A kinetic model for amyloid formation in the prion diseases: importance of seeding.

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Abstract
The transmissible spongiform encephalopathies (TSEs) are neurodegenerative diseases characterized by amyloid formation in the brain. The major amyloid protein is the prion protein (PrP). PrP and the beta-amyloid protein of Alzheimer disease share a similar sequence that, in both cases, may be responsible for the initiation of protein aggregation in vivo. We report here that a peptide based on this sequence in PrP (PrP96-111M) forms amyloid fibrils. The existence of a kinetic barrier to amyloid formation by this peptide was demonstrated, suggesting that formation of an ordered nucleus is the rate-determining step for aggregation. Seeding was demonstrated to occur with PrP96-111M amyloid fibrils but not with amyloid fibrils of a related peptide. This effect is consistent with the proposal that the aggregation of PrP, which characterizes TSE, involves a nucleation event analogous to the seeding of a crystallization.