Towards a Comparison of the Folding of Prion Protein from Different Species

• Author / Creator

  Charrunchon, Sookpichaya

• The formation of an abnormal form of proteins in cells can cause aggregation and neurodegenerative pathology, such as Alzheimer’s, Parkinson’s and prion diseases, which affects both humans and animals. Nowadays, the understanding of the mechanism of prion misfolding and propagation, including effective ways of treating prion diseases, is not clearly identified. This may result from the complexity of the biological ensembles. Optical tweezers, one of the single-molecule force spectroscopy methods, can be used to better understand mechanisms of protein misfolding and dynamics by manipulating small beads attached to single protein molecules, resulting in the mechanical denaturation of protein structure. Previous work studying the mechanical denaturation of structure in hamster prion protein (PrP) by laser tweezers, for example, found that the folding pathways of the native protein were composed of two states of folding and unfolding (Yu et al., 2012; 2013). Although the sequence of PrP is very highly conserved between species, there are a few differences in amino acid residues between PrP in different species. Furthermore, mouse PrP, a model system for studying prion diseases, has a lower susceptibility to the misfolding underlying prion diseases than hamster PrP. Thus, the differences in the protein sequences may lead to differences in the folding and misfolding which may relate to the different susceptibilities. This work is the first single-molecule study of mouse PrP folding; the prion proteins from mice were attached to DNA handles using click chemistry and were studied by optical tweezers in order to compare my results to those of the previous studies on hamster PrP. As a result of the successful attachments, the force- extension curves of mouse prion proteins had close similarities in unfolding behavior compared to those of hamsters. Furthermore, according to the data analysis of the curves, the contour lengths of the mouse prion proteins from the combination of rips were found to be closely matched to the expected length in the protein structure. However, it was challenging to avoid problems caused by attaching the DNA handles to the wrong cysteine residues in the protein. For a more complete understanding of protein misfolding, future work involving the study of protein structure is required. Single-molecule studies of mouse prion proteins can also allow one to study the energy landscapes, specifically the folding pathways of proteins in different species. Information regarding protein structure may be useful for the development of specific therapeutic drugs. Future work on the molecular mechanisms of the prion proteins will not only provide a better understanding of prion diseases, but also other related neurodegenerative disease that share similar mechanisms of protein aggregation.

• Subjects / Keywords

  • Prion protein
  • Biophysics
  • Force spectroscopy
  • Protein folding
  • Optical tweezers
  • Protein misfolding

• Graduation date

  Fall 2017

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/R3VQ2SQ6F

• 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.