Affinage

FNBP1L

Formin-binding protein 1-like · UniProt Q5T0N5

Length
605 aa
Mass
70.1 kDa
Annotated
2026-06-09
19 papers in source corpus 14 papers cited in narrative 14 extracted findings
Cross-family judge vs UniProt: Affinage preferred faithfulness: 8/8 claims corpus-supported (100%)

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

FNBP1L (TOCA-1) is a multidomain PCH/F-BAR protein that couples membrane deformation to Cdc42-driven actin nucleation, functioning as an essential transducer in the Cdc42→N-WASP→Arp2/3 actin assembly pathway (PMID:15260990). Its N-terminal F-BAR/EFC domain binds and tubulates the plasma membrane, while the HR1 domain binds active Cdc42 and the SH3 domain engages N-WASP, allowing TOCA-1 to activate the N-WASP–WIP complex and stimulate Arp2/3-dependent actin polymerization (PMID:15260990, PMID:16885158). TOCA-1 binds active Cdc42 only with micromolar affinity, far weaker than the nanomolar affinity of the N-WASP GBD, and is displaced from Cdc42 by N-WASP, defining it as an early-step effector that facilitates GTPase handover to N-WASP (PMID:27129201). A central mechanistic action is relief of N-WASP autoinhibition: TOCA-1 converts N-WASP from a closed to an open conformation, and Cdc42, N-WASP and TOCA-1 assemble as a trimeric complex on curved membranes to generate motile, clathrin-associated vesicles (PMID:18191793, PMID:20730103). This module operates in clathrin-mediated endocytosis, in tight-junction actin dynamics via a splice isoform whose PDZ-binding motif binds ZO-1 to recruit N-WASP and maintain paracellular barrier function (PMID:19798448, PMID:26063734), in myoblast fusion where TOCA-1 acts upstream of N-WASP (PMID:24861867), and in neuronal collateral branching (PMID:16885158). TOCA-1 requirement is dictated by membrane lipid composition: it is essential for actin polymerization on PI(4,5)P2 membranes but becomes dispensable when PI(3)P is present and Snx9 substitutes as the N-WASP adaptor (PMID:23589871). Its expression is transcriptionally suppressed by p53, which binds within intron 2 and places TOCA-1 downstream of p53 in a pathway controlling tumor cell invasion and metastasis (PMID:25547174). TOCA-1 is also hijacked by bacterial pathogens, being recruited by Shigella and Chlamydia effectors to drive invasion-associated actin remodeling (PMID:18191793, PMID:40231845).

Mechanistic history

Synthesis pass · year-by-year structured walk · 13 steps
  1. 2004 High

    Established that Cdc42-induced actin nucleation requires a second effector beyond the N-WASP–WIP complex, identifying TOCA-1 as that obligatory cofactor.

    Evidence Biochemical purification of endogenous complex from cell extracts with in vitro actin polymerization and binding assays

    PMID:15260990

    Open questions at the time
    • Did not resolve the structural basis of Cdc42 or N-WASP binding
    • In vitro reconstitution did not address membrane context or cellular pathway specificity
  2. 2006 Medium

    Assigned the membrane-deforming F-BAR/EFC domain as the functional module driving TOCA-1's cellular role and linked it to neurite outgrowth control.

    Evidence siRNA knockdown, overexpression and domain-deletion analysis in PC12 cells with morphological readout

    PMID:16885158

    Open questions at the time
    • Single cell-line phenotype
    • Did not establish the in vivo relevance of F-BAR membrane tubulation
  3. 2008 Medium

    Defined the molecular action of TOCA-1 in cells as relief of N-WASP autoinhibition, separating its function from N-WASP recruitment.

    Evidence TOCA-1 knockdown during S. flexneri infection with N-WASP conformation assay and actin-tail imaging

    PMID:18191793

    Open questions at the time
    • Conformational assay in a pathogen-hijacked context
    • Single lab, knockdown only
  4. 2009 High

    Placed TOCA proteins genetically in the WSP-1/N-WASP pathway and tied them to clathrin-mediated endocytosis and junctional actin in vivo.

