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

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

Publication date: Available online 11 April 2013
Source:Journal of Molecular Biology

Author(s): Avigdor Leftin , Constantin Job , Klaus Beyer , Michael F. Brown

Misfolding and aggregation of the intrinsically disordered protein ?-Synuclein (?S) in Lewy body plaques is a characteristic marker 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 ?S. However, little is understood about the effect of ?S on the membrane lipid bilayer. One hypothesis is that intrinsically disordered ?S alters the structural properties of the membrane, thereby stabilizing the bilayer against fusion. Here, we used two-dimensional 13C separated local-field NMR to study interaction of the wild-type ?S (wt-?S) or its N-terminal (1–25) amino acid sequence (N-?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 2D dipolar-recoupling pulse sequence DROSS was implemented to measure isotropic 13C chemical shifts and 13C–1H residual dipolar couplings under magic-angle spinning. Site-specific changes in NMR chemical shifts and segmental order parameters indicate that both wt-?S and N-?S bind to the membrane interface and change lipid packing within raft-like membranes. Mean-torque modeling of 13C-1H NMR order parameters shows ?S induces a remarkable thinning of the bilayer (? 6 Å), accompanied by an increase in phospholipid cross-sectional area (? 10 Å2). 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 ?S in Parkinson’s disease.
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