Huntingtin disrupts lipid bilayers in a polyQ-length dependent manner

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 in htt, leading to a diverse population of aggregate species, such as oligomers, fibrils, and annular aggregates. Furthermore, the length of this polyQ domain is directly related to onset and severity of disease. The first 17 N-terminal amino acids of htt have been shown to further modulate aggregation. Additionally, these 17 amino acids appear 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 Q-lengths (35Q, 46Q, 51Q, and myc-53Q) 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 dependent manner. Furthermore, the addition of an N-terminal myc-tag to the htt exon1 fragments impeded the interaction of htt with the bilayer.

Proteins Containing Expanded Polyglutamine Tracts and Neurodegenerative Disease

“…167, 212, 248 Both normal and mutant htt localizes to numerous subcellular compartments, i.e. endosomes, pre-synaptic, and clathrin-coated vesicles, and dendritic plasma membrane.…”

“…With the localization of htt to membranous surfaces well established, it is appropriate to note that lipids are a common modulator of amyloid formation, as studies of α-synuclein, 254, 255 islet amyloid polypeptide, 256 β-amyloid, 257–259 and polyQ 179, 212, 260, 261 all demonstrate altered aggregation in the presence of membranes when compared to bulk solution. With regards to the amyloid formation in general, several physicochemical properties of lipid membrane, i.e.…”

“…179, 264 Htt aggregates can associate directly lipid membranes and induce local mechanical changes. 68, 179, 212 …”

Membrane Curvature-sensing and Curvature-inducing Activity of Islet Amyloid Polypeptide and Its Implications for Membrane Disruption

“…However, rat IAPP (rIAPP), which does not readily form fibrils (19), has also been seen to cause membrane leakage in vitro (16) and confer some (albeit strongly reduced) cytotoxicity in vivo (12). Also, the nonamyloidogenic hIAPP (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19) fragment as well as a number of nonamyloidogenic full-length variants of IAPP have been observed to cause leakage of synthetic membranes (13,15,20), and hIAPP (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19) and rIAPP (1)(2)(3)(4)(5)…”

In Situ Atomic Force Microscopy Studies on Nucleation and Self-Assembly of Biogenic and Bio-Inspired Materials

“…Legleiter et al have used in situ AFM to directly monitor the interaction between huntingtin (htt) exon 1 protein and brain lipid extract [158]. They observed that the exon1 fragments accumulated on the lipid membranes comprised of total brain lipid extract, which caused disruption of the membrane.…”