Analysis Of The Biochemical And Cellular Activities Of Substrate Binding By The Molecular Chaperone Hsp110/Sse1

Author

Veronica M. Garcia, The University of Texas MD Anderson Cancer Center UTHealth Graduate School of Biomedical SciencesFollow

Author ORCID Identifier

0000-0002-7112-3003

Date of Graduation

5-2017

Document Type

Dissertation (PhD)

Program Affiliation

Microbiology and Molecular Genetics

Degree Name

Doctor of Philosophy (PhD)

Advisor/Committee Chair

Kevin A. Morano, Ph.D.

Committee Member

Catherine Denicourt, Ph.D.

Committee Member

Theresa M. Koehler, Ph.D.

Committee Member

Michael C. Lorenz, Ph.D.

Committee Member

Ambro van Hoof, Ph.D.

Abstract

Molecular chaperones ensure protein quality during protein synthesis, delivery, damage repair, and degradation. The ubiquitous and highly conserved molecular chaperone 70-kDa heat-shock proteins (Hsp70s) are essential in maintaining protein homeostasis by cycling through high and low affinity binding of unfolded protein clients to facilitate folding. The Hsp110 class of chaperones are divergent relatives of Hsp70 that are extremely effective in preventing protein aggregation but lack the hallmark folding activity seen in Hsp70s. Hsp110s serve as Hsp70 nucleotide exchange factors (NEF) that facilitate the Hsp70 folding cycle by inducing release of protein substrate from Hsp70, thus recycling the chaperone for a sequential round of folding and allowing successfully folded substrates to exit the folding cycle. In the model organism Saccharomyces cerevisiae, Hsp110 is represented by the proteins Sse1 and Sse2, which possess an Hsp70-like substrate binding domain (SBD), making them unique among other functionally similar, but structurally distinct, NEFs. Studies of Hsp110 and Sse1 have demonstrated that this chaperone/NEF family can bind polypeptides and prevent proteins from aggregating in vitro and that this ability is conferred by the SBD. However, attempts to study Hsp110 protein binding in vivo have not been successful. To date, the impact of peptide binding by Hsp110 is unknown. This study elucidates and defines substrate binding by the yeast Hsp110 and addresses the contributions of this activity toward protein and cellular homeostasis as well as begins inquiries into substrate binding by the Drosophila melanogaster Hsp110, Hsc70cb. As a major partner of Hsp70, determining cellular Hsp110 activities is a prerequisite to a full understanding of chaperone-mediated protein homeostasis. By studying chaperone functions and activities in yeast and animal models, we can understand human cellular protein quality control systems which can then be pharmacologically targeted to combat protein conformational disorders, including Alzheimer’s, Huntington’s, and Parkinson’s diseases.

Keywords

chaperones, Hsp110, Sse1, protein folding, protein interactions