Synaptobrevin is a synaptic vesicle protein that has an essential role in e
xocytosis and forms the SNARE complex with syntaxin and SNAP-25. We have an
alyzed the structure of isolated synaptobrevin and its binary interaction w
ith syntaxin using NMR spectroscopy. Our results demonstrate that isolated
synaptobrevin is largely unfolded in solution. The entire SNARE motif of sy
naptobrevin is capable of interacting with the isolated C-terminal SNARE mo
tif of syntaxin but only a few residues bind to the full-length cytoplasmic
region of syntaxin. This result suggests an interaction between the N- and
C-terminal regions of syntaxin that competes with core complex assembly.