Nonaggregated α-Synuclein Influences SNARE-Dependent Vesicle Docking via Membrane Binding

Abstract

α-Synuclein (α-Syn), a major component of Lewy body that is considered as the hallmark of Parkinson’s disease (PD), has been implicated in neuroexocytosis. Overexpression of α-Syn decreases the neurotransmitter release. However, the mechanism by which α-Syn buildup inhibits the neurotransmitter release is still unclear. Here, we investigated the effect of nonaggregated α-Syn on SNARE-dependent liposome fusion using fluorescence methods. In ensemble in vitro assays, α-Syn reduces lipid mixing mediated by SNAREs. Furthermore, with the more advanced single-vesicle assay that can distinguish vesicle docking from fusion, we found that α-Syn specifically inhibits vesicle docking, without interfering with the fusion. The inhibition in vesicle docking requires α-Syn binding to acidic lipid containing membranes. Thus, these results imply the existence of at least two mechanisms of inhibition of SNARE-dependent membrane fusion: at high concentrations, nonaggregated α-Syn inhibits docking by binding acidic lipids but not v-SNARE; on the other hand, at much lower concentrations, large α-Syn oligomers inhibit via a mechanism that requires v-SNARE interaction [23431141Proc. Natl. Acad. Sci. U. S. A.201311040874092].

β-Amyloid and α-Synuclein Cooperate To Block SNARE-Dependent Vesicle Fusion

“…37 In this work, the authors used a high concentration of αS monomer; this concentration was greater than a few µM and is much higher than the concentration we tested (Supplementary Figure 4). At such a high concentration, the αS monomer can inhibit fusion by lipid-αS interactions rather than by direct SNARE-αS interactions.…”

α-Synuclein – Regulator of Exocytosis, Endocytosis, or Both?

“…What can we learn from in vitro experiments studying the effect of a-synuclein on vesicle fusion? In assays reconstituting fluorescently labeled lipid vesicles with syntaxin and SNAP-25 in one case, and with VAMP2 in the other, a-synuclein was clearly shown to inhibit vesicle fusion in a concentration-dependent manner [18][19][20]. However, two of these studies argue that no direct binding of a-synuclein to the SNARE complex is needed for this inhibition[ 4 5 3 _ T D $ D I F F ] , and that inhibition is merely due to the lipid interaction of a-synuclein [19,21].…”

Cell Biology and Pathophysiology of α-Synuclein

“…6) (Diao et al 2013), suggesting that α-synuclein provides a buffer of synaptic vesicles without affecting neurotransmitter release itself. In vitro, α-synuclein specifically inhibits vesicle docking without interfering with the fusion process (Lai et al 2014). Overexpression causes accumulation of docked vesicles at synapses and smaller readily releasable pools (RRPs) (Larsen et al 2006).…”