Conformational switch of syntaxin-1 controls synaptic vesicle fusion

Area of Science:

• Neuroscience
• Molecular Biology
• Cell Biology

Background:

• Soluble N-ethylmaleimide-sensitive factor-attachment protein receptor (SNARE) proteins, like syntaxin-1, are crucial for synaptic vesicle fusion.
• Syntaxin-1 exists in two conformations: a closed form and an open form, both interacting with Munc18-1.
• While the open conformation is vital for exocytosis, the role of the closed conformation remains unclear.

Purpose of the Study:

• To investigate the function of the closed conformation of syntaxin-1 in synaptic vesicle fusion.
• To determine the in vivo consequences of exclusively expressing the open conformation of syntaxin-1.

Main Methods:

• Generation of knockin/knockout mice expressing only the open conformation of syntaxin-1B.
• Analysis of Munc18-1 binding to syntaxin-1 in these modified synapses.
• Assessment of synaptic vesicle pool size and fusion rates.

Main Results:

• Mice expressing only open syntaxin-1B were viable but developed generalized seizures.
• Impaired binding of Munc18-1 to syntaxin-1 was observed in these mice.
• A decreased readily releasable vesicle pool and a dramatically enhanced rate of synaptic vesicle fusion were noted.

Conclusions:

• The closed conformation of syntaxin-1 acts as a gatekeeper for initiating synaptic vesicle fusion.
• SNARE-complex/Munc18-1 assemblies mediate the fusion process once initiated.
• Syntaxin-1's conformational states are critical for regulating neurotransmission.