Munc18-1-regulated stage-wise SNARE assembly underlying synaptic exocytosis

Area of Science:

• Neuroscience
• Molecular Biology
• Biophysics

Background:

• Synaptic-soluble N-ethylmaleimide-sensitive factor attachment receptor (SNARE) proteins mediate neurotransmitter release via exocytosis.
• The precise roles of different SNARE assembly stages and the Munc18-1 protein's function in this process remain unclear.

Purpose of the Study:

• To elucidate the distinct functions of SNARE protein domains during assembly and exocytosis.
• To understand the mechanism by which Munc18-1 regulates SNARE complex formation and function.

Main Methods:

• Utilized optical tweezers to observe and analyze the four distinct assembly stages of SNARE proteins (N-terminal, middle, C-terminal, and linker domains).
• Investigated the impact of specific SNARE domain mutations on both SNARE assembly kinetics and exocytosis efficiency.

Main Results:

• Identified specific roles for SNARE domains: N-terminal domain (NTD) in vesicle docking, C-terminal domain (CTD) in fusion, and middle domain (MD) in regulating assembly and fusion.
• Demonstrated that Munc18-1 initiates SNARE assembly, structures the t-SNARE C-terminus independently of the syntaxin N-terminal regulatory domain (NRD), and stabilizes the half-zippered complex in an NRD-dependent manner.

Conclusions:

• SNARE domains possess distinct functional roles in the exocytosis pathway.
• Munc18-1 acts as a crucial molecular chaperone, orchestrating SNARE assembly through specific interactions with different domains to ensure efficient neurotransmitter release.