A 60-KDA PRION PROTEIN (PRP) WITH PROPERTIES OF BOTH THE NORMAL AND SCRAPIE-ASSOCIATED FORMS OF PRP

Scrapie is a transmissible spongiform encephalopathy of sheep and othe r mammals in which disease appears to be caused by the accumulation of an abnormal form of a host protein, prion protein (PrP), in the brain and other tissues. The process by which the normal protease-sensitive form of PrP is converted into the abnormal protease-resistant form is unknown. Several hypotheses predict that oligomeric forms of either t he normal or abnormal PrP may act as intermediates in the conversion p rocess. We have now identified a 60-kDa PrP derived from hamster PrP e xpressed in murine neuroblastoma cells, Peptide mapping studies provid ed evidence that the 60-kDa PrP was composed solely of PrP and, based on its molecular mass, appeared to be a PrP dimer. The 60-kDa PrP was not dissociated under sev eral harsh denaturing conditions, which indi cated that it was covalently linked. It was similar to the disease-ass ociated form of PrP in that it formed large aggre gates. However, it r esembled the normal form of PrP in that it was sensitive to proteinase K and had a short metabolic half-life. The 60-kDa PrP, therefore, had characteristics of both the normal and disease-associated forms of Pr P. Formation and aggregation of the 60-kDa hamster PrP occurs in uninf ected mouse neuroblastoma cells, which suggests that hamster PrP has a predispo sition to aggregate even in the absence of scrapie infec tiv ity. Similar 60-kDa PrP bands were identified in scrapie-infected hams ter brain but not in uninfected brain. Therefore, a 60-kDa molecule mi ght participate in the scrapie-associated conversion of protease-sensi tive PrP to protease-resistant PrP.