{"gene":"EPB41","run_date":"2026-06-09T23:54:43","timeline":{"discoveries":[{"year":2000,"finding":"Crystal structure of the 4.1R N-terminal 30 kDa domain (FERM domain core) reveals a cloverleaf-like architecture with three lobes, each containing a specific binding site for band 3, glycophorin C/D, or p55. Two separate calmodulin (CaM) binding regions are located at the central region: one Ca2+-insensitive alpha-helical site and one Ca2+-sensitive extended-structure site whose binding to CaM weakens 4.1R interactions with target proteins.","method":"X-ray crystallography with functional binding assays","journal":"Nature structural biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structure combined with functional characterization of binding sites and CaM regulation, single rigorous paper with multiple orthogonal methods","pmids":["11017195"],"is_preprint":false},{"year":2000,"finding":"Within the 30 kDa domain, sequences encoded by exon 8 constitute the binding interface for glycophorin C (GPC), and sequences encoded by exon 10 constitute the binding interface for p55. 4.1R increases the affinity of p55 binding to GPC by an order of magnitude, and Ca2+/calmodulin binding to 4.1R decreases its affinity for both p55 and GPC in a Ca2+-dependent manner.","method":"In vitro binding assays with recombinant domain fragments and calmodulin competition assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro reconstitution with domain-mapping and Ca2+/CaM modulation demonstrated in same study","pmids":["10831591"],"is_preprint":false},{"year":2000,"finding":"4.1R forms a ternary complex with spectrin and F-actin at the erythrocyte junctional node; both the intact N-terminus and CH1 domain of the spectrin beta chain bind F-actin and 4.1R. PIP2 greatly enhances the binding of 4.1R to the spectrin beta chain N-terminal region (residues 1-301), suggesting a regulatory switch.","method":"In vitro binding/co-sedimentation assays with recombinant domain truncations and liposome PIP2 competition","journal":"Biochemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro reconstitution with domain mutagenesis, multiple binding partners tested","pmids":["16060676"],"is_preprint":false},{"year":2006,"finding":"4.1R binds PIP2-containing liposomes through its N-terminal 30 kDa membrane-binding domain; PIP2 binding induces a conformational change. Amino acids K63,64 and K265,266 are required for PIP2 binding. PIP2 selectively enhances 4.1R binding to GPC but inhibits binding to band 3, with no effect on p55 binding.","method":"Liposome binding assays, alanine mutagenesis, in vitro pull-down with recombinant proteins","journal":"Biochemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — mutagenesis plus reconstitution in a single study, multiple binding partners tested","pmids":["16669616"],"is_preprint":false},{"year":2008,"finding":"Deletion of 4.1R in mouse red cells causes large reduction of actin and loss of cytoskeletal lattice structure. Pull-down assays showed 4.1R associates with XK, Duffy, and Rh transmembrane proteins, in addition to glycophorin C; absence of 4.1R causes selective reduction of these proteins from the membrane, consistent with 4.1R organizing a macromolecular junctional complex.","method":"4.1R knockout mouse analysis, in vitro pull-down assays, Western blot, flow cytometry","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 / Strong — KO mouse combined with in vitro pull-downs, multiple transmembrane proteins assessed","pmids":["18524950"],"is_preprint":false},{"year":1999,"finding":"A 135 kDa nonerythroid 4.1R isoform specifically interacts with the nuclear mitotic apparatus (NuMA) protein. The minimal interaction sequences map to residues encoded by exons 20 and 21 of 4.1R and residues 1788-1810 of NuMA. 4.1R and NuMA co-localize in the interphase nucleus and redistribute to spindle poles in mitosis; 4.1R forms a complex with NuMA, dynein, and dynactin during cell division.","method":"Yeast two-hybrid, in vitro binding assays, co-immunoprecipitation, co-immunolocalization","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal Co-IP plus yeast two-hybrid plus in vitro binding plus co-localization, replicated in multiple cell contexts","pmids":["10189366"],"is_preprint":false},{"year":2000,"finding":"Two 4.1R isoforms (135 kDa and 150 kDa) interact specifically with the tight junction protein ZO-2. 4.1R co-localizes with ZO-2 and occludin at MDCK tight junctions and co-precipitates with ZO-2, ZO-1, and occludin. The interaction maps to exons 19-21 of 4.1R and residues 1054-1118 of ZO-2. This interaction is specific to confluent (tight junction-forming) cells.","method":"Yeast two-hybrid, immunocolocalization, co-immunoprecipitation, in vitro binding studies","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — yeast two-hybrid plus Co-IP plus in vitro binding plus domain mapping, multiple orthogonal methods","pmids":["10874042"],"is_preprint":false},{"year":1999,"finding":"Nuclear import of the 4.1R80 isoform requires two distant signals: a basic KKKRER peptide encoded by alternative exon 16 (acting as a weak core NLS) and an acidic EED peptide encoded by alternative exon 5. Both motifs are needed for full importin-mediated nuclear import. 4.1R80 binds importin alpha2 (Rch1) with high affinity (KD = 30 nM), and affinity decreases at least 7–20 fold if either motif is absent.","method":"Transfection with epitope-tagged constructs, digitonin-permeabilized cell import assays, resonant mirror protein-protein interaction measurements with recombinant Rch1","journal":"Molecular biology of the cell","confidence":"High","confidence_rationale":"Tier 1 / Strong — reconstituted nuclear import in permeabilized cells, quantitative binding measurements, mutagenesis of both NLS elements","pmids":["10359596"],"is_preprint":false},{"year":1999,"finding":"4.1R-null mice generated by gene knockout exhibit moderate hemolytic anemia, abnormal erythrocyte morphology, decreased membrane stability, and reduced expression of spectrin and ankyrin, demonstrating that 4.1R is required for erythroid membrane skeleton assembly.","method":"Gene knockout (homologous recombination), morphological and biochemical analysis of erythrocytes","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 2 / Strong — complete gene knockout with multiple phenotypic readouts in erythrocytes","pmids":["9927493"],"is_preprint":false},{"year":2011,"finding":"Protein kinase C activation in intact erythrocytes phosphorylates 4.1R at serine 312 and serine 331. Phosphorylation at either site suppresses 4.1R binding to the cytoplasmic domains of GPC, Duffy, and XK, rendering these transmembrane proteins more easily detergent-extractable. Phosphorylation also weakens 4.1R affinity for beta-spectrin, destabilizing the ternary spectrin-actin-4.1R junctional complex.","method":"PKC activation in intact cells, in vitro phosphorylation assays, in vitro protein binding assays with phosphomimetic mutants","journal":"Biochemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — phosphorylation site identification plus in vitro binding assays with mutants, multiple functional consequences tested","pmids":["21542582"],"is_preprint":false},{"year":2001,"finding":"4.1R binds to phosphatidylserine (PS) through a two-step process: initial interaction via positively charged YKRS residues with the serine head group, followed by tight hydrophobic interaction with fatty acid acyl chains. Association with acyl chains impairs 4.1R binding to calmodulin, band 3, and glycophorin C. 4.1R-PS interaction may regulate intracellular sorting of 4.1R.","method":"In vitro liposome binding assays, phospholipase treatments, ionic strength competition, biochemical analyses","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro reconstitution with multiple phospholipase controls and functional consequence (inhibition of protein binding) demonstrated","pmids":["11423550"],"is_preprint":false},{"year":2004,"finding":"Nonerythroid 135 kDa 4.1R isoforms directly interact with microtubules; both the membrane-binding domain and C-terminal domain mediate tubulin association. 4.1R co-localizes with microtubules in mitotic stages. Immunodepletion of 4.1R from cell-free mitotic extract results in randomly dispersed microtubules instead of organized asters; adding back recombinant 135 kDa 4.1R reconstitutes mitotic asters.","method":"In vitro microtubule sedimentation assays, GST pull-downs, immunodepletion from mitotic cell-free extract, reconstitution assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — reconstitution of mitotic aster assembly, immunodepletion/add-back, in vitro sedimentation with domain mapping","pmids":["15184364"],"is_preprint":false},{"year":2004,"finding":"4.1R is phosphorylated by p34cdc2 kinase at Thr60 and Ser679 in a mitosis-specific manner. Phosphorylation is essential for targeting 4.1R to spindle poles and for mitotic microtubule aster assembly in vitro. Phosphorylation enhances 4.1R association with NuMA and tubulin. siRNA depletion of 4.1R from HeLa cells impairs efficient mitotic spindle pole focusing.","method":"In vitro cdc2 kinase assay, phosphorylation site mapping, siRNA knockdown, mitotic aster reconstitution in vitro","journal":"Molecular biology of the cell","confidence":"High","confidence_rationale":"Tier 1 / Strong — kinase assay with site mapping, reconstitution, and genetic loss-of-function with spindle phenotype","pmids":["15525677"],"is_preprint":false},{"year":2008,"finding":"4.1R localizes at centrosomes, specifically at distal/subdistal regions of mature centrioles, in a cell cycle-dependent manner. RNAi depletion of 4.1R perturbs subdistal appendage proteins ninein and outer dense fiber 2/cenexin, reduces interphase microtubule anchoring, causes G1 accumulation in p53-proficient cells, reduces centrosome separation leading to monopolar spindle formation, and causes mislocalization of NuMA.","method":"RNAi knockdown, immunofluorescence/confocal microscopy, cell cycle analysis","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — RNAi with multiple orthogonal cellular phenotype readouts (centrosome, spindle, cell cycle)","pmids":["18212055"],"is_preprint":false},{"year":2009,"finding":"4.1R expressed in gastric epithelial cells directly associates with adherens junction protein beta-catenin. In 4.1R-deficient stomach epithelia, beta-catenin is selectively reduced, E-cadherin linkage to the cytoskeleton is weakened, actin organization is altered, and cell-cell contacts and gastric gland organization are disrupted.","method":"4.1R-null mouse analysis, biochemical co-immunoprecipitation/pull-down, histological examination","journal":"Biochimica et biophysica acta","confidence":"High","confidence_rationale":"Tier 2 / Strong — KO mouse plus direct binding assays, multiple orthogonal phenotypic readouts","pmids":["19376086"],"is_preprint":false},{"year":2009,"finding":"4.1R is recruited to the immunological synapse after TCR stimulation. In 4.1R-deficient CD4+ T cells, LAT phosphorylation and downstream ERK phosphorylation are enhanced, leading to hyperproliferation and increased IL-2/IFNγ production. 4.1R directly binds LAT and thereby inhibits its phosphorylation by ZAP-70.","method":"4.1R-/- mouse model, co-immunoprecipitation, phosphorylation assays, cytokine production measurements","journal":"Blood","confidence":"High","confidence_rationale":"Tier 2 / Strong — KO mouse plus direct binding (Co-IP) plus mechanistic phosphorylation assays, multiple immune readouts","pmids":["19190245"],"is_preprint":false},{"year":2011,"finding":"4.1R co-immunoprecipitates with nuclear envelope proteins emerin and lamin A/C. RNAi depletion of 4.1R causes nuclear dysmorphology, partial redistribution of emerin to cytoplasm, disorganization of lamin A/C, mislocalization of multiple nuclear subcompartment proteins (MAN1, Tpr, Nup62, NuMA, LAP2α), increased nucleus-centrosome distances, increased β-catenin signaling, and nuclear accumulation of β-catenin.","method":"Co-immunoprecipitation, RNAi knockdown, immunofluorescence microscopy in human cells and MEFs","journal":"Journal of cell science","confidence":"High","confidence_rationale":"Tier 2 / Strong — Co-IP plus RNAi with multiple orthogonal phenotypes, replicated in two cell systems","pmids":["21486941"],"is_preprint":false},{"year":2011,"finding":"4.1R expression in keratinocytes is required for cell adhesion, spreading, migration, motility, and epidermal wound healing. In 4.1R-/- keratinocytes, surface expression and activity of β1 integrin are reduced, and actin stress fibers and focal adhesions fail to form on fibronectin.","method":"4.1R-/- mouse model, cell adhesion/migration/spreading assays, flow cytometry for β1 integrin surface expression, wound healing assay","journal":"Journal of cell science","confidence":"High","confidence_rationale":"Tier 2 / Strong — KO mouse with multiple orthogonal functional readouts and surface protein quantification","pmids":["21693581"],"is_preprint":false},{"year":2011,"finding":"4.1R regulates cell migration by localizing to the leading edge; its membrane-binding domain is required for this plasma membrane localization. Co-immunoprecipitation and pull-down identified IQGAP1 as a direct binding partner of 4.1R (via the membrane-binding domain). 