Prion diseases are a group of fatal and incurable neurodegenerative disorders of mammals. They uniquely manifest as sporadic, genetic, and infectious maladies. The agent responsible for prion diseases is the prion. A prion is defined as a proteinaceous infectious particle, which is solely constituted by an alternately folded form of the prion protein (PrP) (Prusiner 1982).
In diseased animals and humans, PrP exists in two forms, the physiological, cel- lular form of PrP, PrPC, and the pathological prion form denoted as PrPSc. The mech- anism whereby nascent PrPSc is generated is currently unknown. Structural studies of either isoform are of great importance for understanding the biology of prion diseases since they may clarify the molecular mechanisms responsible for these pathologies. In this chapter, we present an overview of the studies into PrPC as well as structures of prions.
