The key to any protein's function is its structure. Improperly folded proteins are normally destroyed. But in a wide range of diseases, including prion (from proteinaceous and infectious) diseases and neurodegenerative diseases like Parkinson disease and Alzheimer disease, amyloid fibrils, or plaques--misshapen proteins that aggregate into characteristic ropelike configurations--accumulate in tissue. When amyloid precursors and prions lose their normal conformation, they acquire the ability to infect their neighbors. Like molecular dominoes, the fall of one malformed protein precipitates the downfall of its neighbors, as one protein after another assumes the misshapen form of the first. Any chance of developing methods to contain the expansionist tendencies of these proteins depends on understanding the mechanism of propagation, an area of active research.

An abundance of small protein aggregates, called oligomers, is associated with amyloid fiber growth and formation. Mounting evidence suggests these amyloid intermediates are the "toxic species" underlying amyloid diseases. It is not clear, however, whether amyloids follow a progression from monomer to oligomer to plaque. Using the yeast prion protein Sup35 to study how amyloids form, Jonathan Weissman and colleagues show, surprisingly, that amyloid plaque formation can occur in the absence of the putative toxic oligomers.

In yeast, the Sup35 protein forms self-replicating aggregations reminiscent of amyloid formation and prion propagation. Though yeast aren't susceptible to prion diseases, they do assume what scientists call the yeast prion state. Two protein domains called NM together form self-propagating amyloid fibers that give rise to the yeast prion state. Oligomers, which are typically seen when other proteins form amyloids, have also been seen during this process, some of them near NM fiber ends.

To investigate the role of oligomers in NM amyloid forma
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Contact: Paul Ocampo
pocampo@plos.org
1-415-624-1224
Public Library of Science
20-Sep-2004

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