The synaptophysin-synaptobrevin complex: a hallmark of synaptic vesicle maturation

Area of Science:

• Neuroscience
• Molecular Biology
• Cell Biology

Background:

• Exocytosis relies on a fusion complex including synaptobrevin (VAMP), syntaxin, and SNAP-25.
• Synaptobrevin also binds to synaptophysin, preventing its entry into the fusion complex.
• Understanding regulation of fusion complex assembly is key to neuronal function.

Purpose of the Study:

• Investigate mechanisms regulating synaptobrevin's role in the fusion complex.
• Determine the developmental regulation of the synaptophysin-synaptobrevin complex.
• Clarify the functional significance of the synaptophysin-synaptobrevin interaction in exocytosis.

Main Methods:

• Immunoprecipitation and cross-linking experiments.
• In vitro interaction assays with recombinant proteins and brain extracts.
• Analysis of protein fractions from embryonic and adult rat synaptosomes.

Main Results:

• The synaptophysin-synaptobrevin complex is undetectable in embryonic rat brain but increases during development.
• Synaptobrevin's fusion complex participation is detectable by embryonic day 14.
• Adult synaptosomes contain a cytosolic factor that promotes synaptophysin-synaptobrevin complex formation, absent in embryonic ones.
• Recombinant synaptobrevin binds adult, but not embryonic, synaptophysin.

Conclusions:

• Synaptophysin-synaptobrevin complex formation is developmentally regulated, likely via post-translational modification of synaptophysin.
• This complex serves as a reserve pool of synaptobrevin for exocytosis.
• The synaptophysin-synaptobrevin complex is not essential for basal exocytosis but facilitates recruitment during high synaptic activity.