T. Dresbach et al., A NEURONAL SEC1 HOMOLOG REGULATES NEUROTRANSMITTER RELEASE AT THE SQUID GIANT SYNAPSE, The Journal of neuroscience, 18(8), 1998, pp. 2923-2932
Sec1-related proteins are essential for membrane fusion at distinct st
ages of the constitutive and regulated secretory pathways in eukaryoti
c cells, Studies of neuronal isoforms of the Sec1 protein family have
yielded evidence for both positive and negative regulatory functions o
f these proteins in neurotransmitter release, Here, we have identified
a squid neuronal homolog (s-Sec1) of Sec1 proteins and examined its f
unction in neurotransmitter release at the squid giant synapse, Microi
njection of s-Sec1 into the presynaptic terminal of the giant synapse
inhibited evoked neurotransmitter release, but this effect was prevent
ed by coinjecting the cytoplasmic domain of squid syntaxin (s-syntaxin
), one of the binding partners of s-Sec1, A 24 amino acid peptide frag
ment of s-Sec1, which inhibited the binding of s-Sec1 to s-syntaxin in
vitro, completely blocked release, suggesting an essential function o
f the s-Sec1/s-syntaxin interaction in transmitter release. Electron m
icroscopy showed that injection of s-Sec1 did not change the spatial d
istribution of synaptic vesicles at presynaptic release sites (''activ
e zones''), whereas the inhibitory peptide increased the number of doc
ked vesicles, These distinct morphological effects lead us to conclude
that Sec1 proteins function at different stages of synaptic vesicle e
xocytosis, and that an interaction of s-Sec1 with syntaxin-at a stage
blocked by the peptide-is necessary for docked vesicles to fuse.