Prions

The discovery of infectious proteins, denoted prions, was unexpected. After much debate over the chemical basis of heredity, resolution of this issue began with the discovery that DNA, not protein, from pneumococcus was capable of genetically transforming bacteria (Avery et al. 1944). Four decades later, the discovery that a protein could mimic viral and bacterial pathogens with respect to the transmission of some nervous system diseases (Prusiner 1982) met with great resistance. Overwhelming evidence now shows that Creutzfeldt-Jakob disease (CJD) and related disorders are caused by prions. The prion diseases are characterized by neurodegeneration and lethality. In mammals, prions reproduce by recruiting the normal, cellular isoform of the prion protein (PrPC) and stimulating its conversion into the disease-causing isoform (PrPSc). PrPC and PrPSc have distinct conformations: PrPC is rich in alpha-helical content and has little beta-sheet structure, whereas PrPSc has less alpha-helical content and is rich in beta-sheet structure (Pan et al. 1993). The conformational conversion of PrPC to PrPSc is the fundamental event underlying prion diseases. In this article, we provide an introduction to prions and the diseases they cause.