    Evidence C. elegans loss-of-function genetics and double-mutant epistasis combined with mammalian Co-IP/pulldown

    PMID:19798448

    Open questions at the time
    • WAVE2 association is indirect (via ABI-1) and not mechanistically dissected
    • Endocytic step at which TOCA acts not pinpointed
  5. 2010 Medium

    Demonstrated that Cdc42, N-WASP and TOCA-1 form a trimeric complex on membrane tubules and vesicles in living cells, connecting the module to vesicle motility.

    Evidence FRET/FLIM, overexpression and dominant-negative experiments in live cells with endocytosis markers

    PMID:20730103

    Open questions at the time
    • Overexpression-based system
    • Stoichiometry and spatial order of complex assembly unresolved
  6. 2012 Medium

    Revealed an actin-dependent role for TOCA-1 in nuclear migration acting in parallel to the SUN-KASH nuclear envelope bridge.

    Evidence C. elegans forward genetic screen, double-mutant epistasis and cell-autonomous rescue

    PMID:23150597

    Open questions at the time
    • Direct molecular mechanism linking TOCA-1 to nuclear movement not shown
    • Actin dependence inferred rather than directly demonstrated
  7. 2013 High

    Showed that TOCA-1's requirement is conditional on membrane lipid composition, with Snx9 substituting on PI(3)P-containing membranes.

    Evidence In vitro liposome-based actin polymerization with defined phosphoinositides and selective protein omission

    PMID:23589871

    Open questions at the time
    • Cellular contexts where PI(3)P-driven, TOCA-independent nucleation operates not defined
    • Single biochemical system
  8. 2014 Medium

    Identified p53 as a direct transcriptional repressor of TOCA-1, positioning TOCA-1 downstream of p53 in invasion and metastasis control.

    Evidence ChIP, shRNA knockdown, in vitro invasion assay and in vivo mouse metastasis model

    PMID:25547174

    Open questions at the time
    • Rescue of invasion by double knockdown was partial
    • Single lab; mechanism connecting TOCA-1 actin activity to invasion not dissected
  9. 2014 Medium

    Established TOCA-1 as acting upstream of N-WASP in the actin remodeling required for myoblast fusion.

    Evidence shRNA knockdown, shRNA-resistant and N-WASP overexpression rescue in C2C12 cells with actin staining

    PMID:24861867

    Open questions at the time
    • Fusion-specific membrane event linking TOCA-1 to fusion pore not identified
    • Single cell model
  10. 2015 High

    Defined an alternative splice isoform whose PDZ-binding motif binds ZO-1 to target TOCA-1 and N-WASP to tight junctions and maintain barrier function.

    Evidence CRISPR-Cas9 knockout, isoform-specific rescue, Co-IP, FRAP, paracellular flux and time-lapse microscopy in MDCK cells

    PMID:26063734

    Open questions at the time
    • Tissue-level relevance of the ZO-1-binding isoform not addressed
    • How junctional membrane dynamics couple to barrier flux not fully mechanistic
  11. 2016 High

    Provided the structural and quantitative basis for TOCA-1 as an early Cdc42 effector, showing low-affinity Cdc42 binding and displacement by N-WASP.

    Evidence NMR structure of the HR1 domain, binding affinity measurements, NMR competition/displacement and in vitro actin assays

    PMID:27129201

    Open questions at the time
    • Full-length TOCA-1/Cdc42/N-WASP assembly structure not solved
    • Kinetics of GTPase handover in cells not measured
  12. 2025 Medium

    Extended pathogen exploitation of TOCA-1 to Chlamydia, with effector TmeA directly binding TOCA-1 to drive invasion-associated actin structures.

    Evidence siRNA knockdown, transmission electron microscopy and direct TmeA interaction assays

    PMID:40231845

    Open questions at the time
    • Whether TmeA engages TOCA-1 and N-WASP cooperatively or competitively not resolved
    • Single lab
  13. 2025 Medium

    Placed TOCA-1 within a Cdc42/DOCK11→TOCA-1→N-WASP/Arp2/3 cascade that drives neuronal collateral branch formation via filopodial extension.

