Affinage

PACSIN1

Protein kinase C and casein kinase substrate in neurons protein 1 · UniProt Q9BY11

Length
444 aa
Mass
51.0 kDa
Annotated
2026-06-10
20 papers in source corpus 14 papers cited in narrative 14 extracted findings
Cross-family judge vs UniProt: Affinage preferred faithfulness: 6/7 claims corpus-supported (86%)

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

PACSIN1 is a neuronal F-BAR/SH3 domain adaptor that couples membrane deformation to the trafficking of synaptic receptors and to membrane fusion events along the autophagic and endocytic pathways (PMID:16617342, PMID:31601944). At excitatory synapses it directly and selectively binds the NMDAR subunit NR3A through its NPF motifs, assembling a dynamin/clathrin complex that drives activity-dependent endocytosis of NR3A-containing receptors, and its loss causes NR3A to accumulate at synaptic sites (PMID:16617342). Through distinct modules it also governs AMPA receptor handling, with the F-BAR and SH3 domains required for NMDAR-dependent GluA2 internalization and the PICK1-binding variable region required for AMPAR recycling (PMID:27488904). PACSIN1 is the most abundant interactor of the K+-Cl- cotransporter KCC2 and acts as a negative regulator of KCC2, tuning synaptic inhibition (PMID:29028184). Its SH3 domain engages proline-rich ligands including the TRPV4 N-terminal proline-rich region, where binding rigidifies the adjacent PIP2 site in a hierarchical interaction network (PMID:30244966), and it binds Tau in axons to restrain Tau-microtubule association and control axonal elongation and branching (PMID:23035120). Beyond neurons, PACSIN1 is required for amphisome-lysosome fusion during basal autophagy, where it interacts with the autophagic SNARE SNAP29 and organizes STX17/YKT6 SNARE complex assembly (PMID:35771772), acts as an injured-axon-derived ligand for Schwann-cell LRP1 that transactivates TrkC to support repair signaling (PMID:38372375), and forms a trimolecular complex with TRAF4 and TRAF6 that restrains TLR7-mediated type I interferon production, a balance disrupted by the disease-associated Q59K mutation (PMID:22488361, PMID:36622335). PACSIN1 protein abundance is itself controlled by UBE3A-mediated K48-linked polyubiquitination targeting it for proteasomal degradation (PMID:40671377).

Mechanistic history

Synthesis pass · year-by-year structured walk · 14 steps
  1. 2006 High

    Established PACSIN1 as a receptor-specific endocytic adaptor by showing it directly binds NR3A and drives activity-dependent NMDAR internalization, defining its first mechanistic role at synapses.

    Evidence Co-IP, pulldown, domain mapping and dominant-negative disruption with live imaging in rat hippocampal neurons

    PMID:16617342

    Open questions at the time
    • Does not resolve how NPF-motif binding is regulated by activity
    • No structural detail of the PACSIN1-dynamin-clathrin assembly
  2. 2012 Medium

    Extended PACSIN1 function beyond endocytosis to cytoskeletal regulation by showing it binds Tau and restrains Tau-microtubule association during axon growth.

    Evidence Co-IP, dominant-negative blockade and microtubule binding assays in mouse DRG neurons

    PMID:23035120

    Open questions at the time
    • Binding domain on PACSIN1 not mapped
    • Mechanism by which PACSIN1 limits Tau-MT binding unresolved
  3. 2012 Medium

    Identified a non-neuronal role in innate immunity, showing PACSIN1 is selectively required for TLR7/9-driven type I interferon production.

    Evidence shRNA knockdown in human pDC line and PACSIN1 knockout mice with cytokine ELISA

    PMID:22488361

    Open questions at the time
    • Molecular partners in the IFN cascade not identified at this stage
    • Cell-intrinsic mechanism in pDCs unresolved
  4. 2016 High

    Dissected division of labor among PACSIN1 domains, separating F-BAR/SH3-dependent AMPAR internalization from variable-region/PICK1-dependent recycling.

