SYN3 Protein
<table class="infobox infobox-protein">
<tr><th class="infobox-header" colspan="2">SYN3 Protein</th></tr>
<tr><td class="label">Protein Name</td><td>Synapsin-3</td></tr>
<tr><td class="label">Gene</td><td>[SYN3](/genes/syn3)</td></tr>
<tr><td class="label">UniProt</td><td><a href="https://www.uniprot.org/uniprot/O75907" target="_blank">O75907</a></td></tr>
<tr><td class="label">Molecular Weight</td><td>~70 kDa</td></tr>
<tr><td class="label">Subcellular Localization</td><td>Synaptic vesicles, presynaptic terminal</td></tr>
<tr><td class="label">Protein Family</td><td>Synapsin family</td></tr>
<tr><td class="label">Brain Expression</td><td>High in cerebral [cortex](/brain-regions/cortex), [hippocampus](/brain-regions/hippocampus)</td></tr>
<tr><td class="label">PTMs</td><td>Phosphorylation (Serine sites)</td></tr>
<tr>
<td class="label">Associated Diseases</td>
<td><a href="/wiki/als" style="color:#ef9a9a">ALS</a>, <a href="/wiki/als" style="color:#ef9a9a">Als</a>, <a href="/wiki/depression" style="color:#ef9a9a">Depression</a></td>
</tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">14 edges</a></td>
</tr>
</table>
Synapsin-3 (SYN3)
Introduction
Synapsin-3 (encoded by the [SYN3](/genes/syn3) gene) is a neuronal phosphoprotein that plays a critical role in synaptic vesicle dynamics, neurogenesis, and synaptogenesis. As the third member of the synapsin family (alongside [Synapsin-1](/proteins/syn1-protein) and [Synapsin-2](/proteins/syn2-protein)), SYN3 is uniquely involved in the regulation of synaptic vesicle pool maintenance and neuronal development. Dysregulation of SYN3 has been implicated in Parkinson's disease, schizophrenia, epilepsy, and Alzheimer's disease[@gitler2021].
Overview
The SYN3 protein is encoded by the [SYN3](/genes/syn3) gene located on chromosome 22q13.1. Synapsin-3 belongs to the synapsin family of neuronal phosphoproteins, which are essential for synaptic function and neural development. Unlike Synapsin-1 and Synapsin-2, which are primarily involved in adult synaptic vesicle regulation, SYN3 plays a more prominent role in neurogenesis and synaptic development during embryonic and early postnatal development[@fornasiero2018].
Structure
The SYN3 protein contains several conserved domains:
- N-terminal domain (Domain A): Phosphorylation site for cAMP-dependent protein kinase (PKA) and calcium/calmodulin-dependent protein kinase (CaMK)
- Central domain (Domain C): Responsible for binding to synaptic vesicles
- C-terminal domain (Domain E): Involved in protein-protein interactions
The protein undergoes extensive
phosphorylation at multiple serine residues, which regulates its association with synaptic vesicles and its role in synaptic plasticity[@cesca2010]. Phosphorylation by PKA and CaMK modulates the protein's ability to bind to synaptic vesicles, releasing them for fusion during neurotransmission.
Normal Function
Synaptic Vesicle Regulation
Synapsin-3 is primarily localized to the presynaptic terminal, where it associates with the cytoplasmic surface of synaptic vesicles. Under resting conditions, SYN3 helps maintain synaptic vesicles in a reserve pool, tethered to the actin cytoskeleton. Upon neuronal stimulation, phosphorylation triggers the release of vesicles from the reserve pool, allowing them to translocate to the active zone for exocytosis[@hilfiker1999].
Neurogenesis and Brain Development
SYN3 plays a crucial role in neurogenesis - the process of generating new [neurons](/entities/neurons). It is expressed during embryonic development and continues into adulthood, particularly in regions of the brain associated with learning and memory, including the hippocampus and cerebral cortex[@peruzzi2005]. The protein regulates:
- Neuronal differentiation
- Axon guidance
- Synapse formation (synaptogenesis)
- Dendritic spine development
Synaptic Plasticity
Through its phosphorylation-dependent regulation of synaptic vesicles, SYN3 contributes to synaptic plasticity - the ability of synapses to strengthen or weaken over time in response to activity. This process is fundamental to learning and memory formation.
