The distinct differences in antibody reactivity we observed between freshly immobilized and aged PrP is highly reminiscent of those differences we have described previously between PrPC and PrPSc

The distinct differences in antibody reactivity we observed between freshly immobilized and aged PrP is highly reminiscent of those differences we have described previously between PrPC and PrPSc. affinity conversation, however, remains controversial (Pauly and Harris, 1998; Brown et al., 1999; Lippard, 1999; Waggoner et al., 2000). In neuronal cells, PrPC cycles rapidly between the cell surface and endocytic compartments thought to be clathrin-coated vesicles, and has an overall half-life of 4C6 h (Shyng et al., 1993, 1994; Lehmann et al., 1999). These subcellular compartments have been suggested as the site of conversion of PrPC to PrPSc and generation of prion infectivity (Caughey and Raymond, 1991; Caughey et al., 1991; Borchelt et al., 1992; Harris et al., 1996). Early studies indicated that this physical properties of PrPC and PrPSc Fruquintinib differ markedly. Purified PrPSc has a propensity to form aggregates that have the Fruquintinib morphological characteristics of amyloids, binding to the birefringent dye Congo Red and possessing secondary structure content that is rich in -linens (Pan em et al /em ., 1993; Priola em et al /em ., 1994; Caspi em et al /em ., 1998). The aggregated protein is also partially resistant to proteolysis and is insoluble in non-ionic detergent. In contrast, PrPC contains a paucity of -arrangements, is sensitive to protease digestion and is soluble in non-ionic detergent (Prusiner em et al /em ., 1982; Oesch em et al /em ., 1985; Prusiner, 1994). Whereas relatively little is known of PrPSc conformation, the three-dimensional structures of recombinant mouse (Mo), Syrian hamster (SHa), bovine and human PrP folded into an -helical conformation have been solved by nuclear magnetic resonance (NMR) (Riek em et al /em ., 1996, 1997; Donne em et al /em ., 1997; Lopez Garcia em et al /em ., 2000; Zahn em et al /em ., 2000). In each case, the C-terminal half of the protein (residues 124C231) is usually folded into a core comprising three -helices, one or two short -strands, and a disulfide bridge linking the second and third helices. The N-terminal portion of the protein, spanning residues 23C124, appears to be highly flexible and devoid of any secondary structure under the experimental conditions employed for these studies (Riek em et al /em ., 1996, 1997; Donne em et al /em ., 1997; Zahn em et al /em ., 2000). It seems likely that these recombinant molecules, despite the absence of glycosylation, closely resemble PrPC in its native environment, since antibodies bind well to recombinant PrP and PrP on the surface of living cells (Williamson em et al /em ., 1998). The molecular events leading to the profound conformational changes in PrPC that accompany PrPSc formation are central to prion pathogenesis, but remain poorly understood. There is, however, substantial evidence to support the role of PrPSc as a template directing the fate of PrPC during prion replication (Bessen em et al /em ., 1995; Prusiner, 1997). For example, the properties distinguishing individual prion strains Ntrk2 appear to be enciphered in distinct PrPSc conformations (Telling em et al /em ., 1996; Scott em et al /em ., 1997; Safar em et al /em ., 1998; Wadsworth em et al /em ., 1999). It follows, then, that PrPC represents Fruquintinib a remarkably malleable substrate for infectious prion propagation. Indeed, several avenues of investigation have underlined the inherent plasticity of PrPC structure. Recombinant PrP made up of residues 90C231, corresponding to the protease-resistant core of infectious PrP, has been refolded into both -helical-rich and -sheet-rich structures as well as various intermediates in aqueous buffers (Zhang em et al /em ., Fruquintinib 1997; Jackson em et al /em ., 1999). Particular attention has been focussed around the properties of the 90C145 region of PrP. Studies of synthetic peptides corresponding to residues 109C121 (Gasset em et al Fruquintinib /em ., 1992), 106C126 (Salmona em et al /em ., 1999), 109C145 and 90C145 (Zhang em et al /em ., 1995) indicate that this portion of the protein may adopt conformations rich in either -helices or.