Affinage

ACAP1

Arf-GAP with coiled-coil, ANK repeat and PH domain-containing protein 1 · UniProt Q15027

Length
740 aa
Mass
81.5 kDa
Annotated
2026-06-09
12 papers in source corpus 10 papers cited in narrative 10 extracted findings
Cross-family judge vs UniProt: Affinage preferred faithfulness: 5/5 claims corpus-supported (100%)

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

ACAP1 is an ARF6 GTPase-activating protein that operates as a coat component of the endocytic recycling pathway, sorting cargo from endosomes back to the plasma membrane to control processes such as cell migration and glucose homeostasis (PMID:17664335). It assembles into a novel ARF6-regulated clathrin coat complex that drives stimulation-dependent recycling of integrin beta1 and insulin-stimulated recycling of Glut4 (PMID:17664335), and it localizes to a tubular recycling endosome distinct from the ARAP2/APPL1-positive compartment, with the two ARF6 GAPs exerting opposing effects on integrin internalization and focal adhesions (PMID:25225293). Cargo engagement is switch-regulated: Akt phosphorylation of ACAP1 relieves a localized autoinhibition to enhance binding of a defined recycling sorting signal in the integrin beta1 cytoplasmic tail, coupling recycling to upstream signaling (PMID:16256741, PMID:22645133). Its membrane-deforming activity arises from an unconventional division of labor between adjacent domains, in which the PH domain mediates membrane binding and curvature generation while the BAR domain mediates clustering of ACAP1 molecules into a lattice that deforms the membrane (PMID:25284369). Beyond integrin and Glut4 trafficking, ACAP1 acts in a Rab10-ACAP1-Arf6 cascade that inactivates Arf6 to arrest the M4 muscarinic acetylcholine receptor in early endosomes (PMID:36917255), and it scaffolds a PTPN9-FGFR2 complex to facilitate FGFR2 dephosphorylation, a function requiring its PH and Arf-GAP domains (PMID:37505213).

Mechanistic history

Synthesis pass · year-by-year structured walk · 10 steps
  1. 2005 High

    Established ACAP1 as a signaling-regulated factor in cargo recycling by linking Akt phosphorylation of ACAP1 to integrin beta1 return and cell migration.

    Evidence Dominant-negative/knockdown perturbation, phosphorylation assays, endosomal co-assembly and migration assays

    PMID:16256741

    Open questions at the time
    • Did not define the phosphosite or the structural consequence of phosphorylation
    • Mechanism of coat assembly not yet resolved
  2. 2007 High

    Defined the physical machinery by showing ACAP1 is part of a novel ARF6-regulated clathrin coat complex serving two distinct recycling settings (integrin and Glut4).

    Evidence Electron microscopy, biochemical fractionation, co-immunoprecipitation, knockdown functional assays

    PMID:17664335

    Open questions at the time
    • Stoichiometry and full composition of the coat complex not enumerated
    • How ARF6 cycling is coupled to coat assembly/disassembly unresolved
  3. 2007 Medium

    Identified GULP/CED-6 as a negative regulator that sequesters ACAP1 via a tripartite complex with GDP-bound Arf6, adding a layer of control over ACAP1 GAP activity.

    Evidence Pulldown, co-immunoprecipitation, Arf6-GTP measurement, migration assay, knockdown/overexpression

    PMID:17398097

    Open questions at the time
    • Single lab, no reciprocal structural validation of the tripartite complex
    • Physiological contexts where GULP regulation dominates not mapped
  4. 2012 High

    Resolved the cargo-binding switch by showing Akt phosphorylation relieves a localized autoinhibition and defined the integrin beta1 sorting signal recognized by ACAP1.

    Evidence Structural studies, computational modeling, mutagenesis, cargo-binding and phosphorylation assays

    PMID:22645133

    Open questions at the time
    • High-resolution structure of the autoinhibited vs. relieved state not fully determined
    • Whether other cargoes use an analogous signal not tested
  5. 2014 High

    Explained how ACAP1 deforms membranes, demonstrating the PH domain (not the BAR domain) drives membrane binding and curvature while the BAR domain mediates protein clustering.

    Evidence Electron microscopy, mutagenesis, membrane-binding and tubulation assays, structural analysis

    PMID:25284369

    Open questions at the time
    • Lipid specificity of PH-domain binding not yet defined in this study
    • Coupling of curvature generation to cargo sorting in vivo not addressed
  6. 2014 Medium

    Distinguished ACAP1 from the related Arf6 GAP ARAP2, showing they define separate endosomal compartments with opposing effects on integrin trafficking and focal adhesions.

    Evidence Knockdown, overexpression, colocalization microscopy, focal adhesion and internalization assays

    PMID:25225293

    Open questions at the time
    • Molecular basis for differential compartment targeting not defined
    • Single lab
  7. 2017 Low

    Provided a molecular rationale for the PH domain's lipid preference, identifying two PIP2-preferring pockets and the PH-BAR orientation during membrane binding.

