SYN2

Existing Annotations Review

GO Term	Evidence	Action	Reason
GO:0030672 synaptic vesicle membrane	IBA GO_REF:0000033	ACCEPT	Summary: Synapsin-2 is a peripheral membrane protein that associates with the cytosolic face of synaptic vesicle membranes via its N-terminal domains (A-C domains). The deep research confirms SYN2 is "enriched at presynaptic boutons and axons; peripherally associated with SV membranes on the cytosolic side" [Longfield et al. 2024, Stavsky et al. 2024]. UniProt describes it as a protein that "coats synaptic vesicles" and notes the A region "binds phospholipids with a preference for negatively charged species." Reason: Core localization annotation supported by IBA phylogenetic inference and strongly corroborated by literature showing SYN2 peripheral association with synaptic vesicle membranes. Supporting Evidence: DOI:10.1038/s41467-024-46256-1 Synapsin proteins are encoded by 3 genes (SYN1, SYN2, and SYN3)17–20, and have been shown to bind to the phospholipids of SVs via their N-terminus or to other SV proteins via their proline-rich C-terminus
GO:0097091 synaptic vesicle clustering	IBA GO_REF:0000033	ACCEPT	Summary: Synaptic vesicle clustering is the primary molecular function of SYN2. Multiple 2023-2024 studies demonstrate SYN2 clusters synaptic vesicles into a reserve pool through tetramerization and LLPS mechanisms. The deep research states "SYN2 clusters synaptic vesicles, maintains the reserve pool (RP), regulates mobilization and neurotransmitter release" [Bruentgens et al. 2023, Longfield et al. 2024]. Reason: Core biological process annotation. Synaptic vesicle clustering is the primary function of SYN2, supported by extensive recent literature demonstrating both LLPS and tetramerization-dependent clustering mechanisms. Supporting Evidence: DOI:10.1038/s41467-024-46256-1 One missense mutation known to perturb tetramer assembly (K337Q), used here in our study, was unable to rescue both reserve SV mobility, and reserve SV density at the presynapse in SynTKO neuronal cultures. DOI:10.1101/2023.08.08.549335 SYN2 clusters synaptic vesicles into a reserve pool, modulates their mobility, and thereby supports sustained neurotransmission
GO:0050808 synapse organization	IBA GO_REF:0000033	ACCEPT	Summary: SYN2 contributes to synapse organization through its role in organizing the presynaptic vesicle pools. The deep research indicates synapsins shape "mesoscale SV organization" and are involved in "synapsin-organized mesoscale SV architecture" [Bruentgens et al. 2023]. This is a broader parent term of synaptic vesicle clustering. Reason: Valid broader annotation. SYN2 contributes to synapse organization through organizing the presynaptic vesicle pool architecture, though GO:0097091 (synaptic vesicle clustering) is more specific and informative. Supporting Evidence: DOI:10.1101/2023.08.08.549335 synapsin-organized mesoscale SV architecture in plasticity expression
GO:0005524 ATP binding	IEA GO_REF:0000002	ACCEPT	Summary: SYN2 contains an ATP-grasp domain (IPR013815) and ATP-binding domain (IPR020898). The deep research confirms ATP modulates synapsin function: "ATP within physiological ranges inhibits LLPS (half-max ~1.7 mM for Syn2a) and favors higher-order oligomerization" [Song & Augustine 2023]. This functional ATP interaction is well documented. Reason: Valid IEA annotation based on domain content. The ATP-grasp domain is present in SYN2 and ATP binding is functionally relevant - ATP modulates the balance between LLPS and oligomerization states. Supporting Evidence: DOI:10.1101/2023.03.20.533583 Half-maximal inhibition of Syn2a LLPS by ATP occurred near ~1.7 mM
GO:0007268 chemical synaptic transmission	IEA GO_REF:0000117	ACCEPT	Summary: SYN2 is involved in chemical synaptic transmission by regulating synaptic vesicle availability for neurotransmitter release. Deep research states SYN2 "regulates their mobility, and thereby supports sustained neurotransmission" [Bruentgens et al. 2023]. Reason: Valid annotation. SYN2 participates in chemical synaptic transmission by regulating the reserve pool and vesicle availability for release, supporting sustained neurotransmission. Supporting Evidence: DOI:10.1101/2023.08.08.549335 clusters SVs into a reserve pool, modulates their mobility, and thereby supports sustained neurotransmission
