Parkinson Disease-Associated Protein α-Synuclein Blocks VDAC Providing New Insights into Mitochondrial Toxicity

Abstract

Dysfunction of mitochondrial enzyme complexes, production of reactive oxygen species, mitochondrial outer membrane (MOM) permeabilization, enhanced apoptosis, and structural alterations of mitochondria are believed to be crucial for the onset and progression of Parkinson's disease (PD). Direct participation of small, intrinsically disordered neuronal protein α-synuclein (α-syn) in the pathogenesis of PD has been well documented. However, the mechanisms of α-syn toxicity remain elusive. Here, we studied interaction of α-syn with the major channel of MOM, voltage-dependent anion channel (VDAC), reconstituted into planar lipid membranes. We found that at nanomolar concentrations α-syn reversibly blocks VDAC in a voltage-dependent manner. Negative potentials applied from the side of α-syn addition promote the reaction, thus implicating its acidic C-terminus in the channel blockage. α-syn induces two well-defined blocked states: the first state is ∼ 60% and the second, deeper blocked state is ∼ 17% of the open state conductance. The probability of the second blocked state dramatically increases with the voltage. We found that selectivity of the α-syn-blocked states is less anionic than that of the open state. Kinetic analysis of α-syn-induced blockage events showed that the on-rate strongly increases with the applied voltage. The blocked time distributions are described by single exponents for both blocked states, with their average values displaying biphasic voltage dependence thus suggesting that α-syn is able to translocate through VDAC. This could explain the previously reported interaction of α-syn with mitochondrial complex-I. Even more importantly, because VDAC is a major conduit for the fluxes of ATP, ADP, and other respiratory substrates across MOM, we hypothesize that this newly demonstrated regulation of VDAC by α-syn blockage could constitute a new mechanism of mitochondrial involvement in PD pathology and perhaps also in general neurodegenerative pathogenesis.