Structural Studies of Prions and Prion Protein Polymorphisms in Chronic Wasting Disease

• Author / Creator

  Amidian, Sara

• Prion diseases are a group of deadly neurological disorders caused by the abnormal folding of the prion protein into an infectious form known as PrPSc. Chronic wasting disease is a prion disease affecting cervids such as deer, elk, moose, and reindeer. Despite ongoing efforts to understand prion transmission barriers and ensure public health, the appearance of animal prion strains with zoonotic potential is a major concern. Therefore, a crucial element in addressing this concern is to understand the structure of PrPSc which can contribute to developing strategies aimed at preventing the accumulation and replication of PrPSc. To date, no structural investigations have been conducted on ex-vivo CWD prions. Moreover, due to the inherent flexibility of the N-terminal region of prions, there is a lack of structural data regarding this region across all prion strains. Therefore, in the first part of this study, electron microscopy was used to study the full-length and N-terminally truncated forms of chronic wasting disease (CWD) prions purified from the brains of CWD-positive tg33 mice and white-tailed deer. The CWD prions were found to be morphologically heterogeneous with larger diameters compared to other prion strains. Interestingly, the full-length CWD prion fibrils were decorated with striations while the N-terminally truncated form were not. This suggests a potential correlation between the striations and the N-terminal region of the CWD prions. This observation was likely made possible by the incorporation of ethylenediaminetetraacetic acid (EDTA) during the purification process. EDTA can remove cations that engage with the N-terminus, potentially allowing the N-terminus to independently structure itself, thereby becoming visible for the first time. This finding opens the door to further investigating the N-terminal region of the prions.

  Another interesting phenomenon in prion disease involves the polymorphisms found in the prion protein sequence, which can influence the susceptibility of animals to chronic wasting disease. In the second part of this research, we investigated the effect of white-tailed deer polymorphisms on the structure and stability of prion protein. We performed all-atom molecular dynamics simulations to study the structure and stability of white-tailed deer prion protein for wild type and three polymorphisms: 95H, 96S, and 116G. We demonstrated that proteins carrying polymorphisms display significant differences when compared to wild type protein. The root mean square deviation and radius of gyration calculations illustrated that the conformations in wild type prion protein, 95H, 96S, and 116G are unique and distinct from one another. Additional analyses were conducted by comparing the main-chain flexibility and distance maps of the prion protein residues. Several regions in 96S and 116G became less stable, in contrast to 95H, where increased stability was observed. Hydrogen bond and salt bridge calculations showed 95H, 96S, and 116G affected the bonding patterns within the prion protein structures as compared to the wild type. However, changes in the solvent-accessible surfaces were more substantial indicating that the polymorphisms most probably dictated their dynamic changes by altering the hydrophobic interactions. Using in vitro aggregation assay, we also demonstrated an opposite effect of these polymorphisms on the aggregation propensity of deer prion protein, with 95H favoring and 96S delaying its aggregation. The structural and dynamical descriptors investigated in this study and the differences seen between the simulated structures may aid in better understanding how polymorphisms can affect CWD transmission.

• Subjects / Keywords

  • Prions
  • Chronic wasting disease
  • Prion protein polymorphisms
  • Prion structure
  • Molecular dynamics simulations

• Graduation date

  Fall 2023

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/r3-m3w4-ps05

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.