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A Proteoliposome-Based Efflux Assay to Determine Single-molecule Properties of Cl- Channels and Transporters
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Molecular determinants of complexin clamping and activation function.

Manindra Bera1,2, Sathish Ramakrishnan1,3, Jeff Coleman1,2

  • 1Yale Nanobiology Institute, New Haven, United States.

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Complexin and Synaptotagmin-1 regulate vesicle fusion. Complexin

Keywords:
E. colicalcium regulationcomplexinmembrane fusionmolecular biophysicsneurosciencestructural biologysynaptic vesiclesynaptotagmin

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Area of Science:

  • Neuroscience
  • Molecular Biology
  • Biochemistry

Background:

  • Synaptotagmin-1 and Complexin (a protein) work together to control vesicle fusion.
  • This process is crucial for rapid and synchronized release of neurotransmitters upon calcium ion (Ca2+) influx.
  • Previous research established their synergistic clamping role in maintaining a readily releasable pool of vesicles.

Purpose of the Study:

  • To elucidate the molecular mechanisms underlying Complexin's fusion clamp.
  • To investigate Complexin's specific role in calcium-dependent fusion.
  • To determine how Complexin's structure contributes to its inhibitory and activating functions in vesicle fusion.

Main Methods:

  • Utilized an in vitro single-vesicle fusion assay.
  • Performed systematic truncation and mutational analyses of Complexin.
  • Investigated the interaction between Complexin domains and SNARE complexes.

Main Results:

  • Complexin's inhibitory function requires a delay in fusion kinetics, potentially mediated by Synaptotagmin-1.
  • Continuous alpha-helical accessory-central domains of Complexin are essential for its clamping activity.
  • Specific interactions of Complexin's accessory helix with SNAREpins enhance clamping; its C-terminal domain increases local concentration via membrane interaction.
  • Complexin's helical domains also promote rapid, calcium-synchronized release by increasing fusion probability from the clamped state.

Conclusions:

  • Complexin acts as a fusion clamp, requiring Synaptotagmin-1-mediated kinetic delays.
  • Specific structural domains of Complexin mediate its inhibitory and Ca2+-dependent activating roles in vesicle fusion.
  • Complexin's dual function is critical for precise neuronal exocytosis control.