COOH-terminal sequence of the cellular prion protein directs subcellular trafficking and controls conversion into the scrapie isoform

Efficient formation of scrapie isoform of prion protein (PrPSc) requires targeting PrPSc by glycophosphatidyl inositol (GPI) anchors to caveolae-like domains (CLDs). Redirecting the cellular isoform of prion protein (PrPC) to clathrin-coated pits by creating chimeric PrP molecules with four different COOH-terminal transmembrane domains prevented the formation of PrPSc, To determine if these COOH-terminal transmembrane segments prevented PrPC from refolding into PrPSc by altering the structure of the polypeptide, we fused the 28-aa COOH termini from the Qa protein. Two COOH-terminal Qa segments differing by a single residue direct the transmembrane protein to clathrin-coated pits or the GPI form to CLDs; PrPSc was formed from GPI-anchored PrPC but not from transmembrane PrPC. Our findings argue that PrPSc formation is restricted to a specific subcellular compartment and as such, it is likely to involve auxiliary macromolecules found within CLDs.