The Role of Membrane Context in the Interaction of Polyglutamine Peptides with Lipid Membranes

Abstract

Huntington's disease is a dominant genetic neurodegenerative disorder associated with motor and cognitive decline, caused by a mutation in the poly-glutamine (polyQ) region near the N-terminus of the huntingtin (htt) protein. Expansion of the polyQ region above 35-40 repeats results in the disease that is characterized by inclusion body aggregates of mutated protein. The polyQ expansion in htt is flanked by a 17 amino acid N-terminal sequence (Nt17) and a proline-rich (polyP) region. To investigate the interaction between htt exon1 and lipid membranes, a combination of Langmuir trough techniques and vesicle permeability assays measuring calcein leakage were used to directly monitor the interaction of a variety of synthetic polyQ peptides with total brain lipid extract (TBLE) model membranes doped with specific membrane components. Our data suggests that the Nt17 domain plays a critical role in htt binding and aggregation on lipid membranes, and this lipid/htt interaction is enhanced by the presence of the polyP domain. The exogenous addition of cholesterol, a primary neuronal plasma membrane component reduced in many Huntington's disease models, to the TBLE monolayer caused a notable condensing effect in the membrane at low surface pressures. This resulted in reduced peptide insertion into lipid monolayers and decreased levels of induced vesicle permeability, though the effect does not scale linearly with cholesterol concentration. Results from parallel studies on htt-membrane interaction with sphingomyelin, a major component of membranes in the nervous system, will also be discussed.