Cooperative Inhibition Of Snare-Mediated Vesicle Fusion By Alphasynuclein Monomer And Oligomer

With the discoveries of genetic and neuropathological links between alpha-synuclein (α-Syn) and Parkinson's disease (PD), α-Syn has irrefutably tied to neurodegenerative diseases such as PD and Dementia with Lewy bodies. Because of the increasing evidence of fundamental roles of α-Syn oligomers in disease progression, the oligomeric forms of α-Syn have been potential target for therapeutic interventions for PD. Among a variety of strategies to attenuate the toxicity of α-Syn oligomer, we have focused on its nearest competitor, α-Syn monomer, for lipid membrane and SNARE protein binding. Recent studies show that α-Syn monomer and oligomer exert totally opposite effects on SNARE complex formation via same binding mode. However, it is unknown whether α-Syn monomer and oligomer compete or cooperate with each other. To address this issue, using in vitro bulk lipid mixing assay, we show that monomeric α-Syn synergistically inhibits neuronal SNARE-mediated membrane fusion with oligomeric form of α-Syn at nanomolar concentration when the former binds both anionic lipid membranes and synaptobrevin-2. We find that this cooperative effect is resulted from synaptobrevin-2 carrying vesicle clustering as revealed by cryo-transmission electron-microscopy and fluorescence correlation spectroscopy.