{"gene":"CIB2","run_date":"2026-06-09T22:57:18","timeline":{"discoveries":[{"year":2012,"finding":"CIB2 localizes to mechanosensory stereocilia of inner ear hair cells and to retinal photoreceptor and pigmented epithelium cells. CIB2 significantly decreased ATP-induced calcium responses in heterologous cells, and deafness-causing mutations altered this effect. CIB2 is a member of the vertebrate Usher interactome.","method":"Mouse immunolocalization, heterologous cell calcium response assays, zebrafish and Drosophila functional studies","journal":"Nature genetics","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (localization, calcium assay, in vivo model organisms), replicated across species","pmids":["23023331"],"is_preprint":false},{"year":2017,"finding":"CIB2 binds directly to TMC1 and TMC2 (pore-forming subunits of the hair cell mechanotransducer channel). Loss of CIB2 abolishes mechanoelectrical transduction (MET) currents in auditory hair cells. Deafness-causing CIB2 mutations disrupt these interactions. CIB2 is required for normal operation of mechanotransducer channels and limits growth of transducing stereocilia.","method":"Co-immunoprecipitation (CIB2 with TMC1/2), electrophysiology (MET current recording), two mutant mouse lines (knockout and knock-in)","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal Co-IP, electrophysiology in two independent mouse models, replicated across multiple labs","pmids":["28663585"],"is_preprint":false},{"year":2017,"finding":"Loss of CIB2 (but not CIB1) abolishes mechanoelectrical transduction currents in auditory hair cells and causes profound hearing loss; CIB2 knockout also affects stereocilia development.","method":"CRISPR/Cas9 knockout mice, electrophysiology (MET current recording), auditory brainstem response","journal":"Frontiers in molecular neuroscience","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean KO with defined cellular phenotype, replicated across multiple labs","pmids":["29255404"],"is_preprint":false},{"year":2017,"finding":"MET currents are totally abolished in auditory hair cells of CIB2-/- mice but remain unchanged in vestibular hair cells. CIB2 deficiency leads to stereocilia regression and hair-cell death specifically in the cochlea after birth.","method":"CIB2 knockout mouse, electrophysiology (MET currents in cochlear and vestibular hair cells), histology","journal":"EMBO molecular medicine","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean KO with defined cellular and organ-specific phenotype, multiple orthogonal methods","pmids":["29084757"],"is_preprint":false},{"year":2021,"finding":"CIB2 and CIB3 are structurally similar to KChIP proteins (auxiliary subunits of voltage-gated Kv4 channels). CIB2/3 bind to TMC1/2 through a domain flanked by transmembrane domains 2 and 3, mediated through a conserved CIB hydrophobic groove. CIB2 regulates TMC1/2 localization and function in hair cells. CIB2 and CIB3 function as auxiliary subunits of the MET channel.","method":"X-ray crystallography (co-crystal structure of CIB3 with TMC1 CIB-binding domain), mouse knockouts, functional MET recordings","journal":"Neuron","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structure with mutagenesis, multiple orthogonal methods (structural + functional + in vivo)","pmids":["34089643"],"is_preprint":false},{"year":2021,"finding":"CIB2 negatively regulates mTORC1 signaling by preferentially binding to GDP-loaded (inactive) Rheb, thereby promoting autophagy. CIB2 deficiency leads to reduced lysosomal capacity, impaired autophagic clearance, and increased mTORC1 signaling. Overexpressing CIB2 in LAM patient-derived fibroblasts downregulates hyperactive mTORC1 signaling.","method":"Cib2 knockout mouse (retinal phenotype), co-immunoprecipitation (CIB2 with GDP-Rheb vs GTP-Rheb), biochemical assays for mTORC1 activity, autophagy assays","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 / Moderate — reciprocal binding assay distinguishing GDP vs GTP Rheb, KO mouse with defined pathway phenotype, patient cell validation","pmids":["34162842"],"is_preprint":false},{"year":2023,"finding":"CIB2 and CIB3 act redundantly to regulate MET in vestibular hair cells; double knockout of Cib2 and Cib3 completely abolishes MET currents in vestibular hair cells and causes severe balance deficits. CIB2 and CIB3 play distinct, non-redundant roles in stereocilia maintenance in vestibular striolar vs. extrastriolar regions.","method":"Cib2/Cib3 double knockout mice, electrophysiology (MET current recording), balance behavioral tests, in situ hybridization","journal":"The Journal of neuroscience","confidence":"High","confidence_rationale":"Tier 2 / Strong — double KO with defined cellular phenotype, multiple orthogonal methods, replicates prior finding","pmids":["37001993"],"is_preprint":false},{"year":2008,"finding":"CIB2 is a calcium-binding protein that interacts with integrin α7Bβ1D in skeletal muscle. CIB2 colocalizes with the integrin α7B subunit at the sarcolemma, neuromuscular junctions, and myotendinous junctions.","method":"Co-immunoprecipitation (CIB2 with integrin α7Bβ1D), calcium binding assay, immunolocalization in mouse skeletal muscle","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — co-IP with localization, single lab, two orthogonal methods","pmids":["18611855"],"is_preprint":false},{"year":2009,"finding":"CIB2 (calmyrin2) binds Ca2+ and undergoes a Ca2+/conformational switch; it undergoes N-myristoylation (without Ca2+/myristoyl switch), is membrane-associated, and localizes with Golgi apparatus and dendrite markers in neurons. CIB2 protein and mRNA are induced ~7-fold and ~2-fold, respectively, upon NMDA receptor stimulation via Ca2+, ERK1/2, and PKC pathways.","method":"Calcium binding assays, subcellular fractionation, immunocytochemistry, pharmacological inhibitors (NMDAR antagonists, BAPTA, ERK/PKC inhibitors) in cultured hippocampal neurons","journal":"Archives of biochemistry and biophysics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple biochemical and pharmacological methods, single lab","pmids":["19433056"],"is_preprint":false},{"year":2017,"finding":"CIB2 binds sphingosine kinase 1 (SK1) at the same site as CIB1, but lacks the Ca2+-myristoyl switch function. CIB2 blocks SK1 translocation to the plasma membrane and inhibits its oncogenic signaling, sensitizing cells to TNFα-induced apoptosis and inhibiting Ras-induced neoplastic transformation.","method":"Co-immunoprecipitation, SK1 membrane localization assays, apoptosis assays, transformation assays, tumor xenograft models","journal":"Cancer research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP, functional assays (membrane translocation, apoptosis, in vivo tumor), single lab","pmids":["28729416"],"is_preprint":false},{"year":2018,"finding":"CIB2 preferentially binds Mg2+ (Kd ~290 μM) over Ca2+ (Kd ~0.5 mM) under physiological conditions, likely existing as Mg2+-bound under physiological conditions. CIB2 forms a non-covalent dimer and interacts with α7B integrin in this state. The USH1J-linked E64D mutation disrupts long-range allosteric communication between the N-terminal E64 residue and the EF3 metal-binding site, impairing Mg2+-bound conformation without substantially affecting integrin binding.","method":"Biochemical binding assays, NMR spectroscopy, analytical ultracentrifugation","journal":"Frontiers in molecular neuroscience","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — in vitro biochemical and NMR characterization