SYN1

id: P17600
gene_symbol: SYN1
product_type: PROTEIN
status: COMPLETE
taxon:
  id: NCBITaxon:9606
  label: Homo sapiens
description: >-
  Synapsin-1 is a neuron-specific presynaptic phosphoprotein that coats synaptic vesicles
  and serves as a multivalent scaffold to organize synaptic vesicle (SV) clusters within
  presynaptic boutons. Through its interactions with both SV membranes (via domain A
  phospholipid binding) and the actin cytoskeleton (via domain C), SYN1 maintains the
  reserve pool of synaptic vesicles and regulates their mobilization to the readily
  releasable pool. The central domain C contains an ATP-binding site. SYN1 undergoes
  liquid-liquid phase separation (LLPS) to form dynamic presynaptic condensates that
  compartmentalize SVs. Multiple phosphorylation sites (by PKA, CaMK2, MAPK) and
  SUMOylation regulate its membrane and actin binding properties, thereby controlling
  SV clustering and neurotransmitter release dynamics. Loss-of-function mutations cause
  X-linked epilepsy and intellectual disability due to disrupted excitatory/inhibitory
  balance at synapses.
alternative_products:
- name: IA
  id: P17600-1
- name: IB
  id: P17600-2
  sequence_note: VSP_006316, VSP_006317
existing_annotations:
- term:
    id: GO:0030672
    label: synaptic vesicle membrane
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  review:
    summary: >-
      Synapsin-1 is a peripheral membrane protein that associates with synaptic vesicle membranes
      through its N-terminal domain A, which binds phospholipids with preference for negatively
      charged species [PMID:2110562, UniProt]. The protein coats synaptic vesicles and is
      concentrated at presynaptic terminals associated with SV clusters [Sansevrino 2023,
      Longfield 2024].
    action: ACCEPT
    reason: >-
      This is a core annotation for SYN1. The protein is well-established as a synaptic vesicle-associated
      protein that binds SV membranes extrinsically through its domain A. Deep research confirms
      SYN1 is concentrated at presynaptic terminals and enriched on SV clusters. IBA annotation
      is phylogenetically sound for this conserved function.
    supported_by:
      - reference_id: PMID:2110562
        supporting_text: "Synapsin I is a peripheral membrane protein of synaptic vesicles that mediates their attachment to the cytoskeleton."
      - reference_id: file:human/SYN1/SYN1-deep-research-falcon.md
        supporting_text: "Synapsin-1 is concentrated at presynaptic terminals and enriched on SV clusters."

- term:
    id: GO:0097091
    label: synaptic vesicle clustering
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  review:
    summary: >-
      Synaptic vesicle clustering is the primary function of synapsin-1. The protein maintains
      SV clusters within presynaptic boutons through multivalent interactions with vesicle
      membranes and actin, and through self-oligomerization. Recent studies show SYN1 drives
      vesicle condensation via liquid-liquid phase separation (LLPS) [Alfken 2024, Sansevrino 2023].
      Loss of synapsin family members increases reserve SV mobility [Longfield 2024].
    action: ACCEPT
    reason: >-
      This is the core biological process function of SYN1. Deep research extensively documents
      that synapsin maintains SV clustering and the reserve pool; loss or knockout increases SV
      mobility and reduces vesicle packing. The IBA annotation correctly captures this conserved,
      central function across the synapsin family.
    supported_by:
      - reference_id: file:human/SYN1/SYN1-deep-research-falcon.md
        supporting_text: "Synapsin-1 scaffolds SVs into dynamic clusters that form a reserve pool, modulating short-term plasticity by regulating SV mobility and availability for release."
      - reference_id: file:human/SYN1/SYN1-deep-research-falcon.md
        supporting_text: "In synapsin triple knockout neurons, reserve-pool SV mobility increases; re-expression of synapsin capable of higher-order assembly restores immobilization and nanoclustering."

- term:
    id: GO:0050808
    label: synapse organization
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  review:
    summary: >-
      Synapsin-1 contributes to synapse organization through its role in maintaining synaptic
      vesicle pools and presynaptic structure. The protein is involved in synaptogenesis and
      regulation of axon outgrowth [PMID:21441247, UniProt]. However, this is a broader term
      than the more specific function of synaptic vesicle clustering.
    action: KEEP_AS_NON_CORE
    reason: >-
      While SYN1 does contribute to synapse organization, this is a relatively broad term. The
      more specific function is synaptic vesicle clustering (GO:0097091). Synapse organization
      represents a higher-level process that SYN1 participates in, but is not its primary specific
      function. Keep as non-core to reflect the broader involvement without overstating specificity.
    supported_by:
      - reference_id: PMID:21441247
        supporting_text: "Here we report a Q555X mutation in synapsin 1 (SYN1), an X-linked gene encoding for a neuron-specific phosphoprotein implicated in the regulation of neurotransmitter release and synaptogenesis."

- term:
    id: GO:0003779
    label: actin binding
  evidence_type: IEA
  original_reference_id: GO_REF:0000043
  review:
    summary: >-
      Synapsin-1 domain C binds actin, which is essential for its function in tethering synaptic
      vesicles to the cytoskeleton [PMID:2110562, UniProt]. The actin binding allows synapsin
      to crosslink SVs to the actin cytoskeleton and is regulated by phosphorylation.
    action: ACCEPT
    reason: >-
      Actin binding is a well-documented molecular function of synapsin-1. The UniProt entry
      explicitly annotates domain C (residues 113-420) as actin-binding. Deep research confirms
      domain C interfaces for actin along with vesicle lipids. This IEA from UniProt keywords
      is accurate.
    supported_by:
      - reference_id: PMID:2110562
        supporting_text: "Synapsin I is a peripheral membrane protein of synaptic vesicles that mediates their attachment to the cytoskeleton."
      - reference_id: file:human/SYN1/SYN1-deep-research-falcon.md
        supporting_text: "Synapsin-1's domain C binds ATP/ADP (calcium-facilitated) and actin."

