ABSTRACT
The word "prion" was created in 1982 to name the etiological agent of the transmissible spongiform encephalopathies (TSE), a group of degenerative diseases affecting central nervous system of man and animals, including bovine spongiform encephalopathy (BSE) and variant Creutzfeldt-Jakob disease (vCJD). Prions present two isoforms: PrPC, cellular or normal, which exists in all vertebrates and is sensitive to detergents and proteases, and PrPSc, disease associated, partially resistant. The molecular weight of both PrPC and PrPSc is 30-35 kD; after treatment with detergents and proteases PrPSc originates PrP27-30 (27-30 kD). PrPC is also denominated PrPsens, and PrPSc is PrPres. PrPSc and PrP27-30 cause disease. PrPC presents polymorphisms specifically associated with some TSE. The "prion hypothesis" says that PrPSc transmits its characteristic resistance to PrPC through conformational changes, and accumulation of the protein, without involvement of nucleic acids, causes disease. Most of the hypothesis has been demonstrated with transgenic mice, computer models and recombinant proteins, but the existence of strains of the TSE agents has not been explained. The description of similar mechanisms of propagation of protein conformational properties in Saccharomyces cereviseae has extended the meaning of the prion definition. Although the transmission of conformational changes between PrPC and PrPSc was experimentally shown, the pathogenesis of the TSE remains unknown. The relationship between BSE and vCJD is mentioned.