    Evidence Molecular dynamics simulation and potential-of-mean-force analysis

    PMID:28092439

    Open questions at the time
    • Purely computational with no experimental validation reported
    • Predicted PIP2 pockets not confirmed by binding mutagenesis
  8. 2019 Medium

    Described how ACAP1 transitions from a symmetric solution dimer to an asymmetric membrane-recruited lattice, defining lattice contacts and assembly stages for membrane deformation.

    Evidence Molecular dynamics simulation and electron microscopy structural analysis

    PMID:31291238

    Open questions at the time
    • Lattice contacts not validated by mutagenesis
    • Single lab
  9. 2023 Medium

    Extended ACAP1's role to GPCR trafficking, placing it in a Rab10-ACAP1-Arf6 cascade that arrests M4 muscarinic receptor in early endosomes and hinders resensitization.

    Evidence Co-IP, constitutively active/dominant-negative GTPase constructs, Ca2+ signaling and localization assays, motif deletion mutagenesis

    PMID:36917255

    Open questions at the time
    • Direct Rab10-ACAP1 binding interface not structurally defined
    • Generality across other GPCRs not tested
  10. 2023 Medium

    Revealed a scaffolding function for ACAP1 in receptor regulation, bridging PTPN9 to FGFR2 to enable dephosphorylation, with the PH and Arf-GAP domains required.

    Evidence Co-IP, phosphatase assays, structural modeling, mutagenesis, in vivo and PDX functional assays

    PMID:37505213

    Open questions at the time
    • Whether scaffolding is constitutive or trafficking-regulated unclear
    • Single lab

Open questions

Synthesis pass · forward-looking unresolved questions
  • How ACAP1's recycling coat, GAP activity, membrane-deforming lattice, and receptor-scaffolding functions are coordinated in a single cell remains unresolved.
  • No high-resolution structure of the assembled coat on cargo-loaded membrane
  • Integration of Akt, Rab10, and GULP inputs onto a common ACAP1 pool unmapped
  • Physiological role of the PTPN9-FGFR2 scaffold relative to canonical recycling unknown

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0098772 molecular function regulator activity 3 GO:0005198 structural molecule activity 2 GO:0008289 lipid binding 1 GO:0060090 molecular adaptor activity 1
Localization
GO:0005768 endosome 3 GO:0031410 cytoplasmic vesicle 1
Pathway
R-HSA-162582 Signal Transduction 2 R-HSA-5653656 Vesicle-mediated transport 2 R-HSA-9609507 Protein localization 2
Partners
ARF6FGFR2GULP1ITGB1PTPN9RAB10
Complex memberships
ARF6-regulated clathrin coat complex

