{"gene":"OBSCN","run_date":"2026-06-10T05:19:52","timeline":{"discoveries":[{"year":1996,"finding":"C. elegans UNC-89 (ortholog of OBSCN) is a giant ~6,632 amino acid sarcomeric M-line protein composed of SH3, DH, PH, and multiple Ig domains; loss-of-function results in disorganized thick filaments and absence of M-lines, establishing UNC-89 as a structural component required for M-line assembly.","method":"Genetic cloning, sequencing, immunofluorescence microscopy, and immunoblot with polyclonal antiserum in unc-89 mutant nematodes","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — direct loss-of-function with defined sarcomeric phenotype plus immunolocalization, foundational paper independently confirmed by multiple subsequent studies","pmids":["8603916"],"is_preprint":false},{"year":2004,"finding":"UNC-89 (obscurin ortholog) encodes at least four isoforms, three of which (UNC-89-B, -C, -D) contain two tandem protein kinase domains of the MLCK family (PK1 and PK2); homology modeling suggests PK2 is catalytically active and PK1 is inactive.","method":"cDNA cloning, isoform-specific RNAi, immunoblot with isoform-specific antibodies, homology modeling of kinase domains","journal":"Journal of molecular biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (cloning, RNAi phenotype, antibody localization, structural modeling) in a single rigorous study; subsequently replicated","pmids":["15313609"],"is_preprint":false},{"year":2004,"finding":"The tandem MLCK kinase domains of obscurin/UNC-89 define a novel subfamily conserved from C. elegans to vertebrates; phylogenetic analysis supports obscurin-MLCK as the vertebrate ortholog of UNC-89, with SPEG likely arising from obscurin-MLCK by gene duplication.","method":"Phylogenetic analysis of kinase domain sequences across species; conserved exon structure comparison","journal":"Development genes and evolution","confidence":"Medium","confidence_rationale":"Tier 4 / Moderate — computational/phylogenetic analysis replicated across multiple species but no direct biochemical experiment on the protein","pmids":["15185077"],"is_preprint":false},{"year":2000,"finding":"The PH domain of UNC-89 (obscurin) adopts the canonical PH fold but has an unusual closed conformation with a deep hydrophobic pocket lined with negative charges, strongly negative overall electrostatic potential, and lacks association with inositol-1,4,5-triphosphate, suggesting it mediates protein-protein interactions rather than phospholipid binding.","method":"Heteronuclear NMR structure determination; in vitro inositol-1,4,5-triphosphate binding assay","journal":"Structure","confidence":"High","confidence_rationale":"Tier 1 / Moderate — NMR structure with functional binding assay (negative result for phospholipid binding) in a single rigorous study","pmids":["11080629"],"is_preprint":false},{"year":2008,"finding":"The DH-PH region of UNC-89 (obscurin) functions as a guanine nucleotide exchange factor that activates RHO-1 (C. elegans RhoA) but not CED-10 (Rac), MIG-2 (RhoG), or CDC-42 (Cdc42); partial knockdown of rho-1 phenocopies loss of the UNC-89 DH-PH region, placing this GEF activity upstream of RHO-1 in myosin thick filament organization.","method":"Yeast three-hybrid exchange activity assay; in vitro binding assay; RNAi knockdown of rho-1 with thick filament organization phenotype","journal":"Journal of molecular biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — yeast three-hybrid functional assay plus in vitro binding plus genetic epistasis with defined phenotypic readout, multiple orthogonal methods","pmids":["18801371"],"is_preprint":false},{"year":2008,"finding":"SCPL-1, a CTD-type protein phosphatase, is a binding partner for both PK1 and PK2 kinase domains of UNC-89 (obscurin); interaction requires the kinase domain plus adjacent Ig and Fn3 domains; SCPL-1 has phosphatase activity in vitro and localizes to the M-line and I-band; overexpression of SCPL-1 disorganizes UNC-89 at M-lines.","method":"Yeast two-hybrid