4.1R silencing abolishes localization of IQGAP1 to the leading edge, while IQGAP1 is not required for 4.1R localization.","method":"siRNA knockdown, co-immunoprecipitation, pull-down assays, live-cell migration assays, immunofluorescence","journal":"Journal of cell science","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal pull-down/Co-IP plus siRNA with defined directional epistasis for IQGAP1 localization","pmids":["21750196"],"is_preprint":false},{"year":2013,"finding":"4.1R directly associates with PMCA1b (plasma membrane calcium ATPase 1b) in enterocytes; the interaction involves the membrane-binding domain of 4.1R and the second intracellular loop and C-terminus of PMCA1b. 4.1R-/- mice show impaired intestinal calcium absorption, reduced PMCA1b expression in enterocytes, and secondary hyperparathyroidism.","method":"4.1R-/- mouse model, co-immunoprecipitation, in vitro direct binding assays with recombinant domains, calcium absorption measurements","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — KO mouse with physiological phenotype plus direct binding assays with domain mapping","pmids":["23460639"],"is_preprint":false},{"year":2013,"finding":"4.1R interacts and co-localizes with cortical CLASP2 and is required for the correct number and dynamics of CLASP2 cortical platforms. 4.1R controls CLASP2 binding to microtubules at the cell edge by locally altering GSK3 activity. In 4.1R-knockdown cells, microtubule plus-ends are not tethered to the cell cortex and lose radial distribution.","method":"Co-immunoprecipitation, pull-down assays, siRNA knockdown, live microtubule dynamics imaging, immunofluorescence","journal":"Journal of cell science","confidence":"High","confidence_rationale":"Tier 2 / Strong — Co-IP/pull-down plus siRNA with live-cell imaging of MT dynamics and GSK3 activity readout","pmids":["23943871"],"is_preprint":false},{"year":2012,"finding":"4.1R binds directly to the cytoplasmic domain of NHE1 (Na+/H+ exchanger isoform 1) through an EED motif in the 4.1R FERM domain interacting with two clusters of basic residues (K519R and R556FNKKYVKK) in NHE1. Binding affinity (KD = 100-200 nM) is reduced under hypertonic/acidic conditions and upon Ca2+/CaM binding to the 4.1R FERM domain, suggesting electrostatic regulation.","method":"In vitro direct binding assays with recombinant proteins, resonant mirror detection, affinity measurements","journal":"The Biochemical journal","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro reconstitution with quantitative binding measurements and regulatory modulation tested","pmids":["22731252"],"is_preprint":false},{"year":2000,"finding":"4.1R C-terminal domain (22/24 kDa) directly interacts with eIF3-p44, a subunit of the eukaryotic translation initiation factor 3 complex. Depletion of eIF3-p44 from rabbit reticulocyte lysates abolishes efficient cell-free protein translation, suggesting 4.1R may anchor the translation apparatus to the cytoskeleton.","method":"Yeast two-hybrid, in vitro binding assays, co-immunoprecipitation, cell-free translation depletion","journal":"Blood","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — yeast two-hybrid plus Co-IP plus in vitro binding, single lab, functional consequence demonstrated by depletion of eIF3-p44 not 4.1R itself","pmids":["10887144"],"is_preprint":false},{"year":2004,"finding":"A constitutive domain of 4.1R containing heptad repeats of leucine residues is responsible for association with tubulin; this domain is present in all 4.1R isoforms. In T cells, 4.1R associates with interphase microtubules, and ectopic 4.1R expression causes microtubule disorganization.","method":"GST pull-down with tubulin, co-sedimentation with taxol-polymerized microtubules, confocal microscopy, transfection assays","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — in vitro pull-down plus co-sedimentation with domain mapping, single lab","pmids":["11579097"],"is_preprint":false},{"year":2004,"finding":"4.1R isoforms are present in isolated centrosome preparations and remain at the center of in vitro-assembled microtubule asters. Addition of 4.1R-GST fusion protein increases the number of microtubule asters assembled from isolated centrosomes. Specific 4.1R isoforms that perturb centrosomal distribution of p150Glued and dynein intermediate chain disorganize interphase microtubules after regrowth.","method":"Centrosome isolation, in vitro microtubule aster assembly assays, confocal microscopy, transfection","journal":"Journal of cell science","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — centrosome reconstitution assay plus gain-of-function expression, single lab","pmids":["15564380"],"is_preprint":false},{"year":2000,"finding":"A constitutive core region of 4.1R (encoded by constitutive exons, common to all isoforms) can localize to the nucleus and confer nuclear targeting to a cytosolic reporter. Sequences encoded by exon 5 act as a dominant cytoplasmic retention signal (nuclear export signal). When both exon 5 and exon 16 are present, nuclear targeting by exon 16 dominates over exon 5 cytoplasmic retention.","method":"Transfection of epitope-tagged natural and engineered 4.1R isoforms in COS-7 cells, immunofluorescence, reporter fusion experiments","journal":"Journal of cell science","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — localization experiments with multiple natural and engineered isoforms, single lab","pmids":["10852827"],"is_preprint":false},{"year":2002,"finding":"The exon 5-encoded leucine-rich sequence in 4.1R functions as a nuclear export signal (NES): it binds to export receptor CRM1 in a RanGTP-dependent manner, and two conserved hydrophobic residues are critical for NES function and cytoplasmic localization of 4.1R isoforms containing this sequence.","method":"CRM1 binding assays, RanGTP-dependent interaction tests, site-directed mutagenesis, immunofluorescence of exon 5 mutants","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — CRM1 binding plus mutagenesis plus localization, single lab","pmids":["12427749"],"is_preprint":false},{"year":1999,"finding":"The N-terminal 209 amino acid domain (headpiece, HP) encoded from AUG-1 of high molecular weight 4.1R isoforms abrogates nuclear targeting: ATG-1-translated isoforms localize to plasma membrane and endoplasmic reticulum rather than nucleus, and fusing the 209 aa domain to a nuclear 4.1R isoform inhibits its nuclear entry.","method":"RT-PCR cloning of ATG-1 isoforms, transient transfection with c-Myc-tagged constructs, immunofluorescence, subcellular fractionation","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — localization with fusion constructs and fractionation, multiple isoforms tested, single lab","pmids":["10611314"],"is_preprint":false},{"year":2000,"finding":"Nonerythroid 4.1R isoforms (~105/110 kDa) in skeletal muscle co-purify in a supramolecular complex with sarcomeric proteins myosin, alpha-actin, and alpha-tropomyosin. In vitro binding assays show 4.1R may interact directly with these contractile proteins through its 10 kDa domain. 4.1R protein decorates A-bands in skeletal muscle.","method":"Native complex co-purification, in vitro binding assays with recombinant 10 kDa domain, immunofluorescence/immunohistochemistry","journal":"Molecular biology of the cell","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — native complex isolation plus in vitro binding with domain mapping, single lab","pmids":["11071908"],"is_preprint":false},{"year":2008,"finding":"4.1R deficiency in mice leads to prolonged Q-T interval and action potential duration, larger/slower Ca2+ transients, increased sarcoplasmic reticulum Ca2+ content, reduced Na+/Ca2+ exchanger current density, faster transient inward current inactivation, and increased persistent Na+ current density. 4.1R KO hearts show reduced NaV1.5α expression, indicating 4.1R modulates cardiac ion transporter function.","method":"4.1R-/- mouse ECG, patch-clamp electrophysiology, Ca2+ transient measurements in isolated myocytes","journal":"Circulation research","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — comprehensive KO phenotype with multiple ion transport readouts but mechanism of 4.1R-channel interaction not directly characterized","pmids":["18787192"],"is_preprint":false},{"year":2006,"finding":"4.1R deficiency in mice leads to erythrocyte dehydration with reduced K+ and increased Na+ content; Na/H exchange activity is markedly upregulated with increased Vmax, abnormal osmotic dependence, and loss of okadaic acid-induced Na/H exchange activation. This demonstrates that 4.1R physiologically downregulates Na/H exchange activity.","method":"4.1R-/- mouse model, ion transport assays (Na/H exchange, Na-K pump, NKCC cotransport), pharmacological analyses","journal":"American journal of physiology. Cell physiology","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — complete KO with multiple transport assays, but molecular mechanism of NHE inhibition not directly addressed","pmids":["16774987"],"is_preprint":false},{"year":2006,"finding":"Fox-2 (RBFOX2) binds to conserved UGCAUG elements in the proximal intron downstream of exon 16 of 4.1R pre-mRNA and activates exon 16 inclusion. Knockdown of Fox-2 by siRNA decreases exon 16 splicing. Fox-2 is expressed in mouse erythroblasts and is a physiological activator of the erythroid differentiation-specific exon 16 splicing switch.","method":"SELEX, in vitro RNA binding, HeLa co-transfection minigene assays, siRNA knockdown, immunoblot","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — SELEX plus minigene plus siRNA, single lab","pmids":["16537540"],"is_preprint":false},{"year":2011,"finding":"RBFOX2 activates exon 16 5' splice site utilization by recruiting U1 snRNP through direct interaction between its C-terminal domain and the zinc finger region of U1C, stabilizing the pre-mRNA–U1 snRNP complex. Strengthening the native weak 5' splice site to consensus abolishes RBFOX2 dependence.","method":"Minigene splicing assays, engineered 5' splice site mutants, in vitro protein-protein interaction assays, U1 snRNP recruitment assays","journal":"Molecular and cellular biology","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — mechanistic reconstitution of RBFOX2-U1C interaction and splice site rescue, single lab","pmids":["22083953"],"is_preprint":false},{"year":2004,"finding":"SF2/ASF binds a CAGACAT exonic splicing enhancer in exon 16, stimulates exon 16 inclusion in in vitro and in vivo splicing assays, and its expression is upregulated during erythroid differentiation correlating with exon 16 inclusion.","method":"UV cross-linking/immunoprecipitation, in vitro complementation splicing assays, MEL cell minigene transfection, immunoblot","journal":"Blood","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — in vitro complementation plus cross-linking plus cell assays, single lab","pmids":["15522963"],"is_preprint":false},{"year":2017,"finding":"Splicing factors TIA1 and Pcbp1 bind cooperatively to a UUUUCCCCCC motif between the branch point and 3' splice site of exon 16. RBM39 (whose expression rises during erythroid differentiation) enhances the effect of TIA1 and Pcbp1, interacts with U2AF65 and SF3b155, and promotes U2 snRNP recruitment to the branch point, facilitating exon 16 inclusion.","method":"In vitro RNA binding assays, minigene splicing assays, co-immunoprecipitation of splicing factors, spliceosome assembly assays","journal":"Molecular and cellular biology","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — in vitro binding plus Co-IP of spliceosome factors plus functional splicing assays, single lab","pmids":["28193846"],"is_preprint":false},{"year":2008,"finding":"Alternatively spliced exon 5 of the 4.1R FERM domain encodes a second binding site for p55, distinct from the exon 10-encoded site; both bind independent sites within the D5 domain of p55. Inclusion of exon 5 is necessary for membrane targeting of the full-length 135 kDa 4.1R isoform in epithelial cells.","method":"Competition binding assays, Surface Plasmon Resonance, transfection/immunofluorescence for localization","journal":"Biochimica et biophysica acta","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — SPR