- term:
    id: GO:0005524
    label: ATP binding
  evidence_type: IEA
  original_reference_id: GO_REF:0000002
  review:
    summary: >-
      Synapsin-1 contains an ATP-binding domain (domain C) that is structurally characterized
      as an ATP-grasp fold. The InterPro domains IPR020898 (Synapsin_ATP-bd_dom) and IPR013815
      (ATP_grasp_subdomain_1) support this annotation. ATP binding is calcium-facilitated.
    action: ACCEPT
    reason: >-
      ATP binding is supported by the domain architecture of synapsin-1. The protein has a
      well-characterized ATP-binding domain (domain C) with ATP-grasp fold structure. Deep
      research explicitly states domain C binds ATP/ADP. This IEA from InterPro mapping is accurate.
    supported_by:
      - reference_id: file:human/SYN1/SYN1-deep-research-falcon.md
        supporting_text: "Synapsin-1's domain C binds ATP/ADP (calcium-facilitated) and actin."

- term:
    id: GO:0005794
    label: Golgi apparatus
  evidence_type: IEA
  original_reference_id: GO_REF:0000044
  review:
    summary: >-
      UniProt annotates Golgi apparatus localization based on subcellular location vocabulary
      mapping. This likely reflects transient localization during biosynthesis or trafficking
      rather than the primary functional localization at presynaptic terminals.
    action: KEEP_AS_NON_CORE
    reason: >-
      While UniProt does note Golgi localization (by similarity), the primary functional
      localization of synapsin-1 is at presynaptic terminals and synaptic vesicles. Golgi
      localization may represent biosynthetic pathway rather than functional location.
      Keep as non-core to acknowledge this minor localization without implying it is primary.
    supported_by:
      - reference_id: file:human/SYN1/SYN1-uniprot.txt
        supporting_text: "Golgi apparatus"

- term:
    id: GO:0007268
    label: chemical synaptic transmission
  evidence_type: IEA
  original_reference_id: GO_REF:0000117
  review:
    summary: >-
      Synapsin-1 plays a key role in regulating synaptic transmission by controlling synaptic
      vesicle pools and neurotransmitter release dynamics. Mutations cause impaired synaptic
      function [PMID:21441247, PMID:23406870].
    action: ACCEPT
    reason: >-
      Chemical synaptic transmission is the broader biological context in which SYN1 functions.
      The protein's role in regulating SV trafficking and neurotransmitter release directly
      supports this process. Both literature and the TAS annotation from PMID:2110562 support
      this involvement.
    supported_by:
      - reference_id: PMID:23406870
        supporting_text: "Synapsins (Syns) are synaptic vesicle (SV) phosphoproteins that play multiple roles in synaptic transmission and plasticity (1)."

- term:
    id: GO:0007269
    label: neurotransmitter secretion
  evidence_type: IEA
  original_reference_id: GO_REF:0000002
  review:
    summary: >-
      Synapsin-1 regulates neurotransmitter secretion by controlling the availability of
      synaptic vesicles for release. It maintains the reserve pool and regulates SV mobilization
      to the readily releasable pool. The Q555X mutant causes imbalances in release dynamics
      [PMID:23406870].
    action: ACCEPT
    reason: >-
      Neurotransmitter secretion is a core process that SYN1 regulates. The protein's function
      in SV clustering and reserve pool maintenance directly controls neurotransmitter release.
      This is well-supported by multiple publications.
    supported_by:
      - reference_id: PMID:23406870
        supporting_text: "Syns are implicated in the regulation of SV trafficking between the reserve pool (RP) and the readily releasable pool (RRP) and in facilitating the post-docking steps of release."

- term:
    id: GO:0008021
    label: synaptic vesicle
  evidence_type: IEA
  original_reference_id: GO_REF:0000120
  review:
    summary: >-
      Synapsin-1 is a synaptic vesicle protein that coats SVs and maintains their clustering.
      This localization is fundamental to the protein's function.
    action: ACCEPT
    reason: >-
      Synaptic vesicle localization is the primary cellular component annotation for SYN1.
      The protein is well-established as a synaptic vesicle protein that coats SVs. This is
      also supported by the TAS annotation from PMID:16141272.
    supported_by:
      - reference_id: PMID:2110562
        supporting_text: "Synapsin I is a peripheral membrane protein of synaptic vesicles that mediates their attachment to the cytoskeleton."