screening; biochemical pull-down confirmation; in vitro phosphatase activity assay; immunofluorescence localization; RNAi knockdown","journal":"Molecular biology of the cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — yeast two-hybrid confirmed by biochemical methods, in vitro enzymatic assay, and in vivo overexpression phenotype; multiple orthogonal approaches","pmids":["18337465"],"is_preprint":false},{"year":2009,"finding":"LIM-9 (FHL) forms a complex with SCPL-1 and interacts with UNC-89 (obscurin) through its first kinase domain and the interkinase sequence; a ternary complex of UNC-89 kinase regions, SCPL-1, and LIM-9 was demonstrated; overexpression of SCPL-1 disorganizes UNC-89 at M-lines in vivo.","method":"Yeast two-hybrid; yeast three-hybrid ternary complex assay; biochemical pull-down; immunofluorescence with overexpression","journal":"Journal of molecular biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal interactions confirmed biochemically and by yeast three-hybrid; in vivo functional consequence demonstrated by overexpression","pmids":["19244614"],"is_preprint":false},{"year":2012,"finding":"Large Ig domain-rich isoforms of UNC-89 (obscurin) are required for sarcomere organization, sarcoplasmic reticulum organization, and optimal calcium release during excitation-contraction coupling in C. elegans body wall muscle.","method":"Isoform-specific loss-of-function analysis; calcium imaging in vivo; electron and fluorescence microscopy of SR and sarcomere structure","journal":"PloS one","confidence":"High","confidence_rationale":"Tier 2 / Strong — isoform-specific loss-of-function with multiple cellular readouts (SR structure, sarcomere organization, calcium signaling)","pmids":["22768340"],"is_preprint":false},{"year":2012,"finding":"UNC-89 (obscurin) interacts with the BTB-domain protein MEL-26 at sarcomeric M-lines; loss or gain of function of mel-26 disorganizes myosin thick filaments; UNC-89 normally inhibits the CUL-3/MEL-26 ubiquitin ligase complex toward its substrate MEI-1 (katanin), thereby regulating microtubule-severing activity in muscle.","method":"Yeast two-hybrid; co-immunoprecipitation; immunofluorescence colocalization; genetic epistasis with loss- and gain-of-function alleles; immunoblot for MEI-1 levels in unc-89 mutant","journal":"Molecular biology of the cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — direct interaction confirmed by Co-IP, colocalization, and genetic epistasis with defined molecular mechanism (ubiquitin pathway inhibition)","pmids":["22621901"],"is_preprint":false},{"year":2016,"finding":"The SH3 domain of UNC-89 (obscurin) directly binds paramyosin (a thick filament core protein) with a KD of ~1.1 μM; the interaction requires UNC-89's SH3 domain and residues 294–376 of paramyosin, which are α-helical and proline-free; loss of the SH3 domain causes paramyosin accumulations, and overexpression of the SH3 domain mislocalizes paramyosin.","method":"Yeast two-hybrid; in vitro binding assay with KD determination; immunofluorescence in unc-89 loss-of-function and SH3-overexpression animals; homology modeling","journal":"Molecular biology of the cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — yeast two-hybrid confirmed by quantitative in vitro binding (KD), plus in vivo gain- and loss-of-function localization phenotypes","pmids":["27009202"],"is_preprint":false},{"year":2015,"finding":"OBSCN mutations in human DCM patients are associated with haploinsufficiency: three samples with OBSCN mutations showed 45–72% of control obscurin immunoreactive protein levels compared to DCM samples without OBSCN mutations, establishing protein reduction as a mechanism by which OBSCN mutations contribute to DCM.","method":"Whole exon sequencing of explanted heart tissue; immunoblot quantification of obscurin protein levels in human myofibrils","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — immunoblot in human tissue with small sample size (n=3 mutant samples) but consistent with haploinsufficiency