N-terminal Acetylation Stabilizes N-terminal Helicity in Lipid- and Micelle-bound α-Synuclein and Increases Its Affinity for Physiological Membranes

Background: The functional effects of normal N-terminal acetylation of the Parkinson disease protein -synuclein are unknown. Results:N-Acetylation stabilizes helical structure at the N terminus of membrane-bound forms of synuclein, including a novel partly helical state. Conclusion: Stabilization of helicity increases affinity for membranes similar to synaptic vesicles. Significance:In vivo N-acetylation of -synuclein likely affects its physiological function and dysfunction. The Parkinson disease protein -synuclein is N-terminally acetylated, but most in vitro studies have been performed using unacetylated -synuclein. Binding to lipid membranes is considered key to the still poorly understood function of -synuclein. We report the effects of N-terminal acetylation on -synuclein binding to lipid vesicles of different composition and curvature and to micelles composed of the detergents -octyl-glucoside (BOG) and SDS. In the presence of SDS, N-terminal acetylation results in a slightly increased helicity for the N-terminal approximate to 10 residues of the protein, likely due to the stabilization of N-terminal fraying through the formation of a helix cap motif. In the presence of BOG, a detergent used in previous isolations of helical oligomeric forms of -synuclein, the N-terminally acetylated protein adopts a novel conformation in which the N-terminal approximate to 30 residues bind the detergent micelle in a partly helical conformation, whereas the remainder of the protein remains unbound and disordered. Binding of -synuclein to lipid vesicles with high negative charge content is essentially unaffected by N-terminal acetylation irrespective of curvature, but binding to vesicles of lower negative charge content is increased, with stronger binding observed for vesicles with higher curvature. Thus, the naturally occurring N-terminally acetylated form of -synuclein exhibits stabilized helicity at its N terminus and increased affinity for lipid vesicles similar to synaptic vesicles, a binding target of the protein in vivo. Furthermore, the novel BOG-bound state of N-terminally acetylated -synuclein may serve as a model of partly helical membrane-bound intermediates with a role in -synuclein function and dysfunction.