Synapsin-3 (SYN3) is a neuron-specific, presynaptic vesicle-associated phosphoprotein that is a member of the synapsin family (SYN1, SYN2, SYN3). It maintains and mobilizes the synaptic vesicle reserve pool through phosphorylation-dependent mechanisms. Synapsin-3 negatively modulates dopamine release in dopaminergic terminals and controls recycling/reserve vesicle pool organization. The protein is phosphorylated by PKA at Ser9 and by Cdk5 at Ser404, which are essential for its roles in neuronal morphological maturation, axon specification, and neuronal survival. Unlike other synapsins, SYN3 shows precocious expression during development and is involved in early dopaminergic neuron development upstream of BDNF and Cdk5 signaling. The protein binds ATP (regulated by calcium) and interacts with alpha-synuclein, with implications for Parkinson's disease pathophysiology.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0030672 synaptic vesicle membrane | IBA GO_REF:0000033 | ACCEPT | Summary: Synapsin-3 is a peripheral membrane protein localized to the cytoplasmic surface of synaptic vesicles. The original characterization paper states "Synapsin IIIa is associated with synaptic vesicles" [PMID:9539796]. The IBA annotation is phylogenetically inferred and consistent with the synapsin family function. Reason: This is a well-supported core localization for Synapsin-3. The IBA annotation is consistent with experimental evidence from multiple studies and the UniProt subcellular localization annotation. Synapsins are peripheral membrane proteins on the cytoplasmic surface of synaptic vesicle membranes. Supporting Evidence: PMID:9539796 Synapsin IIIa is associated with synaptic vesicles, and its expression appears to be neuron-specific |
| GO:0097091 synaptic vesicle clustering | IBA GO_REF:0000033 | ACCEPT | Summary: Synaptic vesicle clustering is a core function of the synapsin family. Synapsins are central organizers of the presynaptic vesicle cluster and reserve pool. The specific role of synapsins in maintaining the reserve pool through SV clustering is well documented in the literature. Reason: This represents a core biological process for Synapsin-3. Synapsins maintain the synaptic vesicle reserve pool via SV clustering, and this function is conserved across the synapsin family. The IBA annotation is phylogenetically sound and consistent with literature evidence. Supporting Evidence: PMID:9539796 Synapsins are a family of neuron-specific synaptic vesicle-associated phosphoproteins that have been implicated in synaptogenesis and in the modulation of neurotransmitter release |
| GO:0050808 synapse organization | IBA GO_REF:0000033 | ACCEPT | Summary: Synapsins contribute to synapse organization through their role in maintaining synaptic vesicle pools and presynaptic architecture. The original paper states synapsins have been "implicated in synaptogenesis" [PMID:9539796]. Synapsin-3 specifically contributes to presynaptic organization, though it has unique developmental roles. Reason: This is an appropriate annotation at a general level for the synapsin family's role in organizing presynaptic structure. The IBA annotation is consistent with the established role of synapsins in presynaptic organization and vesicle pool maintenance. Supporting Evidence: PMID:9539796 Synapsins are a family of neuron-specific synaptic vesicle-associated phosphoproteins that have been implicated in synaptogenesis and in the modulation of neurotransmitter release |
| GO:0000166 nucleotide binding | IEA GO_REF:0000043 | ACCEPT | Summary: Synapsin-3 has an ATP-grasp domain (C domain) that binds nucleotides, specifically ATP. This annotation is inferred from UniProt keywords. While ATP binding (GO:0005524) is more specific and accurate, nucleotide binding is not incorrect as a broader term. Reason: The annotation is technically correct as a broader term encompassing ATP binding. Synapsins contain an ATP-binding domain in the conserved C region. While more specific annotations (ATP binding) also exist, this broader IEA annotation does not conflict with the known biochemistry. |
| GO:0005524 ATP binding | IEA GO_REF:0000120 | ACCEPT | Summary: Synapsin-3 contains an ATP-binding domain in its conserved C region. The domain structure includes IPR013815 (ATP_grasp_subdomain_1) and IPR020898 (Synapsin_ATP-bd_dom). Calcium regulates ATP binding to this domain. Reason: ATP binding is a well-supported molecular function for Synapsin-3 based on domain structure. The C domain (region 91-399) is annotated as "actin-binding and synaptic-vesicle binding" and contains ATP-grasp fold domains. The TAS annotation (below) provides literature support for this function. |
