Prions [prahy-on] are infectious, misfolded proteins (large molecules built from small units known as amino acids). They are known to cause many forms of encephalitis, or brain disease, such as scrapie, Creutzfeldt-Jakob Disease, kuru, and Bovine Spongiform Encephalopathy, also known as Mad Cow Disease.

Prions work by changing the shape of proteins in the living things it causes disease in. While normal proteins have lots of alpha helices, or twisted parts, changed proteins have lots of beta sheets, or flat parts. The word ‘prion,’ coined in 1982 by American neurologist, Stanley B. Prusiner, is a portmanteau derived from the words ‘protein’ and ‘infection.’

This is in contrast to all other known infectious agents, which must contain nucleic acids (either DNA, RNA, or both) along with protein components. Prions propagate by transmitting a misfolded protein state. When a prion enters a healthy organism, the prion form of a protein induces existing, properly-folded protein to convert into the disease-associated, prion form; the prion acts as a template to guide the misfolding of more protein into prion form. These newly-formed prions can then go on to convert more proteins themselves, this triggers a chain reaction that produces large amounts of the prion form.

This altered structure is extremely stable and accumulates in infected tissue, causing tissue damage and cell death. This structural stability means that prions are resistant to denaturation (alteration of their form) by chemical and physical agents, making disposal and containment of these particles difficult.

Proteins showing prion-type behavior are also found in some fungi, which has been useful in helping to understand mammalian prions. Interestingly, fungal prions do not appear to cause disease in their hosts and may even confer an evolutionary advantage through a form of protein-based inheritance.


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