Huntingtin Aggregation and Lipid Binding are Influenced by Physicochemical Properties of Membranes

Abstract

Huntington's Disease is a fatal neurodegenerative disorder caused by an expanded glutamine repeat region (polyQ) within the huntingtin protein (htt), resulting in the misfolding and aggregation of htt into toxic aggregate species. The first 17 amino acids at the N-terminus of htt (Nt17) are intrinsically disordered in bulk solution, but adopt an amphipathic α-helical structure in the presence of binding partners, such as lipid membranes. In addition to comprising a lipid binding domain, this amphipathic α-helix has also been directly implicated in the initiation of htt aggregation via self-association with other Nt17 α-helices. Due to this, htt/lipid interaction likely has a large impact on the rate and extent of htt aggregate formation, with potential implications for HD pathogenesis. The interaction between Nt17 and lipid membranes is likely influenced by lipid properties, such as fluidity and lateral pressure. As a result, we undertook a series of experiments to determine the role that membrane physicochemical properties have on htt aggregation and lipid binding. Htt aggregation in the presence and absence of DMPC, POPC, and DOPC lipid vesicles was investigated using thioflavin T aggregation assays and atomic force microscopy (AFM). Huntingtin lipid binding was investigated using electrospray ionization mass spectrometry (ESI-MS), PDA lipid binding assays, and molecular dynamics simulations. Overall, our results suggest that membrane physicochemical properties associated with lipid tail groups alter htt lipid binding and aggregate formation.