| GO:0007268 chemical synaptic transmission | IEA GO_REF:0000117 | ACCEPT | Summary: Synapsin-3 is involved in chemical synaptic transmission through its role in regulating synaptic vesicle pools and neurotransmitter release. The synaptic vesicle cycle review describes how vesicles undergo a trafficking cycle to support rapid neurotransmitter release [PMID:15217342]. Reason: This is an appropriate biological process annotation. While the term is somewhat general, Synapsin-3 clearly participates in chemical synaptic transmission through its regulation of synaptic vesicle pools and neurotransmitter release dynamics. The IEA annotation is consistent with the core functions of the synapsin family. Supporting Evidence: PMID:15217342 To support rapid and repeated rounds of release, synaptic vesicles undergo a trafficking cycle |
| GO:0007269 neurotransmitter secretion | IEA GO_REF:0000002 | ACCEPT | Summary: Synapsin-3 is involved in regulating neurotransmitter secretion. The original publication identifying SYN3 suggests synapsins are implicated "in the modulation of neurotransmitter release" [PMID:9539796]. Reason: This is a core function of the synapsin family. Synapsins regulate the transition of vesicles between reserve and readily releasable pools, thereby modulating neurotransmitter release. The IEA annotation is consistent with literature evidence. Supporting Evidence: PMID:9539796 Synapsins are a family of neuron-specific synaptic vesicle-associated phosphoproteins that have been implicated in synaptogenesis and in the modulation of neurotransmitter release |
| GO:0008021 synaptic vesicle | IEA GO_REF:0000120 | ACCEPT | Summary: Synapsin-3 localizes to synaptic vesicles as a peripheral membrane protein. This is consistent with UniProt subcellular location annotation and literature evidence. The original SYN3 characterization paper explicitly states "Synapsin IIIa is associated with synaptic vesicles" [PMID:9539796]. Reason: Synaptic vesicle localization is well-established for Synapsin-3. The IEA annotation is consistent with experimental evidence and the TAS annotation for the same term (below). This represents a core localization for the protein. Supporting Evidence: PMID:9539796 Synapsin IIIa is associated with synaptic vesicles, and its expression appears to be neuron-specific |
| GO:0030672 synaptic vesicle membrane | IEA GO_REF:0000120 | ACCEPT | Summary: This is a duplicate of the IBA annotation for the same term. Synapsin-3 is a peripheral membrane protein on the cytoplasmic surface of synaptic vesicle membranes. UniProt explicitly annotates this localization. Reason: The annotation is correct and consistent with the IBA annotation for the same term. Both annotations support the well-established localization of Synapsin-3 to synaptic vesicle membranes. Supporting Evidence: PMID:9539796 Synapsin IIIa is associated with synaptic vesicles, and its expression appears to be neuron-specific |
| GO:0031410 cytoplasmic vesicle | IEA GO_REF:0000043 | ACCEPT | Summary: This is a broader term that encompasses synaptic vesicles. Synapsin-3 localizes to synaptic vesicles, which are a type of cytoplasmic vesicle. The annotation is technically correct but less specific than the synaptic vesicle annotations. Reason: While this is a less informative annotation compared to the more specific synaptic vesicle and synaptic vesicle membrane annotations, it is not incorrect. The IEA annotation derived from UniProt keywords is valid as synaptic vesicles are a subtype of cytoplasmic vesicles. |
| GO:0050804 modulation of chemical synaptic transmission | IEA GO_REF:0000117 | ACCEPT | Summary: Synapsin-3 modulates synaptic transmission through its regulation of synaptic vesicle pools. Synapsins are implicated in "the modulation of neurotransmitter release" [PMID:9539796]. Reason: This is an appropriate annotation for Synapsin-3. The protein modulates neurotransmitter release by regulating synaptic vesicle pool dynamics. The annotation is consistent with the known regulatory role of synapsins in synaptic transmission. Supporting Evidence: PMID:9539796 Synapsins are a family of neuron-specific synaptic vesicle-associated phosphoproteins that have been implicated in synaptogenesis and in the modulation of neurotransmitter release |
