[Prion protein structure and its relationships with pathogenesis]

In order to explore the structural domains of prion protein (PrP) that are required for the isoform conversion, prion formation and neurodegenerative effects, we designed a series of PrP deletion mutants and studied, using prion-infected cultured cells and transgemic (Tg) mice, 1) if these mutants can be converted to the abnormal isoform, 2) constitute prions, and 3) cause neurodegeneration when converted and accumulated in mouse brains. We discovered that a mutant PrP with deletions at the N-terminus and the middle portion retained all the three abilities. The molecule named PrP106 was composed of 106 amino acids, nearly a half of 208 composing wild type PrP. The abnormal isoform of PrP106 (PrPSc106) that had been purified from prion-infected Tg mice proved to share, with the abnormal isoform of wild type PrP (PrPSc), unique properties such as high beta-sheet content and propensity to form fibrous aggregates. These findings rationalized the structural analysis of PrPSc106 in comparison with PrPSc. The structure of 2D crystals of the two abnormal PrP isoforms was studied using electron-microscopy, and the data helped to make the 3D structural model of abnormal PrP isoform. Studies with Tg mice expressing other mutant PrPs are currently under way.