    Evidence C. elegans loss-of-function genetics, double-mutant epistasis and live imaging of TOCA-1 at branching sites (preprint)

    PMID:41278672

    Open questions at the time
    • Preprint, not yet peer-reviewed
    • Mechanism of TOCA-1 recruitment to the branch site not defined

Open questions

Synthesis pass · forward-looking unresolved questions
  • How TOCA-1's distinct activities — F-BAR membrane curvature sensing, Cdc42 handover, and N-WASP activation — are spatially and temporally coordinated within a full-length complex in a native membrane remains unresolved.
  • No structure of full-length TOCA-1 bound to Cdc42 and N-WASP on membrane
  • Regulation of isoform choice and recruitment in specific tissues unknown

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0098772 molecular function regulator activity 3 GO:0008092 cytoskeletal protein binding 2 GO:0008289 lipid binding 2 GO:0060090 molecular adaptor activity 2
Localization
GO:0005886 plasma membrane 2 GO:0031410 cytoplasmic vesicle 2
Pathway
R-HSA-162582 Signal Transduction 2 R-HSA-5653656 Vesicle-mediated transport 2
Partners
CDC42WASLWIPF1ZO-1

Evidence

Reading pass · 14 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2004 TOCA-1 (FNBP1L) was biochemically purified as an essential component of the Cdc42 actin assembly pathway. It binds both N-WASP and Cdc42 and activates the N-WASP-WIP/CR16 complex (the predominant form of N-WASP in cells), demonstrating that two distinct Cdc42 effectors — the N-WASP-WIP complex and Toca-1 — cooperate and are both required for Cdc42-induced actin nucleation via the Arp2/3 complex. Biochemical purification from cell extracts, in vitro actin polymerization assay, Co-IP/pulldown binding assays Cell High 15260990
2004 FNBP1L (TOCA-1) was identified in silico as a member of the PCH/FNBP1 protein family sharing domain architecture (FCH/F-BAR, HR1, SH3 domains) with FNBP1 and TRIP10. The HR1 domain was predicted as a Rho-family GTPase (Cdc42/RhoN) binding domain and the SH3 domain was predicted to interact with proline-rich regions of Formin and WASP family proteins. Bioinformatics / in silico domain analysis; cDNA assembly from genome sequences International journal of molecular medicine Low 14654988
2006 TOCA-1 contains an F-BAR/EFC domain at its N-terminus that induces tubular invagination of the plasma membrane. In PC12 neurons, knockdown of Toca-1 significantly enhanced neurite elongation, and overexpression suppressed neurite elongation through the F-BAR/EFC domain, implicating membrane trafficking in Toca-1's neural function. Toca-1 binds N-WASP via its SH3 domain and Cdc42 via its HR1 domain. Toca-1 knockdown (siRNA) and overexpression in PC12 cells; domain deletion analysis; morphological readout of neurite length The Journal of biological chemistry Medium 16885158
2008 In intact mammalian cells infected with S. flexneri, TOCA-1 is required for converting N-WASP from a closed (autoinhibited) conformation to an open (active) conformation during actin tail initiation. While N-WASP recruitment to the bacterial surface is IcsA-dependent, TOCA-1 recruitment is mediated by S. flexneri type III secretion effectors, demonstrating that TOCA-1's role is specifically to relieve N-WASP autoinhibition. Toca-1 knockdown in mammalian cells infected with S. flexneri; N-WASP conformation assay; fluorescence microscopy of actin tails Cell host & microbe Medium 18191793
2009 C. elegans TOCA-1 and TOCA-2 (CeTOCA proteins) are required for efficient clathrin-mediated endocytosis in oocytes. CeTOCA proteins localize to cell-cell junctions and are required for embryonic morphogenesis and junctional actin organization. Double mutant epistasis showed toca genes act in the same pathway as wsp-1 (nematode N-WASP). Mammalian TOCA-1 physically associates with N-WASP directly, and with WAVE2 indirectly via ABI-1. C. elegans genetics (loss-of-function mutants, double mutant epistasis), Co-IP/pulldown in mammalian cells, fluorescence microscopy of endocytosis and junction markers PLoS genetics High 19798448
2010 Cellular co-expression of Toca-1 and N-WASP induces membrane tubulation and formation of motile vesicles associated with clathrin-mediated endocytosis. FRET/FLIM analysis demonstrated that Cdc42, N-WASP, and Toca-1 form a trimeric complex on membrane tubules and vesicles, and that Cdc42 interaction with N-WASP is critical for complex formation. Modulation of Cdc42 interaction with Toca-1 and/or N-WASP affects membrane tubulation, vesicle formation, and vesicle motility. FRET/FLIM in live cells; overexpression and dominant-negative experiments; fluorescence microscopy with endocytosis markers PloS one Medium 20730103