| GO:0005515 protein binding | IPI PMID:33961781 Dual proteome-scale networks reveal cell-specific remodeling... | MARK AS OVER ANNOTATED | Summary: This annotation is based on a high-throughput proteomics study (BioPlex 3.0) that detected SYN3 interaction with SYN2 (Synapsin-2). While the interaction is likely valid (synapsins can oligomerize), "protein binding" is too generic. Reason: While the interaction with SYN2 is documented and synapsins are known to form oligomers, GO:0005515 "protein binding" is an uninformative term that does not capture the specific nature of the interaction. A more specific term such as GO:0042802 "identical protein binding" or a synapsin-specific binding term would be more informative if available. |
| GO:0005515 protein binding | IPI PMID:40205054 Multimodal cell maps as a foundation for structural and func... | MARK AS OVER ANNOTATED | Summary: This annotation is from another high-throughput interactome study (Multimodal cell maps). The interaction partner is again SYN2 based on the GOA data. As with the previous annotation, "protein binding" is too generic. Reason: Same rationale as above. While the protein-protein interaction evidence supports SYN3-SYN2 binding, the GO term "protein binding" is uninformative. The annotation could be retained for completeness but does not provide meaningful functional insight. |
| GO:0014069 postsynaptic density | IEA GO_REF:0000107 | REMOVE | Summary: This annotation is transferred from mouse ortholog via Ensembl Compara. However, Synapsin-3 is characterized as a presynaptic protein associated with synaptic vesicles. The postsynaptic density is a postsynaptic structure, which conflicts with the established presynaptic localization. Reason: This annotation appears inconsistent with the established presynaptic localization of Synapsin-3. Synapsins are well-characterized as presynaptic vesicle-associated proteins. While some postsynaptic localization cannot be completely ruled out, this conflicts with the primary literature characterizing SYN3 as a synaptic vesicle membrane protein. The annotation may reflect an error in the orthology transfer or proteomics detection of contamination. Supporting Evidence: PMID:9539796 Synapsin IIIa is associated with synaptic vesicles, and its expression appears to be neuron-specific |
| GO:0045202 synapse | IEA GO_REF:0000107 | ACCEPT | Summary: Synapsin-3 is localized to synapses, specifically to the presynaptic compartment on synaptic vesicle membranes. This is a broad term that encompasses the more specific synaptic vesicle and synaptic vesicle membrane annotations. Reason: This is a valid but broad localization annotation. Synapsin-3 is indeed present at synapses (specifically in the presynaptic terminal). The annotation is consistent with more specific annotations for synaptic vesicle localization. Supporting Evidence: PMID:9539796 Synapsin IIIa is associated with synaptic vesicles, and its expression appears to be neuron-specific |
| GO:0097091 synaptic vesicle clustering | IEA GO_REF:0000107 | ACCEPT | Summary: This is a duplicate of the IBA annotation for synaptic vesicle clustering. The function is well-supported for the synapsin family. Reason: Duplicate annotation supporting the core function of Synapsin-3 in synaptic vesicle clustering. Both IBA and IEA annotations converge on this core function. Supporting Evidence: PMID:9539796 Synapsins are a family of neuron-specific synaptic vesicle-associated phosphoproteins that have been implicated in synaptogenesis and in the modulation of neurotransmitter release |
| GO:0098850 extrinsic component of synaptic vesicle membrane | IEA GO_REF:0000107 | ACCEPT | Summary: This is an excellent, specific annotation for Synapsin-3. UniProt explicitly states it is a peripheral membrane protein localized to the cytoplasmic surface of synaptic vesicles. This GO term precisely captures the extrinsic (peripheral) nature of Synapsin-3's membrane association. Reason: This is the most precise cellular component annotation for Synapsin-3. Synapsins are peripheral membrane proteins (extrinsic), not integral membrane proteins, and they associate with the cytoplasmic face of synaptic vesicle membranes. Supporting Evidence: PMID:9539796 Synapsin IIIa is associated with synaptic vesicles, and its expression appears to be neuron-specific |
| GO:0098978 glutamatergic synapse | IEA GO_REF:0000107 | KEEP AS NON CORE | Summary: This annotation suggests SYN3 localizes to glutamatergic synapses. Synapsins are present at various types of synapses. The literature emphasizes SYN3's role in dopaminergic neurons specifically, but this does not preclude presence at glutamatergic synapses. Reason: While Synapsin-3 may be present at glutamatergic synapses (synapsins are generally expressed across synapse types), the literature specifically emphasizes its unique role in dopaminergic neurons. The annotation is not wrong but represents a non-specific localization rather than a core feature of SYN3 specifically. |
