Re-examining how complexin inhibits neurotransmitter release

Area of Science:

• Neuroscience
• Molecular Biology
• Cell Biology

Background:

• Complexins are key regulators of neurotransmitter release, exhibiting both activating and inhibitory roles.
• The complexin accessory helix was previously hypothesized to inhibit release by inserting into SNARE complexes, hindering their assembly.

Purpose of the Study:

• To investigate the mechanism by which the complexin accessory helix inhibits neurotransmitter release.
• To challenge the existing model of accessory helix insertion into SNARE complexes.

Main Methods:

• Nuclear Magnetic Resonance (NMR) spectroscopy to study protein-protein interactions in solution.
• Electrophysiological recordings to assess the functional impact of complexin mutations on neurotransmitter release.
• Analysis of complexin mutants with altered charge properties in the accessory helix.

Main Results:

• NMR data indicate the complexin-I accessory helix does not insert into SNARE complexes in solution.
• 'Superclamp' mutants showed minimal stimulatory or no effect on neurotransmitter release, contrary to previous findings.
• A 'poor-clamp' mutant demonstrated inhibitory effects on neurotransmitter release.
• Modulating the negative charge of the accessory helix directly impacted release, with increased negative charge inhibiting and decreased charge stimulating release.

Conclusions:

• The complexin accessory helix inhibits neurotransmitter release through electrostatic repulsion, not direct insertion into SNARE complexes.
• The accessory helix's location between vesicle and plasma membranes facilitates this inhibitory mechanism.
• This study proposes a revised model for complexin-mediated regulation of synaptic transmission.