- term:
    id: GO:0031410
    label: cytoplasmic vesicle
  evidence_type: IEA
  original_reference_id: GO_REF:0000043
  review:
    summary: >-
      This is a parent term of synaptic vesicle. While accurate, it is less specific than
      the more appropriate synaptic vesicle (GO:0008021) annotation.
    action: ACCEPT
    reason: >-
      Accurate but redundant with the more specific synaptic vesicle annotation. IEA annotations
      at this level are acceptable as they reflect the general vesicle association, though
      synaptic vesicle is more informative.
    supported_by:
      - reference_id: file:human/SYN1/SYN1-uniprot.txt
        supporting_text: "Cytoplasmic vesicle"

- term:
    id: GO:0045202
    label: synapse
  evidence_type: IEA
  original_reference_id: GO_REF:0000120
  review:
    summary: >-
      Synapsin-1 is localized to synapses, specifically at presynaptic terminals. This is
      a parent term that encompasses the more specific presynapse localization.
    action: ACCEPT
    reason: >-
      Synapse localization is accurate and well-supported. The protein is concentrated at
      synapses, specifically at the presynaptic compartment. This general localization term
      is appropriate.
    supported_by:
      - reference_id: file:human/SYN1/SYN1-uniprot.txt
        supporting_text: "SUBCELLULAR LOCATION: Synapse"

- term:
    id: GO:0050804
    label: modulation of chemical synaptic transmission
  evidence_type: IEA
  original_reference_id: GO_REF:0000117
  review:
    summary: >-
      Synapsin-1 modulates synaptic transmission by regulating short-term plasticity through
      its control of SV pool dynamics. The Q555X mutation causes altered short-term plasticity
      responses [PMID:23406870].
    action: ACCEPT
    reason: >-
      Modulation of synaptic transmission is a core function of SYN1. The protein's role in
      controlling SV reserve pool and release dynamics directly modulates synaptic transmission
      strength and short-term plasticity.
    supported_by:
      - reference_id: PMID:23406870
        supporting_text: "We identified distinct physiological changes in quantal parameters, release dynamics and STP at inhibitory and excitatory synapses."

- term:
    id: GO:0098793
    label: presynapse
  evidence_type: IEA
  original_reference_id: GO_REF:0000120
  review:
    summary: >-
      Synapsin-1 is predominantly localized to the presynapse where it associates with synaptic
      vesicle clusters. This is the primary functional location of the protein.
    action: ACCEPT
    reason: >-
      Presynapse localization is the core cellular component annotation for SYN1. This is
      supported by IDA evidence from PMID:21441247 as well. The protein functions at presynaptic
      terminals to regulate SV pools.
    supported_by:
      - reference_id: PMID:21441247
        supporting_text: "Here we report a Q555X mutation in synapsin 1 (SYN1), an X-linked gene encoding for a neuron-specific phosphoprotein implicated in the regulation of neurotransmitter release and synaptogenesis."

- term:
    id: GO:0000795
    label: synaptonemal complex
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  review:
    summary: >-
      The synaptonemal complex is a meiosis-specific structure involved in chromosome pairing.
      Synapsin-1 is a neuronal protein involved in synaptic vesicle trafficking, not meiosis.
      This appears to be an erroneous annotation, possibly from confusion between "synaptic"
      and "synaptonemal".
    action: REMOVE
    reason: >-
      This annotation is likely incorrect. The synaptonemal complex is a meiotic structure
      unrelated to synaptic vesicle biology. SYN1 is expressed specifically in neurons and
      functions at presynaptic terminals. There is no evidence supporting synaptonemal complex
      localization, and this may represent a mapping error based on terminological similarity.
    supported_by:
      - reference_id: file:human/SYN1/SYN1-deep-research-falcon.md
        supporting_text: "Synapsin-1 is concentrated at presynaptic terminals and enriched on SV clusters."

- term:
    id: GO:0014069
    label: postsynaptic density
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  review:
    summary: >-
      Synapsin-1 is predominantly a presynaptic protein. While some proteomic studies may
      detect it in postsynaptic density preparations due to contamination or transient
      interactions, its primary localization and function is presynaptic.
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      SYN1 is well-established as a presynaptic protein that associates with synaptic vesicles.
      The postsynaptic density annotation likely comes from proteomic studies that detected
      SYN1, possibly due to contamination of postsynaptic preparations with presynaptic material.
      The primary functional localization is presynaptic.
    supported_by:
      - reference_id: file:human/SYN1/SYN1-deep-research-falcon.md
        supporting_text: "Localization: Synapsin-1 is concentrated at presynaptic terminals."
      - reference_id: PMID:23406870
        supporting_text: "No changes in miniature EPSC (mEPSC) and miniature IPSC (mIPSC) amplitude, as well as in their rise and decay times, were observed"

- term:
    id: GO:0019901
    label: protein kinase binding
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  review:
    summary: >-
      Synapsin-1 is a substrate for multiple protein kinases including PKA, CaMK2, and MAPK.
      Its phosphorylation by these kinases regulates its function. The protein likely binds
      these kinases during phosphorylation events.
    action: ACCEPT
    reason: >-
      Protein kinase binding is supported by the extensive phosphorylation of SYN1 by multiple
      kinases. The protein is a well-documented substrate of PKA, CaMK1, CaMK2, and MAPK/ERK.
      This annotation is also present with ISS evidence (GO_REF:0000024).
    supported_by:
      - reference_id: file:human/SYN1/SYN1-uniprot.txt
        supporting_text: "Substrate of different protein kinases"
      - reference_id: file:human/SYN1/SYN1-deep-research-falcon.md
        supporting_text: "Phosphorylation by PKA/CaMKI/IV (site 1), CaMKII (sites 2/3), and MAPK/Cdk (sites 6/7) toggles synapsin's binding to membranes and actin."

