α-Synuclein kinetically regulates the nascent fusion pore dynamics

Area of Science:

• Neuroscience
• Cell Biology
• Biochemistry

Background:

• Alpha-synuclein (α-synFL) is implicated in Parkinson's disease pathogenesis, but its normal physiological function remains elusive.
• Previous studies on α-synFL's role in membrane fusion and vesicular secretion yielded conflicting results.
• Understanding α-synFL's precise function in regulating exocytosis is crucial for deciphering its role in neuronal function and disease.

Purpose of the Study:

• To investigate the direct role of α-synFL in regulating individual exocytotic release events.
• To elucidate the mechanism by which α-synFL modulates the dynamics of fusion pores, a key intermediate in membrane fusion.
• To determine how regulatory factors and phospholipids influence α-synFL's activity in controlling vesicular secretion.

Main Methods:

• Studied the micromillisecond dynamics of single recombinant fusion pores using advanced biophysical techniques.
• Assessed the interaction of α-synFL with v-SNARE within the trans-SNARE complex.
• Investigated the influence of negatively charged phospholipids, Munc13-1, Munc18, and synaptotagmin1 (syt1) on α-synFL's activity.

Main Results:

• α-Synuclein (α-synFL) forms an inhibitory complex with v-SNARE within the trans-SNARE complex, dependent on negatively charged phospholipids.
• α-SynFL binding decreased the open probability of individual fusion pores, thereby regulating vesicular secretion.
• α-SynFL's inhibitory action was modulated by the number of trans-SNARE complexes and regulatory factors like Munc13-1, Munc18, and synaptotagmin1.

Conclusions:

• α-Synuclein (α-synFL) directly regulates vesicular secretion by modulating fusion pore dynamics.
• The protein acts as a membrane fusion clamp in conjunction with apo-syt1, but its activity is inhibited by Ca2+•syt1.
• This study reveals a critical role for α-synFL in controlling the kinetics of exocytotic release, offering new insights into Parkinson's disease.