concentration of theproteins in the solution and can detect amounts as low as 10 picomolar(trillionths of a mole).
"We hope this system will lead to a method for rapidlyscreening agents that inhibit the binding of LF or EF to these pores,"says NIST's lead investigator John Kasianowicz.
Live anthrax antibodies seem to do exactly that. Whenantibodies were present in the test solution and then LF was added, thecurrent flow remained unchanged, indicating that the anthrax proteinswere unable to bind properly. The long-term goal would be to find drugswith few side effects that also interfere with this binding process.
* K.M. Halverson, R.G. Panchal, T. Nguyen, R. Gussio, S.F. Little,M. Misakian, S. Bavari and J.J. Kasianowicz, "Anthrax Biosensor:Protective Antigen Ion Channel Asymmetric Blockade," Journal ofBiological Chemistry, slated for a November issue, posted online Aug.8, 2005.
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