transSNARE

TransSNARE refers to a trans-SNARE complex, a configuration of SNARE proteins that forms between opposing membranes during vesicle docking and fusion. In this trans arrangement, SNARE motifs from a vesicle-associated v-SNARE interact with SNAREs on the target membrane (t-SNAREs), creating a four-helix bundle that brings the two membranes into close apposition and serves as the core driving force for membrane fusion. The trans SNARE complex is typically formed just before fusion and is distinct from the cis SNARE complex that forms on a single membrane after fusion.

A common neuronal example involves the v-SNARE synaptobrevin/VAMP on synaptic vesicles and t-SNAREs syntaxin-1A and SNAP-25 on the plasma membrane. However, trans SNARE complexes participate in many intracellular trafficking steps beyond neurons, including ER-to-Golgi and endosome pathways, with different SNARE isoforms occupying vesicular and target membranes depending on the organelle.

Functionally, the SNAREs “zipper” together from their N- to C-termini, generating the force needed to merge lipid bilayers and form a fusion pore. This process is tightly regulated: calcium sensors such as synaptotagmin-1 respond to Ca2+ to trigger rapid fusion, while auxiliary factors like complexin modulate the timing, and SM proteins (for example, Munc18) assist in proper SNARE complex assembly. After fusion, the SNAREs reside in the same membrane (cis-SNARE complex) and are disassembled by NSF and alpha-SNAP, allowing SNARE recycling for subsequent rounds of fusion.

TransSNARE is a central concept in understanding how membrane fusion is orchestrated across diverse cellular pathways, not limited to neurotransmitter release.