    Evidence pHluorin-GluA2 live imaging with domain-deletion mutants under NMDAR activation in neurons

    PMID:27488904

    Open questions at the time
    • How the two activities are coordinated temporally unknown
    • PICK1 binding interface not structurally defined
  5. 2017 High

    Defined PACSIN1 as a negative regulator of the chloride cotransporter KCC2, linking it to control of synaptic inhibition.

    Evidence Native KCC2 interactome by MS, biochemical validation, shRNA knockdown with electrophysiology

    PMID:29028184

    Open questions at the time
    • Mechanism by which PACSIN1 lowers KCC2 abundance not defined
    • Direct vs. trafficking-mediated regulation unresolved
  6. 2018 High

    Provided atomic-level basis for SH3-mediated ligand engagement, showing the SH3 domain binds the TRPV4 proline-rich region and hierarchically rigidifies the adjacent PIP2 site.

    Evidence NMR structure of PACSIN3 SH3-TRPV4 PRR complex with affinity measurements for PACSIN1/2/3

    PMID:30244966

    Open questions at the time
    • Functional consequence for TRPV4 channel gating in cells not measured
    • PACSIN1-specific contribution vs. paralogs not isolated
  7. 2019 Low

    Modeled how the F-BAR domain senses and bends membranes, proposing lateral dimer assembly and curvature preference.

    Evidence All-atom and coarse-grained molecular dynamics simulations on lipid membranes

    PMID:31601944

    Open questions at the time
    • Computational only — no experimental validation of the bending mechanism
    • Predicted curvature preference not tested in cells
  8. 2020 Medium

    Provided solution structure of the human PACSIN1 SH3 domain, giving a structural framework for its protein-interaction network.

    Evidence Solution NMR backbone/side-chain assignments and homology modeling

    PMID:32236802

    Open questions at the time
    • No ligand-bound structure of PACSIN1 SH3 itself
    • Limited functional validation
  9. 2021 Medium

    Linked Tau phosphorylation to PACSIN1-dependent synapse weakening, connecting the Tau interaction to AMPAR trafficking.

    Evidence Phosphomutant tau knock-in, electrophysiology, Co-IP and shRNA knockdown in rat CA1 neurons

    PMID:34290082

    Open questions at the time
    • Mechanism linking reduced Tau:PACSIN1 binding to AMPAR redistribution unclear
    • Relevance to tauopathy in vivo untested here
  10. 2022 High

    Established a fusion-machinery role, showing PACSIN1 organizes autophagic SNARE complexes for amphisome-lysosome fusion selectively in basal autophagy.

    Evidence PACSIN1 deletion, EM, colocalization, SNAP29/STX17/YKT6 Co-IP and C. elegans sdpn-1 validation

    PMID:35771772

    Open questions at the time
    • How PACSIN1 distinguishes basal from starvation-induced autophagy unknown
    • Whether SNARE organization requires membrane bending not resolved
  11. 2023 High

    Defined the immune mechanism as a TRAF4/TRAF6 trimolecular complex and showed a disease variant (Q59K) shifts binding to unleash TLR7-driven interferon.

    Evidence CRISPR-edited Q59K/null variants in human cells and mice, Co-IP, luciferase reporters, RNAi

    PMID:36622335

    Open questions at the time
    • Structural basis of the TRAF4/TRAF6/PACSIN1 complex not solved
    • How N-WASP gain-of-binding feeds into TRAF6 activation unresolved
  12. 2024 High

    Identified PACSIN1 as a secreted axon-derived LRP1 ligand that transactivates TrkC to drive Schwann cell repair, revealing an extracellular signaling role.

    Evidence LRP1-Fc ligand capture, Co-IP, conditional Lrp1-knockout mice, downstream effector inhibition and transcriptomics

    PMID:38372375

    Open questions at the time
    • Mechanism of PACSIN1 release from injured axons unknown
    • How an F-BAR/SH3 adaptor acts as an extracellular ligand structurally unexplained
  13. 2024 Medium

    Connected PACSIN1's autophagy function to immune evasion, showing it promotes selective autophagy of MHC-I and suppresses CD8+ T-cell infiltration in gastric cancer.

