Semester

Fall

Date of Graduation

2020

Document Type

Dissertation

Degree Type

PhD

College

Eberly College of Arts and Sciences

Department

Chemistry

Committee Chair

Justin Legleiter

Committee Member

Kenneth Showalter

Committee Member

Michelle Richard-Babb

Committee Member

Stephan J. Valentine

Committee Member

Werner Geldenhuys

Abstract

Huntington Disease (HD) is a fatal neurodegenerative disorder caused by an expanded polyglutamine domain (polyQ) in the first exon of the huntingtin protein (htt-exon1). The major hallmark of HD is the accumulation of aggregates into proteinaceous inclusion bodies. PolyQ expansion in huntingtin promotes self-assembly into a variety of toxic aggregates such as oligomers, fibrils, and amorphous aggregates. The resulting heterogeneous mixture of distinct species makes it difficult to assign a toxic function to specific aggregate structures. In addition, htt interacts with a variety of membranous surfaces. The first 17 amino acids (Nt17) of htt directly flanking the polyQ domain functions in binding lipids and in promoting aggregation based on its ability to form an amphipathic a-helix. Nt17 undergoes several posttranslational modifications that modulate aggregation, subcellular localization, and toxicity of mutant htt. To gain in-depth mechanistic insights into huntingtin aggregation at lipid interfaces, both natural and chemical Nt17 modification strategies were employed. Specifically, the direct impact of SUMOylation was characterized. SUMOylation promoted the formation of large, SDS-soluble amorphous aggregates of htt and significantly inhibited the ability of htt to bind lipid membranes. In addition, the interaction of various htt aggregates species with lipid membrane was determined, and oligomers displayed the largest membrane activity. To further investigate these htt oligomers, a crosslinking strategy was employed that targeted lysine residues within Nt17. Crosslinking htt oligomers compromises their conformational flexibility, inhibiting their membrane activity. Cellular toxicity of crosslinked oligomers was also reduced, suggesting membrane activity may underlie mechanisms associated with htt oligomers.

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