mechanism","pmids":["26406308"],"is_preprint":false},{"year":2017,"finding":"The OBSCN p.Arg4444Trp variant, located in the Ig59 domain that binds titin ZIg9/ZIg10 at Z-disks, decreases titin binding affinity by approximately 15-fold, providing a structural mechanism by which this OBSCN variant may compromise myofibril stability.","method":"Structural modeling of the Ig58/Ig59 domain; quantitative binding assay comparing wild-type and mutant Ig59 binding to titin ZIg9/ZIg10","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct quantitative binding assay demonstrating reduced affinity; single study with defined molecular mechanism","pmids":["29073160"],"is_preprint":false},{"year":2020,"finding":"The interkinase region of UNC-89 (obscurin), a 647-residue proline-rich sequence with low complexity between PK1 and PK2, behaves as an entropic spring (random coil) under single-molecule force spectroscopy; CRISPR/Cas9 deletion of 571 residues of this region causes severe sarcomere disorganization, defective locomotion, and reduced muscle force generation.","method":"Single-molecule force spectroscopy in vitro; CRISPR/Cas9 in-frame deletion in C. elegans; super-resolution microscopy; muscle force measurement","journal":"Journal of molecular biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro single-molecule biophysics combined with CRISPR genetic deletion and multiple functional readouts in a single study","pmids":["32645312"],"is_preprint":false},{"year":2020,"finding":"A frameshift mutation in OBSCN in an ARVC patient disrupts localization and decreases expression of its anchoring protein Ank1.5 in iPSC-derived cardiomyocytes, and is associated with increased L-type calcium currents, lipid accumulation, irregular Z-bands, and activation of adipogenesis pathways (PPARγ, C/EBPα, FABP4).","method":"iPSC differentiation into cardiomyocytes; transmission electron microscopy; immunofluorescence; electrophysiological recording; qRT-PCR; Western blotting","journal":"Theranostics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — iPSC-CM model with multiple orthogonal readouts but single patient/mutation studied","pmids":["33042279"],"is_preprint":false},{"year":2022,"finding":"Bi-allelic loss-of-function OBSCN variants cause reduced OBSCN expression and loss of obscurin protein in patient muscle; patient-derived myoblasts show greater depletion of sarcoplasmic reticulum Ca2+ content under starvation compared to controls, indicating impaired SR Ca2+ pumping/storage when obscurin is absent.","method":"Whole-genome/exome sequencing; immunoblot of patient muscle; SR Ca2+ content measurement in cultured myoblasts under starvation conditions","journal":"Brain","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct measurement of SR Ca2+ function in patient-derived cells with confirmed protein loss; multiple patients but single lab","pmids":["34957489"],"is_preprint":false},{"year":2024,"finding":"PK2 of UNC-89 (obscurin) is a catalytically active kinase domain; inactivation of PK2 (lysine-to-alanine mutation) does not affect sarcomere or SR organization but causes mitochondrial fragmentation associated with increased DRP-1 at mitochondria, increased ATP and glycolysis, altered electron transport chain complexes, increased complex I and decreased complex II basal respiration that cannot be uncoupled, and increased uncoupling protein UCP-4 levels, indicating PK2 signals from sarcomeres to mitochondria to regulate energy metabolism.","method":"CRISPR/Cas9 kinase-dead knock-in (KtoA); fluorescence and electron microscopy of mitochondria; respirometry; metabolite measurement; immunoblot for ETC complexes and DRP-1","journal":"Communications biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — precise catalytic-dead mutation with multiple orthogonal metabolic and morphological readouts, direct mechanistic link between PK2 activity and mitochondrial function","pmids":["39420071"],"is_preprint":false}],"current_model":"Obscurin (OBSCN/UNC-89) is a giant