Syntaxin-binding protein 5

Syntaxin-binding protein 5

Introduction

Syntaxin Binding Protein 5 is an important component in the neurobiology of neurodegenerative diseases. This page provides detailed information about its structure, function, and role in disease processes.

--- [@foss2020]
title: Syntaxin-binding protein 5 [@barak2013]
description: Critical regulator of SNARE complex formation and synaptic vesicle release, with roles in neurodegeneration and synaptic plasticity. [@pabst2000]
--- [@burgalossi2011]

<div class="infobox infobox-protein"> [@sakisaka2008]
<table> [@zhang2019]
<tr><th colspan="2" class="infobox-header">Syntaxin-binding protein 5</th></tr> [@liu2021]
<tr><td class="label">Protein Name</td><td>Syntaxin-binding protein 5 (Tomosyn)</td></tr> [@yamaguchi2018]
<tr><td class="label">Gene</td><td>[STXBP5](/genes/STXBP5)</td></tr>
<tr><td class="label">UniProt ID</td><td>[Q9Y2W1](https://www.uniprot.org/uniprot/Q9Y2W1)</td></tr>
<tr><td class="label">PDB ID</td><td>5W5D, 6CY4</td></tr>
<tr><td class="label">Molecular Weight</td><td>~140 kDa</td></tr>
<tr><td class="label">Subcellular Localization</td><td>Cytoplasm, synaptic vesicles, presynaptic terminals</td></tr>
<tr><td class="label">Protein Family</td><td>LGL (Lethal giant larvae) family</td></tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">1 edges</a></td>
</tr>
</table>
</div>

Overview

Syntaxin-binding protein 5

Introduction

Syntaxin Binding Protein 5 is an important component in the neurobiology of neurodegenerative diseases. This page provides detailed information about its structure, function, and role in disease processes.

--- [@foss2020]
title: Syntaxin-binding protein 5 [@barak2013]
description: Critical regulator of SNARE complex formation and synaptic vesicle release, with roles in neurodegeneration and synaptic plasticity. [@pabst2000]
--- [@burgalossi2011]

<div class="infobox infobox-protein"> [@sakisaka2008]
<table> [@zhang2019]
<tr><th colspan="2" class="infobox-header">Syntaxin-binding protein 5</th></tr> [@liu2021]
<tr><td class="label">Protein Name</td><td>Syntaxin-binding protein 5 (Tomosyn)</td></tr> [@yamaguchi2018]
<tr><td class="label">Gene</td><td>[STXBP5](/genes/STXBP5)</td></tr>
<tr><td class="label">UniProt ID</td><td>[Q9Y2W1](https://www.uniprot.org/uniprot/Q9Y2W1)</td></tr>
<tr><td class="label">PDB ID</td><td>5W5D, 6CY4</td></tr>
<tr><td class="label">Molecular Weight</td><td>~140 kDa</td></tr>
<tr><td class="label">Subcellular Localization</td><td>Cytoplasm, synaptic vesicles, presynaptic terminals</td></tr>
<tr><td class="label">Protein Family</td><td>LGL (Lethal giant larvae) family</td></tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">1 edges</a></td>
</tr>
</table>
</div>

Overview

Syntaxin-binding protein 5 (STXBP5), also known as Tomosyn, is a crucial regulator of synaptic vesicle release and SNARE complex formation. Originally identified in rodents as a syntaxin-binding protein that inhibits SNARE complex assembly, Tomosyn plays a complex role in modulating neurotransmitter release by competing with synaptosome-associated protein 25 (SNAP-25) for syntaxin binding [@bennett1999]. Beyond its well-characterized function in synaptic transmission, STXBP5 has been implicated in various neurological disorders including [Alzheimer's disease](/diseases/alzheimers-disease), [Parkinson's disease](/diseases/parkinsons-disease), and epilepsy [@foss2020].

Structure

STXBP5/Tomosyn is a large, modular protein with several distinct structural domains:

| Domain | Position | Function |
|--------|----------|----------|
| N-terminal WD40 repeat region | aa 1-530 | Mediates protein-protein interactions; forms beta-propeller structure |
| Middle linker region | aa 531-700 | Flexible tether connecting N- and C-terminal domains |
| C-terminal R-SNARE motif | aa 701-756 | Resembles SNARE motif; forms stable complex with syntaxin |

The N-terminal WD40 repeat region adopts a seven-bladed beta-propeller structure that serves as a platform for interactions with multiple synaptic proteins including Rab3, Munc13, and RIM [@barak2013]. The C-terminal SNARE motif (also called "longin" domain) can form a ternary SNARE complex with syntaxin and SNAP-25, but this complex is non-fusogenic, thereby limiting the availability of free SNARE complexes for synaptic vesicle fusion [@pabst2000].

Normal Function

Regulation of SNARE Complex Formation

Tomosyn functions as a molecular brake on neurotransmitter release by competing with SNAP-25 for binding to syntaxin-1. By forming a non-productive Tomosyn-syntaxin-SNAP-25 complex, it reduces the number of available SNARE complexes and thus modulates the kinetics of vesicle fusion [@bennett1999].

