Adsorption of α-Synuclein to SupportedLipid Bilayers: Positioning and Role of Electrostatics

摘要

An amyloid form of the protein α-synuclein is the major component of the intraneuronal inclusions called Lewy bodies, which are the neuropathological hallmark of Parkinson’s disease (PD). α-Synuclein is known to associate with anionic lipid membranes, and interactions between aggregating α-synuclein and cellular membranes are thought to be important for PD pathology. We have studied the molecular determinants for adsorption of monomeric α-synuclein to planar model lipid membranes composed of zwitterionic phosphatidylcholine alone or in a mixture with anionic phosphatidylserine (relevant for plasma membranes) or anionic cardiolipin (relevant for mitochondrial membranes). We studied the adsorption of the protein to supported bilayers, the position of the protein within and outside the bilayer, and structural changes in the model membranes using two complementary techniques—quartz crystal microbalance with dissipation monitoring, and neutron reflectometry. We found that the interaction and adsorbed conformation depend on membrane charge, protein charge, and electrostatic screening. Theresults imply that α-synuclein adsorbs in the headgroup regionof anionic lipid bilayers with extensions into the bulk but does notpenetrate deeply into or across the hydrophobic acyl chain region.The adsorption to anionic bilayers leads to a small perturbation ofthe acyl chain packing that is independent of anionic headgroup identity.We also explored the effect of changing the area per headgroup inthe lipid bilayer by comparing model systems with different degreesof acyl chain saturation. An increase in area per lipid headgroupleads to an increase in the level of α-synuclein adsorptionwith a reduced water content in the acyl chain layer. In conclusion,the association of α-synuclein to membranes and its adsorbedconformation are of electrostatic origin, combined with van der Waalsinteractions, but with a very weak correlation to the molecular structureof the anionic lipid headgroup. The perturbation of the acyl chainpacking upon monomeric protein adsorption favors association withunsaturated phospholipids preferentially found in the neuronal membrane.