Structural Characterization of Mouse Prion Protein in Different Conditions

Transmissible Spongiform Encephalopathies (TSE), also known as prion diseases, are fatal and infectious neurodegenerative diseases. The conformational change of prion protein from α to β is considered to be the main cause of the disease. However, the structural conversion mechanism between cellular prion protein PrPC and its misfolded form PrPSc still remains unknown. It has been known that the N-terminal part of prion protein does not contain any secondary structure while the C-terminal part contains three a-helices and two b-strands. We recently found that, when full-length mouse recombinant prion protein was treated with trypsin, the first cutting site occurs between K105 and T106. It has been reported that PrPC can be partly degraded on membrane and the remained C-terminal part can enter into the cell through endocytosis, convert into b-sheet-rich structure in endosome, and then be exported out through exocytosis. Here we define the segment of 23-105 as the N-terminal part and the segment of 106-230 as the C-terminal part. We employ analytical ultracentrifugation (AUC) and circular dichroism spectroscopy (CD) to explore the structural properties of full-length prion protein and its C-terminal and N-terminal parts. We found out that at pH4.2 condition, increasing salt concentration lead to the comformational change of N-terminal domain. According to thermal stability results, the stability of full-length prion protein remain the same, we suppose that there is no interaction between N- and C-terminal domain. At pH5.2, the stability of full-length prion protein increased while salt concentration increase, we suppose that the N-terminal domain interact with the C-terminal domain.