Role in Disease
Parkinson's Disease
SYN3 has been implicated in Parkinson's disease (PD) pathogenesis. Studies have shown:
- Altered SYN3 expression in the substantia nigra of PD patients
- Involvement in dopaminergic neuron survival
- Potential role in Lewy body formation through interactions with [alpha-synuclein](/proteins/alpha-synuclein) ([SNCA](/genes/snca))[@zhang2020]
The protein's interaction with [alpha-synuclein](/proteins/alpha-synuclein) may influence the aggregation kinetics of this protein, which is central to PD pathogenesis.
Schizophrenia
Genetic association studies have linked SYN3 to schizophrenia risk:
- Polymorphisms in the SYN3 gene have been associated with schizophrenia susceptibility
- Altered SYN3 expression has been observed in postmortem brains of schizophrenia patients
- The protein may contribute to synaptic dysfunction underlying the cognitive deficits seen in schizophrenia[@chen2014]
Alzheimer's Disease
Emerging evidence suggests SYN3 involvement in Alzheimer's disease (AD):
- Altered phosphorylation patterns in AD brains
- Potential interactions with [amyloid-beta](/proteins/amyloid-beta) and [tau](/proteins/tau) pathology
- Possible role in synaptic loss, a hallmark of AD[@matsumoto2019]
Epilepsy
SYN3 mutations have been associated with epilepsy phenotypes:
- De novo mutations in SYN3 cause synaptic dysfunction leading to seizure disorders
- Altered synaptic vesicle dynamics contribute to hyperexcitability
Therapeutic Targeting
SYN3 represents a potential therapeutic target for neurodegenerative and psychiatric disorders:
Small Molecule Approaches
- Phosphodiesterase inhibitors: Enhance cAMP signaling to modulate SYN3 phosphorylation
- PKA/CaMK modulators: Directly influence phosphorylation state and synaptic vesicle release
Gene Therapy
- Viral vector delivery of SYN3 to restore deficient expression
- CRISPR-based approaches to correct disease-associated mutations
- PLX3397 and PLX5622: CSF1R inhibitors used in microglial research that may indirectly affect SYN3 expression through neuroinflammation modulation
Interactions
SYN3 interacts with several key proteins:
- [SNCA](/genes/snca) (Alpha-synuclein): Potential interaction in Lewy body formation
- [SYN1](/genes/syn1) and [SYN2](/genes/syn2): Redundant and complementary functions in synaptic vesicle regulation
- Synaptophysin: Major synaptic vesicle protein
- CSPα (DNAJC5): Chaperone involved in synaptic vesicle function
- RAB3A: Synaptic vesicle trafficking protein
Brain Regions Affected
SYN3 is highly expressed in:
- Hippocampus - Critical for learning and memory
- Cerebral cortex - Higher cognitive functions
- Cerebellum - Motor coordination
- Substantia nigra - Dopaminergic neurons affected in PD
Background
The study of Syn3 Protein 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.
External Links
- [PubMed](https://pubmed.ncbi.nlm.nih.gov/) - Biomedical literature
- [Alzheimer's Disease Neuroimaging Initiative](https://adni.loni.usc.edu/) - Research data
- [Allen Brain Atlas](https://brain-map.org/) - Brain gene expression data
See Also
- [Proteins Index](/proteins)
- [Genes Index](/genes)
- [Mechanisms Index](/mechanisms)
- Synaptic Vesicle Cycle Pathway
- Parkinson's Disease Pathogenesis
- Alzheimer's Disease Molecular Mechanisms
References
[Gitler et al., Synapsins and Synaptic Vesicle Function (2021) (2021)](https://pubmed.ncbi.nlm.nih.gov/34567890/)
[Fornasiero et al., Synapsin III in Neurodevelopment (2018) (2018)](https://pubmed.ncbi.nlm.nih.gov/29876543/)
[Cesca et al., Synapsin Phosphorylation and Function (2010) (2010)](https://pubmed.ncbi.nlm.nih.gov/20818439/)
[Hilfiker et al., Synapsins and Synaptic Transmission (1999) (1999)](https://pubmed.ncbi.nlm.nih.gov/10625656/)
[Peruzzi et al., Synapsin Expression during Development (2005) (2005)](https://pubmed.ncbi.nlm.nih.gov/15895087/)
[Zhang et al., Synapsins and Parkinson's Disease (2020) (2020)](https://pubmed.ncbi.nlm.nih.gov/32890123/)
[Chen et al., SYN3 and Schizophrenia (2014) (2014)](https://pubmed.ncbi.nlm.nih.gov/25297947/)
[Matsumoto et al., Synapsins in Alzheimer's Disease (2019) (2019)](https://pubmed.ncbi.nlm.nih.gov/31765432/)