binding quantification plus localization studies with deletion constructs, single lab","pmids":["18952129"],"is_preprint":false},{"year":2003,"finding":"4.1R interacts with merlin/4.1B interactors including CD44 and betaII-spectrin in meningioma cells. Overexpression of 4.1R reduces meningioma cell proliferation, and 4.1R membrane localization increases under growth arrest conditions.","method":"Co-immunoprecipitation, Western blot, cell proliferation assays, immunofluorescence","journal":"Neurobiology of disease","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — Co-IP with multiple partners, overexpression proliferation assay, localization under growth arrest, single lab","pmids":["12901833"],"is_preprint":false},{"year":2009,"finding":"4.1R directly associates with adherens junction protein beta-catenin via its membrane-binding domain (specifically the armadillo repeats 1-2 of beta-catenin). Epithelial-specific 4.1R isoforms containing exon 17b (4.1R+17b) are exclusively co-localized with AJs; exon 17b-encoded peptide provides a bispecific interaction with the actin cytoskeleton and promotes fodrin-actin complex formation. Depletion of 4.1R+17b or overexpression of 4.1R-17b reduces junctional actin and spectrin and impairs E-cadherin assembly during AJ reassembly.","method":"Co-immunoprecipitation, pull-down assays with recombinant domains, siRNA knockdown, calcium switch AJ reassembly assay, immunofluorescence","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — direct binding domain mapping plus siRNA rescue experiment, single lab","pmids":["31776189"],"is_preprint":false},{"year":2021,"finding":"4.1R functions as a member of the NuMA-LGN-dynein/dynactin complex to regulate mitotic spindle orientation during erythroid differentiation. The 4.1R-NuMA interaction is required for asymmetric segregation of Numb to daughter cells; disruption of this complex increases Notch signaling and decreases erythroblast population.","method":"siRNA depletion, gene replacement, co-immunoprecipitation, immunofluorescence, Notch signaling reporter","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — genetic rescue plus Co-IP plus functional cell fate assays, single lab","pmids":["34364872"],"is_preprint":false},{"year":2015,"finding":"4.1R directly binds Kell blood group protein; pull-down and co-immunoprecipitation from erythrocyte membranes showed a direct interaction, with the R46R motif in the Kell juxta-membrane region binding to lobe B of the 4.1R FERM domain. 4.1R deficiency is associated with reduction of Kell, XK, DARC, and the glycosylated form of urea transporter B.","method":"In vitro pull-down, co-immunoprecipitation, recombinant domain-mapping","journal":"British journal of haematology","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — pull-down plus Co-IP with domain mapping, single lab","pmids":["26455906"],"is_preprint":false},{"year":2016,"finding":"4.1R associates with VHL protein and, when overexpressed, reverses VHL-mediated ubiquitination and degradation of myogenin, stabilizing myogenin protein levels. 4.1R depletion impairs skeletal muscle differentiation, decreasing myosin heavy and light chains, caveolin-3, and myogenin protein (but not mRNA).","method":"siRNA knockdown, co-immunoprecipitation, ubiquitination assays, myoblast differentiation assays, 4.1R-/- MEF MyoD-induced differentiation","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — Co-IP plus ubiquitination rescue plus KO MEF assay, single lab","pmids":["27780863"],"is_preprint":false},{"year":2020,"finding":"In non-small cell lung cancer, EPB41 protein directly associates with ALDOC (aldolase C). Loss of EPB41 releases ALDOC from the EPB41-ALDOC complex, disassembling the beta-catenin destruction complex, reducing beta-catenin proteolytic degradation, and activating Wnt/β-catenin target oncogenes.","method":"Co-immunoprecipitation, in vitro interaction assays, beta-catenin stability and localization assays, tumor xenograft model","journal":"Cancer letters","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — Co-IP plus mechanistic pathway dissection, in vitro and in vivo, single lab","pmids":["33242559"],"is_preprint":false},{"year":2019,"finding":"4.1R binds directly to EGFR and reduces EGFR phosphorylation/activation in keratinocytes. 4.1R knockout augments EGFR-mediated Akt/ERK signaling, causing keratinocyte hyperproliferation that is reversed by EGFR or MEK inhibitors.","method":"Co-immunoprecipitation, immunofluorescence, 4.1R-/- mouse keratinocytes, pharmacological inhibitors","journal":"Experimental cell research","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — Co-IP plus KO phenotype plus pharmacological rescue, single lab","pmids":["31562860"],"is_preprint":false},{"year":2024,"finding":"4.1R directly interacts with TLR4 and inhibits AKT/HIF-1α signaling. 4.1R deficiency enhances glycolytic metabolism via upregulation of PKM2 and promotes M1 macrophage polarization, exacerbating sepsis-induced liver injury.","method":"Co-immunoprecipitation, 4.1R-/- mice, glycolysis assays, PKM2 and HIF-1α pathway analysis","journal":"International immunopharmacology","confidence":"Low","confidence_rationale":"Tier 3 / Weak — Co-IP with TLR4 and pathway analysis, single lab, limited mechanistic detail in abstract","pmids":["38237224"],"is_preprint":false},{"year":2020,"finding":"4.1R is required for FcεRI-mediated mast cell activation. In 4.1R-KO mast cells, antigen-induced phosphorylation of SYK and downstream signaling molecules (LAT1, PLCγ1, SHP1, SHIP, p38, ERK, JNK, STAT5, CBL, mTOR) are reduced while FcεRI β and γ subunit phosphorylation is unaffected. LAT1 and LAT2 are both present in 4.1R immunocomplexes.","method":"4.1R-KO mouse BMMCs, phosphorylation assays, co-immunoprecipitation, degranulation and calcium response assays, passive cutaneous anaphylaxis in vivo","journal":"Frontiers in immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — KO mouse plus Co-IP plus multiple signaling readouts plus in vivo anaphylaxis, single lab","pmids":["31993060"],"is_preprint":false},{"year":2020,"finding":"CADM1 recruits 4.1R to the plasma membrane of small-cell lung cancer cells through its cytoplasmic 4.1 protein-binding motif. Knockdown of 4.1R suppresses the CADM1-enhanced colony formation, indicating 4.1R is required for the oncogenic role of CADM1 in SCLC.","method":"CADM1 deletion/point mutant analysis, siRNA knockdown, soft agar colony formation assay, immunofluorescence","journal":"Biochemical and biophysical research communications","confidence":"Low","confidence_rationale":"Tier 3 / Weak — mutant analysis plus siRNA, single lab, limited mechanistic depth","pmids":["33298314"],"is_preprint":false},{"year":2001,"finding":"An 80 kDa 4.1R polypeptide is enriched ~11-fold in forebrain postsynaptic density (PSD) preparations. Blot overlay assays identified neurofilament L and alpha-internexin as 4.1R-binding proteins in PSDs; a complex containing 80 kDa 4.1R, alpha-internexin, and neurofilament L was immunoprecipitated from brain extract.","method":"Subcellular fractionation, blot overlay assays, co-immunoprecipitation from brain extract","journal":"European journal of biochemistry","confidence":"Low","confidence_rationale":"Tier 3 / Weak — co-IP plus overlay from brain extract, single lab, postsynaptic density enrichment only","pmids":["11179975"],"is_preprint":false},{"year":2019,"finding":"4.1R negatively regulates CD8+ T cell activation by directly binding LAT (co-immunoprecipitation), inhibiting LAT phosphorylation and downstream ERK signaling; 4.1R-/- CD8+ T cells show enhanced proliferation, IL-2 and IFNγ secretion, and T cell-dependent immune responses.","method":"4.1R-/- mouse, co-immunoprecipitation, phosphorylation assays, proliferation and cytokine assays","journal":"Immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — KO mouse plus Co-IP plus functional T cell assays, mechanistically consistent with CD4 data (PMID 19190245), single lab","pmids":["31135971"],"is_preprint":false}],"current_model":"Protein 4.1R (EPB41) is a multifunctional cytoskeletal adaptor whose cloverleaf-shaped FERM domain directly links membrane proteins (band 3, glycophorin C, p55/PALMD, Kell, XK, Duffy, NHE1, PMCA1b, β1-integrin, EGFR, TLR4, CADM1) to the spectrin–actin network; these interactions are dynamically regulated by PIP2, Ca2+/calmodulin, PKC-mediated phosphorylation at Ser312/Ser331, and by alternative splicing of exons 5, 8, 10, 16, and 17b that diversify its binding repertoire across cell types; in nonerythroid cells, cdc2-dependent phosphorylation at Thr60/Ser679 targets the 135 kDa isoform to mitotic spindle poles where it interacts with NuMA, dynein, and dynactin to organize mitotic asters, regulate spindle orientation, and control asymmetric Numb segregation during erythropoiesis; 4.1R also localizes to the nuclear envelope (interacting with emerin and lamin A/C) and tight/adherens junctions (binding ZO-2 and β-catenin) to maintain nuclear architecture and epithelial integrity, and in immune cells it negatively regulates T cell activation by binding LAT and inhibiting ZAP-70-mediated LAT phosphorylation."},"narrative":{"mechanistic_narrative":"Protein 4.1R (EPB41) is a multifunctional cytoskeletal adaptor that links integral membrane proteins to the spectrin–actin network, with its cloverleaf-shaped N-terminal FERM (30 kDa) domain providing three distinct lobes that engage band 3, glycophorin C/D, and the membrane palmitoylated protein p55 [PMID:11017195]. Within this domain, exon 8-encoded sequences form the glycophorin C interface and exon 10-encoded sequences the p55 interface, and 4.1R increases p55–glycophorin C affinity by an order of magnitude, nucleating a ternary spectrin–F-actin junctional complex whose loss in knockout erythrocytes causes hemolytic anemia, membrane instability, and reduced spectrin/ankyrin [PMID:10831591, PMID:16060676, PMID:9927493]. This adaptor function organizes a macromolecular junctional complex that retains multiple transmembrane proteins—glycophorin C, XK, Duffy, Rh, and Kell—at the red cell membrane [PMID:18524950, PMID:26455906]. These interactions are dynamically gated: Ca2+/calmodulin binding weakens 4.1R–target affinity [PMID:11017195, PMID:10831591], PIP2 binding induces a conformational change that selectively enhances glycophorin C binding while inhibiting band 3 binding [PMID:16669616], phosphatidylserine acyl-chain engagement impairs binding to calmodulin, band 3, and glycophorin C [PMID:11423550], and PKC phosphorylation at Ser312/Ser331 suppresses binding to membrane proteins and β-spectrin to destabilize the junction [PMID:21542582]. Beyond the erythrocyte, nonerythroid high-molecular-weight isoforms (135 kDa) directly bind microtubules and tubulin and are essential for organizing mitotic asters: immunodepletion disperses microtubules and recombinant 4.1R restores asters [PMID:15184364, PMID:11579097]. cdc2-dependent phosphorylation at Thr60/Ser679 targets 4.1R to spindle poles and enhances its association with NuMA and tubulin, where it acts within a NuMA–LGN–dynein/dynactin complex to focus spindle poles, regulate spindle orientation, and direct asymmetric Numb segregation during erythroid differentiation [PMID:10189366, PMID:15525677, PMID:34364872]; it also localizes to centrosome subdistal appendages to anchor interphase microtubules [PMID:18212055]. 