In partial fulfillment of the requirements for the degree of
Doctor of Philosophy in Biology
In the
School of Biological Sciences
Aspen Lynn Hirsch
Will defend her dissertation
Modulation of Self-Perpetuating Protein Aggregation by Sequence and External Factors
15, November 2024
12:00 PM
Krone Engineered Biosystems Building (EBB), CHOA Seminar Room
Thesis Advisor:
Yury Chernoff, Ph.D.
School of Biological Sciences
Georgia Institute of Technology
Committee Members:
Matthew Torres, Ph.D.
School of Biological Sciences
Georgia Institute of Technology
Francesca Storici, Ph.D.
School of Biological Sciences
Georgia Institute of Technology
Andreas Bommarius, Ph.D.
School of Chemical and Biological Engineering
Georgia Institute of Technology
Kirill Lobachev, Ph.D.
School of Biological Sciences
Georgia Institute of Technology
ABSTRACT:
The National Aeronautics and Space Administration (NASA) and the European Space Agency (ESA) are studying how to improve the safety of future planetary science sample return missions that would bring back materials to Earth. To address this challenge, NASA has identified the need for an appropriate suite of biological indicators (BIs) that would be used to develop, test, and ultimately validate sample return mission sterilization systems. BIs traditionally used at NASA have been selected based on past mission requirements and mainly focused on bacterial spores. However, spore-based BIs are insufficient as the only analog for a nominal case in sample return missions. Thus, it is important to develop a mitigation strategy that addresses various known forms of biology, from complex organisms to biomolecular assemblies (including self-perpetuating non-nucleic acid containing structures). Yeast aggregating proteins (yeast prions) exhibit behavior similar to mammalian prion protein and have been successfully employed by researchers to understand fundamental prion properties such as aggregation and self-propagation. Despite also being termed “prions,” yeast prions are not hazardous to humans and can be used as a cost-effective and safer alternative to mammalian prions, which is addressed in the first two chapters of this thesis. In the final data chapter, we further characterize the deletion derivative of Sup35NM missing the N-terminal region, and therefore only have a C-terminal PrD, in comparison to the wildtype Sup35NM and derivatives containing deletions of the N-terminal region of the PrD. Our data show that, while the Sup35NM derivative with an N-terminal deletion has a similar lag time to wildtype Sup35NM, the amyloid core of the deletion derivative must be quite different based on seeding dynamics. This work fundamentally advances our understanding of the effect of the environment on yeast amyloid-forming amino acid sequences and amyloid structure via our attempts to perturb it with extreme sterilization modalities, and how sequence factors influence amyloid variant emergence. Furthermore, this work will be directly utilized by NASA and the European Space Agency (ESA) for upcoming mission planning purposes.