SNAP-25 protein

It is now well established that in vivo efficient membrane fusion requires the interaction of small cytoplasmically exposed membrane proteins called soluble N-ethylmaleimide sensitive factor (NSF) attachment receptors (SNAREs) (Sollner et al., 1993). For synaptic vesicle exocytosis, the relevant SNAREs are synaptobrevin/ vesicle-associated membrane protein (VAMP) 1 and 2, syntaxin 1, and synaptosome-associ-ated protein of 25,000 daltons (SNAP-25). Synaptobrevins/ VAMPs are localized primarily on synaptic vesicles, while syntaxin and SNAP-25 are localized primarily on the plasma membrane. Fusion is driven by the progressive zippering of vesicle and plasma membrane SNAREs forming a four-helix bundle (Sutton et al., 1998). Although many other proteins appear to play critical roles in synaptic vesicle exocytosis, it seems likely that SNAREs are the minimal machinery required for fusion (Weber et al., 1998). Once assembled, SNARE complexes are disassembled by NSF, which functions in conjunction with SNAP proteins. 

NSF in conjunction with a-SNAP protein binds to the SNARE complexes. The NSE-catalyzed hydrolysis of ATP then drives dissociation of the SNARE complexes, freeing the SNARE proteins for another round of vesicle fusion. [See J. E. Rothman and T. SOIIner, 1997, Sc/ence 276 1212, and W. Weis and R. Scheller,... 

Fusion of synaptic vesicles with the plasma membrane of axon terminals depends on the same proteins that mediate membrane fusion of other regulated secretory vesicles. The principal v-SNARE in synaptic vesicles (VAMP) tighdy binds syntaxin and SNAP-25, the principal t-SNAREs In the plasma membrane of axon terminals, to form four-helix SNARE complexes. After fusion, SNAP proteins and NSF... 

When an action potential approaches the axon terminal, voltage-gated Ca2+ channels (N-type) open and Ca2+ enters the presynapse. Ca2+ ions bind to proteins that connect the synaptic vesicle with the plasma membrane (acronym SNAP), inducing membrane fusion and consequently exocytosis of the neurotransmitter into the synaptic cleft. Botulinum b toxin contains a specific protease which interferes with synaptobrevin (a vesisle protein which interacts with the SNAP proteins) so that vesicles cannot fuse any longer. The inhibition of acetylcholine release can thus cause paralysis and death. 

In viw PAI and antithrombin are stabilized in their active forms by binding to vitronectin and heparin, respectively. These two serpins seem to have evolved what Max Perutz has called "a spring-loaded safety catch" mechanism that makes them revert to their latent, stable, inactive form unless the catch is kept in a loaded position by another molecule. Only when the safety catch is in the loaded position is the flexible loop of these serpins exposed and ready for action otherwise it snaps back and is buried inside the protein. This remarkable biological control mechanism is achieved by the flexibility that is inherent in protein structures. 

SNAPs is an acronym for soluble NSF attachment proteins. They were originally discovered as cofactors for NSF that mediate the membrane binding of NSF in in vitro transport assays. Several isoforms of SNAPs exist in mammalian cells. SNAPs are also highly conserved proteins. Crystallographic studies indicated that the proteins form a very stiff and twisted sheet that is formed by a series of antiparallel and tightly packed helices connected by short loops. 

Step 6 The general fusion machinery then assembles on the paired SNARE complex it includes an ATPase (NSF NEM-sensitive factor) and the SNAP (soluble NSF attachment factor) proteins. SNAPs bind to the SNARE (SNAP receptor) complex, enabling NSF to bind. 

Much evidence supports a role for these proteins in exocytosis. For instance, injection of recombinant SNAP into the squid giant axon increases vesicular exocytosis. Also, membrane SNAP-25 and syntaxin are both targets for botulinum toxin while the vesicule protein, synaptobrevin, is a target for tetanus and botulinum toxins both these toxins are well known for disrupting transmitter release. 

Maurel, D., Comps-Agrar, L., Brock, C., Rives, M. L., Bourrier, E., Ayoub, M. A., Bazin, H., Tinel, N., Durroux, T. Prezeau, L. et al. (2008). Cell-surface protein-protein interaction analysis with time-resolved FRET and snap-tag technologies Application to GPCR oligomerization. Nat. Methods J, 561-7. 

SNAP-25 Syntaxins Paimitoylated peripheral membrane protein that is cleaved by botulinum toxins A and E and binds to syntaxins. Ubiquitous membrane proteins that are cleaved by botulinum toxin Cl and bind to synaptotagmins, SNAP-25,... 

Some intracellular signal transduction molecules are reduced in schizophrenia. The release of neurotransmitters is regulated by a family of proteins that coordinate vesicular trafficking (see Ch. 9). Of these, the expression of complexin I and II appears to be decreased in prefrontal cortex and subfields of the hippocampal formation, and the ratio of complexin I to complexin II is elevated in the hippocampus [35], SNAP-25 (Synaptosomal Associated Protein, kDa 25) has inconsistently been found to be down-regulated in both these regions. Synapsin expression is also reduced, but more robust decrements have been observed in bipolar disorder (Ch. 55). 

The sample materials from which proteins for proteomics studies may be extracted include fresh or snap-frozen cells from varied sources such as biological fluids, (serum, urine, plasma) and solid tissues such as biopsy specimens. Moreover, proteins isolated from ethanol-fixed paraffin-embedded tissues can be utilized for MS analysis.2 Protocols for the identification of proteins from formalin-fixed paraffin-embedded (FFPE) tissues have been recently developed.3 4 FFPE materials are the most common forms of biopsy archives utilized worldwide, and represent an important advancement for the large-scale interrogation of proteins in archival patient-derived materials. Finally, laser capture microdissected tissues have been successfully used for MS analysis.45... 

All botulin neurotoxins act in a similar way. They only differ in the amino-acid sequence of some protein parts (Prabakaran et al., 2001). Botulism symptoms are provoked both by oral ingestion and parenteral injection. Botulin toxin is not inactivated by enzymes present in the gastrointestinal tracts. Foodborne BoNT penetrates the intestinal barrier, presumably due to transcytosis. It is then transported to neuromuscular junctions within the bloodstream and blocks the secretion of the neurotransmitter acetylcholine. This results in muscle limpness and palsy caused by selective hydrolysis of soluble A-ethylmalemide-sensitive factor activating (SNARE) proteins which participate in fusion of synaptic vesicles with presynaptic plasma membrane. SNARE proteins include vesicle-associated membrane protein (VAMP), synaptobrevin, syntaxin, and synaptosomal associated protein of 25 kDa (SNAP-25). Their degradation is responsible for neuromuscular palsy due to blocks in acetylcholine transmission from synaptic terminals. In humans, palsy caused by BoNT/A lasts four to six months. 

The decisive element in exocytosis is the interaction between proteins known as SNAREs that are located on the vesicular membrane (v-SNAREs) and on the plasma membrane (t-SNAREs). In the resting state (1), the v-SNARE synaptobrevin is blocked by the vesicular protein synaptotagmin. When an action potential reaches the presynaptic membrane, voltage-gated Ca "" channels open (see p. 348). Ca "" flows in and triggers the machinery by conformational changes in proteins. Contact takes place between synaptobrevin and the t-SNARE synaptotaxin (2). Additional proteins known as SNAPs bind to the SNARE complex and allow fusion between the vesicle and the plasma membrane (3). The process is supported by the hydrolysis of GTP by the auxiliary protein Rab. 

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