4.1R maintains nuclear architecture through interactions with emerin and lamin A/C [PMID:21486941] and supports epithelial integrity at adherens junctions by directly binding β-catenin, an exon 17b-dependent linkage that promotes fodrin–actin assembly [PMID:19376086, PMID:31776189], and at tight junctions by binding ZO-2 [PMID:10874042]. Nuclear access of 4.1R is controlled by alternative splicing: exon 16 encodes a core NLS and exon 5 encodes a CRM1-dependent nuclear export signal, with their combination determining nucleocytoplasmic distribution [PMID:10359596, PMID:12427749]. In immune cells, 4.1R is recruited to the immunological synapse and negatively regulates lymphocyte activation by directly binding LAT and inhibiting its ZAP-70-mediated phosphorylation, dampening downstream ERK signaling and cytokine output in CD4+ and CD8+ T cells [PMID:19190245, PMID:31135971]. Physiologically, 4.1R regulates ion transport partners including NHE1, PMCA1b, and cardiac ion currents, and modulates growth-factor and Wnt/β-catenin signaling through partners such as EGFR and ALDOC [PMID:23460639, PMID:22731252, PMID:33242559, PMID:31562860].","teleology":[{"year":1999,"claim":"Establishing that 4.1R is genetically required to build the red cell membrane skeleton converted it from a biochemically defined component to a functionally essential scaffold.","evidence":"Gene knockout mouse with morphological and biochemical erythrocyte analysis","pmids":["9927493"],"confidence":"High","gaps":["Does not resolve which individual binding interactions account for the spectrin/ankyrin reduction","No structural basis provided for the assembly defect"]},{"year":1999,"claim":"Discovery that a 135 kDa nonerythroid isoform binds NuMA and partitions to spindle poles revealed an entirely distinct mitotic role beyond the membrane skeleton.","evidence":"Yeast two-hybrid, reciprocal Co-IP, in vitro binding, and co-localization across cell contexts","pmids":["10189366"],"confidence":"High","gaps":["Did not establish whether the interaction is direct in the spindle context or how it is cell-cycle gated","Functional requirement of the interaction for spindle assembly not yet tested"]},{"year":1999,"claim":"Identifying exon 16 (NLS) and exon 5 (cytoplasmic retention) elements explained how alternative splicing controls subcellular targeting of 4.1R isoforms.","evidence":"Permeabilized-cell import assays and quantitative importin-alpha2 binding measurements with NLS mutagenesis","pmids":["10359596"],"confidence":"High","gaps":["Did not define the regulatory cues that select splice variants in vivo","Nuclear function of imported 4.1R not addressed here"]},{"year":2000,"claim":"The FERM domain crystal structure provided the molecular logic of multivalent membrane-protein binding and its Ca2+/calmodulin regulation.","evidence":"X-ray crystallography of the 30 kDa domain with functional binding-site mapping","pmids":["11017195","10831591"],"confidence":"High","gaps":["Structures of full-length or spliced isoforms not determined","Conformational coupling between lobes during regulation not visualized"]},{"year":2000,"claim":"Mapping the spectrin–F-actin ternary junction and demonstrating ZO-2/tight-junction binding showed 4.1R operates at both the membrane skeleton node and epithelial junctions.","evidence":"In vitro co-sedimentation with domain truncations plus yeast two-hybrid/Co-IP at MDCK tight junctions","pmids":["16060676","10874042"],"confidence":"High","gaps":["PIP2 regulatory switch tested only in vitro","In vivo requirement at epithelial junctions not yet established at this stage"]},{"year":2006,"claim":"Defining PIP2 and phosphatidylserine as conformational and competitive regulators established lipid-controlled switching of 4.1R binding specificity.","evidence":"Liposome binding, alanine mutagenesis, and phospholipase-controlled in vitro assays","pmids":["16669616","11423550"],"confidence":"High","gaps":["Lipid regulation not validated in intact cells","How lipid and Ca2+/CaM inputs are integrated is unresolved"]},{"year":2008,"claim":"Knockout and pull-down evidence that 4.1R retains XK, Duffy, and Rh defined it as the organizer of a macromolecular junctional complex governing transmembrane protein abundance.","evidence":"4.1R knockout mouse erythrocyte analysis with in vitro pull-downs and flow cytometry","pmids":["18524950"],"confidence":"High","gaps":["Stoichiometry and assembly order of the complex not determined","Direct versus indirect retention of each partner not fully separated"]},{"year":2004,"claim":"Direct microtubule binding plus cdc2 phosphorylation at Thr60/Ser679 explained how 4.1R is mobilized to organize mitotic asters and focus spindle poles.","evidence":"In vitro microtubule sedimentation, immunodepletion/add-back reconstitution, cdc2 kinase site mapping, and siRNA spindle-pole phenotype","pmids":["15184364","15525677"],"confidence":"High","gaps":["The kinase(s) acting in cells and timing of dephosphorylation not defined","Relationship between microtubule binding domains and NuMA binding not structurally resolved"]},{"year":2008,"claim":"Centrosome localization data linked 4.1R to interphase microtubule anchoring and centrosome separation, broadening its cytoskeletal role across the cell cycle.","evidence":"RNAi with immunofluorescence and cell-cycle analysis showing appendage protein and NuMA mislocalization","pmids":["18212055"],"confidence":"High","gaps":["Direct centrosomal binding partner not defined","Mechanism connecting 4.1R loss to G1 arrest unresolved"]},{"year":2009,"claim":"Demonstrating direct β-catenin binding and a T cell synapse role showed 4.1R sustains epithelial adhesion and dampens immune activation by directly engaging signaling adaptors.","evidence":"4.1R-null mouse epithelia plus Co-IP/binding; immunological synapse recruitment with LAT binding and phosphorylation assays in CD4+ T cells","pmids":["19376086","19190245"],"confidence":"High","gaps":["How a single adaptor switches between adhesion and immune-inhibitory roles not defined","Spliceoform usage in each context not fully mapped here"]},{"year":2011,"claim":"Nuclear envelope, keratinocyte adhesion, IQGAP1 leading-edge, NHE1 binding, and PKC phosphorylation findings collectively cemented 4.1R as a regulated adaptor across nuclear, migratory, and ion-transport contexts.","evidence":"Co-IP/RNAi for emerin/lamin and IQGAP1; KO keratinocyte adhesion assays; in vitro NHE1 binding; PKC phosphosite mapping with binding assays","pmids":["21486941","21693581","21750196","22731252","21542582"],"confidence":"High","gaps":["Isoform identity driving each non-erythroid function not always defined","Crosstalk between phospho- and lipid-regulation in cells not integrated"]},{"year":2013,"claim":"Direct PMCA1b binding with an intestinal calcium-absorption defect, and CLASP2/cortical microtubule regulation, extended 4.1R function to transporter scaffolding and cortical microtubule capture.","evidence":"4.1R-null mouse calcium physiology with domain-mapped binding; Co-IP plus live MT imaging and GSK3 readout for CLASP2","pmids":["23460639","23943871"],"confidence":"High","gaps":["Tissue-specific isoform requirements not delineated","How 4.1R modulates GSK3 activity locally not mechanistically resolved"]},{"year":2017,"claim":"A series of studies dissecting the erythroid exon 16 splicing switch (RBFOX2, SF2/ASF, TIA1/Pcbp1/RBM39) explained how the differentiation-specific isoform repertoire of 4.1R is generated.","evidence":"SELEX, minigene splicing assays, splicing-factor Co-IP, U1/U2 snRNP recruitment assays","pmids":["16537540","22083953","15522963","28193846"],"confidence":"Medium","gaps":["These are mechanisms of 4.1R regulation rather than 4.1R activity itself","Single-lab minigene-based evidence not validated at endogenous loci in vivo"]},{"year":2021,"claim":"Placing 4.1R within the NuMA–LGN–dynein/dynactin spindle-orientation machinery connected its mitotic activity to asymmetric Numb segregation and erythroid cell-fate control.","evidence":"siRNA depletion, gene replacement, Co-IP, and Notch reporter during erythroid differentiation","pmids":["34364872"],"confidence":"Medium","gaps":["Single lab; in vivo erythropoietic consequences not fully established","Direct contribution of each complex member to Numb partitioning not separated"]},{"year":2024,"claim":"Reports of 4.1R binding EGFR, TLR4, ALDOC, VHL, CADM1, and FcεRI signaling components extended its adaptor role into growth-factor, Wnt, metabolic, and innate/adaptive immune signaling.","evidence":"Co-IP, KO mouse phenotypes, ubiquitination/pathway assays, and colony-formation/xenograft models across multiple single-lab studies","pmids":["31562860","38237224","33242559","27780863","33298314","31993060"],"confidence":"Low","gaps":["Several interactions rest on single Co-IP studies without reciprocal or structural validation","Direct versus indirect nature of binding and the responsible isoforms remain undefined","Physiological relevance of the signaling roles awaits independent confirmation"]},{"year":null,"claim":"How a single gene's spliced isoforms are selected and post-translationally gated to partition 4.1R among membrane skeleton, spindle, nucleus, junctions, and signaling complexes in a given cell remains the central open question.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No unified model linking isoform/phospho/lipid state to functional destination","Structures of full-length isoforms in complex with partners lacking","In vivo contributions of non-erythroid functions to physiology underexplored"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[0,2,4,5,14,18]},{"term_id":"GO:0008092","term_label":"cytoskeletal protein binding","supporting_discovery_ids":[2,11,23,20]},{"term_id":"GO:0008289","term_label":"lipid binding","supporting_discovery_ids":[3,10]},{"term_id":"GO:0005198","term_label":"structural molecule activity","supporting_discovery_ids":[2,4,8]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[15,47,21,30]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[0,4,18,35]},{"term_id":"GO:0005856","term_label":"cytoskeleton","supporting_discovery_ids":[2,11,23]},{"term_id":"GO:0005815","term_label":"microtubule organizing center","supporting_discovery_ids":[13,24]},{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[5,7,16,25]},{"term_id":"GO:0005635","term_label":"nuclear envelope","supporting_discovery_ids":[16]}],"pathway":[{"term_id":"R-HSA-1640170","term_label":"Cell Cycle","supporting_discovery_ids":[5,12,13,38]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[15,47,44]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[15,41,42,47]},{"term_id":"R-HSA-1474244","term_label":"Extracellular matrix organization","supporting_discovery_ids":[6,14,37,17]}],"complexes":["spectrin–actin–4.1R junctional complex","NuMA–LGN–dynein/dynactin spindle complex"],"partners":["GYPC","SLC4A1","MPP1","NUMA1","ZO-2","CTNNB1","EMD","LAT"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P11171","full_name":"Protein 4.1","aliases":["4.1R","Band 4.1","EPB4.1","Erythrocyte membrane protein band 4.1"],"length_aa":864,"mass_kda":97.0,"function":"Protein 4.1 is a major structural element of the erythrocyte membrane skeleton. It plays a key role in regulating membrane physical properties of mechanical stability and deformability by stabilizing spectrin-actin interaction. Recruits DLG1 to membranes. Required for dynein-dynactin complex and NUMA1 recruitment at the mitotic cell cortex during anaphase (PubMed:23870127)","subcellular_location":"Cytoplasm, cytoskeleton; Cytoplasm, cell cortex; Nucleus","url":"https://www.uniprot.org/uniprotkb/P11171/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/EPB41","classification":"Not Classified","n_dependent_lines":1,"n_total_lines":1208,"dependency_fraction":0.0008278145695364238},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"CLNS1A","stoichiometry":4.0},{"gene":"NECAP1","stoichiometry":0.2},{"gene":"NUMA1","stoichiometry":0.2},{"gene":"WDR3","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/EPB41","total_profiled":1310},"omim":[{"mim_id":"616649","title":"SPHEROCYTOSIS, TYPE 2; SPH2","url":"https://www.omim.org/entry/616649"},{"mim_id":"616305","title":"FERM DOMAIN-CONTAINING PROTEIN 4A; FRMD4A","url":"https://www.omim.org/entry/616305"},{"mim_id":"612149","title":"RNA-BINDING FOX1 HOMOLOG 2; RBFOX2","url":"https://www.omim.org/entry/612149"},{"mim_id":"611804","title":"ELLIPTOCYTOSIS 1; EL1","url":"https://www.omim.org/entry/611804"},{"mim_id":"611730","title":"ERYTHROCYTE MEMBRANE PROTEIN BAND 4.1-LIKE 5; EPB41L5","url":"https://www.omim.org/entry/611730"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Plasma membrane","reliability":"Approved"},{"location":"Cell Junctions","reliability":"Approved"},{"location":"Nuclear bodies","reliability":"Additional"},{"location":"Cytokinetic bridge","reliability":"Additional"},{"location":"Mitotic spindle","reliability":"Additional"},{"location":"Cytosol","reliability":"Additional"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in all","driving_tissues":[{"tissue":"retina","ntpm":74.1}],"url":"https://www.proteinatlas.org/search/EPB41"},"hgnc":{"alias_symbol":["4.1R"],"prev_symbol":["EL1"]},"alphafold":{"accession":"P11171","domains":[{"cath_id":"3.10.20.90","chopping":"208-289","consensus_level":"medium","plddt":93.8796,"start":208,"end":289},{"cath_id":"1.20.80.10","chopping":"292-398","consensus_level":"medium","plddt":95.7585,"start":292,"end":398},{"cath_id":"2.30.29.30","chopping":"400-495_508-523","consensus_level":"high","plddt":91.1707,"start":400,"end":523},{"cath_id":"2.20.25","chopping":"786-825","consensus_level":"medium","plddt":72.356,"start":786,"end":825}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P11171","model_url":"https://alphafold.ebi.ac.uk/files/AF-P11171-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P11171-F1-predicted_aligned_error_v6.png","plddt_mean":63.03},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=EPB41","jax_strain_url":"https://www.jax.org/strain/search?query=EPB41"},"sequence":{"accession":"P11171","fasta_url":"https://rest.uniprot.org/uniprotkb/P11171.