    Evidence PACSIN1 knockout, MHC-I/PACSIN1 FISH colocalization, flow cytometry and in vivo tumor models

    PMID:38826133

    Open questions at the time
    • Whether MHC-I autophagy uses the same SNAP29/STX17 machinery untested
    • Direct PACSIN1-MHC-I interaction not demonstrated
  14. 2025 Medium

    Placed PACSIN1 under proteostatic control, showing UBE3A K48-polyubiquitinates it for proteasomal degradation, linking it to AMPAR recycling in disease context.

    Evidence LC-MS/MS proteomics of UBE3A-knockout iPSC cortical neurons and ubiquitination assay

    PMID:40671377

    Open questions at the time
    • Ubiquitination sites on PACSIN1 not mapped
    • Functional link to AMPAR recycling not directly tested

Open questions

Synthesis pass · forward-looking unresolved questions
  • How PACSIN1's membrane-bending F-BAR activity is mechanistically integrated with its diverse SH3-mediated cargo and signaling roles across neurons, autophagy, and immunity remains unresolved.
  • No unified structural model linking F-BAR curvature generation to specific cargo selection
  • Cell-type-specific regulation of the competing interaction network undefined

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0060090 molecular adaptor activity 3 GO:0008092 cytoskeletal protein binding 1 GO:0008289 lipid binding 1 GO:0048018 receptor ligand activity 1
Localization
GO:0005764 lysosome 2 GO:0005886 plasma membrane 2 GO:0005829 cytosol 1
Pathway
R-HSA-112316 Neuronal System 3 R-HSA-168256 Immune System 2 R-HSA-5653656 Vesicle-mediated transport 2 R-HSA-9612973 Autophagy 2
Complex memberships
PACSIN1-TRAF4-TRAF6 complexSTX17/YKT6/SNAP29 autophagic SNARE complex

