STXBP5

STXBP5
Identifiers
Aliases	STXBP5, Tomosyn, LGL3, LLGL3, Nbla04300, syntaxin binding protein 5
External IDs	OMIM: 604586; MGI: 1926058; HomoloGene: 16402; GeneCards: STXBP5; OMA:STXBP5 - orthologs
Gene location (Human)
Chr.	Chromosome 6 (human)
End	147,390,476 bp
Gene location (Mouse)
Chr.	Chromosome 10 (mouse)
End	9,901,079 bp
RNA expression pattern
	Top expressed in
	Brodmann area 23; ; Achilles tendon; ; cerebellar hemisphere; ; endothelial cell; ; Brodmann area 9; ; sperm; ; right hemisphere of cerebellum; ; superior frontal gyrus; ; primary visual cortex; ; Brodmann area 46;
	Top expressed in
	zygote; ; secondary oocyte; ; granulocyte; ; mammillary body; ; paraventricular nucleus of hypothalamus; ; supraoptic nucleus; ; inferior colliculus; ; neural layer of retina; ; habenula; ; dentate gyrus;
	More reference expression data
	n/a
Gene ontology
Molecular function	GTPase activator activity; syntaxin-1 binding; syntaxin binding; myosin II binding;
Cellular component	integral component of membrane; acetylcholine-gated channel complex; membrane; synaptic vesicle; plasma membrane; synapse; cell junction; cytoplasmic vesicle membrane; cytoplasmic vesicle; cytosol; cytoplasm; neuromuscular junction; Schaffer collateral - CA1 synapse; extrinsic component of presynaptic membrane; presynaptic cytosol; SNARE complex;
Biological process	regulation of exocytosis; protein transport; positive regulation of exocytosis; vesicle-mediated transport; exocytosis; regulation of protein secretion; positive regulation of GTPase activity; synaptic vesicle cycle;
	Sources:Amigo / QuickGO
Orthologs
	134957
	78808
	ENSG00000164506
	ENSMUSG00000019790
	Q5T5C0
	Q8K400
	NM_001127715; NM_139244; NM_001394409
	NM_001081344; NM_030191
	NP_001121187; NP_640337
	NP_001074813; NP_001394992; NP_001394993; NP_001394994
	Wikidata
View/Edit Human	View/Edit Mouse

Syntaxin-binding protein 5 is a protein that in humans is encoded by the STXBP5 gene. It is also known as tomosyn, after 友, "friend" in Japanese, for its role as a binding protein.^[5]^[6]^[7]

Function

Syntaxin 1 is a component of the 7S and 20S SNARE complexes which are involved in docking and fusion of synaptic vesicles with the presynaptic plasma membrane. This gene encodes a syntaxin 1 binding protein. In rat, a similar protein dissociates syntaxin 1 from the Munc18/n-Sec1/rbSec1 complex to form a 10S complex, an intermediate which can be converted to the 7S SNARE complex. Thus this protein is thought to be involved in neurotransmitter release by stimulating SNARE complex formation. Alternatively spliced variants have been identified, but their biological validity has not been determined.^[7]

Positional cloning suggested that tomosyn might inhibit neurotransmitter secretion in Caenorhabditis elegans neurons.]^[8] This hypothesis was tested and confirmed, showing that tomosyn specifically inhibits synaptic vesicle priming—the biochemical step immediately preceding vesicle fusion and neurotransmitter release.^[9]

Structure

Two functional domains were originally identified, including one which binds to syntaxin, but recent crystallization of the yeast homolog Sro7 revealed that tomosyn likely has three functional domains: one WD40 domain and one syntaxin-binding domain, as previously recognized, but also another WD40 domain. The study also suggested that tomosyn's 'syntaxin binding domain' is not the reason tomosyn is inhibitory for neurotransmitter release, as originally proposed.^[10] The Sro7-based structure is currently given on SWISS-MODEL, which includes the WD40 domains but not most of the coiled coil syntaxin-binding domain seen in the infobox.^[11]