SNARE Complex Antibodies from Cedarlane
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SNARE proteins are a large protein superfamily consisting of more than 60 members in yeast and mammals. The primary role of these proteins is to mediate fusion of vesicles with their target membrane bound compartments (such as a lysosome). The most well studied SNARE proteins are those involved in mediating synaptic vesicle docking at the pre-synaptic membrane of neurons. During this process syntaxin-1, SNAP-25 and munc18-1 associate and form a complex at the pre-synaptic membrane. This complex interacts with synaptobrevin-2 and synaptotagmin-1 located in synaptic vesicles and initiates docking, priming and fusion at the membrane. This fusion event leads to release of the vesicles cargo into the synaptic cleft, where it can ultimately interact with the post-synaptic neuron.
- ♦ Synaptophysin -
Synaptophysin is a 38 KDa synaptic vesicle (SV) glycoprotein containing four transmembrane domains. It is present in SVs of the neuroendocrine system, brain, spinal cord, retina, adrenal medulla and at neuromuscular junctions. Synaptophysin acts as a maker for neuroedocrine tumours and has been used to study the distribution of synapses within the brain due to its ubiquity at these regions.
Although the exact function of synaptophysin is still unknown, several lines of evidence suggest it may have multiple important roles in SV exo and endocytosis. These include regulation of SNARE assembly, fusion pore formation initiating neurotransmitter release and activation of SV endocytosis. Additionally, it is thought that synaptophysin may have an important role in SV biogenesis. Several gene mutations in synaptophysin have been seen in families affected by X-linked intellectual disability, suggesting dysfunction of this protein may play a role in the disease.
- ♦ VAMP/Synaptobrevin -
Synaptobrevins are highly conserved small integral membrane proteins that are part of the vesicle-associated membrane protein (VAMP) family. They are present in abundance on synaptic vesicles and peptidergic secretory granules, as well as on secretory granules of endocrine cells. Synaptobrevins, along with syntaxins and SNAP-25 are all proteins involved in the formation of SNARE complexes.
Alterations in gene expression and mutations of synaptobrevin have been observed in various neuropsychiatric disorders including ADHD, bipolar disorder, schizophrenia and major depressive disorder. In addition synaptobrevin is cleaved and inactivated by the light chain of the tetanus toxin (TeNT), this affects stability of the SNARE core complex inhibiting neurotransmitter exocytosis.
- ♦ SNAP-25 -
Synaptosomal-associated protein 25 (SNAP-25) is a membrane bound protein localized to the cytosolic face of the pre-synaptic membrane. SNAP-25 is one component of the SNARE core complex which also includes Syntaxin-1 and Synaptobrevin 2. Through interactions with these proteins and synaptotagmin, SNAP-25 regulates vesicle docking and fusion and subsequently neurotransmitter release. SNAP-25 exists as two alternatively spliced isoforms, SNAP-25A and SNAP-25B, that are differentially expressed in neurons and neuroendocrine cells respectively.
Recent studies have shown that some mutations in SNAP25 may predispose humans to attention deficit hyperactivity disorder (ADHD). These findings are consistent with the fact that SNAP-25 reduces Ca2+ responsiveness at glutamatergic synapses. Alterations in gene expression levels of SNAP-25 have also been observed in other neuropsychiatric disorders including schizophrenia and epilepsy.
- ♦ Syntaxin -
Syntaxin 1 is a 35 KDa integral membrane protein that possesses a single C-terminal transmembrane domain, a SNARE domain (H3) and an N-terminal regulatory domain (Habc). Two isoforms of syntaxin 1 have been identified, syntaxin 1a and syntaxin1b. Syntaxin 1a localizes to nerve terminals of sensory neurons and nerve fibres reaching small blood vessels. Whereas syntaxin 1b is localized to motor end plates and muscle spindles.
Deficits in syntaxin 1 phosphorylation by CK2 was observed in several cases of schizophrenia. Lower levels of phosphorylation was shown to reduce binding of syntaxin 1 to SNAP-25 and Munc18-1 leading to decreased SNARE complex formation. Also, expression level of syntaxin 1a was seen to correlate with intelligence in individuals with the neurodevelopmental disorder Williams Syndrome.
- ♦ CDCrel-1 -
CDCrel-1/Septin 5 (Sept5) belongs to the septin family of nucleotide binding GTPases. Septins were originally described in yeast as cell division cycle regulatory proteins involved in cytokinesis and the regulation of cytoskeletal organization. Sept5 is expressed in cells of the nervous system and is seen to associate primarily with vesicles and membranes through its interaction with the SNARE domain of syntaxin 1a. Through its interaction with syntaxin 1A Sept5 acts to inhibit exocytosis, possibly by regulating vesicle targeting and/or fusion. Recently it was shown that Sept5 is phosphorylated by cyclin-dependent kinase 5 (Cdk5) – p35 decreasing it’s binding to syntaxin 1a. This suggests that Cdk5 can modulate synaptic vesicle release by regulating the interactions between Sept5 and syntaxin 1a.
- ♦ Synaptotagmin-1 -
Synaptotagmin-1 is a synaptic vesicle membrane protein that belongs to the synaptotagmins family; characterized by an N-terminal transmembrane region (TMR), a variable linker, and two C-terminal C2-domains. Synaptotagmin-1, the first synaptotagmin studied, is an abundant synaptic vesicle protein that binds Ca2+ and phospholipids via both of its C2 domains and is essential for fast Ca2+- triggered neurotransmitter release.
- ♦ Munc18-1 -
Syntaxin-binding protein 1 (STXBP1) or munc18-1 is an abundant neuronal protein that tightly binds to synaptic fusion protein syntaxin and functions in synaptic vesicle docking and fusion. Munc18-1 modulates neurotransmission through its interaction with syntaxin 1 and is thought to help restrict fusion of vesicles to specific sites of the plasma membrane. Deletion of munc18-1 leads to defects in secretory vesicle docking and the absence of neurotransmitter release. Defects in munc18-1 are the cause of epileptic encephalopathy early infantile type 4 (EIEE4). Affected individuals have neonatal or infantile onset of seizures and suppression-bursts.
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