Phosphatidylethanolamine modulates α-synuclein membrane-binding behavior

Interaction with lipid membranes is important in the physiological and pathological functioning of α-synuclein (αS) in brain neuronal cells. In this study, we investigated the effect of lipid composition on the membrane-binding behavior of αS using multiple biophysical techniques. Circular dichroism measurement revealed that, although negatively charged phospholipids are necessary for αS to bind to small unilamellar vesicles, the presence of phosphatidylethanolamine (PE) significantly enhances α-helical structure formation, specifically within the first 35 αS residues. To obtain residue-level structural insights into the lipid-bound αS conformation, site-directed labeling was performed with acrylodan-an environmentally sensitive fluorophore-at the N-terminal, central non-amyloid β component region, and C-terminal regions after cysteine substitution. Acrylodan fluorescence measurements at varying lipid-to-protein ratios revealed that, in addition to the negatively charged C-terminal region, the non-amyloid β component region adopts a more solvent-exposed lipid-bound conformation than the N-terminal region. Notably, PE induced a more hydrophobic, lipid-bound conformation in the N-terminal region of αS than observed with vesicles lacking PE, whereas it promoted association of the C-terminal region with the membrane surface. Collectively, these findings suggest that both the N-terminal and C-terminal regions contribute to αS binding to PE-containing plasma membranes.