Ultrastructural Studies of Prions

Abstract

The scrapie prion protein denoted PrP 27–30 was discovered by enriching fractions for scrapie infectivity (Prusiner et al. 1982, 1983). This protein migrates during sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) as a broad band with an apparent molecular weight of 27–30 kDa (Bolton et al. 1982; Prusiner et al. 1982). It is derived from PrP^Sc, a 33- to 35-kDa protein, by limited proteolysis (Oesch et al. 1985). A portion of PrP forms long filamentous structures in scrapie-infected brains (DeArmond et al. 1985), and the purified prions apparently aggregate into rod-shaped structures in brain extracts (Meyer et al. 1986; McKinley et al. 1986). These prion aggregates are ultrastructurally and tinctorially indistinguishable from amyloid (Prusiner et al. 1983). Extensive purification of PrP 27–30 was required before convincing evidence linking the rods and prion infectivity could be obtained. Raising antibodies against PrP 27–30 resulted in the demonstration that filaments in tissues and rods in extracts are composed of PrP (DeArmond et al. 1985; Barry et al. 1985). By negative staining, the individual rods measure 10–20 nm in diameter and 100–200 nm in length. In highly purified preparations, rods usually are found in large clusters, but individual rods can be dispersed by brief sonication (Fig. 1).

This work was supported by research grants from the National Institutes of Health (AG02132 and NS14069), the Senator Jacob Javits Center of Excellence in Neuroscience (NS22786), and State of California, Department of Health Services (contract no. 88–94658), as well as gifts from the Sherman Fairchild Foundation and the Fairleigh S. Dickinson, Jr. Foundation, Inc.