Progress in FY2010 was in the following areas: 1. DETERMINATION OF BETA-SHEET STRUCTURES IN YEAST PRIONS. We showed that three yeast prion proteins adopt in-register parallel beta-sheet structures in their prion-active, amyloid fibril states. These include the Ure2p protein that produces the URE3 phenotype, the Sup35 protein that produces the PSI+ phenotype, and the Rnq1 protein that produces the PIN+ phenotype. We showed that the in-register parallel beta-sheet structure is maintained in mutants of Ure2p and Sup35 that have scrambled amino acid sequences in their prion domains, and that this structure is not dependent on hydration. These results should quell suggestions in the literature that yeast prions have beta-helix-like structures, rather than in-register parallel beta-sheet structures. 2. INVESTIGATIONS OF FUNCTIONAL AMYLOIDS. We carried out initial studies of two proteins that are believed to have biological functions in their amyloid state, namely CsgA (which forms so-called curli fibrils on the surface of bacteria, which have an adhesive function) and Pmel17 (which catalyzes melanin production in mammalian melanocytes). Neither CsgA nor Pmel17 fibrils appear to have the in-register parallel beta-sheet structures found in yeast prion fibrils and in beta-amyloid fibrils. Instead, they may have beta-helical structures. An extensive study of Pmel17 fibrils shows that these fibrils are highly polymorphic, and that different polymorphs differ in the identity of pseudo-repeat sequences that comprise the fibril core. 3. INSULIN FIBRIL STRUCTURES. Solid state NMR measurements on fibrils formed by human insulin indicate conversion of native alpha-helices to beta-strands (collaboration with M. Weiss). The solid state NMR data place constraints on possible molecular structures, showing that models for insulin fibrils in the literature (developed in absence of detailed experimental data) are not correct. Insulin fibril formation is a serious public health problem, particularly in areas that lack refrigeration, as stored insulin tends to convert to fibrils at elevated temperatures. 4. MAMMALIAN PRION PROTEIN FIBRILS. Solid state NMR measurements on fibrils formed by recombinant mammalian PrP (full-length, Syrian hamster sequence) show that these fibrils contain parallel beta-sheets, and that the fibril core is formed primarily by a 30-residue segment near the C-terminus (collaboration with I.V. Baskakov). Although these fibrils are not infectious as prions, they may resemble infectious PrP aggregates in many respects.
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