GO:0007269 neurotransmitter secretion	IEA GO_REF:0000002	ACCEPT	Summary: SYN2 regulates neurotransmitter secretion by controlling vesicle availability through reserve pool organization. UniProt states it is "believed to function in the regulation of neurotransmitter release" and "may play a role in noradrenaline secretion by sympathetic neurons." Reason: Valid annotation supported by domain inference and literature. SYN2 indirectly regulates neurotransmitter secretion by controlling vesicle pool organization and mobilization. Supporting Evidence: PMID:15217342 synaptic vesicles undergo a trafficking cycle... leads to the docking and priming of the vesicles for another round of exo- and endocytosis
GO:0008021 synaptic vesicle	IEA GO_REF:0000002	ACCEPT	Summary: SYN2 is a synaptic vesicle-associated protein that peripherally coats vesicles on their cytosolic surface. Deep research confirms "SYN2 is a presynaptic SV-associated scaffold" [Song & Augustine 2023, Longfield et al. 2024]. Reason: Valid localization annotation. SYN2 is physically associated with synaptic vesicles as a peripheral membrane protein. Supporting Evidence: DOI:10.1038/s41467-024-46256-1 we next sought to investigate the role of SV-associated protein Synapsin in mediating the dynamics of this SV pool
GO:0045202 synapse	IEA GO_REF:0000120	ACCEPT	Summary: SYN2 localizes to synapses, specifically to presynaptic terminals. UniProt lists subcellular location as "Synapse." This is a broader parent term; more specific terms like synaptic vesicle membrane are more informative. Reason: Valid but general localization annotation. More specific CC terms like GO:0030672 (synaptic vesicle membrane) are preferred.
GO:0005515 protein binding	IPI PMID:33961781 Dual proteome-scale networks reveal cell-specific remodeling...	MODIFY	Summary: This annotation derives from the BioPlex 3.0 interactome study showing SYN2 interaction with SYN3 (O14994) in high-throughput affinity purification mass spectrometry. While the interaction is likely real given synapsin family members are known to oligomerize, "protein binding" is uninformative. Reason: The term "protein binding" does not convey meaningful information about SYN2 function. The interaction with SYN3 reflects the oligomerization property of synapsins which is central to their vesicle clustering function. Proposed replacements: identical protein binding Supporting Evidence: DOI:10.1038/s41467-024-46256-1 Therefore, Syn2a tetramerization controls its own presynaptic nanoclustering and thereby contributes to the dynamic immobilisation of the SV reserve pool.
GO:0005515 protein binding	IPI PMID:40205054 Multimodal cell maps as a foundation for structural and func...	MODIFY	Summary: This annotation derives from multimodal cell maps study showing SYN2-SYN3 interaction. Same issue as PMID:33961781 - "protein binding" is uninformative. The interaction reflects synapsin oligomerization. Reason: "Protein binding" does not convey meaningful functional information. Should be annotated with more specific term reflecting homo/hetero- oligomerization of synapsin family members. Proposed replacements: identical protein binding Supporting Evidence: DOI:10.1038/s41467-024-46256-1 Finally, we demonstrated that tetramerization of Syn2a controls the mobility of reserve pool SVs in live hippocampal cultures.
GO:0005886 plasma membrane	IEA GO_REF:0000107	MARK AS OVER ANNOTATED	Summary: SYN2 is primarily a synaptic vesicle-associated protein, not a plasma membrane protein. The annotation likely derives from orthology transfer but may reflect transient plasma membrane association during vesicle fusion/recycling. Reason: SYN2 is primarily associated with synaptic vesicles in the cytosol, not the plasma membrane. Any plasma membrane association would be transient during vesicle fusion. The core localization is synaptic vesicle membrane (GO:0030672).
