Figure 2.

The prion diseases (PrD). PrD are a large group of related neurodegenerative conditions, which affect both animals and humans. Included are Creutzfeldt–Jakob disease and Gerstmann-Strãussler-Scheinker in humans, bovine spongiform encephalopathy, or “mad cow disease” in cattle, chronic wasting disease in mule deer and elk, and scrapie in sheep. Prion diseases are unique in that they can be inherited, can occur sporadically, or can be infectious. The infectious agent in the PrD is composed mainly or entirely of an abnormal conformation of a host-encoded glycoprotein called the prion protein (PrPc). The replication of prions implies the transformation of the normal version of this protein PrPc into a misfolded form (PrPsc). An increased concentration of PrPc at the membrane leads to a structural transition toward abnormal intermolecular beta sheet. This dimerization could well be the initial step on the pathway of the conversion into PrPSc.