Parkinson's disease-associated mutants shift equilibrium bound state of alpha-synuclein towards the second helix.

Abstract

α-synuclein regulates neurotransmitter release by binding to the outer lipid membrane of synaptic vesicles. Mutations within the lipid-binding region of α-synuclein are associated with protein aggregates and the progression of Parkinson's Disease (PD). However, the role of lipid-binding in α-synuclein's propensity to aggregate is not fully understood. Here, we explore how a mathematical framework reveals details in protein-membrane interactions that are disrupted by PD-associated mutants. Upon binding, α-synuclein forms two α-helices that insert into the lipid membrane - a process that is mediated by lipid membrane defects. A tryptophan fluorescence assay reveals how PD-associated mutants alter the equilibrium distribution of fully vs. partially bound protein. In unraveling the role of α-synuclein in the progression of PD, we reveal a unifying difference in protein behavior between wild-type α-synuclein and disease-associated mutants. Altogether, our results show that PD-associated point mutations uniformly shift the equilibrium bound state towards the second helix, suggesting that protein aggregation and eventual neurotoxicity may be linked to the equilibrium between the two helices.