What Makes a Prion Infectious?

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Science  26 Feb 2010:
Vol. 327, Issue 5969, pp. 1091-1092
DOI: 10.1126/science.1187790

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Prions are unconventional infectious agents that cause fatal neurological illnesses such as Creutzfeldt-Jakob disease, bovine spongiform encephalopathy, and scrapie. Many hypotheses have been advanced to explain the chemical composition of infectious prions and the mechanism of their formation in the neurons of infected hosts, but none has yet been proven. Perhaps the most provocative proposal has been the “protein-only” hypothesis, which posits that the infectious agent is composed exclusively of a misfolded, host-encoded protein called the prion protein (PrP). However, three decades of investigation have yielded no direct experimental proof for this stringent hypothesis. Moreover, various biochemical studies have suggested that nonproteinaceous cofactors may be required to produce infectious prions, possibly by forming physical complexes with PrP (11–4). On page 1132 of this issue, Wang et al. demonstrate the importance of cofactors for producing recombinant infectious prions in vitro (5). Another study by Li et al. suggests that endogenous cofactors may also influence the strain properties of prions in cells (6).