| GO:0099504 synaptic vesicle cycle | IEA GO_REF:0000107 | ACCEPT | Summary: Synapsin-3 participates in the synaptic vesicle cycle through its role in maintaining vesicle pools and regulating vesicle mobilization. The synaptic vesicle cycle review describes how vesicles undergo trafficking for repeated rounds of release [PMID:15217342]. Reason: The synaptic vesicle cycle is a core process in which Synapsin-3 participates. By maintaining the reserve pool and regulating vesicle mobilization through phosphorylation-dependent mechanisms, synapsins are integral to the vesicle cycling process. Supporting Evidence: PMID:15217342 To support rapid and repeated rounds of release, synaptic vesicles undergo a trafficking cycle |
| GO:0005524 ATP binding | TAS PMID:15217342 The synaptic vesicle cycle. | ACCEPT | Summary: This TAS annotation is based on the Sudhof synaptic vesicle cycle review (2004). Synapsin-3 has a well-characterized ATP-binding domain (C domain). Calcium regulates ATP binding to this domain. Reason: ATP binding is a well-supported molecular function for Synapsin-3 based on domain structure and biochemical evidence. The C domain contains ATP-grasp fold elements (IPR013815, IPR020898) that are characteristic of ATP-binding proteins. |
| GO:0032228 regulation of synaptic transmission, GABAergic | TAS PMID:15217342 The synaptic vesicle cycle. | UNDECIDED | Summary: This annotation suggests SYN3 specifically regulates GABAergic transmission. The Sudhof review (PMID:15217342) is a general review of the synaptic vesicle cycle and does not specifically address Synapsin-3's role in GABAergic synapses. The literature emphasizes SYN3's role in dopaminergic neurons rather than GABAergic neurons. Reason: The cited reference (PMID:15217342) is a general review of the synaptic vesicle cycle that does not specifically address Synapsin-3 or GABAergic transmission. While synapsins are present at various synapse types including GABAergic synapses, there is no specific evidence in the available literature for a particular role of SYN3 in GABAergic transmission. The deep research specifically emphasizes SYN3's unique role in dopaminergic neurons. Additional evidence would be needed to confirm this specific annotation. |
| GO:0007269 neurotransmitter secretion | TAS PMID:9539796 A third member of the synapsin gene family. | ACCEPT | Summary: This TAS annotation is based on the original paper characterizing Synapsin-3. The paper states that synapsins have been implicated "in the modulation of neurotransmitter release" and suggests a role for synapsin III based on similarity to other synapsins. Reason: The original characterization paper predicted this function, which has since been confirmed by subsequent studies showing SYN3's role in regulating dopamine release and synaptic vesicle pool dynamics. This is a core function of the synapsin family. Supporting Evidence: PMID:9539796 The similarities among synapsins I, II, and III in domain organization, neuron-specific expression, and subcellular localization suggest a possible role for synapsin III in the regulation of neurotransmitter release and synaptogenesis |
| GO:0008021 synaptic vesicle | TAS PMID:9539796 A third member of the synapsin gene family. | ACCEPT | Summary: This TAS annotation is based on the original paper characterizing Synapsin-3, which explicitly states "Synapsin IIIa is associated with synaptic vesicles." This is the primary localization for Synapsin-3. Reason: Synaptic vesicle localization is directly stated in the original characterization paper and confirmed by subsequent studies and UniProt annotation. This represents the core localization for Synapsin-3. Supporting Evidence: PMID:9539796 Synapsin IIIa is associated with synaptic vesicles, and its expression appears to be neuron-specific |
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Download this section (compressed HTML)Q: What is the specific role of Synapsin-3 in GABAergic synaptic transmission?
Q: What is the functional significance of the SYN3-SYN2 interaction?
Experiment: Conditional knockout of SYN3 in GABAergic neurons to test role in GABAergic transmission. This would address uncertainty about the GABAergic-specific annotation.
Experiment: Structure-function analysis of SYN3-SYN2 heterodimers. This would elucidate the functional significance of synapsin heteromerization.
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