- term:
    id: GO:0030424
    label: axon
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  review:
    summary: >-
      Synapsin-1 redistributes into the axon during action potential firing as it dissociates
      from synaptic vesicles. This localization is consistent with its presynaptic function
      at axon terminals.
    action: ACCEPT
    reason: >-
      Axon localization is appropriate for SYN1. The protein localizes to presynaptic terminals
      at axon endings and redistributes along the axon during synaptic activity. UniProt notes
      that it dissociates from SVs and redistributes into the axon during AP firing.
    supported_by:
      - reference_id: file:human/SYN1/SYN1-uniprot.txt
        supporting_text: "Dissociates from synaptic vesicles and redistributes into the axon during action potential firing"

- term:
    id: GO:0030425
    label: dendrite
  evidence_type: IEA
  original_reference_id: GO_REF:0000120
  review:
    summary: >-
      While synapsin-1 is predominantly presynaptic, some studies may have detected it in
      dendrites. However, its primary localization and function is at presynaptic terminals,
      not dendrites.
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      SYN1 is well-characterized as a presynaptic protein. Dendritic localization is not
      its primary site of function. Any dendritic detection may represent minor amounts or
      experimental artifacts. The protein is not known to have a functional role in dendrites.
    supported_by:
      - reference_id: file:human/SYN1/SYN1-deep-research-falcon.md
        supporting_text: "Localization: Synapsin-1 is concentrated at presynaptic terminals."

- term:
    id: GO:0030672
    label: synaptic vesicle membrane
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  review:
    summary: >-
      Duplicate of the IBA annotation above. Synapsin-1 associates with synaptic vesicle
      membranes through its domain A phospholipid binding.
    action: ACCEPT
    reason: >-
      This annotation is correct and consistent with the IBA annotation. Multiple evidence
      types supporting the same annotation is appropriate.
    supported_by:
      - reference_id: PMID:2110562
        supporting_text: "Synapsin I is a peripheral membrane protein of synaptic vesicles that mediates their attachment to the cytoskeleton."

- term:
    id: GO:0042802
    label: identical protein binding
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  review:
    summary: >-
      Synapsin-1 forms homodimers and can oligomerize. This self-association is important
      for its function in SV clustering and is mediated in part by domain E. UniProt notes
      homodimer formation.
    action: ACCEPT
    reason: >-
      Identical protein binding (homodimerization) is documented for SYN1. UniProt states
      "Homodimer (By similarity)". This self-association contributes to SV clustering through
      synapsin multimerization.
    supported_by:
      - reference_id: file:human/SYN1/SYN1-uniprot.txt
        supporting_text: "SUBUNIT: Homodimer (By similarity)."
      - reference_id: PMID:23406870
        supporting_text: "Because SV clustering and maintenance of the RP are believed to occur partly through oligomerization of SynI with other Syns (1), we asked whether the Q555X mutation influenced the ability of SynI to oligomerize with other Syn isoforms."

- term:
    id: GO:0044297
    label: cell body
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  review:
    summary: >-
      Synapsin-1 is synthesized in the neuronal cell body before transport to presynaptic
      terminals. Some localization to the cell body may be detected, but the functional
      localization is at presynaptic terminals.
    action: KEEP_AS_NON_CORE
    reason: >-
      Cell body localization likely represents biosynthetic or trafficking intermediates
      rather than the functional location. The primary site of SYN1 function is at presynaptic
      terminals. Keep as non-core to acknowledge this minor localization.
    supported_by:
      - reference_id: file:human/SYN1/SYN1-uniprot.txt
        supporting_text: "Tissue enriched (brain)"

- term:
    id: GO:0048306
    label: calcium-dependent protein binding
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  review:
    summary: >-
      Synapsin-1 ATP binding is calcium-facilitated, and its interactions with membranes
      and other proteins are regulated by calcium-dependent phosphorylation. The protein's
      activity is modulated by calcium signaling.
    action: ACCEPT
    reason: >-
      Calcium-dependent protein binding is consistent with SYN1 biology. The protein's ATP
      binding is calcium-facilitated, and CaMK2 phosphorylation is calcium-dependent.
      These calcium-dependent interactions are central to SYN1 function.
    supported_by:
      - reference_id: file:human/SYN1/SYN1-deep-research-falcon.md
        supporting_text: "Synapsin-1's domain C binds ATP/ADP (calcium-facilitated) and actin."

- term:
    id: GO:0048666
    label: neuron development
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  review:
    summary: >-
      Synapsin-1 is involved in axon outgrowth and synaptogenesis during neuron development.
      The Q555X mutation caused delayed axon elongation [PMID:21441247]. However, this is
      a broader developmental process.
    action: KEEP_AS_NON_CORE
    reason: >-
      While SYN1 does contribute to neuron development through its roles in axon outgrowth
      and synaptogenesis, this is a broad developmental term. The core function of SYN1 is
      in regulating synaptic vesicle dynamics at mature synapses. Keep as non-core.
    supported_by:
      - reference_id: PMID:21441247
        supporting_text: "Here we report a Q555X mutation in synapsin 1 (SYN1), an X-linked gene encoding for a neuron-specific phosphoprotein implicated in the regulation of neurotransmitter release and synaptogenesis."
      - reference_id: file:human/SYN1/SYN1-uniprot.txt
        supporting_text: "Also involved in the regulation of axon outgrowth and synaptogenesis"

- term:
    id: GO:0048786
    label: presynaptic active zone
  evidence_type: IEA
  original_reference_id: GO_REF:0000120
  review:
    summary: >-
      While synapsin-1 is presynaptic, it is primarily associated with the reserve pool of
      synaptic vesicles that are more distant from the active zone. During stimulation,
      SYN1 redistributes toward the active zone. The active zone itself is distinct from
      the SV reserve pool where SYN1 primarily resides.
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      SYN1 is primarily associated with synaptic vesicle clusters in the reserve pool,
      which is distinct from the active zone. While it may transiently localize near the
      active zone during vesicle mobilization, the active zone per se is not its primary
      localization. The protein redistributes toward the AZ during stimulation.
    supported_by:
      - reference_id: PMID:23406870
        supporting_text: "At rest, the distribution of WT-hSynI was comparable with that reported for the endogenous protein (27) and was characterized by fewer metal particles located near the plasma membrane, when compared with those located in the more central region of the synapse."