sarcomeric M-line and Z-disk scaffold protein whose N-terminal DH-PH region functions as a RhoA (RHO-1) GEF for myosin thick filament organization; its SH3 domain binds paramyosin, its Ig domains anchor it to titin at Z-disks, its elastic interkinase region acts as an entropic spring for sarcomere mechanics, its PK2 kinase domain is catalytically active and signals to mitochondria to regulate energy metabolism and morphology, its PK1 and PK2 domains interact with the phosphatase SCPL-1 and the LIM protein LIM-9 at M-lines, and it modulates CUL-3/MEL-26 ubiquitin ligase activity toward the microtubule-severing enzyme katanin; loss of obscurin disrupts SR organization and Ca2+ handling, and haploinsufficiency of OBSCN is linked to dilated and hypertrophic cardiomyopathy."},"narrative":{"mechanistic_narrative":"Obscurin (OBSCN; C. elegans ortholog UNC-89) is a giant multidomain sarcomeric scaffold protein required for assembly and maintenance of the muscle contractile apparatus, particularly the M-line [PMID:8603916]. Loss of function disorganizes myosin thick filaments and abolishes M-lines, establishing it as a structural organizer of the sarcomere [PMID:8603916], and its large Ig-rich isoforms additionally organize the sarcoplasmic reticulum and support optimal Ca2+ release during excitation-contraction coupling [PMID:22768340]. Obscurin engages multiple structural partners to build this architecture: its SH3 domain directly binds the thick-filament core protein paramyosin (KD ~1.1 μM), with SH3 loss causing paramyosin accumulations [PMID:27009202], and an Ig domain (Ig59) anchors the protein at Z-disks by binding titin ZIg9/ZIg10 [PMID:29073160]. Its N-terminal DH-PH module acts as a guanine nucleotide exchange factor specific for RHO-1/RhoA, placing obscurin upstream of RhoA in thick-filament organization; the PH domain adopts a closed, electronegative fold that mediates protein interactions rather than phosphoinositide binding [PMID:11080629, PMID:18801371]. The protein carries tandem MLCK-family kinase domains (PK1, inactive; PK2, catalytically active) separated by a 647-residue interkinase region that behaves as an entropic spring conferring sarcomere mechanical integrity [PMID:15313609, PMID:32645312]. The kinase region scaffolds a regulatory hub with the CTD-phosphatase SCPL-1 and the FHL/LIM protein LIM-9 at M-lines [PMID:18337465, PMID:19244614], while active PK2 transmits a signal from the sarcomere to mitochondria to control mitochondrial morphology and energy metabolism [PMID:39420071]. Obscurin also restrains the CUL-3/MEL-26 ubiquitin ligase, limiting degradation of the microtubule-severing katanin MEI-1 to protect thick-filament organization [PMID:22621901]. In humans, OBSCN haploinsufficiency and loss-of-function variants reduce obscurin protein and impair sarcomeric integrity and SR Ca2+ handling, linking the gene to dilated and arrhythmogenic cardiomyopathy and to a myopathy with defective SR Ca2+ storage [PMID:26406308, PMID:33042279, PMID:34957489].","teleology":[{"year":1996,"claim":"Established obscurin/UNC-89 as a structural component required for M-line assembly, answering whether this giant protein has a defined role in sarcomere architecture.","evidence":"Genetic cloning and immunolocalization in unc-89 loss-of-function nematodes","pmids":["8603916"],"confidence":"High","gaps":["Did not define which domains drive M-line assembly","Mechanism of thick-filament disorganization not resolved"]},{"year":2000,"claim":"Determined that the PH domain adopts a closed, electronegative fold lacking phosphoinositide binding, reframing it as a protein-interaction module rather than a lipid sensor.","evidence":"Heteronuclear NMR structure with in vitro inositol-triphosphate binding assay","pmids":["11080629"],"confidence":"High","gaps":["Protein partner of the PH domain not identified","In vivo relevance of the closed conformation untested"]},{"year":2004,"claim":"Defined the tandem MLCK-family kinase domains (PK1, PK2) and their isoform