α-Synuclein kinetically regulates the nascent fusion pore dynamics

alpha-Synuclein (alpha-syn(FL)) is central to the pathogenesis of Parkinson's disease (PD), in which its nonfunctional oligomers accumulate and result in abnormal neurotransmission. The normal physiological function of this intrinsically disordered protein is still unclear. Although several previous studies demonstrated alpha-syn(FL)'s role in various membrane fusion steps, they produced conflicting outcomes regarding vesicular secretion. Here, we assess alpha-syn(FL)'s role in directly regulating individual exocytotic release events. We studied the micromillisecond dynamics of single recombinant fusion pores, the crucial kinetic intermediate of membrane fusion that tightly regulates the vesicular secretion in different cell types. alpha-Syn(FL) accessed v-SNARE within the trans-SNARE complex to form an inhibitory complex. This activity was dependent on negatively charged phospholipids and resulted in decreased open probability of individual pores. The number of trans-SNARE complexes influenced alpha-syn(FL)'s inhibitory action. Regulatory factors that arrest SNARE complexes in different assembly states differentially modulate alpha-syn(FL)'s ability to alter fusion pore dynamics. alpha-syn(FL) regulates pore properties in the presence of Munc13-1 and Munc18, which stimulate alpha-SNAP/NSF-resistant SNARE complex formation. In the presence of synaptotagmin1(syt1), alpha-syn(FL) contributes with apo-syt1 to act as a membrane fusion clamp, whereas Ca2+center dot syt1 triggered alpha-syn(FL)-resistant SNARE complex formation that rendered alpha-syn(FL) inactive in modulating pore properties. This study reveals a key role of alpha-syn(FL) in controlling vesicular secretion.

Automated summary

Alpha-synuclein plays a crucial role in the pathogenesis of Parkinson's disease by directly regulating individual exocytotic release events, controlling vesicular secretion. It forms an inhibitory complex to decrease the open probability of fusion pores, influenced by various factors. This study reveals the key role of alpha-synuclein in modulating pore properties and highlights its regulatory action in membrane fusion.