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P11171/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P11171"}},"corpus_meta":[{"pmid":"18524950","id":"PMC_18524950","title":"Protein 4.1R-dependent multiprotein complex: new insights into the structural organization of the red blood cell membrane.","date":"2008","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/18524950","citation_count":198,"is_preprint":false},{"pmid":"26407012","id":"PMC_26407012","title":"Optimization of a Novel Binding Motif to (E)-3-(3,5-Difluoro-4-((1R,3R)-2-(2-fluoro-2-methylpropyl)-3-methyl-2,3,4,9-tetrahydro-1H-pyrido[3,4-b]indol-1-yl)phenyl)acrylic Acid (AZD9496), a Potent and Orally Bioavailable Selective Estrogen Receptor Downregulator and Antagonist.","date":"2015","source":"Journal of medicinal chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/26407012","citation_count":139,"is_preprint":false},{"pmid":"15071791","id":"PMC_15071791","title":"Hereditary elliptocytosis: spectrin and protein 4.1R.","date":"2004","source":"Seminars in hematology","url":"https://pubmed.ncbi.nlm.nih.gov/15071791","citation_count":128,"is_preprint":false},{"pmid":"10874042","id":"PMC_10874042","title":"Characterization of the interaction between protein 4.1R and ZO-2. 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Two separate calmodulin (CaM) binding regions are located at the central region: one Ca2+-insensitive alpha-helical site and one Ca2+-sensitive extended-structure site whose binding to CaM weakens 4.1R interactions with target proteins.\",\n      \"method\": \"X-ray crystallography with functional binding assays\",\n      \"journal\": \"Nature structural biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structure combined with functional characterization of binding sites and CaM regulation, single rigorous paper with multiple orthogonal methods\",\n      \"pmids\": [\"11017195\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"Within the 30 kDa domain, sequences encoded by exon 8 constitute the binding interface for glycophorin C (GPC), and sequences encoded by exon 10 constitute the binding interface for p55. 4.1R increases the affinity of p55 binding to GPC by an order of magnitude, and Ca2+/calmodulin binding to 4.1R decreases its affinity for both p55 and GPC in a Ca2+-dependent manner.\",\n      \"method\": \"In vitro binding assays with recombinant domain fragments and calmodulin competition assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro reconstitution with domain-mapping and Ca2+/CaM modulation demonstrated in same study\",\n      \"pmids\": [\"10831591\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"4.1R forms a ternary complex with spectrin and F-actin at the erythrocyte junctional node; both the intact N-terminus and CH1 domain of the spectrin beta chain bind F-actin and 4.1R. PIP2 greatly enhances the binding of 4.1R to the spectrin beta chain N-terminal region (residues 1-301), suggesting a regulatory switch.\",\n      \"method\": \"In vitro binding/co-sedimentation assays with recombinant domain truncations and liposome PIP2 competition\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro reconstitution with domain mutagenesis, multiple binding partners tested\",\n      \"pmids\": [\"16060676\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"4.1R binds PIP2-containing liposomes through its N-terminal 30 kDa membrane-binding domain; PIP2 binding induces a conformational change. Amino acids K63,64 and K265,266 are required for PIP2 binding. PIP2 selectively enhances 4.1R binding to GPC but inhibits binding to band 3, with no effect on p55 binding.\",\n      \"method\": \"Liposome binding assays, alanine mutagenesis, in vitro pull-down with recombinant proteins\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — mutagenesis plus reconstitution in a single study, multiple binding partners tested\",\n      \"pmids\": [\"16669616\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Deletion of 4.1R in mouse red cells causes large reduction of actin and loss of cytoskeletal lattice structure. Pull-down assays showed 4.1R associates with XK, Duffy, and Rh transmembrane proteins, in addition to glycophorin C; absence of 4.1R causes selective reduction of these proteins from the membrane, consistent with 4.1R organizing a macromolecular junctional complex.\",\n      \"method\": \"4.1R knockout mouse analysis, in vitro pull-down assays, Western blot, flow cytometry\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — KO mouse combined with in vitro pull-downs, multiple transmembrane proteins assessed\",\n      \"pmids\": [\"18524950\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"A 135 kDa nonerythroid 4.1R isoform specifically interacts with the nuclear mitotic apparatus (NuMA) protein. The minimal interaction sequences map to residues encoded by exons 20 and 21 of 4.1R and residues 1788-1810 of NuMA. 4.1R and NuMA co-localize in the interphase nucleus and redistribute to spindle poles in mitosis; 4.1R forms a complex with NuMA, dynein, and dynactin during cell division.\",\n      \"method\": \"Yeast two-hybrid, in vitro binding assays, co-immunoprecipitation, co-immunolocalization\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal Co-IP plus yeast two-hybrid plus in vitro binding plus co-localization, replicated in multiple cell contexts\",\n      \"pmids\": [\"10189366\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"Two 4.1R isoforms (135 kDa and 150 kDa) interact specifically with the tight junction protein ZO-2. 4.1R co-localizes with ZO-2 and occludin at MDCK tight junctions and co-precipitates with ZO-2, ZO-1, and occludin. The interaction maps to exons 19-21 of 4.1R and residues 1054-1118 of ZO-2. This interaction is specific to confluent (tight junction-forming) cells.\",\n      \"method\": \"Yeast two-hybrid, immunocolocalization, co-immunoprecipitation, in vitro binding studies\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — yeast two-hybrid plus Co-IP plus in vitro binding plus domain mapping, multiple orthogonal methods\",\n      \"pmids\": [\"10874042\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"Nuclear import of the 4.1R80 isoform requires two distant signals: a basic KKKRER peptide encoded by alternative exon 16 (acting as a weak core NLS) and an acidic EED peptide encoded by alternative exon 5. Both motifs are needed for full importin-mediated nuclear import. 4.1R80 binds importin alpha2 (Rch1) with high affinity (KD = 30 nM), and affinity decreases at least 7–20 fold if either motif is absent.\",\n      \"method\": \"Transfection with epitope-tagged constructs, digitonin-permeabilized cell import assays, resonant mirror protein-protein interaction measurements with recombinant Rch1\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — reconstituted nuclear import in permeabilized cells, quantitative binding measurements, mutagenesis of both NLS elements\",\n      \"pmids\": [\"10359596\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"4.1R-null mice generated by gene knockout exhibit moderate hemolytic anemia, abnormal erythrocyte morphology, decreased membrane stability, and reduced expression of spectrin and ankyrin, demonstrating that 4.1R is required for erythroid membrane skeleton assembly.\",\n      \"method\": \"Gene knockout (homologous recombination), morphological and biochemical analysis of erythrocytes\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — complete gene knockout with multiple phenotypic readouts in erythrocytes\",\n      \"pmids\": [\"9927493\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Protein kinase C activation in intact erythrocytes phosphorylates 4.1R at serine 312 and serine 331. Phosphorylation at either site suppresses 4.1R binding to the cytoplasmic domains of GPC, Duffy, and XK, rendering these transmembrane proteins more easily detergent-extractable. Phosphorylation also weakens 4.1R affinity for beta-spectrin, destabilizing the ternary spectrin-actin-4.1R junctional complex.\",\n      \"method\": \"PKC activation in intact cells, in vitro phosphorylation assays, in vitro protein binding assays with phosphomimetic mutants\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — phosphorylation site identification plus in vitro binding assays with mutants, multiple functional consequences tested\",\n      \"pmids\": [\"21542582\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"4.1R binds to phosphatidylserine (PS) through a two-step process: initial interaction via positively charged YKRS residues with the serine head group, followed by tight hydrophobic interaction with fatty acid acyl chains. Association with acyl chains impairs 4.1R binding to calmodulin, band 3, and glycophorin C. 4.1R-PS interaction may regulate intracellular sorting of 4.1R.\",\n      \"method\": \"In vitro liposome binding assays, phospholipase treatments, ionic strength competition, biochemical analyses\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro reconstitution with multiple phospholipase controls and functional consequence (inhibition of protein binding) demonstrated\",\n      \"pmids\": [\"11423550\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Nonerythroid 135 kDa 4.1R isoforms directly interact with microtubules; both the membrane-binding domain and C-terminal domain mediate tubulin association. 4.1R co-localizes with microtubules in mitotic stages. Immunodepletion of 4.1R from cell-free mitotic extract results in randomly dispersed microtubules instead of organized asters; adding back recombinant 135 kDa 4.1R reconstitutes mitotic asters.\",\n      \"method\": \"In vitro microtubule sedimentation assays, GST pull-downs, immunodepletion from mitotic cell-free extract, reconstitution assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — reconstitution of mitotic aster assembly, immunodepletion/add-back, in vitro sedimentation with domain mapping\",\n      \"pmids\": [\"15184364\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"4.1R is phosphorylated by p34cdc2 kinase at Thr60 and Ser679 in a mitosis-specific manner. Phosphorylation is essential for targeting 4.1R to spindle poles and for mitotic microtubule aster assembly in vitro. Phosphorylation enhances 4.1R association with NuMA and tubulin. siRNA depletion of 4.1R from HeLa cells impairs efficient mitotic spindle pole focusing.\",\n      \"method\": \"In vitro cdc2 kinase assay, phosphorylation site mapping, siRNA knockdown, mitotic aster reconstitution in vitro\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — kinase assay with site mapping, reconstitution, and genetic loss-of-function with spindle phenotype\",\n      \"pmids\": [\"15525677\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"4.1R localizes at centrosomes, specifically at distal/subdistal regions of mature centrioles, in a cell cycle-dependent manner. RNAi depletion of 4.1R perturbs subdistal appendage proteins ninein and outer dense fiber 2/cenexin, reduces interphase microtubule anchoring, causes G1 accumulation in p53-proficient cells, reduces centrosome separation leading to monopolar spindle formation, and causes mislocalization of NuMA.\",\n      \"method\": \"RNAi knockdown, immunofluorescence/confocal microscopy, cell cycle analysis\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — RNAi with multiple orthogonal cellular phenotype readouts (centrosome, spindle, cell cycle)\",\n      \"pmids\": [\"18212055\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"4.1R expressed in gastric epithelial cells directly associates with adherens junction protein beta-catenin. In 4.1R-deficient stomach epithelia, beta-catenin is selectively reduced, E-cadherin linkage to the cytoskeleton is weakened, actin organization is altered, and cell-cell contacts and gastric gland organization are disrupted.\",\n      \"method\": \"4.1R-null mouse analysis, biochemical co-immunoprecipitation/pull-down, histological examination\",\n      \"journal\": \"Biochimica et biophysica acta\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — KO mouse plus direct binding assays, multiple orthogonal phenotypic readouts\",\n      \"pmids\": [\"19376086\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"4.1R is recruited to the immunological synapse after TCR stimulation. In 4.1R-deficient CD4+ T cells, LAT phosphorylation and downstream ERK phosphorylation are enhanced, leading to hyperproliferation and increased IL-2/IFNγ production. 4.1R directly binds LAT and thereby inhibits its phosphorylation by ZAP-70.