Molecular Mechanisms of Wild-type and Mutant Prion Formation

Prion diseases are a class of infectious neurodegenerative disorders which affect humans and many other mammalian species. The causative agent is a unique pathogen known as a prion or PrPSc, a misfolded form of a host-encoded glycoprotein which replicates by templated conformational change. Distinct strains of prions with unique phenotypic and pathologic presentations appear to be encoded by subtle conformational changes within the misfolded protein. While the general manner of prion transmission is known, our detailed understanding of these mechanisms remains incomplete, limiting efforts for the discovery or design of therapeutic treatments for these fatal diseases. In vitro synthesis of infectious PrPSc using wild-type protein relies on the presence of auxiliary cofactor molecules in a strain and species dependent manner. To examine the molecular mechanism and structural impacts of cofactor activity, I have developed new methods for in vitro prion production at large scale to enable analysis by solid-state NMR, a first in the field. Comparison of infectious and noninfectious conformers suggests specific domains and structural transitions associated with maintenance of the infectious conformation. These amplification protocols have also enabled the production of conformationally diverse prion strains in a manner not possible with existing methodologies. Experiments generating prions from defined minimal components highlight the complex interplay between cofactor availability and reaction conditions and provide the first direct demonstration of genetic prion disease-associated point mutations conferring distinct PrPSc conformations in vitro. Prion diseases are currently invariably fatal, whether originating from sporadic, infectious, or genetic etiology. New genetic models in mice of inherited prion disease allowed me to perform the first preclinical therapeutic study with measurable disease endpoints for Fatal Familial Insomnia and familial Creutzfeldt-Jakob disease. Efforts to iii repurpose drugs developed for the treatment of wild-type prions were unsuccessful, highlighting distinct mechanisms of pathogenesis for mutant prions and arguing for drug discovery efforts in laboratory models specific to genetic forms of the disease