α-Synuclein is the primary protein found in Lewy bodies, the protein and lipid aggregates associated with Parkinson’s disease and Lewy body dementia. The protein folds into a uniquely long amphipathic α-helix (AH) when bound to a membrane, and at high enough concentrations, it induces large-scale remodeling of membranes (tubulation and vesiculation). By engineering a less hydrophobic variant of α-Synuclein, we previously showed that the energy associated with binding of α-Synuclein’s AH correlates with the extent of membrane remodeling (Braun et al. in J Am Chem Soc 136:9962–9972, 2014). In this study, we combine fluorescence correlation spectroscopy, electron microscopy, and vesicle clearance assays with coarse-grained molecular dynamics simulations to test the impact of decreasing the length of the amphipathic helix on membrane binding energy and tubulation. We show that truncation of α-Synuclein’s AH length by approximately 15% reduces both its membrane binding affinity (by fivefold) and membrane remodeling capacity (by nearly 50% on per mole of bound protein basis). Results from simulations correlate well with the experiments and lend support to the idea that at high protein density there is a stabilization of individual, protein-induced membrane curvature fields. The extent to which these curvature fields are stabilized, a function of binding energy, dictates the extent of tubulation. Somewhat surprisingly, we find that this stabilization does not correlate directly with the geometric distribution of the proteins on the membrane surface.
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All simulations and analysis were completed at the Minnesota Supercomputing Institute (MSI). This work was supported in part by the National Institutes of Health R01 NS084998 (to JNS) and NRSA Fellowship F31 NS077634 (to ARB), in addition to GM102815 (to ER) and predoctoral training grant GM008283 (to VCD and MML). No competing financial interests have been declared.
The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript.
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Braun, A.R., Lacy, M.M., Ducas, V.C. et al. α-Synuclein’s Uniquely Long Amphipathic Helix Enhances its Membrane Binding and Remodeling Capacity. J Membrane Biol 250, 183–193 (2017). https://doi.org/10.1007/s00232-017-9946-1
- Membrane remodeling