GO:0014069 postsynaptic density	IEA GO_REF:0000107	REMOVE	Summary: SYN2 is canonically a presynaptic protein that associates with synaptic vesicles. Postsynaptic localization would be unexpected given its known function in vesicle clustering and mobilization. This may be an artifact of orthology transfer or contamination in proteomic studies. Reason: SYN2 is a presynaptic protein. All literature and deep research consistently describe it as "presynaptic" and associated with synaptic vesicles at the cytosolic face. Postsynaptic density localization is not consistent with its established function.
GO:0017156 calcium-ion regulated exocytosis	IEA GO_REF:0000107	KEEP AS NON CORE	Summary: SYN2 is phosphorylated in response to calcium signaling (by CaMKII) and this regulates vesicle mobilization. However, SYN2 is not directly involved in the calcium-triggered exocytosis machinery but rather in regulating the availability of vesicles for release. Reason: SYN2 indirectly supports calcium-regulated exocytosis by making vesicles available through reserve pool regulation, but it is not part of the core calcium-sensing or fusion machinery. Its primary role is vesicle clustering and mobilization.
GO:0030672 synaptic vesicle membrane	IEA GO_REF:0000107	ACCEPT	Summary: Duplicate annotation for synaptic vesicle membrane via orthology transfer. Same as IBA annotation - SYN2 is peripherally associated with synaptic vesicle membranes. Reason: Valid CC annotation, consistent with IBA annotation and literature. Duplicates with different evidence codes are acceptable.
GO:0031201 SNARE complex	IEA GO_REF:0000107	REMOVE	Summary: SYN2 is not a component of the SNARE complex. The SNARE complex consists of SNAP-25, syntaxin, and VAMP/synaptobrevin. SYN2 functions upstream in vesicle clustering/mobilization, not in the fusion machinery itself. Reason: SYN2 is not a SNARE protein and is not part of the SNARE complex. This is likely an erroneous annotation from orthology transfer. SYN2 regulates vesicle pools but is not directly part of the fusion machinery.
GO:0042802 identical protein binding	IEA GO_REF:0000107	ACCEPT	Summary: SYN2 can form oligomers including tetramers (Syn2a isoform specifically). The deep research confirms "Synapsin-2a can tetramerize, and this assembly property is central to reserve-pool organization" [Longfield et al. 2024]. Reason: Valid MF annotation supported by literature. Syn2a tetramerization is well-documented and functionally important for vesicle clustering. More specific than generic "protein binding." Supporting Evidence: DOI:10.1038/s41467-024-46256-1 Synapsin 2a tetramerisation selectively controls the presynaptic nanoscale organisation of reserve synaptic vesicles
GO:0097091 synaptic vesicle clustering	IEA GO_REF:0000107	ACCEPT	Summary: Duplicate annotation for synaptic vesicle clustering via orthology transfer. Same as IBA annotation - this is a core function of SYN2. Reason: Valid BP annotation consistent with IBA annotation and core function of SYN2. Duplicates with different evidence codes are acceptable.
GO:0098685 Schaffer collateral - CA1 synapse	IEA GO_REF:0000107	KEEP AS NON CORE	Summary: SYN2 is expressed in hippocampal neurons including Schaffer collateral synapses. This is a very specific synapse-type annotation that reflects expression data rather than specific function at this synapse type. Reason: While SYN2 is likely present at Schaffer collateral synapses as a broadly expressed synaptic vesicle protein, this specific synapse-type annotation adds limited functional insight beyond general synaptic localization.
GO:0098978 glutamatergic synapse	IEA GO_REF:0000107	ACCEPT	Summary: SYN2 functions at both glutamatergic (excitatory) and GABAergic (inhibitory) synapses, but with different mechanisms. Deep research shows "at excitatory synapses, tetramerization (prominently via Synapsin-2a) expands RP size" [Song & Augustine 2023]. Reason: Valid localization. SYN2 (particularly Syn2a via tetramerization) functions at glutamatergic synapses to organize the reserve pool. However, SYN2 also functions at inhibitory synapses. Supporting Evidence: DOI:10.1101/2023.03.20.533583 at excitatory synapses, tetramerization (prominently via Synapsin-2a) expands RP size and accelerates mobilization