Evidence

Reading pass · 14 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2006 PACSIN1/syndapin1 directly and selectively binds the carboxy-terminal domain of the NMDAR subunit NR3A through its NPF motifs, assembles a complex including dynamin and clathrin, and mediates activity-dependent endocytosis of NR3A-containing NMDARs from the dendritic plasma membrane; disruption of PACSIN1 function causes NR3A accumulation at synaptic sites. Co-immunoprecipitation, pulldown assays, dominant-negative disruption in cultured rat hippocampal neurons, live-cell imaging of endocytosis Nature neuroscience High 16617342
2017 PACSIN1 is the most abundant interactor of the K+-Cl- cotransporter KCC2 in the mouse brain; shRNA knockdown of PACSIN1 in hippocampal neurons increases KCC2 expression and hyperpolarizes the reversal potential for Cl-, establishing PACSIN1 as a negative regulator of KCC2 and thus of synaptic inhibition. Functional proteomics (native KCC2 interactome by mass spectrometry), biochemical validation of PACSIN1-KCC2 interaction, shRNA knockdown with electrophysiological readout eLife High 29028184
2016 PACSIN1 plays dual roles in controlling NMDAR-dependent GluA2 (AMPAR subunit) internalization and recycling; the F-BAR and SH3 domains are required for NMDAR-dependent GluA2 internalization, while the variable region (which binds PICK1) is required for correct AMPAR recycling but not internalization. pHluorin-GluA2 live-cell imaging, structure-function analysis with domain deletion mutants, NMDAR activation assays in neurons Scientific reports High 27488904
2012 PACSIN1 regulates TLR7/9-mediated type I interferon production in plasmacytoid dendritic cells (pDCs); shRNA knockdown in human pDC line inhibits type I IFN response to TLR9 ligand, and PACSIN1-deficient mice show reduced IFN-α production in response to CpG-ODN and virus without affecting proinflammatory cytokine production, indicating a specific role in the type I IFN signaling cascade. shRNA knockdown in human pDC cell line, PACSIN1 knockout mice, cytokine measurement by ELISA European journal of immunology Medium 22488361
2018 The SH3 domains of PACSIN1, 2, and 3 bind the proline-rich region (PRR) of the TRPV4 N-terminus as a class I polyproline II helix (with a conserved cis-proline break); PACSIN/Syndapin SH3 domain binding rigidifies both the PRR and the adjacent PIP2 binding site, and PACSIN binding influences the PIP2 binding site but not vice versa, establishing a hierarchical interaction network. NMR structure determination of PACSIN3 SH3 domain–TRPV4 PRR complex, binding affinity measurements for PACSIN1/2/3 SH3 domains, NMR chemical shift mapping Structure High 30244966
2012 PACSIN1 interacts with Tau in axons; PACSIN1 blockade impairs axonal elongation and increases primary axonal branching in mouse DRG neurons by increasing Tau binding to microtubules, causing Tau accumulation in the central domain of growth cones and promoting microtubule network stability. Co-immunoprecipitation, dominant-negative PACSIN1 blockade in mouse DRG neurons, microtubule binding assays, immunofluorescence The Journal of biological chemistry Medium 23035120
2021 Phosphorylation of Tau at serine residues 396/404 (pTau) decreases Tau:PACSIN1 binding and evokes PACSIN1-dependent functional and structural synapse weakening; knockdown of PACSIN1 increases AMPAR-mediated current at extrasynaptic regions, supporting a role for these proteins in AMPAR trafficking regulation. In vitro genetic knock-in of phosphorylation mutant human tau in rat CA1 hippocampal neurons, electrophysiology, Co-immunoprecipitation, shRNA knockdown The Journal of neuroscience Medium 34290082
2022 PACSIN1 is required for amphisome-lysosome fusion during basal (nutrient-rich) autophagy but not starvation-induced autophagy; PACSIN1 interacts with the autophagic SNARE protein SNAP29 and is required for proper assembly of STX17 and YKT6 SNARE complexes. PACSIN1 is also required for lysophagy and aggrephagy but not mitophagy, indicating cargo-specific fusion mechanisms. PACSIN1 deletion, electron microscopy, co-localization analysis, Co-immunoprecipitation with SNAP29/STX17/YKT6, C. elegans sdpn-1 deletion as ortholog validation PLoS genetics High 35771772
2023 PACSIN1 forms a trimolecular complex with TRAF4 and TRAF6 to regulate type I IFN signaling; the disease-associated Q59K mutation augments PACSIN1 binding to N-WASP while decreasing binding to TRAF4, leading to unrestrained TRAF6-mediated type I IFN activation and selective enhancement of TLR7 (but not TLR9) signaling. CRISPR/Cas9 introduction of Q59K and null variants, co-immunoprecipitation, luciferase reporter assays, RNA interference, immunofluorescence, flow cytometry Arthritis & rheumatology High 36622335
2019 Molecular dynamics simulations show that PACSIN1 F-BAR domain has internal structural flexibility and that two PACSIN1 dimers spontaneously assemble via lateral interactions; the assembled dimers bend tensionless lipid membranes, and a single PACSIN1 dimer senses membrane curvature by preferentially binding buckled membranes at a preferred curvature. All-atom and coarse-grained molecular dynamics simulations of PACSIN1 on lipid membranes Scientific reports Low 31601944
2024 PACSIN1 released from injured axons binds to the Schwann cell receptor LRP1; recombinant PACSIN1 activates c-Jun and ERK1/2 in Schwann cells in an LRP1-dependent and NMDA-R-dependent manner, and transactivates the receptor tyrosine kinase TrkC to promote Schwann cell repair signaling, migration, and survival. LRP1-Fc ligand capture from injured nerve, Co-IP validation, recombinant PACSIN1 treatment with LRP1 silencing and TrkC inhibition/silencing, intraneural injection in conditional Lrp1-knockout mice, transcriptome profiling Glia High 38372375
2024 PACSIN1 promotes lysosomal fusion and selective autophagy of MHC-I, thereby degrading MHC-I and suppressing antigen presentation and CD8+ T-cell infiltration in gastric cancer; PACSIN1 deficiency inhibits MHC-I autophagy and increases MHC-I surface expression. PACSIN1 knockout, FISH colocalization of PACSIN1 and MHC-I, flow cytometry for MHC-I and CD8+ T cells, in vivo tumor models Acta biochimica et biophysica Sinica Medium 38826133
2025 UBE3A (the Angelman syndrome E3 ubiquitin ligase) polyubiquitinates PACSIN1 with K48-linked chains to target it for proteasomal degradation; loss of UBE3A increases PACSIN1 protein abundance in human cortical neurons, with implications for AMPA receptor recycling. LC-MS/MS proteomics of UBE3A knockout vs. wild-type human iPSC-derived cortical neurons, ubiquitination assay Molecular and cellular biology Medium 40671377
2020 NMR backbone and side-chain assignments of the human PACSIN1 SH3 domain identified five β-strands linked by flexible loops, consistent with a canonical SH3 fold, providing structural context for its interaction network. Solution NMR (2D HSQC/HMQC and multiple 3D experiments), homology modeling Biomolecular NMR assignments Medium 32236802

