Dynamic formation of the protein-lipid prefusion complex

Area of Science:

• Neuroscience
• Biophysics
• Molecular Biology

Background:

• Synaptic vesicles (SVs) release neurotransmitters via fusion with the presynaptic membrane (PM).
• Synaptotagmin 1 (Syt1) acts as a Ca²⁺ sensor, initiating fusion by potentially inserting into the PM.
• The SNARE complex mediates SV-PM attachment, with complexin (Cpx) enhancing Ca²⁺-dependent fusion.

Purpose of the Study:

• To investigate the molecular mechanism of Syt1-mediated synaptic vesicle fusion using all-atom molecular dynamics.
• To elucidate the role of Syt1, SNARE complex, and Cpx interactions in triggering membrane fusion.
• To model the conformational transitions leading to the prefusion state of the protein-lipid complex.

Main Methods:

• All-atom molecular dynamics simulations.
• Investigating the interactions between Syt1, SNARE complex, Cpx, and lipid bilayers (PM and SVs).
• Analyzing conformational changes and complex formation.

Main Results:

• The PM-Syt1-SNARE-Cpx complex can form a non-fusogenic "dead-end" state where Syt1 binds the PM without insertion.
• Simulations revealed a sequence of conformational transitions leading to a prefusion state, with Syt1 C2 domains penetrating the PM.
• Direct interactions between Syt1 and Cpx were identified as essential for promoting the prefusion state transitions.

Conclusions:

• A detailed all-atom dynamic model for the formation of the prefusion PM-Syt1-SNARE-Cpx complex was developed.
• Direct Syt1-Cpx interactions are critical for Syt1 to transition into the presynaptic membrane, facilitating synaptic vesicle fusion.
• Disruption of the Syt1-Cpx interaction pathway can lead to non-fusogenic dead-end states.