Prion protein oligomer and its neurotoxicity

The prion diseases, also known as transmissible spongiform encephalopathies, are fatal neurodegenerative disorders. According to the ＇protein only＇ hypothesis, the key molecular event in the pathogenesis of priori disease is the conformational conversion of the host-derived cellular prion protein （PrPc） into a misfolded form （scrapie PrP, prpSC）. Increasing evidence has shown that the most infectious factor is the smaller subfibrillar oligomers formed by prion proteins. Both the prion oligomer and PrPsc are rich in β-sheet structure and resistant to the proteolysis of pro- teinase K. The prion oligomer is soluble in physiologic environments whereas PrPsc is insoluble. Various prion oligomers are formed in different conditions. Prion oligomers exhibited more neurotoxicity both in vitro and in vivo than the fibrillar forms of PrPsc, implying that prion oligo- mers could be potential drug targets for attacking prion diseases. In this article, we describe recent experimental evidence regarding prion oligomers, with a special focus on prion oligomer formation and its neurotoxicity.