with mutagenesis, single lab","pmids":["30174586"],"is_preprint":false},{"year":2016,"finding":"CIB2 knockdown strongly impairs HIV-1 replication in Jurkat cells and primary CD4+ T lymphocytes specifically at the viral entry step. CIB2 knockdown reduces surface expression of CXCR4, CCR5, and integrin α4β7, suggesting a mechanism for reduced viral entry.","method":"siRNA knockdown, viral entry assays, flow cytometry for surface receptor expression","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — KD with specific step assay and mechanism (receptor expression), single lab, two cell types","pmids":["27489023"],"is_preprint":false},{"year":2019,"finding":"CIB2 is monomeric under all tested conditions (contrary to prior dimer report), with uncommon hydrodynamic properties due to high hydrophobic solvent accessible surface. CIB2 interacts with the α7B integrin cytosolic region proximal to the membrane in a 1:1 stoichiometry, with kinetically favored binding in the presence of Mg2+ and absence of Ca2+.","method":"Native mass spectrometry, chemical cross-linking/MS, analytical gel filtration, dynamic light scattering, surface plasmon resonance, molecular dynamics simulations","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — multiple orthogonal biophysical methods, single lab; contradicts prior dimer claim","pmids":["31636333"],"is_preprint":false},{"year":2023,"finding":"CIB2 competes with CIB1 for calcineurin binding, inhibiting CIB1-mediated calcineurin activation in atrial cardiomyocytes. Cardiomyocyte-specific Cib2 knockout enhances atrial fibrillation occurrence and atrial fibrosis under stress, while Cib2 overexpression mitigates these effects.","method":"Cardiomyocyte-specific Cib2 knockout and overexpression mouse models, in vivo electrophysiology, biochemical competition assays (CIB2 vs CIB1 for calcineurin)","journal":"Circulation","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic models with defined in vivo phenotype and biochemical competition assay, single lab","pmids":["37128899"],"is_preprint":false},{"year":2025,"finding":"CIB2 and CIB3 form heteromeric complexes with TMC1 and TMC2 through at least two cytoplasmic domains; NMR spectroscopy validated CIB2/3 interaction with TMC1 fragments. Molecular dynamics simulations predict TMCs are structurally stabilized by CIB proteins to form cation channels. Intact CIB2/3-TMC1/2 complexes are required for MET function in mouse cochlea, vestibular organs, and zebrafish inner ear and lateral line.","method":"AlphaFold2 modeling, NMR spectroscopy (TMC1 fragment interactions), molecular dynamics simulations, mouse/zebrafish knockout functional MET recordings","journal":"eLife","confidence":"High","confidence_rationale":"Tier 1 / Strong — NMR structural validation, MD simulations, multi-species in vivo functional data, multiple orthogonal methods in single study","pmids":["39773557"],"is_preprint":false},{"year":2025,"finding":"CIB2 acts as a Ca2+ sensor for MET: the TMC1-CIB2 complex undergoes a Ca2+-induced conformational change. A vertebrate-specific binding site on TMC1 (CR3 region) interacts with apo-CIB2. Disruption of CIB2 calcium-binding site perturbs MET channel conductivity ex vivo. Dominant deafness mutations in TMC1 cluster around the putative ion pore or at CIB2-binding interfaces.","method":"X-ray crystallography (CIB2-TMC1 complex structure), ex vivo cochlea MET recordings, mutagenesis of CIB2 calcium-binding site","journal":"Developmental cell","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structure with functional validation by mutagenesis and ex vivo electrophysiology","pmids":["39889697"],"is_preprint":false},{"year":2025,"finding":"Crystal structure of the mammalian CIB2-TMC1 complex at high resolution reveals that cation-bound CIB2 forms a negatively charged surface interacting with a positively charged TMC1 N-terminus. Ca2+ modulates CIB2 interaction with both the N-terminal domain and the loop 1 region of TMC1, with Ca2+-bound CIB2 capable of simultaneously binding both regions. Pathogenic CIB2 variants show diminished calcium-binding affinities and differential effects on dual TMC1 binding sites.","method":"X-ray crystallography, mutagenesis, calcium binding assays","journal":"Communications biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structure combined with mutagenesis and binding assays","pmids":["40000792"],"is_preprint":false},{"year":2024,"finding":"CIB2 mechanically constrains TMC1/2 conformations to ensure proper force sensitivity and dynamic range of MET channels. The deafness-causing R186W CIB2 mutation increases resting open probability of MET channels, steepens MET I-X curve, abolishes fast adaptation, and increases leftward I-X curve shifts upon depolarization. R186W also disrupts electron-dense material at stereocilia tips and causes loss of BAIAP2L2 from the same location.","method":"New mouse knock-in model (R186W), electrophysiology (MET current recording with fast piezo probe), AlphaFold2 structural prediction, electron microscopy","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — detailed electrophysiology in knock-in mouse with structural prediction, single lab, preprint","pmids":["37461484"],"is_preprint":true},{"year":2024,"finding":"CIB2 interacts with whirlin through the CIB2 EF2 domain and the whirlin HHD2 domain. Overexpression of whirlin in Cib2-/- mice does not rescue stereocilia morphology, and double heterozygous Cib2/Whrn mice have normal hearing, indicating CIB2 has independent functions in stereocilia staircase development distinct from whirlin.","method":"Deletion constructs and nanoscale pulldown (NanoSPD) assays, AlphaFold2 multimer modeling, double mutant mouse genetics, auditory testing","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — nanoscale pulldown with structural modeling and genetic epistasis, single lab, preprint","pmids":["39131343"],"is_preprint":true},{"year":2023,"finding":"CIB2 interacts with ADGRV1 (USH2C protein) and both share a common interactome including TRiC/CCT chaperonin complex and BBS chaperonin-like proteins. CIB2 and ADGRV1 co-localize at photoreceptor cilia.","method":"Tandem affinity purification/mass spectrometry, co-immunoprecipitation validation, immunohistochemistry","journal":"Frontiers in cell and developmental biology","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — AP-MS with Co-IP validation and localization, single lab","pmids":["37427378"],"is_preprint":false},{"year":2024,"finding":"CIB2 EF3 motif preferentially binds Mg2+ and EF4 binds Ca2+, with high mobility in EF4 regardless of bound metal. The Mg2+/Ca2+-bound state of CIB2 is structurally flexible, with pico-nanosecond motions induced in a region involved in target (α7B integrin) recognition.","method":"Solution NMR (amide nitrogen relaxation), molecular dynamics simulations, ITC, DSC","journal":"International journal of biological macromolecules","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — solution NMR with MD simulations, single lab, no mutagenesis","pmids":["39586446"],"is_preprint":false},{"year":2015,"finding":"The CIB2 p.Arg186Trp mutation disrupts inhibition of ATP-induced Ca2+ responses in heterologous cells but does not alter interactions with whirlin or targeting to hair cell stereocilia tips.","method":"Heterologous cell calcium response assay, co-immunoprecipitation (CIB2 with whirlin), ex vivo hair cell expression","journal":"PloS one","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, single mutation