Filaments of the Ure2p prion protein have a cross-beta core structure |
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Authors: | Baxa Ulrich Cheng Naiqian Winkler Dennis C Chiu Thang K Davies David R Sharma Deepak Inouye Hideyo Kirschner Daniel A Wickner Reed B Steven Alasdair C |
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Affiliation: | Laboratory of Structural Biology, National Institute of Arthritis, Musculoskeletal, and Skin Diseases, National Institutes of Health, Bethesda, MD 20892, USA. |
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Abstract: | Formation of filaments by the Ure2 protein constitutes the molecular mechanism of the [URE3] prion in yeast. According to the "amyloid backbone" model, the N-terminal asparagine-rich domains of Ure2p polymerize to form an amyloid core fibril that is surrounded by C-terminal domains in their native conformation. Protease resistance and Congo Red binding as well as beta-sheet content detected by spectroscopy-all markers for amyloid-have supported this model, as has the close resemblance between 40 A N-domain fibrils and the fibrillar core of intact Ure2p filaments visualized by cryo-electron microscopy and scanning transmission electron microscopy. Here, we present electron diffraction and X-ray diffraction data from filaments of Ure2p, of N-domains alone, of fragments thereof, and of an N-domain-containing fusion protein that demonstrate in each case the 4.7A reflection that is typical for cross-beta structure and highly indicative of amyloid. This reflection was observed for specimens prepared by air-drying with and without sucrose embedding. To confirm that the corresponding structure is not an artifact of air-drying, the reflection was also demonstrated for specimens preserved in vitreous ice. Local area electron diffraction and X-ray diffraction from partially aligned specimens showed that the 4.7A reflection is meridional and therefore the underlying structure is cross-beta. |
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