Properties of scrapie prion proteins in liposomes and amyloid rods

The scrapie prion protein (PrP 27-30) has been demonstrated to be required for infectivity. Aggregates of PrP 27-30 form insoluble amyloid rods which resist dissociation by non-denaturing detergents. Mixtures of the detergent cholate and phospholipids were found to solubilize PrP 27-30 with full retention of scrapie prion infectivity. No evidence for a prion-associated nucleic acid could be found when the phospholipid vesicles with PrP 27-30 were digested with nucleases and Zn2+. Under digestion conditions which allowed hydrolysis of exogenous nucleic acids, no diminution of prion infectivity was observed. Tobacco mosaic virions added to the liposomes at a concentration 100 times lower than the scrapie prion titre could be seen by electron microscopy. These studies indicate that there is no subpopulation of filamentous scrapie viruses hidden amongst the prion rods - indeed, they would have been observed among the liposomes. The partitioning of PrP 27-30 and scrapie infectivity into phospholipid vesicles argues for a central role of PrP 27-30 in scrapie pathogenesis and establishes that the prion amyloid rods are not essential for infectivity.