Affinage

PPP1R9A

Neurabin-1 · UniProt Q9ULJ8

Length
1098 aa
Mass
123.3 kDa
Annotated
2026-06-10
11 papers in source corpus 7 papers cited in narrative 7 extracted findings
Cross-family judge vs UniProt: Affinage preferred faithfulness: 6/6 claims corpus-supported (100%)

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

Neurabin-I (PPP1R9A) is a neuronal F-actin-binding scaffold that couples protein phosphatase 1 (PP1) to the actin cytoskeleton to control actin rearrangement, neuronal morphology, and cortical neuron migration (PMID:12052877, PMID:17699587). It localizes to the actin cytoskeleton via an N-terminal F-actin-binding domain and recruits active PP1 through a (457)KIKF(460) docking motif; this complex drives stress-fiber disassembly and filopodium extension, whereas disrupting the KIKF motif or inhibiting PP1 restores stress fibers (PMID:12052877). Neurabin-I binds and inhibits PP1 with nanomolar affinity and shows isoform selectivity (PP1γ1 > PP1α > PP1β), with flanking and PP1 C-terminal sequences setting the hierarchy that is confirmed in PP1γ-null mouse brain (PMID:10504266, PMID:12016225). Its activity is gated by phosphorylation: PKA phosphorylation at Ser-461 sharply reduces PP1 binding, providing cAMP-dependent control of PP1 localization, while Cdk5 phosphorylation regulates F-actin association and governs neurite outgrowth, Rac1 activation, and radial migration during corticogenesis (PMID:10504266, PMID:17699587). Neurabin-I also serves as a direct Rac3 partner required for Rac3-induced neuritogenesis by anchoring Rac3 to growth-cone F-actin (PMID:16525025). A splice variant (Bau) lacking actin-binding domains interacts with the tumor suppressor Bin1 and suppresses transformation (PMID:10427963), and atypical hyper-N-glycosylation of neurabin-I renders it a B-cell receptor autoantigen in primary CNS lymphoma (PMID:30249786).

Mechanistic history

Synthesis pass · year-by-year structured walk · 7 steps
  1. 1999 High

    Establishing that neurabin-I is a high-affinity PP1 inhibitor whose binding is controlled by phosphorylation answered how a scaffold could both target and modulate phosphatase activity.

    Evidence GST pulldown, yeast two-hybrid, in vitro PP1 activity assay, HPLC-MS phosphosite mapping, and S461E phosphomimetic mutagenesis

    PMID:10504266

    Open questions at the time
    • Did not establish the cellular consequences of Ser-461 phosphorylation in neurons
    • Upstream signals activating PKA toward this site not defined
  2. 1999 Low

    Identification of the Bau splice variant binding Bin1 raised the possibility of a nuclear/cytosolic, actin-independent role distinct from the canonical PP1 scaffold function.

    Evidence Bin1 interaction screen, domain-deletion analysis, subcellular localization, and transformation suppression assay

    PMID:10427963

    Open questions at the time
    • Single lab without reciprocal Co-IP or in vitro reconstitution of the Bin1 interaction
    • Functional tumor-suppression assay was single-method
    • Mechanism linking Bin1 binding to growth suppression unknown
  3. 2002 High

    Live imaging and mutational dissection tied the neurabin-I/PP1 complex directly to actin dynamics, showing the KIKF docking motif is required to convert stress fibers into filopodia.

    Evidence GFP-fusion live imaging, deletion/point mutants, immune-complex phosphatase assays, and PP1 pharmacological inhibition in Cos7, HEK293, and hippocampal neurons

    PMID:12052877

    Open questions at the time
    • PP1 substrates downstream of the complex that drive actin remodeling not identified
    • Role of dimerization domains in vivo not resolved
  4. 2002 High

    Defining PP1 isoform selectivity (PP1γ1 > PP1α > PP1β) clarified which phosphatase holoenzymes neurabin-I assembles, and the determinants encoding that hierarchy.

    Evidence Reciprocal immunoprecipitation from rat brain and PP1γ-null mouse brain, recombinant peptide binding, and chimeric neurabin/PP1 analysis

    PMID:12016225

    Open questions at the time
    • Functional consequence of isoform preference for specific substrates not defined
    • Whether selectivity differs across neuronal compartments unknown
  5. 2006 Medium

    Identifying Rac3 as a direct partner showed neurabin-I links a Rho-family GTPase to growth-cone F-actin, making it a required mediator of neuritogenesis.