characterization with limited mechanistic depth","pmids":["26426422"],"is_preprint":false},{"year":2024,"finding":"CIB2 knockdown inhibits myoblast proliferation (S-phase arrest, downregulation of CDK4/Cyclin D/E) and promotes differentiation in goat myogenic satellite cells via the integrin α7β1-PI3K/AKT axis. CTCF acts as a transcriptional repressor of CIB2 by binding an intragenic region.","method":"siRNA knockdown, cell cycle analysis, RT-qPCR, RNA-seq, ChIP assay","journal":"Cells","confidence":"Low","confidence_rationale":"Tier 3 / Weak — siRNA in a non-human (goat) satellite cell system, single lab, limited pathway validation","pmids":["40801631"],"is_preprint":false}],"current_model":"CIB2 is an EF-hand Ca2+/Mg2+-binding protein that functions as an auxiliary subunit of the mechanotransduction (MET) channel complex in cochlear hair cells: it directly binds to TMC1 and TMC2 (the pore-forming channel subunits) through at least two cytoplasmic interfaces, structurally stabilizes the TMC1/2 channel, acts as a Ca2+ sensor that undergoes conformational changes upon Ca2+ binding to modulate MET channel conductivity, and is required for TMC1/2 localization and function at stereocilia tips; CIB2 also interacts with integrin α7Bβ1D in skeletal muscle, negatively regulates mTORC1 signaling by binding inactive GDP-Rheb, inhibits sphingosine kinase 1 membrane translocation, and in atrial cardiomyocytes competes with CIB1 to inhibit calcineurin activation, with deafness-causing mutations consistently disrupting these CIB2-TMC1/2 interactions and Ca2+/Mg2+-sensing mechanisms."},"narrative":{"mechanistic_narrative":"CIB2 is an EF-hand divalent-cation-binding protein that serves as an obligate auxiliary subunit of the hair-cell mechanoelectrical transduction (MET) channel, where it is required for sensory transduction underlying hearing and balance [PMID:28663585, PMID:34089643]. It binds directly to the pore-forming subunits TMC1 and TMC2, and loss of CIB2 abolishes MET currents in cochlear hair cells while causing post-natal stereocilia regression and hair-cell death; deafness-causing mutations disrupt these interactions [PMID:28663585, PMID:29084757]. Structural work establishes that CIB2 (with its paralog CIB3) engages TMC1/2 through at least two cytoplasmic interfaces, including a conserved hydrophobic groove flanked by transmembrane domains and a vertebrate-specific TMC1 site, and that cation-bound CIB2 presents a negatively charged surface that contacts the positively charged TMC1 N-terminus to structurally stabilize the channel [PMID:34089643, PMID:39773557, PMID:40000792]. Beyond a scaffolding role, CIB2 acts as a Ca2+ sensor: Ca2+ binding drives a conformational change in the TMC1-CIB2 complex that modulates channel conductivity, and disruption of the CIB2 Ca2+-binding site or pathogenic variants with diminished cation affinity perturb MET function [PMID:39889697, PMID:40000792]. Biophysically, CIB2 preferentially binds Mg2+ over Ca2+ and is likely Mg2+-loaded under physiological conditions, with distinct EF3 (Mg2+) and EF4 (Ca2+) metal sites [PMID:30174586, PMID:39586446]. CIB2 and CIB3 act redundantly in vestibular hair cells, where double knockout abolishes MET currents and causes balance deficits [PMID:37001993]. Outside the inner ear, CIB2 interacts with integrin α7Bβ1D at muscle junctions [PMID:18611855], negatively regulates mTORC1 by preferentially binding GDP-Rheb to promote autophagy [PMID:34162842], inhibits sphingosine kinase 1 membrane translocation [PMID:28729416], and competes with CIB1 to restrain calcineurin activation in atrial cardiomyocytes [PMID:37128899].","teleology":[{"year":2012,"claim":"Establishing that CIB2 localizes to stereocilia and modulates calcium responses placed an uncharacterized deafness gene into the inner-ear sensory and Usher interactome context.","evidence":"Mouse immunolocalization, heterologous calcium-response assays, and zebrafish/Drosophila functional studies","pmids":["23023331"],"confidence":"High","gaps":["Did not identify the direct molecular partner mediating MET","Mechanism of calcium-response modulation in heterologous cells unresolved"]},{"year":2008,"claim":"Identification of CIB2 as a calcium-binding integrin α7Bβ1D partner at muscle junctions defined an early biochemical activity and binding partner before its inner-ear role was known.","evidence":"Co-immunoprecipitation, calcium-binding assay, and immunolocalization in mouse skeletal muscle","pmids":["18611855"],"confidence":"Medium","gaps":["Functional consequence of the integrin interaction in muscle not defined","Single lab"]},{"year":2009,"claim":"Characterizing CIB2 as a myristoylated, membrane-associated Ca2+-conformational-switch protein induced by NMDA receptor signaling broadened its biochemical profile beyond muscle.","evidence":"Calcium binding, subcellular fractionation, immunocytochemistry, and pharmacological inhibitors in hippocampal neurons","pmids":["19433056"],"confidence":"Medium","gaps":["No defined neuronal physiological role","Functional target of the Ca2+ switch not identified"]},{"year":2017,"claim":"Demonstrating direct CIB2-TMC1/TMC2 binding and loss of MET currents in CIB2-null hair cells identified CIB2 as an essential component of the cochlear mechanotransduction machinery.","evidence":"Reciprocal Co-IP, electrophysiology, and multiple knockout/knock-in mouse lines across labs","pmids":["28663585","29255404","29084757"],"confidence":"High","gaps":["Structural basis of the interaction not yet resolved","Did not explain cochlea-vs-vestibule specificity"]},{"year":2021,"claim":"Crystallographic capture of CIB binding to a TMC1 cytoplasmic domain via a conserved hydrophobic groove established CIB2/3 as KChIP-like auxiliary subunits that govern channel localization and function.","evidence":"X-ray co-crystal structure (CIB3-TMC1 domain) with mutagenesis, knockouts, and MET recordings","pmids":["34089643"],"confidence":"High","gaps":["Full-length channel architecture and second interface not resolved","How cation binding feeds into channel gating untested in this study"]},{"year":2021,"claim":"Discovery that CIB2 preferentially binds GDP-Rheb to suppress mTORC1 and promote autophagy revealed a signaling function distinct from its channel role, with relevance to LAM.","evidence":"Cib2 knockout mouse, GDP-vs-GTP-Rheb Co-IP, mTORC1/autophagy assays, and patient fibroblast rescue","pmids":["34162842"],"confidence":"High","gaps":["Relationship between mTORC1 role and MET-channel role unclear","Tissue specificity of Rheb regulation not defined"]},{"year":2018,"claim":"Biophysical metal-binding measurements showed CIB2 favors Mg2+ over Ca2+ physiologically and mapped how the E64D deafness mutation allosterically impairs the Mg2+-bound state.","evidence":"Binding assays, NMR, and analytical ultracentrifugation with mutagenesis","pmids":["30174586"],"confidence":"Medium","gaps":["Oligomeric state disputed by later study","Physiological metal occupancy in hair cells not directly measured"]},{"year":2019,"claim":"Refined biophysics established CIB2 as monomeric and defined a 1:1 Mg2+-favored interaction with the α7B integrin cytosolic region, correcting the earlier dimer model.","evidence":"Native MS, cross-linking/MS, gel filtration, DLS, SPR, and MD simulations","pmids":["31636333"],"confidence":"Medium","gaps":["Contradicts prior dimer report; reconciliation incomplete","Single lab"]},{"year":2023,"claim":"Genetic dissection showed CIB2 and CIB3 act redundantly for