Trans-SNARE complexes

Fig. 2 The conformational cycle of SNAREs. SNAREs cycle between two extreme conformations, the unstructured monomeric SNAREs and the fully assembled cis-SNARE complexes. Initially, SNAREs on the membranes destined to fuse establish trans-SNARE complexes between the opposed membranes. Proceeding SNARE complex assembly forces the membranes tightly together enforcing membrane fusion. The resulting cis-SNARE complexes are disassembled into free SNAREs by the ATPase NSF and its co-factor, a process that consumes ATP and fuels the SNAREs with energy for undergoing a new SNARE cycle (for details see text).

In eukaryotes, soluble N-ethylmaleimide-sensitive factor (NSF) adaptor proteins (SNAPs) receptors (SNAREs) are known to be required for docking and fusion of intracellular transport vesicles with acceptor/target membranes. The fusion of vesicles in the secretory pathway involves target-SNAREs (t-SNAREs) on the target membrane and vesicle-SNAREs (v-SNAREs) on vesicle membranes that recognize each other and assemble into trans-SNARE complexes (Sollner et al., 1993). 

Tai, G., Lu, L., and Hong, W. (2004). Participation of the syntaxin 5/Ykt6/GS28/GS15 SNARE complex in transport from the early-recycling endosome to the trans-Golgi network. Mol. BioL Cell 15, 4011-4022. 

Free SNAREs are presumably short-lived, as they can form complexes among themselves, including homophilic oligomerization into clusters or with SNARE interacting proteins. It is becoming apparent that initial trans-contact between SNAREs... 

Monomeric SNARE Acceptor complex Trans-complex... 

Stimulus-evoked, calcium-dependent release of ACh from the cholinergic synapse normally occurs through the formation of a fusion complex between ACh-containing vesicles and the intracellular leaflet of the nerve terminal membrane (Amon et al., 2001). This synaptic vesicle (SV) fusion complex consists of several proteins of the SNARE family, including a 25-kDa synaptosomal associated protein (SNAP-25), vesicle-associated membrane protein (VAMP, or synaptobrevin), and the synaptic membrane protein syntaxin. Other SNARE proteins have been identified as components of membrane trans-porf systems in yeast and mammals but have not been implicated as targets for BoNTs. Meanwhile, type A and E neurotoxins cleave SNAP-25, while types B, D, F, and G act on VAMP and type Cl toxin cleaves both syntaxin and SNAP-25. Neurotoxin-mediated cleavage of any of these substrates disrupts the processes involved in the exocytotic release of ACh and leads to flaccid paralysis of the affected skeletal muscles. 

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