The Interactin of Huntingtin Exon1 with Lipid Bilayers is Regulated by polyQ Length and polyQ Flanking Sequences

Abstract

Huntington's Disease (HD) is a neurodegenerative disorder that is defined by the accumulation of nanoscale aggregates comprised of the huntingtin (htt) protein. Aggregation is directly caused by an expanded polyglutamine (polyQ) domain near the N-terminus of htt, leading to a diverse population of aggregate species, including oligomers and fibrils. Furthermore, the length of the polyQ domain is directly related to onset and severity of disease. The first 17 amino acids on the N-terminus (N17) and the polyproline (polyP) domain on the C-terminal side of the polyQ domain have been shown to further modulate the aggregation process. Additionally, N17 appears to have lipid binding properties as htt interacts with a variety of membrane-containing structures present in cells, such as organelles, and interactions with these membrane surfaces may further modulate htt aggregation. To investigate the interaction between htt exon1 and lipid bilayers, in situ atomic force microscopy (AFM) was used to directly monitor the aggregation of htt exon1 constructs with varying polyQ-length or synthetic peptides with different combinations of polyQ domain flanking sequences associated with htt exon1 on supported lipid membranes comprised of total brain lipid extract. The exon1 fragments accumulated on the lipid membranes, causing disruption of the membrane, in a polyQ-length dependent manner. By adding N-terminal tags to the htt exon1 fragments, the interaction with the lipid bilayer was impeded. Synthetic peptides lacking the N17 flanking sequence had no appreciable interaction with lipid bilayers. Interestingly, polyQ peptides with the N17 flanking sequence interacted with the bilayer. This interaction was further modulated by the addition of the polyP domain.