vestibular MET yet have non-redundant roles in regional stereocilia maintenance, explaining the cochlea-specific severity of CIB2 loss.","evidence":"Cib2/Cib3 double-knockout mice, MET electrophysiology, balance tests, in situ hybridization","pmids":["37001993"],"confidence":"High","gaps":["Molecular basis of region-specific roles unresolved","Compensation mechanism not defined"]},{"year":2023,"claim":"CIB2 was shown to restrain calcineurin signaling by competing with CIB1 in atrial cardiomyocytes, linking it to atrial fibrillation and fibrosis under stress.","evidence":"Cardiomyocyte-specific knockout/overexpression mice, in vivo electrophysiology, and CIB2-vs-CIB1 competition assays","pmids":["37128899"],"confidence":"Medium","gaps":["Structural basis of competition not defined","Single lab"]},{"year":2025,"claim":"High-resolution structures of the mammalian CIB2-TMC1 complex defined the dual cytoplasmic binding interfaces and showed Ca2+ binding drives a conformational change that tunes channel conductivity, establishing CIB2 as the MET channel's cation sensor.","evidence":"X-ray crystallography, NMR, MD simulations, ex vivo MET recordings, and multi-species knockouts with calcium-site mutagenesis","pmids":["39773557","39889697","40000792"],"confidence":"High","gaps":["How CIB2 conformational change is mechanically coupled to gating not fully resolved","In vivo cation occupancy during transduction not directly measured"]},{"year":null,"claim":"How CIB2's multiple roles (MET auxiliary subunit, integrin partner, mTORC1/Rheb regulator, SK1 inhibitor, calcineurin competitor) are integrated within a single protein and partitioned across tissues remains unresolved.","evidence":"No single study reconciles the divergent CIB2 functions","pmids":[],"confidence":"Medium","gaps":["No unifying model linking channel and signaling roles","Tissue-specific partner selection mechanism unknown","Stereocilia development functions distinct from whirlin remain mechanistically undefined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[1,4,14,15,16]},{"term_id":"GO:0140299","term_label":"molecular sensor activity","supporting_discovery_ids":[15,16]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[4,5,13,15]},{"term_id":"GO:0005198","term_label":"structural molecule activity","supporting_discovery_ids":[4,14]}],"localization":[{"term_id":"GO:0005929","term_label":"cilium","supporting_discovery_ids":[0,19]},{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[7,8]},{"term_id":"GO:0005794","term_label":"Golgi apparatus","supporting_discovery_ids":[8]},{"term_id":"GO:0005856","term_label":"cytoskeleton","supporting_discovery_ids":[1,4,17]}],"pathway":[{"term_id":"R-HSA-112316","term_label":"Neuronal System","supporting_discovery_ids":[1,4,15]},{"term_id":"R-HSA-9709957","term_label":"Sensory Perception","supporting_discovery_ids":[1,3,6]},{"term_id":"R-HSA-9612973","term_label":"Autophagy","supporting_discovery_ids":[5]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[5,13]}],"complexes":["TMC1/TMC2 MET channel complex"],"partners":["TMC1","TMC2","CIB3","ITGA7","RHEB","SPHK1","PPP3 (CALCINEURIN)","WHRN"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"O75838","full_name":"Calcium and integrin-binding family member 2","aliases":["Kinase-interacting protein 2","KIP 2"],"length_aa":187,"mass_kda":21.6,"function":"Calcium- and integrin-binding protein that plays a role in intracellular calcium homeostasis (By similarity). Acts as an auxiliary subunit of the sensory mechanoelectrical transduction (MET) channel in hair cells (By similarity). Essential for mechanoelectrical transduction (MET) currents in auditory hair cells and thereby required for hearing (By similarity). Regulates the function of hair cell mechanotransduction by controlling the distribution of transmembrane channel-like proteins TMC1 and TMC2, and by regulating the function of the MET channels in hair cells (By similarity). Required for the maintenance of auditory hair cell stereocilia bundle morphology and function and for hair-cell survival in the cochlea (By similarity). Critical for proper photoreceptor cell maintenance and function (By similarity). Plays a role in intracellular calcium homeostasis by decreasing ATP-induced calcium release (PubMed:23023331, PubMed:26173970, PubMed:26426422)","subcellular_location":"Cytoplasm; Cell projection, stereocilium; Photoreceptor inner segment; Cell projection, cilium, photoreceptor outer segment; Cell membrane, sarcolemma","url":"https://www.uniprot.org/uniprotkb/O75838/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/CIB2","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1208,"dependency_fraction":0.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/CIB2","total_profiled":1310},"omim":[{"mim_id":"612632","title":"USHER SYNDROME, TYPE IH; USH1H","url":"https://www.omim.org/entry/612632"},{"mim_id":"609439","title":"DEAFNESS, AUTOSOMAL RECESSIVE 48; DFNB48","url":"https://www.omim.org/entry/609439"},{"mim_id":"605564","title":"CALCIUM- AND INTEGRIN-BINDING PROTEIN 2; CIB2","url":"https://www.omim.org/entry/605564"},{"mim_id":"276900","title":"USHER SYNDROME, TYPE I; USH1","url":"https://www.omim.org/entry/276900"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Uncertain","locations":[{"location":"Nucleoplasm","reliability":"Uncertain"},{"location":"Primary cilium transition zone","reliability":"Additional"},{"location":"Centrosome","reliability":"Additional"},{"location":"Cytosol","reliability":"Additional"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in all","driving_tissues":[{"tissue":"heart muscle","ntpm":46.8},{"tissue":"lymphoid tissue","ntpm":44.7}],"url":"https://www.proteinatlas.org/search/CIB2"},"hgnc":{"alias_symbol":["KIP2"],"prev_symbol":["DFNB48","USH1J"]},"alphafold":{"accession":"O75838","domains":[{"cath_id":"1.10.238.10","chopping":"9-97","consensus_level":"high","plddt":91.6029,"start":9,"end":97},{"cath_id":"1.10.238.10","chopping":"103-181","consensus_level":"high","plddt":89.5392,"start":103,"end":181}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/O75838","model_url":"https://alphafold.ebi.ac.uk/files/AF-O75838-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-O75838-F1-predicted_aligned_error_v6.png","plddt_mean":88.62},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=CIB2","jax_strain_url":"https://www.jax.org/strain/search?query=CIB2"},"sequence":{"accession":"O75838","fasta_url":"https://rest.uniprot.org/uniprotkb/O75838.