Solid-State 13C NMR Reveals Annealing of Raft-Like Membranes Containing Cholesterol by the Intrinsically Disordered Protein α-Synuclein

Misfolding and aggregation of the intrinsically disordered protein alpha-Synuclein (alpha S) in Lewy body plaques are characteristic markers of late-stage Parkinson's disease. It is well established that membrane binding is initiated at the N-terminus of the protein and affects biasing of conformational ensembles of alpha S. However, little is understood about the effect of alpha S on the membrane lipid bilayer. One hypothesis is that intrinsically disordered alpha S alters the structural properties of the membrane, thereby stabilizing the bilayer against fusion. Here, we used two-dimensional C-13 separated local-field NMR to study interaction of the wild-type alpha-Synuclein (wt-alpha S) or its N-terminal (1-25) amino acid sequence (N-alpha S) with a cholesterol-enriched ternary membrane system. This lipid bilayer mimics cellular raft-like domains in the brain that are proposed to be involved in neuronal membrane fusion. The two-dimensional dipolar-recoupling pulse sequence DROSS (dipolar recoupling on-axis with scaling and shape preservation) was implemented to measure isotropic C-13 chemical shifts and C-13-H-1 residual dipolar couplings under magic-angle spinning. Site-specific changes in NMR chemical shifts and segmental order parameters indicate that both wt-alpha S and N-alpha S bind to the membrane interface and change lipid packing within raft-like membranes. Mean-torque modeling of 13C-1H NMR order parameters shows that alpha S induces a remarkable thinning of the bilayer (approximate to 6 angstrom), accompanied by an increase in phospholipid cross-sectional area (approximate to 10 angstrom 2). This perturbation is characterized as membrane annealing and entails structural remodeling of the raft-like liquid-ordered phase. We propose this process is implicated in regulation of synaptic membrane fusion that may be altered by aggregation of alpha S in Parkinson's disease. (C) 2013 Elsevier Ltd. All rights reserved.