- term:
    id: GO:0050808
    label: synapse organization
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  review:
    summary: >-
      Duplicate of the IBA annotation above. SYN1 contributes to synapse organization
      through its role in maintaining synaptic vesicle pools.
    action: KEEP_AS_NON_CORE
    reason: >-
      Consistent with the IBA annotation review above. This is a broader term than the
      more specific synaptic vesicle clustering function.
    supported_by:
      - reference_id: PMID:21441247
        supporting_text: "Here we report a Q555X mutation in synapsin 1 (SYN1), an X-linked gene encoding for a neuron-specific phosphoprotein implicated in the regulation of neurotransmitter release and synaptogenesis."

- term:
    id: GO:0098685
    label: Schaffer collateral - CA1 synapse
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  review:
    summary: >-
      This is a specific synapse type in the hippocampus. While synapsin-1 is expressed
      in hippocampal neurons and likely present at Schaffer collateral synapses, this
      is an overly specific localization term for a broadly expressed synaptic protein.
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      SYN1 is broadly expressed in neurons throughout the brain, not specifically at
      Schaffer collateral-CA1 synapses. While it is present at these synapses (as it is
      at most glutamatergic synapses), annotating a specific synapse type is overly specific
      for a generally expressed synaptic vesicle protein.
    supported_by:
      - reference_id: file:human/SYN1/SYN1-uniprot.txt
        supporting_text: "Tissue enriched (brain)"

- term:
    id: GO:0098693
    label: regulation of synaptic vesicle cycle
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  review:
    summary: >-
      Synapsin-1 regulates the synaptic vesicle cycle by controlling SV clustering, reserve
      pool maintenance, and mobilization of vesicles for release. This is a core function.
    action: ACCEPT
    reason: >-
      Regulation of the synaptic vesicle cycle is a core function of SYN1. The protein
      controls SV trafficking between reserve and readily releasable pools, which is
      central to the SV cycle.
    supported_by:
      - reference_id: PMID:23406870
        supporting_text: "Syns are implicated in the regulation of SV trafficking between the reserve pool (RP) and the readily releasable pool (RRP) and in facilitating the post-docking steps of release."

- term:
    id: GO:0098850
    label: extrinsic component of synaptic vesicle membrane
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  review:
    summary: >-
      Synapsin-1 is a peripheral membrane protein that associates extrinsically with
      synaptic vesicle membranes through its N-terminal domain A.
    action: ACCEPT
    reason: >-
      This is an accurate and specific cellular component term for SYN1. The protein is
      a peripheral (extrinsic) membrane protein that binds the cytoplasmic surface of
      SV membranes, not a transmembrane protein.
    supported_by:
      - reference_id: PMID:2110562
        supporting_text: "Synapsin I is a peripheral membrane protein of synaptic vesicles that mediates their attachment to the cytoskeleton."

- term:
    id: GO:0099504
    label: synaptic vesicle cycle
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  review:
    summary: >-
      Synapsin-1 participates in the synaptic vesicle cycle by regulating SV clustering,
      reserve pool dynamics, and vesicle availability for release.
    action: ACCEPT
    reason: >-
      Participation in the synaptic vesicle cycle is well-established for SYN1. The protein
      regulates key steps in the cycle including reserve pool maintenance and SV mobilization.
    supported_by:
      - reference_id: PMID:15217342
        supporting_text: "Neurotransmitter release is mediated by exocytosis of synaptic vesicles at the presynaptic active zone of nerve terminals."

- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:23406870
  review:
    summary: >-
      The PMID:23406870 paper demonstrates that SYN1 interacts with SYN2 through
      co-immunoprecipitation. The Q555X mutation virtually abolished the ability of SynI
      to interact with SynIIa and strongly reduced interaction with SynIIb.
    action: MODIFY
    reason: >-
      While the paper does demonstrate protein binding (specifically to SYN2), the generic
      "protein binding" term is not informative. A more specific term would be preferable,
      though the current GO may not have a perfect term. Consider keeping as is since the
      specific binding partner (SYN2) is documented.
    proposed_replacement_terms:
      - id: GO:0042802
        label: identical protein binding
    additional_reference_ids:
      - PMID:23406870
    supported_by:
      - reference_id: PMID:23406870
        supporting_text: "We found that the Q555X truncation virtually abolished the ability of SynI to interact with SynIIa and strongly reduced the interaction with SynIIb."

- term:
    id: GO:0098793
    label: presynapse
  evidence_type: IDA
  original_reference_id: PMID:21441247
  review:
    summary: >-
      The paper demonstrates presynapse localization through immunofluorescence studies
      showing SYN1 targeting to nerve terminals. The variants had differential effects
      on nerve terminal targeting.
    action: ACCEPT
    reason: >-
      Presynapse localization is directly demonstrated by PMID:21441247 through imaging
      of fluorescent SYN1 at presynaptic terminals. This is a core localization annotation.
    supported_by:
      - reference_id: PMID:21441247
        supporting_text: "The missense A550T and T567A mutants displayed impaired targeting to nerve terminals."

