Infectious proteins known as prions have been identified as the cause of "mad cow" disease (BSE). The culprits are "incorrectly folded" proteins that can "infect" healthy proteins. The molecular bases for such prion diseases are not yet fully understood.
Why are some proteins infectious while others are not? A team headed by Beat Meier (ETH Zurich, Switzerland) and Raimon Sabat¨¦ (University of Bordeaux, France) has examined two different forms of a prion-forming protein domain by means of NMR spectroscopy. In the journal Angewandte Chemie, the researchers report that the infectious and non-infectious forms differ markedly in their molecular structure.
The word prion is derived from the term Proteinaceous Infectious Particle. These are proteins that can fold in different ways. Pathogenic prions are dangerous because they can convert physiological, non-pathogenic molecules into the diseased form. Often, prions largely consist of ¦Â-sheet structures. These are accordion-like folded protein ribbons that can easily aggregate into thread-like structures (amyloid fibrils).
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The research team took on the prion-forming domain of the fungal protein HET-s. At a pH value of 7-under physiological conditions-this domain forms infectious fibrils. In acidic solution, at pH 3, it also forms fibrils, but these are not infectious.