University of California researchers say a newly determined structure of the biological particles called prions may help explain how they cause infectious deadly diseases. Aberrant prions cause scrapie in sheep, bovine spongiform encephalopathy (BSE or "mad cow disease") in cows, and various afflictions in people. The scientists say their finding might also explain prion disease variety and eventually lead to breeding disease-resistant animals.
The research is detailed in the peer-reviewed journal Biochemistry, published by the American Chemical Society (ACS), the world's largest scientific society. It is being released on the ACS Web April 9 and appears in the print edition of the journal on April 27.
Prions are proteins normally found in the brain of all animals. Changes in their three-dimensional structure can cause infectious, fatal neurodegenerative disorders. Further, altered prions seem to act as templates that convert normal prions to the infectious form. Relatively few people suffer from prion diseases, but they cause large problems in sheep flocks and cattle herds. The disease rarely passes between species, but there is evidence that people can be infected by eating tainted beef.
The economic and political consequences of such scares have made understanding the novel mechanisms of prion diseases a very visible quest. Dr. Stanley B. Prusiner, from the University of California at San Francisco (UCSF), was awarded the 1997 Nobel Prize in Physiology or Medicine for discovering prions. He is a collaborator on the current Biochemistry paper.
"Our structural studies show that an important part of the prion protein exhibits multiple structures," according to co-author and UCSF pharmaceutical chemist Thomas L. James, Ph.D. He says that specific area "marks the region susceptible to the structural change from the normal cellular form to the infectious form of the protein."
James adds that "the multiple structures evident are probably related to the different types of prion diseases which an individual can potentially get." Prion variants affect different parts of the human brain, causing either Creutzfeldt-Jakob disease (CJD), Fatal Familial Insomnia (FFI), Kuru, or Gerstmann-Straussler- Scheinker (GSS) disease.
To reduce risks to laboratory workers, the scientists studied a prion protein from Syrian hamsters. They describe the normal prion structure and show the region of structural instability. James says that area coincides with a sequence of genetic instructions in which different mutations can lead to various diseases. Further, he claims that their structure provides a chemical explanation for the variety of infectious prions.
Previous epidemiological studies, in both humans and sheep, showed that individuals with positively charged amino acid residues in certain regions of their normal prions do not get prion diseases. James says their 3-D structure shows those residues to be fairly close to one another. "This suggests," he asserts, "that breeding animals with mutations to positively charged residues in that region will produce a scrapie-resistant or BSE (mad cow)-resistant herd."
A nonprofit organization with a membership of nearly 159,000 chemists and chemical engineers, the American Chemical Society publishes scientific journals and databases, convenes major research conferences, and provides educational, science policy and career programs in chemistry. Its main offices are in Washington, D.C., and Columbus, Ohio.
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