Date of Award
Doctor of Philosophy (PhD)
Protein misfolding is a common phenomenon that can have severe consequences on cellular and organismal health. Despite this, the causes of protein misfolding remain poorly understood. Prions are a class of proteins that, when misfolded, can convert other molecules into a heritable, non-native conformation. The yeast Saccharomyces cerevisiae naturally harbors several diverse prion-forming proteins; thus, it is an ideal model with which to investigate the factors that influence misfolding and aggregation.This thesis utilizes the yeast prions [PSI+] and [RNQ+] to investigate two distinct steps of the protein misfolding pathway: interactions with chaperones and their cofactors, and heterologous templating by other misfolded proteins. Chaperones are proteins that help other proteins fold correctly, yet we have found that chaperones can have non-intuitive effects upon cells that harbor the prion [PSI+]. An overabundance of the Hsp70 chaperone Ssa1 relative to the Hsp70 Ssb1 exacerbates [PSI+]-related toxicity. This toxicity can be rescued by overexpressing a Hsp70 nucleotide exchange factor, Sse1, that may improve Ssb1 functionality in the presence of excess available Ssa1. Our results imply that the balance of molecular chaperones is finely tuned and is crucial to maintaining protein homeostasis.Interestingly, the [PSI+] prion cannot form without the presence of an inducing factor, which is most commonly the [RNQ+] prion. The nature of the interaction between [PSI+] and [RNQ+] was previously unknown. Here, we have demonstrated that the two proteins undergo cross-seeding reaction, wherein the prion-forming proteins bind to one another to template the formation of [PSI+]. Blocking or restoring a binding site can have significant impacts upon the frequency of prion formation. As cross-seeding has been implicated in several human pathologies, these results may inform key principles that can be utilized to research disease prevention.
Chair and Committee
Kendall Blumer, Barak Cohen, Sergej Djuranovic, Chris Weihl,
Keefer, Kathryn Morgan, "Factors that Contribute to de novo Protein Misfolding and Prion Formation in Saccharomyces cerevisiae" (2017). Arts & Sciences Electronic Theses and Dissertations. 1117.