Regulation of SNARE‐Dependent Membrane Fusion by Alpha‐Synuclein

Abstract

Neurotransmitter release is a foundation of all thoughts in central nervous system. Communication between these neurons is mediated by the release and uptake of neurotransmitters through vesicle fusion at the synapses. The SNARE (Soluble N-ethylmaleimide-sensitive factor Attachment Protein Receptor) proteins are believed to mediate neurotransmitter release by promoting fusion of neurotransmitter laden presynaptic vesicle with the presynaptic membrane. Defects in the regulation of neurotransmission are believed to be the primary cause for many neurological diseases. The key to a better understanding of neurological diseases may lie in a more complete understanding of the molecular machine responsible for synaptic vesicle fusion. Alpha-synuclein (αS) has long been a protein of great interest because of its pathological aggregation in neuronal plaque and Lewy bodies which are associated with Parkinson's Disease and Lewy Bodies Dementia, respectively. Despite its medical significance, the normal function of αS has been elusive. αS is a 14 kDa soluble protein, abundantly present (several μM) in the presynapse. Thus, not surprisingly, αS has been found to play roles in various aspects of vesicle recycling. Very interestingly, however, αS has emerged as an important regulator for SNARE-dependent vesicle fusion. We used an in vitro single-vesicle fusion assay which allowed for the precise variation of the αS concentration. This assay provided the opportunity to dissect the impact of αS on individual vesicle fusion steps such as docking and lipid mixing along the membrane fusion pathway. The assay is effective in analyzing single fusion events in a natural, millisecond timescale between vesicle and a supported-bilayer. Using this assay, we have found that αS enhances vesicle docking by a factor of 10 at excessive 20 μM which is as much as 4 times higher than a normal cellular concentration. Detailed analysis reveals that the effect of αS on SNARE-dependent membrane fusion is largely on vesicle docking with no significant changes in lipid mixing observed. It also suggests that αS plays a role in accelerating and stabilizing large fusion pore formation. αS may be pathologically involved in neurological diseases, but it also is a crucial SNARE regulator by enhancing presynaptic vesicle docking and stabilizing the membrane fusion pore. αS may be pathologically involved in neurological diseases, but it also is a crucial SNARE regulator This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.