A conformational switch in complexin is required for synaptotagmin to trigger synaptic fusion

Area of Science:

• Molecular Biology
• Neuroscience
• Biochemistry

Background:

• Complexin regulates membrane fusion during neurotransmitter release.
• The accessory helix of complexin undergoes conformational changes.
• SNARE proteins mediate membrane fusion.

Purpose of the Study:

• To investigate the role of complexin's conformational switch in calcium-triggered exocytosis.
• To elucidate the mechanism by which synaptotagmin-Ca(2+) triggers fusion.
• To understand the regulation of SNARE complex assembly by complexin.

Main Methods:

• Targeted mutagenesis of complexin and SNARE proteins.
• Förster resonance energy transfer (FRET) spectroscopy to monitor conformational changes.
• Functional assays reconstituting calcium-triggered exocytosis.

Main Results:

• Complexin's switch from an 'open' to a 'closed' conformation is essential for synaptotagmin-Ca(2+) to trigger fusion.
• Fusion requires specific aspartate residues in the v-SNARE switch region to zipper.
• Complexin's accessory helix release facilitates v-SNARE zippering and fusion pore opening.

Conclusions:

• Complexin's conformational switching is a critical regulatory step in clamp release during exocytosis.
• The transition from open to closed conformation in complexin is triggered by accessory helix release.
• This mechanism allows for the precise timing of membrane fusion events in neurotransmission.