Helical α-Synuclein Forms Highly Conductive Ion Channels

Abstract

Alpha-synuclein (alphaS) is a cytosolic protein involved in the etiology of Parkinson's disease (PD). Disordered in an aqueous environment, alphaS develops a highly helical conformation when bound to membranes having a negatively charged surface and a large curvature. It exhibits a membrane-permeabilizing activity that has been attributed to oligomeric protofibrillar forms. In this study, monomeric wild-type alphaS and two mutants associated with familial PD, E46K and A53T, formed ion channels with well-defined conductance states in membranes containing 25-50% anionic lipid and 50% phosphatidylethanolamine (PE) in the presence of a trans-negative potential. Another familial mutant, A30P, known to have a lower membrane affinity, did not form ion channels. Ca2+ prevented channel formation when added to membranes before alphaS and decreased channel conductance when added to preformed channels. In contrast to the monomer, membrane permeabilization by oligomeric alphaS was not characterized by formation of discrete channels, a requirement for PE lipid, or a membrane potential. Channel activity, alpha-helical content, thermal stability of membrane-bound alphaS determined by far-UV CD, and lateral mobility of alphaS bound to planar membranes measured by fluorescence correlation spectroscopy were correlated. It was inferred that discrete ion channels with well-defined conductance states were formed in the presence of a membrane potential by one or several molecules of monomeric alphaS in an alpha-helical conformation and that such channels may have a role in the normal function and/or pathophysiology of the protein.

α-Synuclein Shows High Affinity Interaction with Voltage-dependent Anion Channel, Suggesting Mechanisms of Mitochondrial Regulation and Toxicity in Parkinson Disease

“…It was reported that at concentrations of 140 -700 nM, ␣-syn could form pores in the planar membranes, but only in the presence of the negatively charged or nonlamellar lipids (49). In our control experiments without VDAC, a pore formation activity of ␣-syn has never been observed in neutral diphytanoyl-phosphatidylcholine membranes used in our experiments and at ␣-syn concentrations up to 300 nM.…”

α-Synuclein Stimulates a Dopamine Transporter-dependent Chloride Current and Modulates the Activity of the Transporter

“…The ␣-synuclein-mediated increase in DATmediated inward currents can be a consequence of the direct interactions between these two proteins or secondary to formation of conductive pores (67), a result of pathological levels of ␣-synuclein inside the neuron. These membrane pores can influence membrane conductance (35,68), which in turn can impact DAT properties. The data presented in this study cannot exclude these possibilities.…”

α-Synuclein Senses Lipid Packing Defects and Induces Lateral Expansion of Lipids Leading to Membrane Remodeling

“…The binding of ␣-Syn to membranes might induce the permeabilization of lipid bilayers via pore or conductive ion channel formation (22)(23)(24)(25). Alternatively, ␣-Syn has been suggested to induce membrane remodeling events, such as the nascent budding and tubulation of vesicles (26 -28).…”