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/O75838/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/O75838"}},"corpus_meta":[{"pmid":"23023331","id":"PMC_23023331","title":"Alterations of the CIB2 calcium- and integrin-binding protein cause Usher syndrome type 1J and nonsyndromic deafness DFNB48.","date":"2012","source":"Nature genetics","url":"https://pubmed.ncbi.nlm.nih.gov/23023331","citation_count":203,"is_preprint":false},{"pmid":"28663585","id":"PMC_28663585","title":"CIB2 interacts with TMC1 and TMC2 and is essential for mechanotransduction in auditory hair cells.","date":"2017","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/28663585","citation_count":149,"is_preprint":false},{"pmid":"29255404","id":"PMC_29255404","title":"Loss of CIB2 Causes Profound Hearing Loss and Abolishes Mechanoelectrical Transduction in Mice.","date":"2017","source":"Frontiers in molecular neuroscience","url":"https://pubmed.ncbi.nlm.nih.gov/29255404","citation_count":106,"is_preprint":false},{"pmid":"29084757","id":"PMC_29084757","title":"CIB2, defective in isolated deafness, is key for auditory hair cell mechanotransduction and 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affiliated with the German Society for Oto-Rhino-Laryngology - Head and Neck Surgery","url":"https://pubmed.ncbi.nlm.nih.gov/27771768","citation_count":10,"is_preprint":false},{"pmid":"35408910","id":"PMC_35408910","title":"Calcium- and Integrin-Binding Protein 2 (CIB2) in Physiology and Disease: Bright and Dark Sides.","date":"2022","source":"International journal of molecular sciences","url":"https://pubmed.ncbi.nlm.nih.gov/35408910","citation_count":10,"is_preprint":false},{"pmid":"27489023","id":"PMC_27489023","title":"CIB1 and CIB2 are HIV-1 helper factors involved in viral entry.","date":"2016","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/27489023","citation_count":10,"is_preprint":false},{"pmid":"37398045","id":"PMC_37398045","title":"Complexes of vertebrate TMC1/2 and CIB2/3 proteins form hair-cell mechanotransduction cation channels.","date":"2024","source":"bioRxiv : the preprint server for 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biology","url":"https://pubmed.ncbi.nlm.nih.gov/37461484","citation_count":4,"is_preprint":false},{"pmid":"40000792","id":"PMC_40000792","title":"Structural insights into calcium-dependent CIB2-TMC1 interaction in hair cell mechanotransduction.","date":"2025","source":"Communications biology","url":"https://pubmed.ncbi.nlm.nih.gov/40000792","citation_count":3,"is_preprint":false},{"pmid":"39586446","id":"PMC_39586446","title":"Structural dynamics of calcium and integrin-binding protein 2 (CIB2) reveal uncommon flexibility and heterogeneous calcium and magnesium loading.","date":"2024","source":"International journal of biological macromolecules","url":"https://pubmed.ncbi.nlm.nih.gov/39586446","citation_count":3,"is_preprint":false},{"pmid":"39264588","id":"PMC_39264588","title":"CIB2 mediates acquired gefitinib resistance by inducing ZEB1 expression and epithelial-mesenchymal 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Loss","date":"2024-07-24","source":"bioRxiv","url":"https://doi.org/10.1101/2024.07.24.604958","citation_count":0,"is_preprint":true},{"pmid":null,"id":"bio_10.1101_2024.08.22.609173","title":"Transmembrane channel-like 4 and 5 proteins at microvillar tips are potential ion channels and lipid scramblases","date":"2024-08-23","source":"bioRxiv","url":"https://doi.org/10.1101/2024.08.22.609173","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":18130,"output_tokens":5688,"usd":0.069855,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":14212,"output_tokens":4015,"usd":0.085718,"stage2_stop_reason":"end_turn"},"total_usd":0.155573,"stage1_batch_id":"msgbatch_01ACAxJQabDsht39JXeWG22d","stage2_batch_id":"msgbatch_01QEU22A9U5sbPTgsMzTmvSf","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2012,\n      \"finding\": \"CIB2 localizes to mechanosensory stereocilia of inner ear hair cells and to retinal photoreceptor and pigmented epithelium cells. CIB2 significantly decreased ATP-induced calcium responses in heterologous cells, and deafness-causing mutations altered this effect. CIB2 is a member of the vertebrate Usher interactome.\",\n      \"method\": \"Mouse immunolocalization, heterologous cell calcium response assays, zebrafish and Drosophila functional studies\",\n      \"journal\": \"Nature genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (localization, calcium assay, in vivo model organisms), replicated across species\",\n      \"pmids\": [\"23023331\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"CIB2 binds directly to TMC1 and TMC2 (pore-forming subunits of the hair cell mechanotransducer channel). Loss of CIB2 abolishes mechanoelectrical transduction (MET) currents in auditory hair cells. Deafness-causing CIB2 mutations disrupt these interactions. CIB2 is required for normal operation of mechanotransducer channels and limits growth of transducing stereocilia.\",\n      \"method\": \"Co-immunoprecipitation (CIB2 with TMC1/2), electrophysiology (MET current recording), two mutant mouse lines (knockout and knock-in)\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal Co-IP, electrophysiology in two independent mouse models, replicated across multiple labs\",\n      \"pmids\": [\"28663585\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Loss of CIB2 (but not CIB1) abolishes mechanoelectrical transduction currents in auditory hair cells and causes profound hearing loss; CIB2 knockout also affects stereocilia development.\",\n      \"method\": \"CRISPR/Cas9 knockout mice, electrophysiology (MET current recording), auditory brainstem response\",\n      \"journal\": \"Frontiers in molecular neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean KO with defined cellular phenotype, replicated across multiple labs\",\n      \"pmids\": [\"29255404\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"MET currents are totally abolished in auditory hair cells of CIB2-/- mice but remain unchanged in vestibular hair cells. CIB2 deficiency leads to stereocilia regression and hair-cell death specifically in the cochlea after birth.\",\n      \"method\": \"CIB2 knockout mouse, electrophysiology (MET currents in cochlear and vestibular hair cells), histology\",\n      \"journal\": \"EMBO molecular medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean KO with defined cellular and organ-specific phenotype, multiple orthogonal methods\",\n      \"pmids\": [\"29084757\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"CIB2 and CIB3 are structurally similar to KChIP proteins (auxiliary subunits of voltage-gated Kv4 channels). CIB2/3 bind to TMC1/2 through a domain flanked by transmembrane domains 2 and 3, mediated through a conserved CIB hydrophobic groove. CIB2 regulates TMC1/2 localization and function in hair cells. CIB2 and CIB3 function as auxiliary subunits of the MET channel.\",\n      \"method\": \"X-ray crystallography (co-crystal structure of CIB3 with TMC1 CIB-binding domain), mouse knockouts, functional MET recordings\",\n      \"journal\": \"Neuron\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structure with mutagenesis, multiple orthogonal methods (structural + functional + in vivo)\",\n      \"pmids\": [\"34089643\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"CIB2 negatively regulates mTORC1 signaling by preferentially binding to GDP-loaded (inactive) Rheb, thereby promoting autophagy. CIB2 deficiency leads to reduced lysosomal capacity, impaired autophagic clearance, and increased mTORC1 signaling. Overexpressing CIB2 in LAM patient-derived fibroblasts downregulates hyperactive mTORC1 signaling.\",\n      \"method\": \"Cib2 knockout mouse (retinal phenotype), co-immunoprecipitation (CIB2 with GDP-Rheb vs GTP-Rheb), biochemical assays for mTORC1 activity, autophagy assays\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal binding assay distinguishing GDP vs GTP Rheb, KO mouse with defined pathway phenotype, patient cell validation\",\n      \"pmids\": [\"34162842\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"CIB2 and CIB3 act redundantly to regulate MET in vestibular hair cells; double knockout of Cib2 and Cib3 completely abolishes MET currents in vestibular hair cells and causes severe balance deficits. CIB2 and CIB3 play distinct, non-redundant roles in stereocilia maintenance in vestibular striolar vs. extrastriolar regions.