Drug Target For The Most Potent Botulinum Neurotoxin Determined

[Guest guest]

Drug Target For The Most Potent Botulinum Neurotoxin Determined

http://medicalnewscenter.com/out/out.cgi?

http://www.sciencedaily.com/releases/2008/04/080429102646.htm

(especially note 5th paragraph about nerves)

Botulinum neurotoxin -- responsible for the deadly food poisoning

disease botulism and for the beneficial effects of smoothing out

facial wrinkles - can also be used as a dreaded biological weapon.

When ingested or inhaled, less than a billionth of an ounce can cause

muscle paralysis and eventual death. Although experimental vaccines

administered prior to exposure can inhibit the destructive action of

this neurotoxin - the most deadly protein known to humans -- no

effective pharmacological treatment exists.

Now, scientists at the U.S. Department of Energy's Brookhaven

National Laboratory and the U.S. Army Medical Research Institute of

Infectious Diseases (USAMRIID) have taken the first step toward

designing an effective antidote to the most potent form of the toxin.

They have found that they can trick the toxin to bypass its normal

binding protein, thereby blocking its deadly action.

" We have found a highly efficient inhibitor of botulinum neurotoxin

type A - the most potent of seven neurotoxins produced by the

bacterium Clostridium botulinum. This finding can lead to a very

effective drug to stop the devastating effects of the toxin, " said

Brookhaven Lab biologist Subramanyam Swaminathan, the study's co-

principal investigator. " We intend to do further research to tailor

the inhibitor for the best results. "

" We are excited about the success of this work and the prospects it

holds for future drug development, " said USAMRIID principal

investigator S. Ashraf Ahmed, who initiated the structure-based

inhibitor design as part of the Institute's bio-defense research

program.

To cause its deadly effects, the botulinum neurotoxin first binds to

a nerve cell membrane, which curves inward, incorporating the toxin

into a vesicle that drifts inside the cell. The toxin eventually

travels from the vesicle to the cytosol, the internal fluid of the

cell. The toxin then cleaves specific proteins in the cytosol,

thereby blocking the release of neurotransmitters - chemicals nerve

cells use to communicate with one another and with muscles. Blockage

of this communication paralyzes muscles - including those that enable

breathing.

To block the toxin's action, the researchers designed four " decoy "

protein fragments that mimic the structure of the protein to which

the toxin ordinarily binds. The toxin then attaches itself to the

decoy fragments instead of to the cell's protein. This re-routing of

the toxin allows neurotransmitters to keep functioning, thus stopping

the toxin's pathological effects.

The scientists used x-ray techniques at Brookhaven's National

Synchrotron Light Source (NSLS) to see how the toxin binds to the

protein inhibitors. They found that all four decoy proteins are

efficient at inhibiting the toxin's binding to the cell's protein,

but one of them in particular is by far the best of any known

inhibitors. The scientists' next step in this process is to transform

the most effective of the four protein fragments into a drug-like

molecule before clinical testing is done.

" This study represents an impressive collaboration in identifying

potential inhibitors of the toxin for therapeutic use, " said Colonel

W. Korch, Jr., USAMRIID's commander. " It builds upon the

successes we have realized in developing effective next-generation

vaccines to protect our citizens against the toxin's deadly effects

prior to exposure. "

The scientists did not work with intact Clostridium botulinum

bacteria. Instead, they produced a functional fragment of the

neurotoxin protein, which is not toxic. The research is performed in

strict compliance with Brookhaven's Institutional Biosafety Committee

regulations according to standards set by the U.S. Centers for

Disease Control and Prevention. Only authorized scientists have

access to the laboratory.

The results of their research are reported in the April 22, 2008

online issue of the Journal of Biological Chemistry. This research

was funded by the Defense Threat Reduction Agency of the U.S.

Department of Defense. The NSLS is supported by the U.S. Department

of Energy's Office of Basic Energy Sciences, Office of Science.