The infectious prion appears to be composed almost exclusively of cellular prion protein PrP, a protein required for normal cellular function. However, when PrP comes into contact with a prion particle, it changes its normal shape (“structure”) and will become part of the densely packed infectious prion particle. By imprinting this misfolded protein structure onto normal PrP, the prion particles can multiply and spread through the nervous system, thereby causing neuronal loss.
The successful transmission of both human and animal prions to laboratory animals several decades ago has unravelled one of the most intriguing phenomena in prion research. Prions can cause distinct neurological diseases that differ by the time it takes them to cause serious illness, by the type of clinical symptoms and by the pathologic changes they cause in the brain. Genetic information is normally encoded by nucleic acid such as DNA and RNA. But how can infectious protein particles that lack such genetic information store strain information? Accumulating evidence now argues that the prion particles that cause different prion diseases also differ slightly in their respective three-dimensional structures. By the way PrP folds into infectious prions composed of many PrP molecules, it appears to gain infectious properties that allow the newly formed particle to specifically interact with or replicate in certain cell types and cause distinct pathogenic changes.