- term:
    id: GO:2000300
    label: regulation of synaptic vesicle exocytosis
  evidence_type: IMP
  original_reference_id: PMID:21441247
  review:
    summary: >-
      The paper shows that SYN1 mutations fail to rescue defects in synaptic vesicle pool
      size and trafficking in SynI knockout neurons. The Q555X mutant had dramatic impact
      on SV dynamics. Wild-type SYN1 rescued the knockout phenotype.
    action: ACCEPT
    reason: >-
      This IMP annotation is well-supported by the paper. The rescue experiments demonstrate
      that SYN1 regulates SV exocytosis, as the mutants failed to rescue defects in SV pool
      size and trafficking while wild-type SYN1 did.
    supported_by:
      - reference_id: PMID:21441247
        supporting_text: "When expressed in synapsin I (SynI) knockout (KO) neurons, all the D-domain mutants failed in rescuing the impairment in the size and trafficking of synaptic vesicle pools, whereas the wild-type human SynI fully reverted the KO phenotype."

- term:
    id: GO:0106006
    label: cytoskeletal protein-membrane anchor activity
  evidence_type: TAS
  original_reference_id: PMID:2110562
  review:
    summary: >-
      The paper describes synapsin I as mediating attachment of synaptic vesicles to the
      cytoskeleton. This molecular function captures SYN1's role in linking SVs to actin.
    action: ACCEPT
    reason: >-
      This is an excellent molecular function annotation for SYN1. The protein links synaptic
      vesicle membranes to the actin cytoskeleton, serving as an anchor between the two.
    supported_by:
      - reference_id: PMID:2110562
        supporting_text: "Synapsin I is a peripheral membrane protein of synaptic vesicles that mediates their attachment to the cytoskeleton."

- term:
    id: GO:0005856
    label: cytoskeleton
  evidence_type: IDA
  original_reference_id: PMID:24327345
  review:
    summary: >-
      PMID:24327345 is about DYRK1A, not SYN1. The paper mentions that DYRK1A phosphorylates
      synaptic proteins including synaptojanin 1 and amphiphysin I, and shows DYRK1A
      association with cytoskeleton. This may be a misassigned annotation.
    action: UNDECIDED
    reason: >-
      The cited paper is primarily about DYRK1A localization and phosphorylation, not SYN1.
      While it mentions SYN1 tangentially in the context of DYRK1A substrates, it does not
      directly demonstrate SYN1 cytoskeleton localization. However, SYN1 is known to bind
      actin (cytoskeleton). The annotation itself may be correct but the reference appears
      to be misassigned.
    additional_reference_ids:
      - PMID:2110562
    supported_by:
      - reference_id: PMID:2110562
        supporting_text: "Synapsin I is a peripheral membrane protein of synaptic vesicles that mediates their attachment to the cytoskeleton."

- term:
    id: GO:0046928
    label: regulation of neurotransmitter secretion
  evidence_type: TAS
  original_reference_id: PMID:21563316
  review:
    summary: >-
      PMID:21563316 is a review about synaptic vesicle trafficking and Parkinson's disease.
      It discusses how SV trafficking affects neurotransmitter release. SYN1's role in
      regulating neurotransmitter secretion through SV pool control is well-established.
    action: ACCEPT
    reason: >-
      Regulation of neurotransmitter secretion is a core function of SYN1. The protein
      controls SV availability for release, directly regulating neurotransmitter secretion
      rates and dynamics.
    supported_by:
      - reference_id: PMID:21563316
        supporting_text: "Presynaptic terminals maintain neurotransmitter release during repeated rounds of stimulation using local recycling of synaptic vesicles (SV)."
      - reference_id: file:human/SYN1/SYN1-uniprot.txt
        supporting_text: "Acts as a regulator of synaptic vesicles trafficking, involved in the control of neurotransmitter release at the pre-synaptic terminal"

- term:
    id: GO:0005524
    label: ATP binding
  evidence_type: TAS
  original_reference_id: PMID:15217342
  review:
    summary: >-
      PMID:15217342 is a review of the synaptic vesicle cycle by Sudhof. While it discusses
      many SV proteins, the specific ATP binding activity of SYN1 is well-documented
      through its domain C ATP-grasp fold.
    action: ACCEPT
    reason: >-
      ATP binding is well-established for SYN1 through its domain C ATP-binding site.
      Multiple sources confirm this molecular function.
    supported_by:
      - reference_id: file:human/SYN1/SYN1-deep-research-falcon.md
        supporting_text: "Synapsin-1's domain C binds ATP/ADP (calcium-facilitated) and actin."

- term:
    id: GO:2000300
    label: regulation of synaptic vesicle exocytosis
  evidence_type: NAS
  original_reference_id: PMID:10099709
  review:
    summary: >-
      PMID:10099709 is a review on genetics of synaptic vesicle function. While it covers
      synaptic vesicle proteins including synapsins, the NAS evidence code indicates a
      non-traceable author statement. The function itself is well-supported by other evidence.
    action: ACCEPT
    reason: >-
      Although NAS is a weaker evidence code, the annotation is correct and supported by
      stronger evidence (IMP from PMID:21441247). Regulation of SV exocytosis is a core
      function of SYN1.
    supported_by:
      - reference_id: PMID:10099709
        supporting_text: "Synaptic transmission starts with the release of neurotransmitters by exocytosis of synaptic vesicles."