Synaptic Vesicle Priming

Tomosyn interacts with Munc13 and RIM, essential proteins for synaptic vesicle priming. These interactions position Tomosyn at the active zone where it helps regulate the size of the readily releasable pool of vesicles [@burgalossi2011].

Regulation of Exocytosis Timing

Different isoforms of Tomosyn (generated by alternative splicing) have distinct effects on release kinetics. Tomosyn-1 is primarily inhibitory, while some splice variants may facilitate release in certain contexts [@sakisaka2008].

Role in Disease

Alzheimer's Disease

STXBP5/Tomosyn has been implicated in Alzheimer's disease pathogenesis:

• Synaptic dysfunction: Altered Tomosyn expression contributes to synaptic vesicle release deficits in Alzheimer's disease models
• [Amyloid-beta](/proteins/amyloid-beta) interaction: Amyloid-beta oligomers affect Tomosyn localization and function in hippocampal [neurons](/entities/neurons)
• Memory deficits: Mouse models of Alzheimer's disease show increased Tomosyn expression, which correlates with memory impairments [@zhang2019]

Parkinson's Disease

• Dopamine release: Tomosyn regulates dopamine release from striatal terminals
• [Alpha-synuclein](/proteins/alpha-synuclein) interaction: Dysregulation of Tomosyn may contribute to synaptic deficits in Parkinson's disease
• Therapeutic potential: Targeting Tomosyn-mediated signaling may improve dopaminergic transmission [@liu2021]

Epilepsy

• Seizure susceptibility: Altered Tomosyn expression and splicing have been observed in epileptic tissue
• Excitatory-inhibitory balance: By modulating GABAergic and glutamatergic release, Tomosyn influences neuronal network excitability [@yamaguchi2018]

Cancer

STXBP5 has been studied as a potential tumor suppressor:

• Reduced expression: STXBP5 is downregulated in several cancers including gastric cancer and glioma
• Metastasis suppression: Loss of Tomosyn promotes cell migration and invasion in vitro

Therapeutic Targeting

STXBP5 represents a potential therapeutic target:

Neurological Disorders

• Memory enhancement: Inhibiting Tomosyn function may improve synaptic plasticity and memory in Alzheimer's disease
• Anti-epileptic strategies: Modulating Tomosyn expression or splicing could reduce seizure frequency

Drug Development

• Small molecule inhibitors targeting the Tomosyn-syntaxin interaction are under development
• Antisense oligonucleotides modulating STXBP5 expression show promise in preclinical models

Interacting Partners

| Partner | Interaction Type | Functional Outcome |
|---------|-----------------|-------------------|
| Syntaxin-1 | Direct binding | Inhibits SNARE complex formation |
| SNAP-25 | Part of ternary complex | Forms non-fusogenic SNARE complex |
| Munc13-1 | Direct binding | Regulates vesicle priming |
| RIM | Direct binding | Localizes to active zones |
| Rab3A | Direct binding | Modulates Tomosyn localization |
| Munc18 | Indirect | Regulates syntaxin availability |

Research Tools

• Knockout mice: Stxbp5 knockout mice show increased spontaneous release but altered evoked release
• Transgenic lines: Reporter lines for monitoring Tomosyn expression in vivo
• Structural studies: Crystal structures of WD40 domain and SNARE complex (PDB: 5W5D, 6CY4)

Background

The study of Syntaxin Binding Protein 5 has evolved significantly over the past decades. Research in this area has revealed important insights into the underlying mechanisms of neurodegeneration and continues to drive therapeutic development.

Historical context and key discoveries in this field have shaped our current understanding and will continue to guide future research directions.

Cross-Links

• [STXBP5 Gene](/genes/STXBP5)
• [SNARE Complex](/proteins/snare-complex)
• [Synaptic Vesicle Cycle](/mechanisms/synaptic-vesicle-cycle)
• [Alzheimer's Disease](/diseases/alzheimers-disease)
• [Parkinson's Disease](/diseases/parkinsons-disease)

See Also

• [SNAP25 Protein](/proteins/SNAP25-Protein)
• Syntaxin-1 Protein
• Munc18 Protein
• Munc13 Protein
• Synaptotagmin Protein

External Links

• [UniProt: STXBP5](https://www.uniprot.org/uniprot/Q9Y2W1)
• [NCBI Protein: STXBP5](https://www.ncbi.nlm.nih.gov/protein/NP_001010989)
• [GeneCards: STXBP5](https://www.genecards.org/cgi-bin/carddisp.pl?gene=STXBP5)
• [PDB: STXBP5 Structures](https://www.rcsb.org/structure/5W5D)

Brain Atlas Resources

• [Allen Human Brain Atlas](https://human.brain-map.org/) — protein expression data
• [Allen Cell Type Atlas](https://celltypes.brain-map.org/) — cell type specific expression
• [BrainSpan Atlas](https://brainspan.org/) — developmental transcriptome
• [Allen Mouse Brain Atlas](https://mouse.brain-map.org/) — mouse brain expression

References