\",\n      \"method\": \"4.1R-/- mouse model, co-immunoprecipitation, phosphorylation assays, cytokine production measurements\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — KO mouse plus direct binding (Co-IP) plus mechanistic phosphorylation assays, multiple immune readouts\",\n      \"pmids\": [\"19190245\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"4.1R co-immunoprecipitates with nuclear envelope proteins emerin and lamin A/C. RNAi depletion of 4.1R causes nuclear dysmorphology, partial redistribution of emerin to cytoplasm, disorganization of lamin A/C, mislocalization of multiple nuclear subcompartment proteins (MAN1, Tpr, Nup62, NuMA, LAP2α), increased nucleus-centrosome distances, increased β-catenin signaling, and nuclear accumulation of β-catenin.\",\n      \"method\": \"Co-immunoprecipitation, RNAi knockdown, immunofluorescence microscopy in human cells and MEFs\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — Co-IP plus RNAi with multiple orthogonal phenotypes, replicated in two cell systems\",\n      \"pmids\": [\"21486941\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"4.1R expression in keratinocytes is required for cell adhesion, spreading, migration, motility, and epidermal wound healing. In 4.1R-/- keratinocytes, surface expression and activity of β1 integrin are reduced, and actin stress fibers and focal adhesions fail to form on fibronectin.\",\n      \"method\": \"4.1R-/- mouse model, cell adhesion/migration/spreading assays, flow cytometry for β1 integrin surface expression, wound healing assay\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — KO mouse with multiple orthogonal functional readouts and surface protein quantification\",\n      \"pmids\": [\"21693581\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"4.1R regulates cell migration by localizing to the leading edge; its membrane-binding domain is required for this plasma membrane localization. Co-immunoprecipitation and pull-down identified IQGAP1 as a direct binding partner of 4.1R (via the membrane-binding domain). 4.1R silencing abolishes localization of IQGAP1 to the leading edge, while IQGAP1 is not required for 4.1R localization.\",\n      \"method\": \"siRNA knockdown, co-immunoprecipitation, pull-down assays, live-cell migration assays, immunofluorescence\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal pull-down/Co-IP plus siRNA with defined directional epistasis for IQGAP1 localization\",\n      \"pmids\": [\"21750196\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"4.1R directly associates with PMCA1b (plasma membrane calcium ATPase 1b) in enterocytes; the interaction involves the membrane-binding domain of 4.1R and the second intracellular loop and C-terminus of PMCA1b. 4.1R-/- mice show impaired intestinal calcium absorption, reduced PMCA1b expression in enterocytes, and secondary hyperparathyroidism.\",\n      \"method\": \"4.1R-/- mouse model, co-immunoprecipitation, in vitro direct binding assays with recombinant domains, calcium absorption measurements\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — KO mouse with physiological phenotype plus direct binding assays with domain mapping\",\n      \"pmids\": [\"23460639\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"4.1R interacts and co-localizes with cortical CLASP2 and is required for the correct number and dynamics of CLASP2 cortical platforms. 4.1R controls CLASP2 binding to microtubules at the cell edge by locally altering GSK3 activity. In 4.1R-knockdown cells, microtubule plus-ends are not tethered to the cell cortex and lose radial distribution.\",\n      \"method\": \"Co-immunoprecipitation, pull-down assays, siRNA knockdown, live microtubule dynamics imaging, immunofluorescence\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — Co-IP/pull-down plus siRNA with live-cell imaging of MT dynamics and GSK3 activity readout\",\n      \"pmids\": [\"23943871\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"4.1R binds directly to the cytoplasmic domain of NHE1 (Na+/H+ exchanger isoform 1) through an EED motif in the 4.1R FERM domain interacting with two clusters of basic residues (K519R and R556FNKKYVKK) in NHE1. Binding affinity (KD = 100-200 nM) is reduced under hypertonic/acidic conditions and upon Ca2+/CaM binding to the 4.1R FERM domain, suggesting electrostatic regulation.\",\n      \"method\": \"In vitro direct binding assays with recombinant proteins, resonant mirror detection, affinity measurements\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro reconstitution with quantitative binding measurements and regulatory modulation tested\",\n      \"pmids\": [\"22731252\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"4.1R C-terminal domain (22/24 kDa) directly interacts with eIF3-p44, a subunit of the eukaryotic translation initiation factor 3 complex. Depletion of eIF3-p44 from rabbit reticulocyte lysates abolishes efficient cell-free protein translation, suggesting 4.1R may anchor the translation apparatus to the cytoskeleton.\",\n      \"method\": \"Yeast two-hybrid, in vitro binding assays, co-immunoprecipitation, cell-free translation depletion\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — yeast two-hybrid plus Co-IP plus in vitro binding, single lab, functional consequence demonstrated by depletion of eIF3-p44 not 4.1R itself\",\n      \"pmids\": [\"10887144\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"A constitutive domain of 4.1R containing heptad repeats of leucine residues is responsible for association with tubulin; this domain is present in all 4.1R isoforms. In T cells, 4.1R associates with interphase microtubules, and ectopic 4.1R expression causes microtubule disorganization.\",\n      \"method\": \"GST pull-down with tubulin, co-sedimentation with taxol-polymerized microtubules, confocal microscopy, transfection assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — in vitro pull-down plus co-sedimentation with domain mapping, single lab\",\n      \"pmids\": [\"11579097\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"4.1R isoforms are present in isolated centrosome preparations and remain at the center of in vitro-assembled microtubule asters. Addition of 4.1R-GST fusion protein increases the number of microtubule asters assembled from isolated centrosomes. Specific 4.1R isoforms that perturb centrosomal distribution of p150Glued and dynein intermediate chain disorganize interphase microtubules after regrowth.\",\n      \"method\": \"Centrosome isolation, in vitro microtubule aster assembly assays, confocal microscopy, transfection\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — centrosome reconstitution assay plus gain-of-function expression, single lab\",\n      \"pmids\": [\"15564380\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"A constitutive core region of 4.1R (encoded by constitutive exons, common to all isoforms) can localize to the nucleus and confer nuclear targeting to a cytosolic reporter. Sequences encoded by exon 5 act as a dominant cytoplasmic retention signal (nuclear export signal). When both exon 5 and exon 16 are present, nuclear targeting by exon 16 dominates over exon 5 cytoplasmic retention.\",\n      \"method\": \"Transfection of epitope-tagged natural and engineered 4.1R isoforms in COS-7 cells, immunofluorescence, reporter fusion experiments\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — localization experiments with multiple natural and engineered isoforms, single lab\",\n      \"pmids\": [\"10852827\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"The exon 5-encoded leucine-rich sequence in 4.1R functions as a nuclear export signal (NES): it binds to export receptor CRM1 in a RanGTP-dependent manner, and two conserved hydrophobic residues are critical for NES function and cytoplasmic localization of 4.1R isoforms containing this sequence.\",\n      \"method\": \"CRM1 binding assays, RanGTP-dependent interaction tests, site-directed mutagenesis, immunofluorescence of exon 5 mutants\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — CRM1 binding plus mutagenesis plus localization, single lab\",\n      \"pmids\": [\"12427749\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"The N-terminal 209 amino acid domain (headpiece, HP) encoded from AUG-1 of high molecular weight 4.1R isoforms abrogates nuclear targeting: ATG-1-translated isoforms localize to plasma membrane and endoplasmic reticulum rather than nucleus, and fusing the 209 aa domain to a nuclear 4.1R isoform inhibits its nuclear entry.\",\n      \"method\": \"RT-PCR cloning of ATG-1 isoforms, transient transfection with c-Myc-tagged constructs, immunofluorescence, subcellular fractionation\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — localization with fusion constructs and fractionation, multiple isoforms tested, single lab\",\n      \"pmids\": [\"10611314\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"Nonerythroid 4.1R isoforms (~105/110 kDa) in skeletal muscle co-purify in a supramolecular complex with sarcomeric proteins myosin, alpha-actin, and alpha-tropomyosin. In vitro binding assays show 4.1R may interact directly with these contractile proteins through its 10 kDa domain. 4.1R protein decorates A-bands in skeletal muscle.\",\n      \"method\": \"Native complex co-purification, in vitro binding assays with recombinant 10 kDa domain, immunofluorescence/immunohistochemistry\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — native complex isolation plus in vitro binding with domain mapping, single lab\",\n      \"pmids\": [\"11071908\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"4.1R deficiency in mice leads to prolonged Q-T interval and action potential duration, larger/slower Ca2+ transients, increased sarcoplasmic reticulum Ca2+ content, reduced Na+/Ca2+ exchanger current density, faster transient inward current inactivation, and increased persistent Na+ current density. 4.1R KO hearts show reduced NaV1.5α expression, indicating 4.1R modulates cardiac ion transporter function.\",\n      \"method\": \"4.1R-/- mouse ECG, patch-clamp electrophysiology, Ca2+ transient measurements in isolated myocytes\",\n      \"journal\": \"Circulation research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — comprehensive KO phenotype with multiple ion transport readouts but mechanism of 4.1R-channel interaction not directly characterized\",\n      \"pmids\": [\"18787192\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"4.1R deficiency in mice leads to erythrocyte dehydration with reduced K+ and increased Na+ content; Na/H exchange activity is markedly upregulated with increased Vmax, abnormal osmotic dependence, and loss of okadaic acid-induced Na/H exchange activation. This demonstrates that 4.1R physiologically downregulates Na/H exchange activity.\",\n      \"method\": \"4.1R-/- mouse model, ion transport assays (Na/H exchange, Na-K pump, NKCC cotransport), pharmacological analyses\",\n      \"journal\": \"American journal of physiology. Cell physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — complete KO with multiple transport assays, but molecular mechanism of NHE inhibition not directly addressed\",\n      \"pmids\": [\"16774987\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Fox-2 (RBFOX2) binds to conserved UGCAUG elements in the proximal intron downstream of exon 16 of 4.1R pre-mRNA and activates exon 16 inclusion. Knockdown of Fox-2 by siRNA decreases exon 16 splicing. Fox-2 is expressed in mouse erythroblasts and is a physiological activator of the erythroid differentiation-specific exon 16 splicing switch.\",\n      \"method\": \"SELEX, in vitro RNA binding, HeLa co-transfection minigene assays, siRNA knockdown, immunoblot\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — SELEX plus minigene plus siRNA, single lab\",\n      \"pmids\": [\"16537540\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"RBFOX2 activates exon 16 5' splice site utilization by recruiting U1 snRNP through direct interaction between its C-terminal domain and the zinc finger region of U1C, stabilizing the pre-mRNA–U1 snRNP complex. Strengthening the native weak 5' splice site to consensus abolishes RBFOX2 dependence.\",\n      \"method\": \"Minigene splicing assays, engineered 5' splice site mutants, in vitro protein-protein interaction assays, U1 snRNP recruitment assays\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — mechanistic reconstitution of RBFOX2-U1C interaction and splice site rescue, single lab\",\n      \"pmids\": [\"22083953\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"SF2/ASF binds a CAGACAT exonic splicing enhancer in exon 16, stimulates exon 16 inclusion in in vitro and in vivo splicing assays, and its expression is upregulated during erythroid differentiation correlating with exon 16 inclusion.