distribution, and placed obscurin-MLCK as the vertebrate ortholog of UNC-89, raising the question of catalytic function.","evidence":"cDNA/isoform cloning with RNAi and homology modeling; phylogenetic kinase-domain analysis across species","pmids":["15313609","15185077"],"confidence":"High","gaps":["Catalytic activity of PK2 inferred by modeling, not measured","Substrates of the kinase domains unknown"]},{"year":2008,"claim":"Showed the DH-PH region is a RhoA-specific GEF acting upstream of RHO-1 in thick-filament organization, assigning a signaling function to obscurin's N-terminus.","evidence":"Yeast three-hybrid exchange assay, in vitro binding, and rho-1 RNAi epistasis","pmids":["18801371"],"confidence":"High","gaps":["Downstream RhoA effectors in muscle not defined","Regulation of GEF activity unknown"]},{"year":2008,"claim":"Identified the CTD-phosphatase SCPL-1 as a binding partner of both kinase domains and showed its overexpression disorganizes obscurin, establishing a kinase-phosphatase signaling module at the M-line.","evidence":"Yeast two-hybrid, pull-down, in vitro phosphatase assay, and overexpression localization in C. elegans","pmids":["18337465"],"confidence":"High","gaps":["Phosphatase substrates within the complex not identified","Whether obscurin kinase activity opposes SCPL-1 unresolved"]},{"year":2009,"claim":"Extended the M-line module by demonstrating a ternary complex of obscurin kinase regions, SCPL-1, and the LIM protein LIM-9, defining a multiprotein signaling scaffold.","evidence":"Yeast two- and three-hybrid, pull-down, and overexpression immunofluorescence","pmids":["19244614"],"confidence":"High","gaps":["Functional output of the ternary complex not defined","Phosphorylation events within the complex uncharacterized"]},{"year":2012,"claim":"Linked obscurin to ubiquitin-pathway regulation by showing it binds MEL-26 and inhibits CUL-3/MEL-26-mediated degradation of katanin MEI-1, connecting the sarcomere to microtubule-severing control.","evidence":"Yeast two-hybrid, Co-IP, colocalization, genetic epistasis, and MEI-1 immunoblot in unc-89 mutant","pmids":["22621901"],"confidence":"High","gaps":["How obscurin biochemically inhibits the ligase unknown","Role of microtubule severing in normal muscle not fully defined"]},{"year":2012,"claim":"Demonstrated that large Ig-rich isoforms organize the sarcoplasmic reticulum and support Ca2+ release, expanding obscurin's role beyond the contractile lattice to excitation-contraction coupling.","evidence":"Isoform-specific loss-of-function with in vivo calcium imaging and ultrastructural microscopy","pmids":["22768340"],"confidence":"High","gaps":["Molecular link between obscurin and SR membranes not identified","Which Ig domains mediate SR organization unresolved"]},{"year":2016,"claim":"Established a direct, quantitative SH3-paramyosin interaction required for paramyosin localization, identifying a specific thick-filament binding mechanism.","evidence":"Yeast two-hybrid, in vitro KD determination, and gain/loss-of-function localization in C. elegans","pmids":["27009202"],"confidence":"High","gaps":["Structural basis of the non-canonical SH3-helix interaction not solved at atomic resolution","How this interaction integrates with M-line assembly unclear"]},{"year":2020,"claim":"Showed the interkinase region is an entropic spring whose deletion severely disorganizes sarcomeres and reduces force, assigning a mechanical function to this low-complexity sequence.","evidence":"Single-molecule force spectroscopy, CRISPR/Cas9 in-frame deletion, super-resolution microscopy, and force measurement","pmids":["32645312"],"confidence":"High","gaps":["In vivo tensile load on the region not directly measured","Whether the spring links specific sarcomeric anchors unresolved"]},{"year":2024,"claim":"Demonstrated that PK2 is catalytically active and signals from the sarcomere to mitochondria to control fission and energy metabolism, separating obscurin's kinase signaling from its structural functions.","evidence":"CRISPR/Cas9 