\",\n      \"method\": \"Cib2/Cib3 double knockout mice, electrophysiology (MET current recording), balance behavioral tests, in situ hybridization\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — double KO with defined cellular phenotype, multiple orthogonal methods, replicates prior finding\",\n      \"pmids\": [\"37001993\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"CIB2 is a calcium-binding protein that interacts with integrin α7Bβ1D in skeletal muscle. CIB2 colocalizes with the integrin α7B subunit at the sarcolemma, neuromuscular junctions, and myotendinous junctions.\",\n      \"method\": \"Co-immunoprecipitation (CIB2 with integrin α7Bβ1D), calcium binding assay, immunolocalization in mouse skeletal muscle\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — co-IP with localization, single lab, two orthogonal methods\",\n      \"pmids\": [\"18611855\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"CIB2 (calmyrin2) binds Ca2+ and undergoes a Ca2+/conformational switch; it undergoes N-myristoylation (without Ca2+/myristoyl switch), is membrane-associated, and localizes with Golgi apparatus and dendrite markers in neurons. CIB2 protein and mRNA are induced ~7-fold and ~2-fold, respectively, upon NMDA receptor stimulation via Ca2+, ERK1/2, and PKC pathways.\",\n      \"method\": \"Calcium binding assays, subcellular fractionation, immunocytochemistry, pharmacological inhibitors (NMDAR antagonists, BAPTA, ERK/PKC inhibitors) in cultured hippocampal neurons\",\n      \"journal\": \"Archives of biochemistry and biophysics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple biochemical and pharmacological methods, single lab\",\n      \"pmids\": [\"19433056\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"CIB2 binds sphingosine kinase 1 (SK1) at the same site as CIB1, but lacks the Ca2+-myristoyl switch function. CIB2 blocks SK1 translocation to the plasma membrane and inhibits its oncogenic signaling, sensitizing cells to TNFα-induced apoptosis and inhibiting Ras-induced neoplastic transformation.\",\n      \"method\": \"Co-immunoprecipitation, SK1 membrane localization assays, apoptosis assays, transformation assays, tumor xenograft models\",\n      \"journal\": \"Cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP, functional assays (membrane translocation, apoptosis, in vivo tumor), single lab\",\n      \"pmids\": [\"28729416\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"CIB2 preferentially binds Mg2+ (Kd ~290 μM) over Ca2+ (Kd ~0.5 mM) under physiological conditions, likely existing as Mg2+-bound under physiological conditions. CIB2 forms a non-covalent dimer and interacts with α7B integrin in this state. The USH1J-linked E64D mutation disrupts long-range allosteric communication between the N-terminal E64 residue and the EF3 metal-binding site, impairing Mg2+-bound conformation without substantially affecting integrin binding.\",\n      \"method\": \"Biochemical binding assays, NMR spectroscopy, analytical ultracentrifugation\",\n      \"journal\": \"Frontiers in molecular neuroscience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro biochemical and NMR characterization with mutagenesis, single lab\",\n      \"pmids\": [\"30174586\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"CIB2 knockdown strongly impairs HIV-1 replication in Jurkat cells and primary CD4+ T lymphocytes specifically at the viral entry step. CIB2 knockdown reduces surface expression of CXCR4, CCR5, and integrin α4β7, suggesting a mechanism for reduced viral entry.\",\n      \"method\": \"siRNA knockdown, viral entry assays, flow cytometry for surface receptor expression\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — KD with specific step assay and mechanism (receptor expression), single lab, two cell types\",\n      \"pmids\": [\"27489023\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"CIB2 is monomeric under all tested conditions (contrary to prior dimer report), with uncommon hydrodynamic properties due to high hydrophobic solvent accessible surface. CIB2 interacts with the α7B integrin cytosolic region proximal to the membrane in a 1:1 stoichiometry, with kinetically favored binding in the presence of Mg2+ and absence of Ca2+.\",\n      \"method\": \"Native mass spectrometry, chemical cross-linking/MS, analytical gel filtration, dynamic light scattering, surface plasmon resonance, molecular dynamics simulations\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — multiple orthogonal biophysical methods, single lab; contradicts prior dimer claim\",\n      \"pmids\": [\"31636333\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"CIB2 competes with CIB1 for calcineurin binding, inhibiting CIB1-mediated calcineurin activation in atrial cardiomyocytes. Cardiomyocyte-specific Cib2 knockout enhances atrial fibrillation occurrence and atrial fibrosis under stress, while Cib2 overexpression mitigates these effects.\",\n      \"method\": \"Cardiomyocyte-specific Cib2 knockout and overexpression mouse models, in vivo electrophysiology, biochemical competition assays (CIB2 vs CIB1 for calcineurin)\",\n      \"journal\": \"Circulation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic models with defined in vivo phenotype and biochemical competition assay, single lab\",\n      \"pmids\": [\"37128899\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"CIB2 and CIB3 form heteromeric complexes with TMC1 and TMC2 through at least two cytoplasmic domains; NMR spectroscopy validated CIB2/3 interaction with TMC1 fragments. Molecular dynamics simulations predict TMCs are structurally stabilized by CIB proteins to form cation channels. Intact CIB2/3-TMC1/2 complexes are required for MET function in mouse cochlea, vestibular organs, and zebrafish inner ear and lateral line.\",\n      \"method\": \"AlphaFold2 modeling, NMR spectroscopy (TMC1 fragment interactions), molecular dynamics simulations, mouse/zebrafish knockout functional MET recordings\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — NMR structural validation, MD simulations, multi-species in vivo functional data, multiple orthogonal methods in single study\",\n      \"pmids\": [\"39773557\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"CIB2 acts as a Ca2+ sensor for MET: the TMC1-CIB2 complex undergoes a Ca2+-induced conformational change. A vertebrate-specific binding site on TMC1 (CR3 region) interacts with apo-CIB2. Disruption of CIB2 calcium-binding site perturbs MET channel conductivity ex vivo. Dominant deafness mutations in TMC1 cluster around the putative ion pore or at CIB2-binding interfaces.\",\n      \"method\": \"X-ray crystallography (CIB2-TMC1 complex structure), ex vivo cochlea MET recordings, mutagenesis of CIB2 calcium-binding site\",\n      \"journal\": \"Developmental cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structure with functional validation by mutagenesis and ex vivo electrophysiology\",\n      \"pmids\": [\"39889697\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Crystal structure of the mammalian CIB2-TMC1 complex at high resolution reveals that cation-bound CIB2 forms a negatively charged surface interacting with a positively charged TMC1 N-terminus. Ca2+ modulates CIB2 interaction with both the N-terminal domain and the loop 1 region of TMC1, with Ca2+-bound CIB2 capable of simultaneously binding both regions. Pathogenic CIB2 variants show diminished calcium-binding affinities and differential effects on dual TMC1 binding sites.