Evidence

Reading pass · 10 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2005 ACAP1 participates in stimulation-dependent recycling of integrin beta1 to control cell migration, and this role requires phosphorylation of ACAP1 by Akt, which is regulated by a canonical signaling pathway. Disrupting ACAP1 or Akt activities, or their assembly with endosomal beta1, inhibits beta1 recycling and cell migration. Dominant-negative and knockdown experiments, phosphorylation assays, endosomal co-assembly assays, cell migration assays Developmental Cell High 16256741
2007 ACAP1, an ARF6 GAP, is a component of a novel clathrin coat complex regulated by ARF6 that mediates endocytic recycling of integrin (stimulation-dependent, for cell migration) and Glut4 (insulin-stimulated, for glucose homeostasis). Electron microscopy, biochemical fractionation, co-immunoprecipitation, knockdown functional assays The Journal of Cell Biology High 17664335
2007 GULP/CED-6 regulates ACAP1 and Arf6 signaling: GULP binds directly to GDP-bound Arf6 via its PTB domain, associates with ACAP1 at endogenous levels, reverses Arf6-GTP decrease induced by ACAP1, counters ACAP1-mediated inhibition of cell migration, and forms a tripartite complex with ACAP1 and GDP-bound Arf6, suggesting sequestration of ACAP1 as one mechanism. Pulldown assays, co-immunoprecipitation, Arf6-GTP measurement, cell migration assay, knockdown/overexpression Current Biology Medium 17398097
2012 Akt phosphorylation of ACAP1 relieves a localized autoinhibitory mechanism to enhance cargo binding. A critical sequence in the cytoplasmic domain of integrin beta1 recognized by ACAP1 was defined and shown to act as a recycling sorting signal. Structural and modeling studies support phosphorylation-relieved autoinhibition as the regulatory mechanism. Structural studies, computational modeling, mutagenesis, cargo-binding assays, phosphorylation assays The Journal of Biological Chemistry High 22645133
2014 ACAP1's BAR domain cannot bind membrane or impart curvature on its own but requires its neighboring PH domain; specific residues within the PH domain mediate both membrane binding and curvature generation, while the BAR domain enables clustering of ACAP1 proteins at the membrane by interacting with BAR domains of neighboring ACAP1 molecules. Electron microscopy, mutagenesis, membrane-binding assays, membrane tubulation assays, structural analysis Developmental Cell High 25284369
2014 ACAP1 and ARAP2 are distinct Arf6 GAPs that define separate endosomal compartments with opposing effects: ACAP1 knockdown accelerated integrin beta1 internalization and ACAP1 overexpression reduced focal adhesions, while ARAP2 had the opposite effects. ACAP1 localizes to a tubular recycling endosome distinct from the ARAP2/APPL1-positive compartment. Knockdown, overexpression, colocalization by fluorescence microscopy, focal adhesion analysis, integrin internalization assays The Journal of Biological Chemistry Medium 25225293
2017 Molecular dynamics simulations revealed that the PH domain of ACAP1 has two binding pockets with preference for PIP2 lipids, and defined the orientation of PH domain relative to the BAR domain during membrane binding, providing molecular basis for protein-lipid interactions during membrane remodeling. Molecular dynamics simulation, potential of mean force (PMF) analysis The Journal of Physical Chemistry B Low 28092439
2019 ACAP1 dimerizes into a symmetrical structure in solution but is recruited asymmetrically to the membrane through dynamic behavior. Computational refinement and EM studies identified critical protein contacts within the ACAP1 lattice and revealed multiple stages of lattice assembly enabling membrane deformation. Molecular dynamics simulation, electron microscopy structural analysis PLoS Computational Biology Medium 31291238
2023 Rab10-GTP recruits the Arf6 GAP ACAP1 to inactivate Arf6, acting as part of a Rab10-ACAP1-Arf6 cascade that arrests M4 muscarinic acetylcholine receptor in Rab5-positive early endosomes and hinders receptor resensitization. M4 binds Rab10-GTP via the motif 386RKKRQMAA393 in the third intracellular loop; deletion of this motif causes M4 to bypass Rab10 control and switch to Rab4-facilitated fast recycling. Co-immunoprecipitation, constitutively active/dominant-negative GTPase constructs, Ca2+ signaling assays, endosomal localization by fluorescence microscopy, motif deletion mutagenesis Cellular and Molecular Life Sciences Medium 36917255
2023 ACAP1 mediates the interaction between the sec14p domain of PTPN9 and FGFR2, facilitating PTPN9 dephosphorylation of FGFR2 at pY656/657. The PH and Arf-GAP domains of ACAP1 are required for this interaction. The 'YRETRRKE' motif of the sec14p domain and Y471 of PTPN9 are key residues for the sec14p-ACAP1-FGFR2 complex. Co-immunoprecipitation, phosphatase activity assays, structural modeling of FGFR2-PTPN9 complex, mutagenesis, in vitro and in vivo functional assays, PDX models Hepatology Medium 37505213

Source papers

Stage 0 corpus · 12 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2005 Phosphorylation of ACAP1 by Akt regulates the stimulation-dependent recycling of integrin beta1 to control cell migration. Developmental cell 137 16256741
2007 An ACAP1-containing clathrin coat complex for endocytic recycling. The Journal of cell biology 104 17664335
2014 The Arf6 GTPase-activating proteins ARAP2 and ACAP1 define distinct endosomal compartments that regulate integrin α5β1 traffic. The Journal of biological chemistry 41 25225293
2014 A PH domain in ACAP1 possesses key features of the BAR domain in promoting membrane curvature. Developmental cell 33 25284369
2007 Regulation of Arf6 and ACAP1 signaling by the PTB-domain-containing adaptor protein GULP. Current biology : CB 28 17398097
2012 Mechanistic insights into regulated cargo binding by ACAP1 protein. The Journal of biological chemistry 26 22645133
2023 PTPN9 dephosphorylates FGFR2 pY656/657 through interaction with ACAP1 and ameliorates pemigatinib effect in cholangiocarcinoma. Hepatology (Baltimore, Md.) 14 37505213
2017 Molecular Details of the PH Domain of ACAP1BAR-PH Protein Binding to PIP-Containing Membrane. The journal of physical chemistry. B 13 28092439
2022 ACAP1 Deficiency Predicts Inferior Immunotherapy Response in Solid Tumors. Cancers 12 36497434
2023 A Rab10-ACAP1-Arf6 GTPases cascade modulates M4 muscarinic acetylcholine receptor trafficking and signaling. Cellular and molecular life sciences : CMLS 5 36917255
2019 ACAP1 assembles into an unusual protein lattice for membrane deformation through multiple stages. PLoS computational biology 5 31291238
2015 An ACAP1 coat complex acting in endocytic recycling. Methods in cell biology 1 26360030

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