\",\n      \"method\": \"UV cross-linking/immunoprecipitation, in vitro complementation splicing assays, MEL cell minigene transfection, immunoblot\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — in vitro complementation plus cross-linking plus cell assays, single lab\",\n      \"pmids\": [\"15522963\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Splicing factors TIA1 and Pcbp1 bind cooperatively to a UUUUCCCCCC motif between the branch point and 3' splice site of exon 16. RBM39 (whose expression rises during erythroid differentiation) enhances the effect of TIA1 and Pcbp1, interacts with U2AF65 and SF3b155, and promotes U2 snRNP recruitment to the branch point, facilitating exon 16 inclusion.\",\n      \"method\": \"In vitro RNA binding assays, minigene splicing assays, co-immunoprecipitation of splicing factors, spliceosome assembly assays\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — in vitro binding plus Co-IP of spliceosome factors plus functional splicing assays, single lab\",\n      \"pmids\": [\"28193846\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Alternatively spliced exon 5 of the 4.1R FERM domain encodes a second binding site for p55, distinct from the exon 10-encoded site; both bind independent sites within the D5 domain of p55. Inclusion of exon 5 is necessary for membrane targeting of the full-length 135 kDa 4.1R isoform in epithelial cells.\",\n      \"method\": \"Competition binding assays, Surface Plasmon Resonance, transfection/immunofluorescence for localization\",\n      \"journal\": \"Biochimica et biophysica acta\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — SPR binding quantification plus localization studies with deletion constructs, single lab\",\n      \"pmids\": [\"18952129\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"4.1R interacts with merlin/4.1B interactors including CD44 and betaII-spectrin in meningioma cells. Overexpression of 4.1R reduces meningioma cell proliferation, and 4.1R membrane localization increases under growth arrest conditions.\",\n      \"method\": \"Co-immunoprecipitation, Western blot, cell proliferation assays, immunofluorescence\",\n      \"journal\": \"Neurobiology of disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — Co-IP with multiple partners, overexpression proliferation assay, localization under growth arrest, single lab\",\n      \"pmids\": [\"12901833\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"4.1R directly associates with adherens junction protein beta-catenin via its membrane-binding domain (specifically the armadillo repeats 1-2 of beta-catenin). Epithelial-specific 4.1R isoforms containing exon 17b (4.1R+17b) are exclusively co-localized with AJs; exon 17b-encoded peptide provides a bispecific interaction with the actin cytoskeleton and promotes fodrin-actin complex formation. Depletion of 4.1R+17b or overexpression of 4.1R-17b reduces junctional actin and spectrin and impairs E-cadherin assembly during AJ reassembly.\",\n      \"method\": \"Co-immunoprecipitation, pull-down assays with recombinant domains, siRNA knockdown, calcium switch AJ reassembly assay, immunofluorescence\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — direct binding domain mapping plus siRNA rescue experiment, single lab\",\n      \"pmids\": [\"31776189\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"4.1R functions as a member of the NuMA-LGN-dynein/dynactin complex to regulate mitotic spindle orientation during erythroid differentiation. The 4.1R-NuMA interaction is required for asymmetric segregation of Numb to daughter cells; disruption of this complex increases Notch signaling and decreases erythroblast population.\",\n      \"method\": \"siRNA depletion, gene replacement, co-immunoprecipitation, immunofluorescence, Notch signaling reporter\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — genetic rescue plus Co-IP plus functional cell fate assays, single lab\",\n      \"pmids\": [\"34364872\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"4.1R directly binds Kell blood group protein; pull-down and co-immunoprecipitation from erythrocyte membranes showed a direct interaction, with the R46R motif in the Kell juxta-membrane region binding to lobe B of the 4.1R FERM domain. 4.1R deficiency is associated with reduction of Kell, XK, DARC, and the glycosylated form of urea transporter B.\",\n      \"method\": \"In vitro pull-down, co-immunoprecipitation, recombinant domain-mapping\",\n      \"journal\": \"British journal of haematology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — pull-down plus Co-IP with domain mapping, single lab\",\n      \"pmids\": [\"26455906\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"4.1R associates with VHL protein and, when overexpressed, reverses VHL-mediated ubiquitination and degradation of myogenin, stabilizing myogenin protein levels. 4.1R depletion impairs skeletal muscle differentiation, decreasing myosin heavy and light chains, caveolin-3, and myogenin protein (but not mRNA).\",\n      \"method\": \"siRNA knockdown, co-immunoprecipitation, ubiquitination assays, myoblast differentiation assays, 4.1R-/- MEF MyoD-induced differentiation\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — Co-IP plus ubiquitination rescue plus KO MEF assay, single lab\",\n      \"pmids\": [\"27780863\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"In non-small cell lung cancer, EPB41 protein directly associates with ALDOC (aldolase C). Loss of EPB41 releases ALDOC from the EPB41-ALDOC complex, disassembling the beta-catenin destruction complex, reducing beta-catenin proteolytic degradation, and activating Wnt/β-catenin target oncogenes.\",\n      \"method\": \"Co-immunoprecipitation, in vitro interaction assays, beta-catenin stability and localization assays, tumor xenograft model\",\n      \"journal\": \"Cancer letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — Co-IP plus mechanistic pathway dissection, in vitro and in vivo, single lab\",\n      \"pmids\": [\"33242559\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"4.1R binds directly to EGFR and reduces EGFR phosphorylation/activation in keratinocytes. 4.1R knockout augments EGFR-mediated Akt/ERK signaling, causing keratinocyte hyperproliferation that is reversed by EGFR or MEK inhibitors.\",\n      \"method\": \"Co-immunoprecipitation, immunofluorescence, 4.1R-/- mouse keratinocytes, pharmacological inhibitors\",\n      \"journal\": \"Experimental cell research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — Co-IP plus KO phenotype plus pharmacological rescue, single lab\",\n      \"pmids\": [\"31562860\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"4.1R directly interacts with TLR4 and inhibits AKT/HIF-1α signaling. 4.1R deficiency enhances glycolytic metabolism via upregulation of PKM2 and promotes M1 macrophage polarization, exacerbating sepsis-induced liver injury.\",\n      \"method\": \"Co-immunoprecipitation, 4.1R-/- mice, glycolysis assays, PKM2 and HIF-1α pathway analysis\",\n      \"journal\": \"International immunopharmacology\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — Co-IP with TLR4 and pathway analysis, single lab, limited mechanistic detail in abstract\",\n      \"pmids\": [\"38237224\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"4.1R is required for FcεRI-mediated mast cell activation. In 4.1R-KO mast cells, antigen-induced phosphorylation of SYK and downstream signaling molecules (LAT1, PLCγ1, SHP1, SHIP, p38, ERK, JNK, STAT5, CBL, mTOR) are reduced while FcεRI β and γ subunit phosphorylation is unaffected. LAT1 and LAT2 are both present in 4.1R immunocomplexes.\",\n      \"method\": \"4.1R-KO mouse BMMCs, phosphorylation assays, co-immunoprecipitation, degranulation and calcium response assays, passive cutaneous anaphylaxis in vivo\",\n      \"journal\": \"Frontiers in immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — KO mouse plus Co-IP plus multiple signaling readouts plus in vivo anaphylaxis, single lab\",\n      \"pmids\": [\"31993060\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"CADM1 recruits 4.1R to the plasma membrane of small-cell lung cancer cells through its cytoplasmic 4.1 protein-binding motif. Knockdown of 4.1R suppresses the CADM1-enhanced colony formation, indicating 4.1R is required for the oncogenic role of CADM1 in SCLC.\",\n      \"method\": \"CADM1 deletion/point mutant analysis, siRNA knockdown, soft agar colony formation assay, immunofluorescence\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — mutant analysis plus siRNA, single lab, limited mechanistic depth\",\n      \"pmids\": [\"33298314\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"An 80 kDa 4.1R polypeptide is enriched ~11-fold in forebrain postsynaptic density (PSD) preparations. Blot overlay assays identified neurofilament L and alpha-internexin as 4.1R-binding proteins in PSDs; a complex containing 80 kDa 4.1R, alpha-internexin, and neurofilament L was immunoprecipitated from brain extract.\",\n      \"method\": \"Subcellular fractionation, blot overlay assays, co-immunoprecipitation from brain extract\",\n      \"journal\": \"European journal of biochemistry\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — co-IP plus overlay from brain extract, single lab, postsynaptic density enrichment only\",\n      \"pmids\": [\"11179975\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"4.1R negatively regulates CD8+ T cell activation by directly binding LAT (co-immunoprecipitation), inhibiting LAT phosphorylation and downstream ERK signaling; 4.1R-/- CD8+ T cells show enhanced proliferation, IL-2 and IFNγ secretion, and T cell-dependent immune responses.\",\n      \"method\": \"4.1R-/- mouse, co-immunoprecipitation, phosphorylation assays, proliferation and cytokine assays\",\n      \"journal\": \"Immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — KO mouse plus Co-IP plus functional T cell assays, mechanistically consistent with CD4 data (PMID 19190245), single lab\",\n      \"pmids\": [\"31135971\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"Protein 4.1R (EPB41) is a multifunctional cytoskeletal adaptor whose cloverleaf-shaped FERM domain directly links membrane proteins (band 3, glycophorin C, p55/PALMD, Kell, XK, Duffy, NHE1, PMCA1b, β1-integrin, EGFR, TLR4, CADM1) to the spectrin–actin network; these interactions are dynamically regulated by PIP2, Ca2+/calmodulin, PKC-mediated phosphorylation at Ser312/Ser331, and by alternative splicing of exons 5, 8, 10, 16, and 17b that diversify its binding repertoire across cell types; in nonerythroid cells, cdc2-dependent phosphorylation at Thr60/Ser679 targets the 135 kDa isoform to mitotic spindle poles where it interacts with NuMA, dynein, and dynactin to organize mitotic asters, regulate spindle orientation, and control asymmetric Numb segregation during erythropoiesis; 4.1R also localizes to the nuclear envelope (interacting with emerin and lamin A/C) and tight/adherens junctions (binding ZO-2 and β-catenin) to maintain nuclear architecture and epithelial integrity, and in immune cells it negatively regulates T cell activation by binding LAT and inhibiting ZAP-70-mediated LAT phosphorylation.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"Protein 4.1R (EPB41) is a multifunctional cytoskeletal adaptor that links integral membrane proteins to the spectrin–actin network, with its cloverleaf-shaped N-terminal FERM (30 kDa) domain providing three distinct lobes that engage band 3, glycophorin C/D, and the membrane palmitoylated protein p55 [#0]. Within this domain, exon 8-encoded sequences form the glycophorin C interface and exon 10-encoded sequences the p55 interface, and 4.1R increases p55–glycophorin C affinity by an order of magnitude, nucleating a ternary spectrin–F-actin junctional complex whose loss in knockout erythrocytes causes hemolytic anemia, membrane instability, and reduced spectrin/ankyrin [#1, #2, #8]. This adaptor function organizes a macromolecular junctional complex that retains multiple transmembrane proteins—glycophorin C, XK, Duffy, Rh, and Kell—at the red cell membrane [#4, #39]. These interactions are dynamically gated: Ca2+/calmodulin binding weakens 4.1R–target affinity [#0, #1], PIP2 binding induces a conformational change that selectively enhances glycophorin C binding while inhibiting band 3 binding [#3], phosphatidylserine acyl-chain engagement impairs binding to calmodulin, band 3, and glycophorin C [#10], and PKC phosphorylation at Ser312/Ser331 suppresses binding to membrane proteins and β-spectrin to destabilize the junction [#9]. Beyond the erythrocyte, nonerythroid high-molecular-weight isoforms (135 kDa) directly bind microtubules and tubulin and are essential for organizing mitotic asters: immunodepletion disperses microtubules and recombinant 4.1R restores asters [#11, #23]. cdc2-dependent phosphorylation at Thr60/Ser679 targets 4.1R to spindle poles and enhances its association with NuMA and tubulin, where it acts within a NuMA–LGN–dynein/dynactin complex to focus spindle poles, regulate spindle orientation, and direct asymmetric Numb segregation during erythroid differentiation [#5, #12, #38]; it also localizes to centrosome subdistal appendages to anchor interphase microtubules [#13]. 