Deciphering the Molecular Basis of the Species Barrier in Prion Disease Using Bank Vole PrP
Prion disease is an infectious and fatal neurodegeneration condition which depends on the structural reconfiguration of a predominantly α-helical cellular protein called PrPC into a β-sheet rich conformer referred to as scrapie or PrPSc. The infectious nature of this conformer enables it to template the conversion of PrPC into additional copies of PrPSc, the efficiency of which depends on the sequence-encoded structural compatibility of the two molecules. PrPC and PrPSc from different species do not share an identical amino acid sequence and therefore are often not structurally compatible for efficient templated misfolding, a phenomenon referred to as the species barrier. Bank vole (Bv) PrP is an exception, as it serves as an efficient substrate for templated misfolding with essentially all prions identified to date. This universal acceptor phenotype is a rare example of structural compatibility between PrPC and PrPSc in the absence of sequence similarity. How BvPrP is able to function as this structurally compatible substrate across a great diversity of prion strains is a mystery. Throughout this thesis, I explore the anomalous behaviour of BvPrP by creating in vivo and in vitro tools to decipher the molecular basis of the species barrier. We generated BvPrP knock-in mice to map and characterize the network of proteins that are found in the proximity of BvPrP, that could serve as putative modulators of cross-species prion replication. Unable to tease apart novel protein-protein interactions in vivo, I established a cellular paradigm of cross-species prion replication in cultured cells using CAD5-PrP knockout cells expressing BvPrPC. This model served as a critical platform for i) characterizing the consequences of prion strain adaptation using BvPrP and ii) dissecting key regions of BvPrP and specific amino acids which are critical for cross-species prion replication. Through this work, I showcase the importance of the distal C-terminal amino acids (227, 230) of PrP in prion replication, as well as highlighting amino acids which enable BvPrPC to function as a universal acceptor of prions. Overall, this thesis clarifies the molecular determinants of the species barrier and provides the basis for generating superior animal and cellular models for studying prion disease.
Bank Vole, Mad cow disease, Prion Protein, Prions, Protein aggregates, Species Barrier
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