v-SNARE transmembrane domains function as catalysts for vesicle fusion

Area of Science:

• Cell biology
• Biophysics
• Neuroscience

Background:

• Vesicle fusion relies on SNARE protein complexes.
• The precise roles of SNARE transmembrane domains (TMDs) in fusion are not fully understood.
• SNARE TMDs are often considered passive anchors, but their active contribution is debated.

Purpose of the Study:

• To investigate the mechanistic role of the synaptobrevin-2 TMD in membrane fusion.
• To determine if TMD conformational flexibility influences exocytosis and fusion pore dynamics.
• To elucidate how TMD structure impacts the kinetics of vesicle fusion.

Main Methods:

• Site-directed mutagenesis of the synaptobrevin-2 TMD to alter its helix-stabilizing or destabilizing properties.
• Analysis of Ca(2+)-triggered exocytosis in response to TMD mutations.
• Measurement of fusion pore expansion rates using electrophysiological techniques.

Main Results:

• Introducing helix-stabilizing leucine residues in the synaptobrevin-2 TMD significantly impaired exocytosis and slowed fusion pore dilation.
• Increasing helix-destabilizing valine or isoleucine residues restored normal secretion and accelerated fusion pore expansion.
• These findings indicate that the synaptobrevin-2 TMD actively influences fusion kinetics.

Conclusions:

• The conformational flexibility of the synaptobrevin-2 TMD is essential for efficient Ca(2+)-triggered exocytosis.
• The synaptobrevin-2 TMD actively promotes membrane fusion and regulates fusion pore expansion.
• TMD structural flexibility acts as a catalyst, controlling the rate of fusion pore expansion during vesicle fusion.