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Jennifer Abrams

Advisor: Kevin A. Morano, Ph.D.

Accepted postdoctoral position at the Institute for Neurodegenerative Diseases at The University of California, San Francisco after receiving PhD

The Hsp70 class of molecular chaperones play critical roles in protein homeostasis via an ATP-dependent folding cycle. Cytosolic Hsp70s in the budding yeast Saccharomyces cerevisiae, Ssa and Ssb, interact with up to three distinct nucleotide exchange factors (NEFs) homologous to human counterparts; Sse1/Sse2/HSP110, Fes1/HspBP1, and Snl1/Bag-1. In an effort to understand the differential functional contributions of the cytosolic NEFs to protein homeostasis (“proteostasis”), I carried out a comparative genetic, biochemical and cell biological analyses. For these studies, I developed protocols to monitor protein disaggregation and reactivation in a near real-time coupled assay that revealed the importance of aggregate dynamics in solubilization of proteins for refolding. This coupled experimental approach represents an important step toward developing tools necessary to monitor in vivo mechanisms of proteostasis.

This work determined that the Hsp110, Sse1, is the primary NEF contributing to most Hsp70 functions and uncovered a unique role for Fes1 in Ssa-mediated regulation of the cytosolic heat shock response, while revealing no significant contributions from Snl1 and Sse2. These findings suggest that NEFs do have overlapping functions, but their distinct associations with the Hsp70s as well as unique structural components could contribute to differential roles in proteostasis.

Additionally, this study uncovered that relative levels of Snl1 and Sse1 are important for optimal growth. To probe this relationship, I exploited the Snl1 overexpression toxicity phenotype exhibited in the absence of Sse1 to examine which unique characteristics of Snl1 are important for its function.  I discovered that Snl1 localization to the ER membrane was required for toxicity and that Sse1-mediated alleviation of this phenotype was Ssb-dependent.  These results demonstrate a network of interactions that supports a hypothesis where Snl1 plays a role in translation regulation.

This investigation was conducted to gain a better understanding of NEF roles within the Hsp70 chaperone network. These dynamics are critical to obtain successful treatments that can reverse the debilitating effects of neurodegenerative disorders such as Alzheimer’s and Parkinson’s diseases.  Pharmacological targeting of molecular chaperones and their co-factors, such as the NEFs, is an attractive therapeutic goal that may contribute to improving human health, most notably in the aging population.

Research Info

Functional analysis of cytosolic Hsp70 nucleotide exchange factor networks in yeast