GO:0099504 synaptic vesicle cycle	IEA GO_REF:0000107	ACCEPT	Summary: SYN2 integrates with the synaptic vesicle cycle by regulating reserve pool size and vesicle mobilization. Deep research states SYN2 "integrates with the SV cycle as a regulator of RP size and mobilization kinetics" [Stavsky et al. 2024]. Reason: Valid BP annotation. SYN2 is a key regulator of the synaptic vesicle cycle, specifically at the reserve pool mobilization step. Supporting Evidence: DOI:10.7554/eLife.89687 Note that h-α-syn(orange) attenuates SV recycling only if the neurons are also co-expressing the ‘a’ isoforms – synapsins Ia, IIa, and IIIa
GO:0005515 protein binding	IPI PMID:23406870 Epileptogenic Q555X SYN1 mutant triggers imbalances in relea...	MODIFY	Summary: This annotation derives from co-immunoprecipitation experiments showing SYN1 (P17600) oligomerizes with SYN2 isoforms (SynIIa and SynIIb). The paper states "We found that the Q555X truncation virtually abolished the ability of SynI to interact with SynIIa and strongly reduced the interaction with SynIIb. These data indicate that SynI/SynII hetero-oligomerization, which is thought to play an important role in SV clustering, is strongly affected by the mutation." Reason: The interaction is well documented but "protein binding" is uninformative. This represents hetero-oligomerization between synapsin family members which is functionally important for vesicle clustering. Proposed replacements: identical protein binding Supporting Evidence: PMID:23406870 We found that the Q555X truncation virtually abolished the ability of SynI to interact with SynIIa and strongly reduced the interaction with SynIIb. These data indicate that SynI/SynII hetero-oligomerization, which is thought to play an important role in SV clustering, is strongly affected by the mutation.
GO:0007269 neurotransmitter secretion	ISS GO_REF:0000024	ACCEPT	Summary: ISS annotation from mouse ortholog Q64332. SYN2 regulates neurotransmitter secretion indirectly by controlling vesicle availability. Consistent with the IEA annotation. Reason: Valid annotation supported by sequence similarity to characterized mouse ortholog and consistent with SYN2 function in vesicle pool regulation.
GO:0030672 synaptic vesicle membrane	ISS GO_REF:0000024	ACCEPT	Summary: ISS annotation from mouse ortholog. SYN2 is peripherally associated with synaptic vesicle membranes. Consistent with IBA and IEA annotations. Reason: Valid CC annotation consistent with other evidence codes and literature.
GO:0045202 synapse	ISS GO_REF:0000024	ACCEPT	Summary: ISS annotation from mouse ortholog. SYN2 localizes to synapses, specifically presynaptic terminals. Consistent with IEA annotation. Reason: Valid but general CC annotation. More specific terms like synaptic vesicle membrane are preferred.
GO:0005524 ATP binding	TAS PMID:15217342 The synaptic vesicle cycle.	ACCEPT	Summary: TAS annotation from Sudhof's comprehensive review "The synaptic vesicle cycle." Synapsins contain ATP-binding domains and ATP modulates their function. The abstract discusses synaptic vesicle trafficking machinery but does not specifically address SYN2 ATP binding. Reason: Valid MF annotation. While the reference is a review, ATP binding by synapsins is well-established from domain structure (ATP-grasp domain) and functional studies showing ATP modulates LLPS/oligomerization. Supporting Evidence: DOI:10.1101/2023.03.20.533583 ATP within physiological ranges inhibits LLPS... and favors higher-order oligomerization
GO:0007268 chemical synaptic transmission	TAS PMID:8964517 Cloning and sequencing analysis of a human synapsin IIb-enco...	ACCEPT	Summary: TAS annotation from the original cloning paper for human synapsin IIb. The paper describes synapsin IIb as "an abundant peripheral membrane protein of synaptic vesicles" involved in synaptic function. This is consistent with SYN2 role in synaptic transmission. Reason: Valid BP annotation. SYN2 supports chemical synaptic transmission through its role in vesicle pool organization and mobilization. Supporting Evidence: PMID:8964517 Cloning and sequencing of the gene encoding human synapsin IIb, an abundant peripheral membrane protein of synaptic vesicles

Gene Description

Existing Annotations Review

Core Functions

Homo- and hetero-oligomerization (tetramerization for Syn2a, heterodimers with SYN1/SYN3) is central to SYN2 function in vesicle clustering.

References

Suggested Questions for Experts

Suggested Experiments

Deep Research

Falcon

📄 View Raw YAML