Subcellular distribution and physicochemical properties of scrapie‐associated precursor protein and relationship with scrapie agent

We studied the biologic properties of hamster-adapted scrapie (strain 263K) and its relationship to the precursor protein of scrapie (PrP33–35 Sc ). The highest titer of infectious material and the greatest concentration of PrP33-35 sc were in the fractions containing microsomal and synaptosomal membranes. We found traces of infectivity in the absence of PrP33–35 Sc associated with matrix protein. Partitioning of membranes with neutral chloroform-methanol resulted in concentration of PrP33–35 Sc and infectivity within the interphase layer. Recombination of membrane glycoproteins (interphase) with lipids extracted from homologous brains decreased infectivity 24 logs. Temperature-dependent phase separation of infected synaptosomal and microsomal membranes with Triton X-114 yielded a phospholipid-rich phase containing a high concentration of PrP33–35 S and greatest infectivity titers. This material spontaneously formed liposomes, indicating that PrP33–35 Sc and PrP33–35 C precursor proteins are highly hydrophobic intrinsic membrane components integrated with phospholipids. Homologous membrane phospholipids appear to prevent aggregation of the scrapie isoform of PrP and maintain high levels of infectivity.