\",\n      \"method\": \"X-ray crystallography, mutagenesis, calcium binding assays\",\n      \"journal\": \"Communications biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structure combined with mutagenesis and binding assays\",\n      \"pmids\": [\"40000792\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"CIB2 mechanically constrains TMC1/2 conformations to ensure proper force sensitivity and dynamic range of MET channels. The deafness-causing R186W CIB2 mutation increases resting open probability of MET channels, steepens MET I-X curve, abolishes fast adaptation, and increases leftward I-X curve shifts upon depolarization. R186W also disrupts electron-dense material at stereocilia tips and causes loss of BAIAP2L2 from the same location.\",\n      \"method\": \"New mouse knock-in model (R186W), electrophysiology (MET current recording with fast piezo probe), AlphaFold2 structural prediction, electron microscopy\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — detailed electrophysiology in knock-in mouse with structural prediction, single lab, preprint\",\n      \"pmids\": [\"37461484\"],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"CIB2 interacts with whirlin through the CIB2 EF2 domain and the whirlin HHD2 domain. Overexpression of whirlin in Cib2-/- mice does not rescue stereocilia morphology, and double heterozygous Cib2/Whrn mice have normal hearing, indicating CIB2 has independent functions in stereocilia staircase development distinct from whirlin.\",\n      \"method\": \"Deletion constructs and nanoscale pulldown (NanoSPD) assays, AlphaFold2 multimer modeling, double mutant mouse genetics, auditory testing\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — nanoscale pulldown with structural modeling and genetic epistasis, single lab, preprint\",\n      \"pmids\": [\"39131343\"],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"CIB2 interacts with ADGRV1 (USH2C protein) and both share a common interactome including TRiC/CCT chaperonin complex and BBS chaperonin-like proteins. CIB2 and ADGRV1 co-localize at photoreceptor cilia.\",\n      \"method\": \"Tandem affinity purification/mass spectrometry, co-immunoprecipitation validation, immunohistochemistry\",\n      \"journal\": \"Frontiers in cell and developmental biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — AP-MS with Co-IP validation and localization, single lab\",\n      \"pmids\": [\"37427378\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"CIB2 EF3 motif preferentially binds Mg2+ and EF4 binds Ca2+, with high mobility in EF4 regardless of bound metal. The Mg2+/Ca2+-bound state of CIB2 is structurally flexible, with pico-nanosecond motions induced in a region involved in target (α7B integrin) recognition.\",\n      \"method\": \"Solution NMR (amide nitrogen relaxation), molecular dynamics simulations, ITC, DSC\",\n      \"journal\": \"International journal of biological macromolecules\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — solution NMR with MD simulations, single lab, no mutagenesis\",\n      \"pmids\": [\"39586446\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"The CIB2 p.Arg186Trp mutation disrupts inhibition of ATP-induced Ca2+ responses in heterologous cells but does not alter interactions with whirlin or targeting to hair cell stereocilia tips.\",\n      \"method\": \"Heterologous cell calcium response assay, co-immunoprecipitation (CIB2 with whirlin), ex vivo hair cell expression\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, single mutation characterization with limited mechanistic depth\",\n      \"pmids\": [\"26426422\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"CIB2 knockdown inhibits myoblast proliferation (S-phase arrest, downregulation of CDK4/Cyclin D/E) and promotes differentiation in goat myogenic satellite cells via the integrin α7β1-PI3K/AKT axis. CTCF acts as a transcriptional repressor of CIB2 by binding an intragenic region.\",\n      \"method\": \"siRNA knockdown, cell cycle analysis, RT-qPCR, RNA-seq, ChIP assay\",\n      \"journal\": \"Cells\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — siRNA in a non-human (goat) satellite cell system, single lab, limited pathway validation\",\n      \"pmids\": [\"40801631\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"CIB2 is an EF-hand Ca2+/Mg2+-binding protein that functions as an auxiliary subunit of the mechanotransduction (MET) channel complex in cochlear hair cells: it directly binds to TMC1 and TMC2 (the pore-forming channel subunits) through at least two cytoplasmic interfaces, structurally stabilizes the TMC1/2 channel, acts as a Ca2+ sensor that undergoes conformational changes upon Ca2+ binding to modulate MET channel conductivity, and is required for TMC1/2 localization and function at stereocilia tips; CIB2 also interacts with integrin α7Bβ1D in skeletal muscle, negatively regulates mTORC1 signaling by binding inactive GDP-Rheb, inhibits sphingosine kinase 1 membrane translocation, and in atrial cardiomyocytes competes with CIB1 to inhibit calcineurin activation, with deafness-causing mutations consistently disrupting these CIB2-TMC1/2 interactions and Ca2+/Mg2+-sensing mechanisms.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"CIB2 is an EF-hand divalent-cation-binding protein that serves as an obligate auxiliary subunit of the hair-cell mechanoelectrical transduction (MET) channel, where it is required for sensory transduction underlying hearing and balance [#1, #4]. It binds directly to the pore-forming subunits TMC1 and TMC2, and loss of CIB2 abolishes MET currents in cochlear hair cells while causing post-natal stereocilia regression and hair-cell death; deafness-causing mutations disrupt these interactions [#1, #3]. Structural work establishes that CIB2 (with its paralog CIB3) engages TMC1/2 through at least two cytoplasmic interfaces, including a conserved hydrophobic groove flanked by transmembrane domains and a vertebrate-specific TMC1 site, and that cation-bound CIB2 presents a negatively charged surface that contacts the positively charged TMC1 N-terminus to structurally stabilize the channel [#4, #14, #16]. Beyond a scaffolding role, CIB2 acts as a Ca2+ sensor: Ca2+ binding drives a conformational change in the TMC1-CIB2 complex that modulates channel conductivity, and disruption of the CIB2 Ca2+-binding site or pathogenic variants with diminished cation affinity perturb MET function [#15, #16]. Biophysically, CIB2 preferentially binds Mg2+ over Ca2+ and is likely Mg2+-loaded under physiological conditions, with distinct EF3 (Mg2+) and EF4 (Ca2+) metal sites [#10, #20]. CIB2 and CIB3 act redundantly in vestibular hair cells, where double knockout abolishes MET currents and causes balance deficits [#6]. Outside the inner ear, CIB2 interacts with integrin \\u03b17B\\u03b21D at muscle junctions [#7], negatively regulates mTORC1 by preferentially binding GDP-Rheb to promote autophagy [#5], inhibits sphingosine kinase 1 membrane translocation [#9], and competes with CIB1 to restrain calcineurin activation in atrial cardiomyocytes [#13].\",\n  \"teleology\": [\n    {\n      \"year\": 2012,\n      \"claim\": \"Establishing that CIB2 localizes to stereocilia and modulates calcium responses placed an uncharacterized deafness gene into the inner-ear sensory and Usher interactome context.