We propose to investigate by chemical and structural techniques a mechanism that converts a normal precursor protein to a pathologic and disease-associated form. The system we will use involves the scrapie agent amyloid protein (Sp33-37); an abnormally modified, degradation-resistant isoform of a normal cellular protein (Cp33-37). Scrapie in animals is one of the transmissible spongiform encephalopathies; a group of neurodegenerative disorders that includes the human diseases Creutzfeldt-Jakob, kuru, and the Gerstmann-Straussler syndrome. The accumulation of amyloid proteins and plaques in scrapie-diseased brain makes scrapie the best available animal model for amyloidogenesis in Alzheimer's disease. In purified fractions containing high titers of the scrapie agent, Sp33-37 is the major protein. Proteinase-K treatment of Sp33-37 results in the production of PrP 27-30, a protease- resistant sialoglycoprotein previously identified as a component of the transmissible scrapie agent. The mRNA encoding Sp33-37 and its cellular homologue Cp33-37 is found in brain and several non- neural tissues. We have identified by immunochemical means Sp33-37 and Cp33-37 in scrapie-affected and normal brains, respectively, but not in other tissues. We have purified Sp33-37 and partially purified Cp33-37. Cp33-37 will be purified, then chemically and structurally analyzed. Peptide mapping, amino acid composition, HPLC analysis of residues, protein sequencing, deglycosylation, dephosphorylation, and immunochemical analysis of Sp33-37 and Cp33-37 will be done in a search for specific differences. This normal protein will be isolated from hamster and two mouse strains to determine if specific host protein variations correlate with biologically distinct scrapie agent forms. Our work will produce direct structural comparisons between the normal and scrapie isoforms of p33-37. These experiments have been designed to test the hypothesis that abnormal modification of Cp33-37 result in the accumulation of Sp33-37, a degradation- resistant, amyloid protein, which is the major structural protein of the scrapie agent. Our research will interact with other projects in progress at this Institute, especially studies on Sp33-37 purified from scrapie agent strains in genotypically different hosts by Bolton et al., and work on scrapie associated fribrils (SAF) by Kascsak et al.
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