- term:
    id: GO:0008021
    label: synaptic vesicle
  evidence_type: TAS
  original_reference_id: PMID:16141272
  review:
    summary: >-
      PMID:16141272 is about Rab3a and Rab5a, not directly about SYN1. However, it discusses
      synaptic vesicle proteins in general. SYN1 localization to synaptic vesicles is
      well-established by other sources.
    action: ACCEPT
    reason: >-
      Synaptic vesicle localization is accurate for SYN1, though this particular reference
      is not ideal. The annotation is well-supported by other evidence and is a core
      localization for the protein.
    supported_by:
      - reference_id: PMID:2110562
        supporting_text: "Synapsin I is a peripheral membrane protein of synaptic vesicles that mediates their attachment to the cytoskeleton."

- term:
    id: GO:0019901
    label: protein kinase binding
  evidence_type: ISS
  original_reference_id: GO_REF:0000024
  review:
    summary: >-
      Protein kinase binding is inferred by sequence similarity. SYN1 is a substrate of
      multiple kinases and likely binds them during phosphorylation.
    action: ACCEPT
    reason: >-
      Protein kinase binding is consistent with SYN1 being a major phosphoprotein substrate
      of PKA, CaMK2, and MAPK. The ISS annotation is appropriate.
    supported_by:
      - reference_id: file:human/SYN1/SYN1-uniprot.txt
        supporting_text: "Substrate of different protein kinases"

- term:
    id: GO:0007268
    label: chemical synaptic transmission
  evidence_type: TAS
  original_reference_id: PMID:2110562
  review:
    summary: >-
      The Sudhof 1990 paper describes the structure of human synapsin I and its role as
      a synaptic vesicle protein involved in mediating SV attachment to the cytoskeleton,
      which is essential for synaptic transmission.
    action: ACCEPT
    reason: >-
      Chemical synaptic transmission involvement is well-supported. SYN1's role in SV
      trafficking is essential for synaptic transmission. The TAS annotation from this
      foundational paper is appropriate.
    supported_by:
      - reference_id: PMID:2110562
        supporting_text: "Synapsin I is a peripheral membrane protein of synaptic vesicles that mediates their attachment to the cytoskeleton."

references:
- id: GO_REF:0000002
  title: Gene Ontology annotation through association of InterPro records with GO terms
  findings: []
- id: GO_REF:0000024
  title: Manual transfer of experimentally-verified manual GO annotation data to orthologs
    by curator judgment of sequence similarity
  findings: []
- id: GO_REF:0000033
  title: Annotation inferences using phylogenetic trees
  findings: []
- id: GO_REF:0000043
  title: Gene Ontology annotation based on UniProtKB/Swiss-Prot keyword mapping
  findings: []
- id: GO_REF:0000044
  title: Gene Ontology annotation based on UniProtKB/Swiss-Prot Subcellular Location
    vocabulary mapping, accompanied by conservative changes to GO terms applied by
    UniProt
  findings: []
- id: GO_REF:0000107
  title: Automatic transfer of experimentally verified manual GO annotation data to
    orthologs using Ensembl Compara
  findings: []
- id: GO_REF:0000117
  title: Electronic Gene Ontology annotations created by ARBA machine learning models
  findings: []
- id: GO_REF:0000120
  title: Combined Automated Annotation using Multiple IEA Methods
  findings: []
- id: PMID:10099709
  title: 'Genetics of synaptic vesicle function: toward the complete functional anatomy
    of an organelle.'
  findings:
  - statement: Review of synaptic vesicle protein functions
    supporting_text: "Synaptic transmission starts with the release of neurotransmitters by exocytosis of synaptic vesicles."
- id: PMID:15217342
  title: The synaptic vesicle cycle.
  findings:
  - statement: Comprehensive review of SV cycle mechanisms
    supporting_text: "Neurotransmitter release is mediated by exocytosis of synaptic vesicles at the presynaptic active zone of nerve terminals."
- id: PMID:16141272
  title: Real-time imaging of Rab3a and Rab5a reveals differential roles in presynaptic
    function.
  findings:
  - statement: Study on synaptic vesicle protein dynamics
    supporting_text: "We investigated the roles of two Rab-family proteins, Rab3a and Rab5a, in hippocampal synaptic transmission using real-time fluorescence imaging."
- id: PMID:2110562
  title: The structure of the human synapsin I gene and protein.
  findings:
  - statement: Foundational paper describing SYN1 gene structure
    supporting_text: "Synapsin I is a peripheral membrane protein of synaptic vesicles that mediates their attachment to the cytoskeleton."
  - statement: Describes domain organization and alternative splicing
    supporting_text: "Domain C, the central homologous domain implicated in the binding of synapsin I to actin and to synaptic vesicles, is divided into nine exons."
  - statement: Documents SYN1 as peripheral membrane protein of synaptic vesicles
    supporting_text: "Synapsin I is a peripheral membrane protein of synaptic vesicles that mediates their attachment to the cytoskeleton."
- id: PMID:21441247
  title: SYN1 loss-of-function mutations in autism and partial epilepsy cause impaired
    synaptic function.
  findings:
  - statement: Identified Q555X mutation in SYN1 in epilepsy/ASD patients
    supporting_text: "Here we report a Q555X mutation in synapsin 1 (SYN1), an X-linked gene encoding for a neuron-specific phosphoprotein implicated in the regulation of neurotransmitter release and synaptogenesis."
  - statement: Demonstrated failure of mutants to rescue SV pool defects in KO neurons
    supporting_text: "When expressed in synapsin I (SynI) knockout (KO) neurons, all the D-domain mutants failed in rescuing the impairment in the size and trafficking of synaptic vesicle pools, whereas the wild-type human SynI fully reverted the KO phenotype."
  - statement: Showed role in axon outgrowth and synaptogenesis
    supporting_text: "Here we report a Q555X mutation in synapsin 1 (SYN1), an X-linked gene encoding for a neuron-specific phosphoprotein implicated in the regulation of neurotransmitter release and synaptogenesis."
  - statement: Documented phosphorylation by CaMK2 and MAPK1
    supporting_text: "The majority of these SYN1 mutations were clustered in the proline-rich D-domain which is substrate of multiple protein kinases."
- id: PMID:21563316
  title: Synaptic vesicle trafficking and Parkinson's disease.
  findings:
  - statement: Review on SV trafficking in neurodegeneration
    supporting_text: "Presynaptic terminals maintain neurotransmitter release during repeated rounds of stimulation using local recycling of synaptic vesicles (SV)."
- id: PMID:23406870
  title: Epileptogenic Q555X SYN1 mutant triggers imbalances in release dynamics and
    short-term plasticity.
  findings:
  - statement: Detailed analysis of Q555X mutant effects on synaptic function
    supporting_text: "We identified distinct physiological changes in quantal parameters, release dynamics and STP at inhibitory and excitatory synapses."
  - statement: Demonstrated differential effects on excitatory vs inhibitory synapses
    supporting_text: "No changes in miniature EPSC (mEPSC) and miniature IPSC (mIPSC) amplitude, as well as in their rise and decay times, were observed"
  - statement: Showed SYN1 forms oligomers with SYN2
    supporting_text: "We found that the Q555X truncation virtually abolished the ability of SynI to interact with SynIIa and strongly reduced the interaction with SynIIb."
  - statement: Documented network hyperexcitability from SYN1 mutations
    supporting_text: "These imbalances triggered an overt hyperexcitability compatible with a causal role of Syn I mutations in the development of epilepsy and ASD."
- id: PMID:24327345
  title: Intracellular distribution of differentially phosphorylated dual-specificity
    tyrosine phosphorylation-regulated kinase 1A (DYRK1A).
  findings:
  - statement: Primarily about DYRK1A, not SYN1
- id: file:human/SYN1/SYN1-deep-research-falcon.md
  title: Deep research synthesis on SYN1 function (2023-2024 literature)
  findings:
  - statement: SYN1 scaffolds SVs into dynamic clusters forming reserve pool
  - statement: LLPS mechanism for SV condensation
  - statement: PTM regulation by phosphorylation and SUMOylation
  - statement: Presynaptic localization on SV clusters

