Structures at the Core of Mammalian Prions
Prion diseases, also known as Transmissible Spongiform Encephalopathies, are neurodegenerative diseases that pose a major threat to both humans and animals. They fall into a category of misfolding diseases known as amyloidoses where accumulation of fibrous protein aggregates correlates with disease symptoms. Unlike other amyloid diseases, prion diseases are infectious and not strictly linked with age. Victims of prion diseases experience dementia, hallucinations, and an inability to take care of themselves among other symptoms before inevitably succumbing to disease. While the time between presentation of symptoms and death is often less than one year, symptoms can take decades to appear. This makes the immediate cause of sporadic disease difficult to determine.
Prion diseases currently lack any form of treatment or means of prevention outside of selective breeding in sheep, which takes advantage of a disease-preventing sequence polymorphism. Infectious prions share β-sheet rich cores that produce a cross-β diffraction pattern not observed in natively folded PrPC. Knowledge of the atomic structures adopted by prions will aid not only in structure-based drug design and prion disease prevention, but also provide answers to the centuries old question of what makes a protein infectious.
The aim of this dissertation is to uncover the structural characteristics of prions that distinguish them from other amyloids. The dissertation is also aimed at uncovering molecular explanations for species barriers, whereby PrPSc from one species converts PrPC of another species to a misfolded form with an efficiency dependent on both the original and newly infected host prions. These aims will be achieved through a combination of technological advancements made in atomic-level amyloid structure determination, with a focus on micro-crystal electron diffraction (MicroED) of the building blocks that make up prion cores (chapters 1 and 2) and single particle cryo-electron microscopy (cryo-EM) of prion filaments (chapters 3 and 4).