v-SNARE actions during Ca(2+)-triggered exocytosis.

Area of Science:

• Cell Biology
• Biophysics
• Neuroscience

Background:

• Soluble NSF Attachment Protein REceptor (SNARE) proteins mediate membrane fusion during exocytosis.
• The precise role of SNAREs in driving the force for secretory vesicle fusion upon calcium increase remains unclear.

Purpose of the Study:

• To investigate the role of the molecular distance between the SNARE motif and transmembrane anchor of synaptobrevin II in chromaffin granule exocytosis.
• To determine if SNAREs provide the molecular force for calcium-triggered vesicle fusion.

Main Methods:

• Genetic modification of synaptobrevin II by inserting flexible linkers of varying lengths.
• Analysis of chromaffin granule priming, exocytosis initiation kinetics, and fusion pore dynamics using stepwise calcium elevation.
• Time-resolved measurements of fusion events at millisecond scale.

Main Results:

• Extending the linker region of synaptobrevin II impaired granule priming and delayed exocytosis initiation.
• Increased linker length attenuated fusion pore fluctuations and slowed pore expansion in a dose-dependent manner.
• These findings indicate a critical role for short SNARE protein distances in driving calcium-triggered membrane fusion.

Conclusions:

• Vesicular SNARE proteins provide the molecular force for calcium-triggered membrane fusion during exocytosis.
• A continuous molecular pulling mechanism by SNAREs guides vesicles through fusion stages at millisecond timescales.