core_functions:
- molecular_function:
    id: GO:0106006
    label: cytoskeletal protein-membrane anchor activity
  description: >-
    Synapsin-1 serves as a molecular anchor that links synaptic vesicle membranes to the
    actin cytoskeleton. Through its domain A (phospholipid binding) and domain C (actin binding),
    the protein tethers SVs to the cytoskeleton, maintaining the reserve pool of synaptic
    vesicles at presynaptic terminals.
  directly_involved_in:
  - id: GO:0097091
    label: synaptic vesicle clustering
  - id: GO:2000300
    label: regulation of synaptic vesicle exocytosis
  locations:
  - id: GO:0098793
    label: presynapse
  - id: GO:0098850
    label: extrinsic component of synaptic vesicle membrane
  supported_by:
  - reference_id: PMID:2110562
    supporting_text: >-
      Synapsin I is a peripheral membrane protein of synaptic vesicles that mediates their attachment to the cytoskeleton.
  - reference_id: PMID:23406870
    supporting_text: >-
      Syns are implicated in the regulation of SV trafficking between the reserve pool (RP) and the readily releasable pool (RRP).

proposed_new_terms: []

suggested_questions:
- question: >-
    What are the specific contributions of different synapsin family members (SYN1,
    SYN2, SYN3) to excitatory vs inhibitory synapse function? Studies show differential
    effects at excitatory and inhibitory synapses, but the specific roles of each
    family member are not fully delineated.
- question: >-
    How does SUMOylation at K687 regulate SYN1 function in the reserve pool? Recent
    research identifies SUMOylation as a regulator of reserve pool size, but the
    molecular mechanism is not fully understood.
- question: >-
    What is the structural basis for SYN1 liquid-liquid phase separation and how is
    it regulated by PTMs? LLPS is emerging as a key mechanism for SV clustering, but
    the structural details of synapsin condensate formation need further characterization.

suggested_experiments:
- description: >-
    Cryo-EM structural analysis of SYN1 condensates with synaptic vesicles to determine
    the organization of SYN1 at vesicle-vesicle interfaces. Understanding the structural
    basis of LLPS-mediated SV clustering would provide molecular insight into how SYN1
    organizes the reserve pool.
  hypothesis: >-
    SYN1 forms organized multivalent networks at vesicle-vesicle interfaces through
    its intrinsically disordered domains.
- description: >-
    Site-directed mutagenesis of phosphorylation and SUMOylation sites followed by
    live-cell imaging of SV dynamics in neurons. This would delineate the specific
    contributions of each PTM to SYN1 function in regulating SV mobility and release.
  hypothesis: >-
    Specific phosphorylation sites have distinct effects on SYN1-membrane vs SYN1-actin
    interactions.