Source papers

Stage 0 corpus · 20 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2006 Endocytosis and synaptic removal of NR3A-containing NMDA receptors by PACSIN1/syndapin1. Nature neuroscience 171 16617342
2011 SdPI, the first functionally characterized Kunitz-type trypsin inhibitor from scorpion venom. PloS one 57 22087336
2017 Native KCC2 interactome reveals PACSIN1 as a critical regulator of synaptic inhibition. eLife 40 29028184
2016 PACSIN1 regulates the dynamics of AMPA receptor trafficking. Scientific reports 39 27488904
2012 PACSIN1 regulates the TLR7/9-mediated type I interferon response in plasmacytoid dendritic cells. European journal of immunology 37 22488361
2018 Structural Basis of TRPV4 N Terminus Interaction with Syndapin/PACSIN1-3 and PIP2. Structure (London, England : 1993) 34 30244966
1986 Evidence for different receptor sites for the novel cardiotonic S-DPI 201-106, ATX II and veratridine on the cardiac sodium channel. European journal of pharmacology 32 2426127
2019 Curvature induction and sensing of the F-BAR protein Pacsin1 on lipid membranes via molecular dynamics simulations. Scientific reports 31 31601944
2012 PACSIN1, a Tau-interacting protein, regulates axonal elongation and branching by facilitating microtubule instability. The Journal of biological chemistry 24 23035120
2021 Regulation of Synapse Weakening through Interactions of the Microtubule Associated Protein Tau with PACSIN1. The Journal of neuroscience : the official journal of the Society for Neuroscience 20 34290082
2022 PACSIN1 is indispensable for amphisome-lysosome fusion during basal autophagy and subsets of selective autophagy. PLoS genetics 17 35771772
2023 De Novo PACSIN1 Gene Variant Found in Childhood Lupus and a Role for PACSIN1/TRAF4 Complex in Toll-like Receptor 7 Activation. Arthritis & rheumatology (Hoboken, N.J.) 16 36622335
2024 PACSIN1 promotes immunosuppression in gastric cancer by degrading MHC-I. Acta biochimica et biophysica Sinica 10 38826133
2010 Defense against cannibalism: the SdpI family of bacterial immunity/signal transduction proteins. The Journal of membrane biology 10 20563570
2024 Axon-derived PACSIN1 binds to the Schwann cell survival receptor, LRP1, and transactivates TrkC to promote gliatrophic activities. Glia 4 38372375
2025 The Ubiquitin E3 Ligase UBE3A Regulates GRIPAP1 and PACSIN1 Proteins Linked to the Endocytic Recycling of AMPA Receptors. Molecular and cellular biology 1 40671377
2020 1H, 13C, and 15N chemical shift assignment of human PACSIN1/syndapin I SH3 domain in solution. Biomolecular NMR assignments 1 32236802
2018 Functional analysis of DNA methylation of the PACSIN1 promoter in pig peripheral blood mononuclear cells. Journal of cellular biochemistry 1 30537176
2025 pacsin1 inhibits antiviral immunity by promoting MITA degradation through autophagy in miiuy croaker, Miichthysmiiuy. Fish & shellfish immunology 0 39923887
2025 ANKK1, ANKRD50, GRK5, PACSIN1 and VPS8 are novel candidate genes associated with late onset Parkinson's disease: Definition of a novel predictive protocol based on polygenic model of inheritance. Neurobiology of disease 0 40494419

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