\",\n      \"evidence\": \"Mouse immunolocalization, heterologous calcium-response assays, and zebrafish/Drosophila functional studies\",\n      \"pmids\": [\"23023331\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not identify the direct molecular partner mediating MET\", \"Mechanism of calcium-response modulation in heterologous cells unresolved\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Identification of CIB2 as a calcium-binding integrin \\u03b17B\\u03b21D partner at muscle junctions defined an early biochemical activity and binding partner before its inner-ear role was known.\",\n      \"evidence\": \"Co-immunoprecipitation, calcium-binding assay, and immunolocalization in mouse skeletal muscle\",\n      \"pmids\": [\"18611855\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional consequence of the integrin interaction in muscle not defined\", \"Single lab\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Characterizing CIB2 as a myristoylated, membrane-associated Ca2+-conformational-switch protein induced by NMDA receptor signaling broadened its biochemical profile beyond muscle.\",\n      \"evidence\": \"Calcium binding, subcellular fractionation, immunocytochemistry, and pharmacological inhibitors in hippocampal neurons\",\n      \"pmids\": [\"19433056\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No defined neuronal physiological role\", \"Functional target of the Ca2+ switch not identified\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Demonstrating direct CIB2-TMC1/TMC2 binding and loss of MET currents in CIB2-null hair cells identified CIB2 as an essential component of the cochlear mechanotransduction machinery.\",\n      \"evidence\": \"Reciprocal Co-IP, electrophysiology, and multiple knockout/knock-in mouse lines across labs\",\n      \"pmids\": [\"28663585\", \"29255404\", \"29084757\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of the interaction not yet resolved\", \"Did not explain cochlea-vs-vestibule specificity\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Crystallographic capture of CIB binding to a TMC1 cytoplasmic domain via a conserved hydrophobic groove established CIB2/3 as KChIP-like auxiliary subunits that govern channel localization and function.\",\n      \"evidence\": \"X-ray co-crystal structure (CIB3-TMC1 domain) with mutagenesis, knockouts, and MET recordings\",\n      \"pmids\": [\"34089643\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full-length channel architecture and second interface not resolved\", \"How cation binding feeds into channel gating untested in this study\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Discovery that CIB2 preferentially binds GDP-Rheb to suppress mTORC1 and promote autophagy revealed a signaling function distinct from its channel role, with relevance to LAM.\",\n      \"evidence\": \"Cib2 knockout mouse, GDP-vs-GTP-Rheb Co-IP, mTORC1/autophagy assays, and patient fibroblast rescue\",\n      \"pmids\": [\"34162842\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relationship between mTORC1 role and MET-channel role unclear\", \"Tissue specificity of Rheb regulation not defined\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Biophysical metal-binding measurements showed CIB2 favors Mg2+ over Ca2+ physiologically and mapped how the E64D deafness mutation allosterically impairs the Mg2+-bound state.\",\n      \"evidence\": \"Binding assays, NMR, and analytical ultracentrifugation with mutagenesis\",\n      \"pmids\": [\"30174586\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Oligomeric state disputed by later study\", \"Physiological metal occupancy in hair cells not directly measured\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Refined biophysics established CIB2 as monomeric and defined a 1:1 Mg2+-favored interaction with the \\u03b17B integrin cytosolic region, correcting the earlier dimer model.\",\n      \"evidence\": \"Native MS, cross-linking/MS, gel filtration, DLS, SPR, and MD simulations\",\n      \"pmids\": [\"31636333\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Contradicts prior dimer report; reconciliation incomplete\", \"Single lab\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Genetic dissection showed CIB2 and CIB3 act redundantly for vestibular MET yet have non-redundant roles in regional stereocilia maintenance, explaining the cochlea-specific severity of CIB2 loss.\",\n      \"evidence\": \"Cib2/Cib3 double-knockout mice, MET electrophysiology, balance tests, in situ hybridization\",\n      \"pmids\": [\"37001993\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular basis of region-specific roles unresolved\", \"Compensation mechanism not defined\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"CIB2 was shown to restrain calcineurin signaling by competing with CIB1 in atrial cardiomyocytes, linking it to atrial fibrillation and fibrosis under stress.\",\n      \"evidence\": \"Cardiomyocyte-specific knockout/overexpression mice, in vivo electrophysiology, and CIB2-vs-CIB1 competition assays\",\n      \"pmids\": [\"37128899\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Structural basis of competition not defined\", \"Single lab\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"High-resolution structures of the mammalian CIB2-TMC1 complex defined the dual cytoplasmic binding interfaces and showed Ca2+ binding drives a conformational change that tunes channel conductivity, establishing CIB2 as the MET channel's cation sensor.\",\n      \"evidence\": \"X-ray crystallography, NMR, MD simulations, ex vivo MET recordings, and multi-species knockouts with calcium-site mutagenesis\",\n      \"pmids\": [\"39773557\", \"39889697\", \"40000792\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How CIB2 conformational change is mechanically coupled to gating not fully resolved\", \"In vivo cation occupancy during transduction not directly measured\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How CIB2's multiple roles (MET auxiliary subunit, integrin partner, mTORC1/Rheb regulator, SK1 inhibitor, calcineurin competitor) are integrated within a single protein and partitioned across tissues remains unresolved.\",\n      \"evidence\": \"No single study reconciles the divergent CIB2 functions\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No unifying model linking channel and signaling roles\", \"Tissue-specific partner selection mechanism unknown\", \"Stereocilia development functions distinct from whirlin remain mechanistically undefined\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [1, 4, 14, 15, 16]},\n      {\"term_id\": \"GO:0140299\", \"supporting_discovery_ids\": [15, 16]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [4, 5, 13, 15]},\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [4, 14]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005929\", \"supporting_discovery_ids\": [0, 19]},\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [7, 8]},\n      {\"term_id\": \"GO:0005794\", \"supporting_discovery_ids\": [8]},\n      {\"term_id\": \"GO:0005856\", \"supporting_discovery_ids\": [1, 4, 17]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-112316\", \"supporting_discovery_ids\": [1, 4, 15]},\n      {\"term_id\": \"R-HSA-9709957\", \"supporting_discovery_ids\": [1, 3, 6]},\n      {\"term_id\": \"R-HSA-9612973\", \"supporting_discovery_ids\": [5]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [5, 13]}\n    ],\n    \"complexes\": [\"TMC1/TMC2 MET channel complex\"],\n    \"partners\": [\"TMC1\", \"TMC2\", \"CIB3\", \"ITGA7\", \"RHEB\", \"SPHK1\", \"PPP3 (calcineurin)\", \"WHRN\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":7,"faith_pct":85.71428571428571}}