Progress and problems in the biology, diagnostics, and therapeutics of prion diseases
J. Clin. Invest. Adriano Aguzzi, et al. 114:153 doi:10.1172/JCI22438 [Go to this article.]

Figure 1
Models of PrP^C to PrP^Sc conversion. (A) The heterodimer model proposes that upon infection of an appropriate host cell, the incoming PrP^Sc (orange) starts a catalytic cascade using PrP^C (blue) or a partially unfolded intermediate arising from stochastic fluctuations in PrP^C conformations as a substrate, converting it by a conformational change into a new β-sheet–rich protein. The newly formed PrP^Sc (green-orange) will in turn convert new PrP^C molecules. (B) The noncatalytic nucleated polymerization model proposes that the conformational change of PrP^C into PrP^Sc is thermodynamically controlled: the conversion of PrP^C to PrP^Sc is a reversible process but at equilibrium strongly favors the conformation of PrP^C. Converted PrP^Sc is established only when it adds onto a fibril-like seed or aggregate of PrP^Sc. Once a seed is present, further monomer addition is accelerated.