    Evidence Yeast two-hybrid, co-fractionation, co-localization, and antisense knockdown with domain-deletion rescue in primary neurons

    PMID:16525025

    Open questions at the time
    • No in vitro reconstitution confirming direct Rac3 binding
    • Relationship between Rac3 anchoring and the PP1 scaffold function unresolved
  6. 2007 High

    Demonstrating Cdk5 phosphorylation of neurabin-I controls F-actin association placed the protein within corticogenesis, linking a kinase to neuronal migration and morphology.

    Evidence In vitro Cdk5 kinase assay, phosphosite mutagenesis with rescue, in utero electroporation, F-actin co-sedimentation, and Rac1 activity assay

    PMID:17699587

    Open questions at the time
    • Exact Cdk5 phosphosite residue(s) and their interplay with PKA/Ser-461 not integrated
    • Mechanistic link between F-actin binding and Rac1 activation incomplete
  7. 2018 Medium

    Discovery that hyper-N-glycosylated neurabin-I acts as a BCR autoantigen extended its relevance beyond neuronal cytoskeletal biology into CNS lymphoma immunopathology.

    Evidence Mass-spectrometric N-glycosylation site mapping (ASN1277), BCR transfection into lymphoma lines, BCR signaling/proliferation assays, and immunotoxin cytotoxicity assay

    PMID:30249786

    Open questions at the time
    • Single lab; in vivo relevance of the autoantigen mechanism not established
    • How the neuronal scaffold becomes hyper-glycosylated and exposed to BCRs unknown

Open questions

Synthesis pass · forward-looking unresolved questions
  • How the multiple regulatory inputs (PKA at Ser-461, Cdk5, Rac3/Rac1) are integrated to coordinate PP1 targeting with actin remodeling in defined neuronal compartments remains unresolved.
  • No unified model of combinatorial phosphoregulation
  • PP1 substrates that effect actin changes downstream of the complex not identified
  • Structural basis of simultaneous F-actin, PP1, and Rac3 engagement unknown

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0060090 molecular adaptor activity 3 GO:0008092 cytoskeletal protein binding 2 GO:0098772 molecular function regulator activity 2
Localization
GO:0005856 cytoskeleton 2 GO:0005634 nucleus 1
Pathway
R-HSA-162582 Signal Transduction 2 R-HSA-1266738 Developmental Biology 1
Partners
BIN1PP1PPP1CAPPP1CCRAC3