2012 In C. elegans, a mutation in toca-1 was isolated in a forward genetic screen as an enhancer of the nuclear migration defect of unc-84 (a SUN protein). TOCA-1 functions cell-autonomously to move P-cell nuclei in a pathway that acts in parallel to the SUN-KASH nuclear envelope bridge pathway, likely through an actin-dependent mechanism. Forward genetic screen; double mutant epistasis (toca-1; unc-84); cell-autonomous rescue experiments Genetics Medium 23150597
2013 On curved membranes containing PI(4,5)P2 as the sole phosphoinositide, actin polymerization requires Toca-1 (along with Cdc42, N-WASP, and the Arp2/3 complex). When PI(3)P is also present on curved membranes, actin polymerization becomes more efficient and independent of Toca-1, with Snx9 acting as a specific adaptor that can replace Toca-1 to mobilize N-WASP and Arp2/3. In vitro reconstituted liposome-based actin polymerization assay with defined phosphoinositide compositions; protein depletion experiments Proceedings of the National Academy of Sciences of the United States of America High 23589871
2014 p53 transcriptionally suppresses Toca-1 expression by binding within intron 2 of the toca-1 gene and reducing histone acetylation at its promoter. Stabilization of WT p53 reduces Toca-1 mRNA and protein. Combined silencing of p53 and Toca-1 partially rescued invasion and lung metastasis phenotypes caused by p53 silencing alone, placing Toca-1 downstream of p53 in a pathway controlling invasion. Chromatin immunoprecipitation (ChIP), shRNA-mediated stable knockdown, in vitro invasion assay, in vivo mouse metastasis model Breast cancer research : BCR Medium 25547174
2014 Toca-1 knockdown in C2C12 myoblasts impairs myotube formation without affecting differentiation markers (MyoD, MyHC) or N-cadherin localization, but causes prominent actin fiber accumulation indicative of defective actin turnover. The myogenic defect is rescued by N-WASP overexpression, placing Toca-1 upstream of N-WASP in the actin remodeling pathway required for myoblast fusion. shRNA knockdown in C2C12 cells; shRNA-resistant rescue construct; N-WASP overexpression rescue; actin staining; myotube quantification Biochimica et biophysica acta Medium 24861867
2015 An alternative splice of TOCA-1 adds a PDZ-binding motif that binds ZO-1, targeting TOCA-1 to tight junction barrier contacts in MDCK epithelial cells. This isoform recruits N-WASP to tight junctions. CRISPR-Cas9 knockout of TOCA-1 increases paracellular flux and impairs tight junction membrane contact dynamics (by long-term time-lapse microscopy), without altering FRAP kinetics of ZO-1 or occludin. Reexpression of TOCA-1 with, but not without, the PDZ-binding motif rescues flux and membrane dynamics. CRISPR-Cas9 knockout; FRAP; paracellular flux assay; Co-IP (ZO-1/TOCA-1); isoform-specific rescue; time-lapse microscopy; ultrastructural analysis Molecular biology of the cell High 26063734
2016 The crystal/NMR structure of the TOCA1 HR1 domain was solved, revealing structural features distinct from other HR1 domains. Quantitative binding measurements showed TOCA1 HR1 binds active Cdc42 with micromolar affinity, in contrast to the nanomolar affinity of the N-WASP GBD for Cdc42. NMR competition experiments demonstrated that the N-WASP Cdc42-binding domain displaces TOCA1 HR1 from Cdc42, supporting a model where TOCA1 acts as an early-step Cdc42 effector that facilitates handover to N-WASP. NMR structure determination; isothermal titration calorimetry (ITC) or equivalent binding affinity measurements; NMR competition/displacement assay; in vitro actin polymerization assay The Journal of biological chemistry High 27129201
2025 C. trachomatis effector TmeA directly interacts with TOCA-1 (in addition to N-WASP). siRNA-mediated knockdown of TOCA-1 impairs C. trachomatis-mediated pedestal-like structure formation, as assessed by transmission electron microscopy, identifying TOCA-1 as a host factor hijacked for bacterial invasion-associated actin remodeling. siRNA knockdown; transmission electron microscopy; direct interaction assay (pulldown/Co-IP with TmeA) mSphere Medium 40231845
2025 In C. elegans PLM neurons, TOCA-1 is recruited to the branching site at the time of collateral branch formation and is required for branch formation. Epistasis experiments showed that cdc-42 and the GEF dock-11 are upstream of toca-1, while wsp-1 (N-WASP) and the Arp2/3 complex act in the same pathway downstream, directly orchestrating filopodial extension. Loss of TOCA-1 disrupts branching without affecting anterior-posterior or dorsal-ventral branch positioning. C. elegans genetics (loss-of-function mutants, double mutant epistasis); live fluorescence imaging of TOCA-1 localization at branching sites bioRxivpreprint Medium 41278672