kinase-dead knock-in with mitochondrial imaging, respirometry, metabolite assays, and ETC/DRP-1 immunoblots in C. elegans","pmids":["39420071"],"confidence":"High","gaps":["Direct PK2 substrate(s) not identified","Molecular relay from PK2 to DRP-1/mitochondria unknown"]},{"year":2022,"claim":"Connected obscurin loss to human disease by showing bi-allelic loss-of-function variants deplete obscurin and impair SR Ca2+ storage in patient muscle and myoblasts, and that cardiac variants reduce protein or partner localization.","evidence":"Human sequencing with immunoblot and SR Ca2+ measurements; iPSC-cardiomyocyte modeling of an ARVC frameshift; haploinsufficiency quantification and titin-binding affinity assay","pmids":["34957489","33042279","26406308","29073160"],"confidence":"Medium","gaps":["Small patient numbers per study","Causal proof of cardiomyopathy from single variants not established in animal models"]},{"year":null,"claim":"The direct substrate(s) of the active PK2 kinase and the molecular relay linking sarcomeric obscurin signaling to mitochondrial fission remain unidentified.","evidence":"","pmids":[],"confidence":"High","gaps":["No phosphorylation substrate of PK2 mapped","Connection between PK2 activity and DRP-1 recruitment mechanistically unresolved"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[1,15]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[4,8]},{"term_id":"GO:0005198","term_label":"structural molecule activity","supporting_discovery_ids":[0,7]},{"term_id":"GO:0008092","term_label":"cytoskeletal protein binding","supporting_discovery_ids":[9,11]},{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[4]}],"localization":[{"term_id":"GO:0005856","term_label":"cytoskeleton","supporting_discovery_ids":[0,8,9]},{"term_id":"GO:0005783","term_label":"endoplasmic reticulum","supporting_discovery_ids":[7,14]}],"pathway":[{"term_id":"R-HSA-397014","term_label":"Muscle contraction","supporting_discovery_ids":[0,7,12]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[4]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[10,13,14]}],"complexes":["UNC-89/SCPL-1/LIM-9 M-line complex"],"partners":["PARAMYOSIN","TITIN","SCPL-1","LIM-9","MEL-26","RHO-1","ANK1.5"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q5VST9","full_name":"Obscurin","aliases":["Obscurin-RhoGEF","Obscurin-myosin light chain kinase","Obscurin-MLCK"],"length_aa":7968,"mass_kda":868.5,"function":"Structural component of striated muscles which plays a role in myofibrillogenesis. Probably involved in the assembly of myosin into sarcomeric A bands in striated muscle (PubMed:11448995, PubMed:16205939). Has serine/threonine protein kinase activity and phosphorylates N-cadherin CDH2 and sodium/potassium-transporting ATPase subunit ATP1B1 (By similarity). Binds (via the PH domain) strongly to phosphatidylinositol 3,4-bisphosphate (PtdIns(3,4)P2) and phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P2), and to a lesser extent to phosphatidylinositol 3-phosphate (PtdIns(3)P), phosphatidylinositol 4-phosphate (PtdIns(4)P), phosphatidylinositol 5-phosphate (PtdIns(5)P) and phosphatidylinositol 3,4,5-trisphosphate (PtdIns(3,4,5)P3) (PubMed:28826662)","subcellular_location":"Cytoplasm, myofibril, sarcomere, M line; Cytoplasm, myofibril, sarcomere, Z line; Cell membrane, sarcolemma; Nucleus","url":"https://www.uniprot.org/uniprotkb/Q5VST9/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/OBSCN","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/OBSCN","total_profiled":1310},"omim":[{"mim_id":"620235","title":"RHABDOMYOLYSIS, SUSCEPTIBILITY TO, 1; RHABDO1","url":"https://www.omim.org/entry/620235"},{"mim_id":"618791","title":"POTASSIUM CHANNEL TETRAMERIZATION DOMAIN-CONTAINING PROTEIN 6; KCTD6","url":"https://www.omim.org/entry/618791"},{"mim_id":"612641","title":"ANKYRIN 1; ANK1","url":"https://www.omim.org/entry/612641"},{"mim_id":"608616","title":"OBSCURIN; OBSCN","url":"https://www.omim.org/entry/608616"},{"mim_id":"188840","title":"TITIN; TTN","url":"https://www.omim.org/entry/188840"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Plasma