Structural Elucidation of [RNQ+] prions Transmissible Infectivity

Author's Department/Program

Biology and Biomedical Sciences: Biochemistry


English (en)

Date of Award

Summer 9-1-2014

Degree Type


Degree Name

Doctor of Philosophy (PhD)

Chair and Committee

Heather True-Krob


Protein conformational disorders are a hallmark of protein aggregation and understanding these diseases requires a large degree of knowledge pertaining to protein folding and misfolding. Neurodegenerative diseases associated with humans are commonly found to be the result of aggregated proteins or prions present in the brain. Prions are obtained by one of these three means: familial, acquired, or sporadic; with the majority of cases found in nature being sporadic. A variety of organisms posses proteins that are capable of undergoing conformational changes to become a prion. Here we use the model organism Saccharomyces cerevisiae to study the effects prions have within the cell.

To study the mechanism of variation in protein misfolding and prion propagation, we have taken advantage of the colorimetric assay of the yeast prions [RNQ+] and [PSI+]. These prions result from the aggregation of the proteins Rnq1 and Sup35, respectively. Changes in phenotype allows for the investigation of the structure and toxicity of yeast fibrils formed in vivo, while correlating them to what is observed in vitro.

I looked to investigate the fibril polymorphism of aggregates and prions associated with prion disease by using yeast prions as a mode of toxicity and propagation. The transmissible infectivity of in vitro formed fibers were tested by introduction into yeast and assayed for any presence of heterogeneity. Significant phenotypic variation, similar to what is observed with mammalian prions strains, is observed within yeast also. To decipher how structural differences between infectious and non-infectious amyloid form, we formulated the hypothesis that structural differences in Rnq1 prion formation account for drastic changes within the amyloid. Here I show that different strains of [RNQ+] can propagate from a single fibril mixture. In addition, I show that fibril characteristics change also, i.e. kinetics, stability, and transmissible infectivity. Distinguishing the mechanism involved in determining strain differences provides us with a framework to understand the differences in prions strains observed. The implications presented here aide in the conundrum surrounding pathogenesis of protein misfolding disorders and can possibly help develop therapies for individuals with neurodegenerative diseases.


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