Source papers

Stage 0 corpus · 19 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2004 Toca-1 mediates Cdc42-dependent actin nucleation by activating the N-WASP-WIP complex. Cell 368 15260990
2013 Childhood intelligence is heritable, highly polygenic and associated with FNBP1L. Molecular psychiatry 176 23358156
2009 Requirements for F-BAR proteins TOCA-1 and TOCA-2 in actin dynamics and membrane trafficking during Caenorhabditis elegans oocyte growth and embryonic epidermal morphogenesis. PLoS genetics 57 19798448
2015 A complex of ZO-1 and the BAR-domain protein TOCA-1 regulates actin assembly at the tight junction. Molecular biology of the cell 55 26063734
2010 Cdc42 interaction with N-WASP and Toca-1 regulates membrane tubulation, vesicle formation and vesicle motility: implications for endocytosis. PloS one 55 20730103
2006 Regulation of neuronal morphology by Toca-1, an F-BAR/EFC protein that induces plasma membrane invagination. The Journal of biological chemistry 51 16885158
2004 Identification and characterization of human FNBP1L gene in silico. International journal of molecular medicine 48 14654988
2013 Phosphoinositides and membrane curvature switch the mode of actin polymerization via selective recruitment of toca-1 and Snx9. Proceedings of the National Academy of Sciences of the United States of America 46 23589871
2008 Bacterial actin assembly requires toca-1 to relieve N-wasp autoinhibition. Cell host & microbe 46 18191793
2016 Investigation of the Interaction between Cdc42 and Its Effector TOCA1: HANDOVER OF Cdc42 TO THE ACTIN REGULATOR N-WASP IS FACILITATED BY DIFFERENTIAL BINDING AFFINITIES. The Journal of biological chemistry 27 27129201
2012 toca-1 is in a novel pathway that functions in parallel with a SUN-KASH nuclear envelope bridge to move nuclei in Caenorhabditis elegans. Genetics 23 23150597
2014 Toca-1 is suppressed by p53 to limit breast cancer cell invasion and tumor metastasis. Breast cancer research : BCR 17 25547174
2004 Regulation of WASP: PIP2 Pipped by Toca-1? Cell 8 15260983
2014 Myogenesis defect due to Toca-1 knockdown can be suppressed by expression of N-WASP. Biochimica et biophysica acta 7 24861867
2025 Chlamydia trachomatis TmeA promotes pedestal-like structure formation through N-WASP and TOCA-1 interactions. mSphere 3 40231845
2016 (1)H, (13)C and (15)N resonance assignments of the Cdc42-binding domain of TOCA1. Biomolecular NMR assignments 1 26988723
2025 Impairment of endocytosis-related factors FNBP1L, ARHGAP24, and ATP6V1B1 increases HIV-1 entry into dendritic cells. Journal of virology 0 40029073
2025 The actin assembly regulator toca-1 regulates collateral branching in C. elegans. bioRxiv : the preprint server for biology 0 41278672
2024 Chlamydia trachomatis TmeA promotes pedestal formation through N-WASP and TOCA-1 interactions. bioRxiv : the preprint server for biology 0 39554107

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