Structural models amyloid filaments

Fig. 4. New structural models for amyloid and prion filaments with the parallel and in-register arrangement of //-strands in the //-sheets. //-Strands are denoted by arrows. The filaments are formed by hydrogen-bonded stacks of repetitive units. Axial projections of single repetitive units corresponding to each model are shown on the top. Lateral views of the overall structures are on the bottom. (A) The core of a //-helical model of the //-amyloid protofilament (Petkova et al., 2002). Two such protofilaments coil around one another to form a //-amyloid fibril. (B) The core of a //-helical model of the HET-s prion fibril (Ritter et al., 2005). The repetitive unit consists of two //-helical coils. (C) The core of a superpleated //-structura l model suggested for yeast prion Ure2p protofilaments and other amyloids (Kajava et al., 2004).

Kajava, A. V., Baxa, U., Wickner, R. B., and Steven, A. C. (2004). A model for Ure2p prion filaments and other amyloids The parallel superpleated beta-structure. Proc. Natl. Acad. Sci. USA 101, 7885-7890. 

In this model (Fay et al., 2005), portions of the N- and C-terminal regions, specifically residues 6 and 137, are in close proximity in the fibril, and the C-terminal domain retains a native-like structure. There is evidence that this non-amyloid-like fibril can convert to the cross-/ -containing filament with heat treatment, incubation at low pH (Bousset et al., 2003), or extensive drying (Fay et al., 2005), but it is unclear what sort of structural change might link the two fibril types. 

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