The primed SNARE-complexin-synaptotagmin complex for neuronal exocytosis

Area of Science:

• Neuroscience
• Molecular Biology
• Structural Biology

Background:

• Evoked synchronous neurotransmitter release relies on synaptotagmin, complexin, and SNARE proteins.
• The precise molecular mechanisms of their cooperation remain largely unknown.

Purpose of the Study:

• To elucidate the structural basis of the interaction between synaptotagmin-1, complexin, and SNARE proteins in the pre-fusion state.
• To understand how these interactions regulate synchronized neurotransmitter release.

Main Methods:

• Crystal structure determination of the primed pre-fusion SNARE-complexin-synaptotagmin-1 complex.
• Biochemical assays and mutagenesis to assess the functional importance of identified interfaces.

Main Results:

• Revealed a novel tripartite interface between synaptotagmin-1 and the SNARE-complexin bundle, in addition to a primary interface.
• Demonstrated that disrupting either interface significantly impairs evoked synchronous release in neurons.
• Showed that Ca2+ binding to synaptotagmin-1 unlocks the complex, enabling SNARE zippering and membrane fusion.

Conclusions:

• Both identified synaptotagmin-1 interfaces are critical for the primed pre-fusion state and synchronized neurotransmitter release.
• The tripartite complex must be unlocked by Ca2+ for membrane fusion to initiate, explaining the roles of complexin and synaptotagmin-1 in timing release.