Evidence

Reading pass · 7 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2002 Neurabin I localizes to the actin cytoskeleton via its N-terminal F-actin-binding domain and promotes disassembly of stress fibers; deletion of C-terminal coiled-coil and SAM domains abolishes dimerization and induces filopodium extension. Neurabin I recruits active PP1 via a PP1-docking sequence (457)KIKF(460), and mutation of this motif or pharmacological PP1 inhibition abolishes filopodia and restores stress fibers, establishing that the neurabin I/PP1 complex controls actin rearrangement. PKA phosphorylation of serine-461 impairs PP1 binding, and p70S6K is excluded from neurabin I/PP1 complexes, requiring PP1 displacement for its own recruitment to neurabin I. GFP-fusion live imaging, deletion/point mutant analysis, immune complex phosphatase assays, okadaic acid/calyculin A pharmacological inhibition, in vitro and in vivo PKA phosphorylation assays in Cos7, HEK293, and hippocampal neurons Molecular and cellular biology High 12052877
1999 Neurabin I binds and inhibits PP1 (Ki = 2.7 nM for a GST-neurabin I fragment containing residues 318–661) via its PP1-binding domain (residues 456–460). PKA phosphorylates neurabin I at serine-461 (identified by HPLC-MS), significantly reducing PP1 binding and a S461E phosphomimetic mutant showed 35-fold reduced inhibitory potency, establishing a cAMP-dependent regulatory mechanism for PP1 activity and localization. GST pulldown, overlay assay, yeast two-hybrid, co-immunoprecipitation, in vitro PP1 activity assay, in vitro PKA phosphorylation, HPLC-MS phosphosite identification, S461E phosphomimetic mutagenesis Biochemistry High 10504266
2002 Neurabin I (and neurabin II/spinophilin) preferentially recruits PP1gamma1 and PP1alpha over PP1beta from rat brain. The rank order of PP1 isoform selectivity is PP1gamma1 > PP1alpha > PP1beta. Sequences flanking the conserved PP1-binding motif and C-terminal sequences unique to PP1 isoforms together determine selectivity. In PP1gamma null mice, both neurabins show enhanced association with PP1alpha but not PP1beta, confirming isoform hierarchy in vivo. Immunoprecipitation from rat brain and PP1gamma null mouse brain, in vitro binding of recombinant peptides to brain extracts, chimeric neurabin and chimeric PP1/PP2A analysis, in vitro PP1 activity assay The Journal of biological chemistry High 12016225
2007 Cdk5 directly phosphorylates Neurabin-I and controls its association with F-actin. Gain and loss of Neurabin-I expression affect neuronal morphology, neurite outgrowth, Rac1 activation, and radial migration of cortical neurons. Mutation of the Cdk5 phosphorylation site reduces the morphological and migratory phenotypic consequences of Neurabin-I overexpression both in vitro and in vivo, demonstrating that Cdk5-mediated phosphorylation regulates Neurabin-I function in the actin cytoskeleton during corticogenesis. In vitro kinase assay (Cdk5 phosphorylation), phosphorylation-site mutagenesis, antisense/overexpression in primary cortical neurons and in utero electroporation (in vivo), F-actin co-sedimentation, Rac1 activity assay Molecular biology of the cell High 17699587
2006 Neurabin I is a direct binding partner of Rac3 (a neuronal Rho-family GTPase), identified by yeast two-hybrid. Neurabin I co-partitions and co-localizes with Rac3 at growth cones, and Neurabin I antisense oligonucleotides abolish Rac3-induced neuritogenesis, which is rescued by exogenous Neurabin I but not by a Neurabin I mutant lacking the Rac3-binding domain, establishing Neurabin I as a required mediator of Rac3-induced neuritogenesis by anchoring Rac3 to growth cone F-actin. Yeast two-hybrid, biochemical co-fractionation, co-localization by light microscopy, antisense knockdown, domain-deletion rescue experiments in primary neurons Molecular biology of the cell Medium 16525025
1999 Bau, a splice form of Neurabin-I lacking actin- and p70S6K-binding domains but retaining coiled-coil domains, interacts with the tumor suppressor Bin1 (interaction requires the U3 region alternately spliced in muscle cells), localizes to the nucleus and cytosol, and suppresses oncogene-mediated transformation and inhibits tumor cell growth. Protein interaction screen (Bin1-based), domain-deletion analysis, subcellular localization, transformation suppression assay Cell adhesion and communication Low 10427963
2018 Neurabin-I is atypically hyper-N-glycosylated at ASN1277, rendering it immunogenic and enabling it to act as a B-cell receptor autoantigen in primary CNS lymphoma (PCNSL); this modified neurabin-I induces BCR pathway activation and proliferation of lymphoma cell lines transfected with neurabin-I-reactive BCRs, and a BCR-binding epitope of neurabin-I conjugated to Pseudomonas exotoxin killed lymphoma cells expressing the respective BCRs. Identification of N-glycosylation site (ASN1277) by mass spectrometry/sequencing, BCR transfection into lymphoma cell lines, BCR signaling and proliferation assays, immunotoxin cytotoxicity assay Blood Medium 30249786

Source papers

Stage 0 corpus · 11 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2002 Targeting protein phosphatase 1 (PP1) to the actin cytoskeleton: the neurabin I/PP1 complex regulates cell morphology. Molecular and cellular biology 101 12052877
2002 The neuronal actin-binding proteins, neurabin I and neurabin II, recruit specific isoforms of protein phosphatase-1 catalytic subunits. The Journal of biological chemistry 75 12016225
1999 Regulation of neurabin I interaction with protein phosphatase 1 by phosphorylation. Biochemistry 71 10504266
2007 Neurabin-I is phosphorylated by Cdk5: implications for neuronal morphogenesis and cortical migration. Molecular biology of the cell 32 17699587
2018 Hyper-N-glycosylated SAMD14 and neurabin-I as driver autoantigens of primary central nervous system lymphoma. Blood 31 30249786
2015 Altered prefrontal cortical MARCKS and PPP1R9A mRNA expression in schizophrenia and bipolar disorder. Schizophrenia research 26 25757715
2006 Rac3-induced neuritogenesis requires binding to Neurabin I. Molecular biology of the cell 16 16525025
2011 Assessment of genomic imprinting of PPP1R9A, NAP1L5 and PEG3 in pigs. Genetika 11 21675243
2011 Molecular cloning, mRNA expression and imprinting status of PEG3, NAP1L5 and PPP1R9A genes in pig. Genes & genetic systems 9 21498922
2020 Integration of the B-Cell Receptor Antigen Neurabin-I/SAMD14 Into an Antibody Format as New Therapeutic Approach for the Treatment of Primary CNS Lymphoma. Frontiers in oncology 5 33282736
1999 Bau, a splice form of Neurabin-I that interacts with the tumor suppressor Bin1, inhibits malignant cell transformation. Cell adhesion and communication 4 10427963

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