A prion (IPA: /ˈpriːɒn/[1]listen (help·info)) — combination of the first two syllables of the words proteinaceous and infectious (-on by analogy to virion)[2] — is a poorly-understood hypothetical infectious agent that, according to the "protein only" hypothesis, is composed entirely of proteins.[3] Prions are thought to cause a number of diseases in a variety of mammals, including bovine spongiform encephalopathy (BSE, also known as "mad cow disease") in cattle and Creutzfeldt-Jakob disease (CJD) in humans. All thus-far hypothesized prion diseases affect the structure of the brain or other neural tissue, and all are currently untreatable and thought to be fatal.[4] In general usage, prion can refer to both the theoretical unit of infection or the specific protein (e.g. PrP) that is thought to be the infective agent, whether or not it is in an infective state.
Prions are hypothesized to infect and propagate by refolding abnormally into a structure which is able to convert normal molecules of the protein into the abnormally structured form. All known prions induce the formation of an amyloid fold, in which the protein polymerises into an aggregate consisting of tightly packed beta sheets. This altered structure is extremely stable and accumulates in infected tissue, causing cell death and tissue damage.[5] This stability means that prions are resistant to denaturation by chemical and physical agents, making disposal and containment of these particles difficult.
Proteins showing prion-type behavior are also found in some fungi and this has been quite important in helping to understand mammalian prions. However, 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.[6]
Last update: 2008-05-06 13:31:57 Prion | Copyright 2008 HubHip.com