4.1R maintains nuclear architecture through interactions with emerin and lamin A/C [#16] and supports epithelial integrity at adherens junctions by directly binding β-catenin, an exon 17b-dependent linkage that promotes fodrin–actin assembly [#14, #37], and at tight junctions by binding ZO-2 [#6]. Nuclear access of 4.1R is controlled by alternative splicing: exon 16 encodes a core NLS and exon 5 encodes a CRM1-dependent nuclear export signal, with their combination determining nucleocytoplasmic distribution [#7, #26]. In immune cells, 4.1R is recruited to the immunological synapse and negatively regulates lymphocyte activation by directly binding LAT and inhibiting its ZAP-70-mediated phosphorylation, dampening downstream ERK signaling and cytokine output in CD4+ and CD8+ T cells [#15, #47]. Physiologically, 4.1R regulates ion transport partners including NHE1, PMCA1b, and cardiac ion currents, and modulates growth-factor and Wnt/β-catenin signaling through partners such as EGFR and ALDOC [#19, #21, #41, #42].\",\n  \"teleology\": [\n    {\n      \"year\": 1999,\n      \"claim\": \"Establishing that 4.1R is genetically required to build the red cell membrane skeleton converted it from a biochemically defined component to a functionally essential scaffold.\",\n      \"evidence\": \"Gene knockout mouse with morphological and biochemical erythrocyte analysis\",\n      \"pmids\": [\"9927493\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Does not resolve which individual binding interactions account for the spectrin/ankyrin reduction\", \"No structural basis provided for the assembly defect\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Discovery that a 135 kDa nonerythroid isoform binds NuMA and partitions to spindle poles revealed an entirely distinct mitotic role beyond the membrane skeleton.\",\n      \"evidence\": \"Yeast two-hybrid, reciprocal Co-IP, in vitro binding, and co-localization across cell contexts\",\n      \"pmids\": [\"10189366\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not establish whether the interaction is direct in the spindle context or how it is cell-cycle gated\", \"Functional requirement of the interaction for spindle assembly not yet tested\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Identifying exon 16 (NLS) and exon 5 (cytoplasmic retention) elements explained how alternative splicing controls subcellular targeting of 4.1R isoforms.\",\n      \"evidence\": \"Permeabilized-cell import assays and quantitative importin-alpha2 binding measurements with NLS mutagenesis\",\n      \"pmids\": [\"10359596\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not define the regulatory cues that select splice variants in vivo\", \"Nuclear function of imported 4.1R not addressed here\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"The FERM domain crystal structure provided the molecular logic of multivalent membrane-protein binding and its Ca2+/calmodulin regulation.\",\n      \"evidence\": \"X-ray crystallography of the 30 kDa domain with functional binding-site mapping\",\n      \"pmids\": [\"11017195\", \"10831591\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structures of full-length or spliced isoforms not determined\", \"Conformational coupling between lobes during regulation not visualized\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Mapping the spectrin–F-actin ternary junction and demonstrating ZO-2/tight-junction binding showed 4.1R operates at both the membrane skeleton node and epithelial junctions.\",\n      \"evidence\": \"In vitro co-sedimentation with domain truncations plus yeast two-hybrid/Co-IP at MDCK tight junctions\",\n      \"pmids\": [\"16060676\", \"10874042\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"PIP2 regulatory switch tested only in vitro\", \"In vivo requirement at epithelial junctions not yet established at this stage\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Defining PIP2 and phosphatidylserine as conformational and competitive regulators established lipid-controlled switching of 4.1R binding specificity.\",\n      \"evidence\": \"Liposome binding, alanine mutagenesis, and phospholipase-controlled in vitro assays\",\n      \"pmids\": [\"16669616\", \"11423550\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Lipid regulation not validated in intact cells\", \"How lipid and Ca2+/CaM inputs are integrated is unresolved\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Knockout and pull-down evidence that 4.1R retains XK, Duffy, and Rh defined it as the organizer of a macromolecular junctional complex governing transmembrane protein abundance.\",\n      \"evidence\": \"4.1R knockout mouse erythrocyte analysis with in vitro pull-downs and flow cytometry\",\n      \"pmids\": [\"18524950\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Stoichiometry and assembly order of the complex not determined\", \"Direct versus indirect retention of each partner not fully separated\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Direct microtubule binding plus cdc2 phosphorylation at Thr60/Ser679 explained how 4.1R is mobilized to organize mitotic asters and focus spindle poles.\",\n      \"evidence\": \"In vitro microtubule sedimentation, immunodepletion/add-back reconstitution, cdc2 kinase site mapping, and siRNA spindle-pole phenotype\",\n      \"pmids\": [\"15184364\", \"15525677\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"The kinase(s) acting in cells and timing of dephosphorylation not defined\", \"Relationship between microtubule binding domains and NuMA binding not structurally resolved\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Centrosome localization data linked 4.1R to interphase microtubule anchoring and centrosome separation, broadening its cytoskeletal role across the cell cycle.\",\n      \"evidence\": \"RNAi with immunofluorescence and cell-cycle analysis showing appendage protein and NuMA mislocalization\",\n      \"pmids\": [\"18212055\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct centrosomal binding partner not defined\", \"Mechanism connecting 4.1R loss to G1 arrest unresolved\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Demonstrating direct β-catenin binding and a T cell synapse role showed 4.1R sustains epithelial adhesion and dampens immune activation by directly engaging signaling adaptors.\",\n      \"evidence\": \"4.1R-null mouse epithelia plus Co-IP/binding; immunological synapse recruitment with LAT binding and phosphorylation assays in CD4+ T cells\",\n      \"pmids\": [\"19376086\", \"19190245\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How a single adaptor switches between adhesion and immune-inhibitory roles not defined\", \"Spliceoform usage in each context not fully mapped here\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Nuclear envelope, keratinocyte adhesion, IQGAP1 leading-edge, NHE1 binding, and PKC phosphorylation findings collectively cemented 4.1R as a regulated adaptor across nuclear, migratory, and ion-transport contexts.\",\n      \"evidence\": \"Co-IP/RNAi for emerin/lamin and IQGAP1; KO keratinocyte adhesion assays; in vitro NHE1 binding; PKC phosphosite mapping with binding assays\",\n      \"pmids\": [\"21486941\", \"21693581\", \"21750196\", \"22731252\", \"21542582\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Isoform identity driving each non-erythroid function not always defined\", \"Crosstalk between phospho- and lipid-regulation in cells not integrated\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Direct PMCA1b binding with an intestinal calcium-absorption defect, and CLASP2/cortical microtubule regulation, extended 4.1R function to transporter scaffolding and cortical microtubule capture.\",\n      \"evidence\": \"4.1R-null mouse calcium physiology with domain-mapped binding; Co-IP plus live MT imaging and GSK3 readout for CLASP2\",\n      \"pmids\": [\"23460639\", \"23943871\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Tissue-specific isoform requirements not delineated\", \"How 4.1R modulates GSK3 activity locally not mechanistically resolved\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"A series of studies dissecting the erythroid exon 16 splicing switch (RBFOX2, SF2/ASF, TIA1/Pcbp1/RBM39) explained how the differentiation-specific isoform repertoire of 4.1R is generated.\",\n      \"evidence\": \"SELEX, minigene splicing assays, splicing-factor Co-IP, U1/U2 snRNP recruitment assays\",\n      \"pmids\": [\"16537540\", \"22083953\", \"15522963\", \"28193846\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"These are mechanisms of 4.1R regulation rather than 4.1R activity itself\", \"Single-lab minigene-based evidence not validated at endogenous loci in vivo\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Placing 4.1R within the NuMA–LGN–dynein/dynactin spindle-orientation machinery connected its mitotic activity to asymmetric Numb segregation and erythroid cell-fate control.\",\n      \"evidence\": \"siRNA depletion, gene replacement, Co-IP, and Notch reporter during erythroid differentiation\",\n      \"pmids\": [\"34364872\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab; in vivo erythropoietic consequences not fully established\", \"Direct contribution of each complex member to Numb partitioning not separated\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Reports of 4.1R binding EGFR, TLR4, ALDOC, VHL, CADM1, and FcεRI signaling components extended its adaptor role into growth-factor, Wnt, metabolic, and innate/adaptive immune signaling.\",\n      \"evidence\": \"Co-IP, KO mouse phenotypes, ubiquitination/pathway assays, and colony-formation/xenograft models across multiple single-lab studies\",\n      \"pmids\": [\"31562860\", \"38237224\", \"33242559\", \"27780863\", \"33298314\", \"31993060\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Several interactions rest on single Co-IP studies without reciprocal or structural validation\", \"Direct versus indirect nature of binding and the responsible isoforms remain undefined\", \"Physiological relevance of the signaling roles awaits independent confirmation\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How a single gene's spliced isoforms are selected and post-translationally gated to partition 4.1R among membrane skeleton, spindle, nucleus, junctions, and signaling complexes in a given cell remains the central open question.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No unified model linking isoform/phospho/lipid state to functional destination\", \"Structures of full-length isoforms in complex with partners lacking\", \"In vivo contributions of non-erythroid functions to physiology underexplored\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [0, 2, 4, 5, 14, 18]},\n      {\"term_id\": \"GO:0008092\", \"supporting_discovery_ids\": [2, 11, 23, 20]},\n      {\"term_id\": \"GO:0008289\", \"supporting_discovery_ids\": [3, 10]},\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [2, 4, 8]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [15, 47, 21, 30]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 4, 18, 35]},\n      {\"term_id\": \"GO:0005856\", \"supporting_discovery_ids\": [2, 11, 23]},\n      {\"term_id\": \"GO:0015630\", \"supporting_discovery_ids\": [11, 20]},\n      {\"term_id\": \"GO:0005815\", \"supporting_discovery_ids\": [13, 24]},\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [5, 7, 16, 25]},\n      {\"term_id\": \"GO:0005635\", \"supporting_discovery_ids\": [16]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1640170\", \"supporting_discovery_ids\": [5, 12, 13, 38]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [15, 47, 44]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [15, 41, 42, 47]},\n      {\"term_id\": \"R-HSA-1474244\", \"supporting_discovery_ids\": [6, 14, 37, 17]}\n    ],\n    \"complexes\": [\n      \"spectrin–actin–4.1R junctional complex\",\n      \"NuMA–LGN–dynein/dynactin spindle complex\"\n    ],\n    \"partners\": [\n      \"GYPC\",\n      \"SLC4A1\",\n      \"MPP1\",\n      \"NUMA1\",\n      \"ZO-2\",\n      \"CTNNB1\",\n      \"EMD\",\n      \"LAT\"\n    ],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":8,"faith_total":8,"faith_pct":100.0}}