Conformational change of Syntaxin-3b in regulating SNARE complex assembly in the ribbon synapses

Area of Science:

• Neuroscience
• Molecular Biology
• Cell Biology

Background:

• Neurotransmitter release is crucial for synaptic vesicle fusion, mediated by the soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) complex.
• The precise molecular mechanisms regulating SNARE complex assembly and function remain incompletely understood.

Purpose of the Study:

• To investigate the conformational dynamics of the syntaxin-3b isoform in retinal ribbon synapses.
• To elucidate how syntaxin-3b conformation influences SNARE complex formation and neurotransmitter release.

Main Methods:

• Utilized single-molecule fluorescence resonance energy transfer (smFRET) to monitor syntaxin-3b conformational changes.
• Analyzed the impact of a phosphomimetic mutation (T14E) and Munc18-1 binding on syntaxin-3b conformation and SNARE complex assembly.

Main Results:

• Syntaxin-3b predominantly exists in a self-inhibiting closed conformation, limiting ternary SNARE complex formation.
• A T14E mutation induced an open conformation, enhancing SNARE complex assembly.
• Munc18-1 binding largely inhibited SNARE complex formation, but the T14E mutation partially relieved this inhibition.

Conclusions:

• Syntaxin-3b conformational state is a key regulator of SNARE complex assembly.
• Phosphorylation-induced conformational changes in syntaxin-3b act as a switch to initiate neurotransmitter release.
• This study proposes a model for syntaxin-3b-mediated regulation of neurotransmission in retinal ribbon synapses.