Alpha-Synuclein Blocks VDAC Suggesting Mechanism of Mitochondrial Regulation and Toxicity in Parkinson Disease

Abstract

Alpha-synuclein (α-syn), an intrinsically disordered neuronal protein, is implicated in the etiology of Parkinson disease (PD) and a number of other neurodegenerative dementias. Though recent research demonstrates the involvement of α-syn in a variety of mitochondrial dysfunction in neurodegeneration, the molecular mechanism of α-syn toxicity and its effect on neuronal mitochondria remain vague. We demonstrate a functional interaction between α-syn and the voltage-dependent anion channel (VDAC), the major conduit for ATP and other bioenergetics metabolites in the mitochondrial outer membrane. We found that at nanomolar concentrations, the full-length α-syn, its 45 amino acid C-terminal truncated mutant, as well as β- and α-synuclein isoforms induce reversible and highly voltage-dependent blockage of VDAC reconstituted into planar lipid bilayers. Binding parameters varied with each isoform, revealing the key role of the negatively charged C-terminal of synucleins in blocking a positively charged pore of VDAC. Synuclein-blocked states of VDAC differ in ionic selectivity, implying the existence of several conformation states of synuclein molecules in the channel pore. We propose a model of α-syn interaction with VDAC, in which the negatively charged C-terminus of α-syn enters the net-positive channel pore, providing a steric block for ATP flux. Experiments with a yeast strain deficient in VDAC1 demonstrate that α-syn toxicity in yeast depends on VDAC, revealing α-syn interaction with the channel in living cells. Thus, our findings show the long-sought physiological and pathophysiological roles for monomeric α-syn, which reconcile previous observations of various synuclein effects on mitochondrial bioenergetics.