membrane","reliability":"Approved"},{"location":"Cytosol","reliability":"Approved"}],"tissue_specificity":"Group enriched","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"skeletal muscle","ntpm":320.2},{"tissue":"tongue","ntpm":105.3}],"url":"https://www.proteinatlas.org/search/OBSCN"},"hgnc":{"alias_symbol":["KIAA1556","UNC89","KIAA1639","ARHGEF30"],"prev_symbol":[]},"alphafold":{"accession":"Q5VST9","domains":[],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q5VST9","model_url":"","pae_url":"","plddt_mean":null},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=OBSCN","jax_strain_url":"https://www.jax.org/strain/search?query=OBSCN"},"sequence":{"accession":"Q5VST9","fasta_url":"https://rest.uniprot.org/uniprotkb/Q5VST9.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q5VST9/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q5VST9"}},"corpus_meta":[{"pmid":"8603916","id":"PMC_8603916","title":"The Caenorhabditis elegans gene unc-89, required fpr muscle M-line assembly, encodes a giant modular protein composed of Ig and signal transduction domains.","date":"1996","source":"The Journal of cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/8603916","citation_count":157,"is_preprint":false},{"pmid":"26406308","id":"PMC_26406308","title":"OBSCN Mutations Associated with Dilated Cardiomyopathy and Haploinsufficiency.","date":"2015","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/26406308","citation_count":72,"is_preprint":false},{"pmid":"15313609","id":"PMC_15313609","title":"Three new isoforms of Caenorhabditis elegans UNC-89 containing MLCK-like protein kinase domains.","date":"2004","source":"Journal of molecular biology","url":"https://pubmed.ncbi.nlm.nih.gov/15313609","citation_count":67,"is_preprint":false},{"pmid":"18337465","id":"PMC_18337465","title":"A novel protein phosphatase is a binding partner for the protein kinase domains of UNC-89 (Obscurin) in Caenorhabditis elegans.","date":"2008","source":"Molecular biology of the cell","url":"https://pubmed.ncbi.nlm.nih.gov/18337465","citation_count":44,"is_preprint":false},{"pmid":"15185077","id":"PMC_15185077","title":"Orthologous relationship of obscurin and Unc-89: phylogeny of a novel family of tandem myosin light chain kinases.","date":"2004","source":"Development genes and evolution","url":"https://pubmed.ncbi.nlm.nih.gov/15185077","citation_count":42,"is_preprint":false},{"pmid":"22768340","id":"PMC_22768340","title":"Large isoforms of UNC-89 (obscurin) are required for muscle cell architecture and optimal calcium release in Caenorhabditis elegans.","date":"2012","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/22768340","citation_count":37,"is_preprint":false},{"pmid":"18801371","id":"PMC_18801371","title":"The DH-PH region of the giant protein UNC-89 activates RHO-1 GTPase in Caenorhabditis elegans body wall muscle.","date":"2008","source":"Journal of molecular biology","url":"https://pubmed.ncbi.nlm.nih.gov/18801371","citation_count":36,"is_preprint":false},{"pmid":"29073160","id":"PMC_29073160","title":"A novel FLNC frameshift and an OBSCN variant in a family with distal muscular dystrophy.","date":"2017","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/29073160","citation_count":35,"is_preprint":false},{"pmid":"19244614","id":"PMC_19244614","title":"A LIM-9 (FHL)/SCPL-1 (SCP) complex interacts with the C-terminal protein kinase regions of UNC-89 (obscurin) in Caenorhabditis elegans muscle.","date":"2009","source":"Journal of molecular biology","url":"https://pubmed.ncbi.nlm.nih.gov/19244614","citation_count":32,"is_preprint":false},{"pmid":"22621901","id":"PMC_22621901","title":"UNC-89 (obscurin) binds to MEL-26, a BTB-domain protein, and affects the function of MEI-1 (katanin) in striated muscle of Caenorhabditis elegans.","date":"2012","source":"Molecular biology of the cell","url":"https://pubmed.ncbi.nlm.nih.gov/22621901","citation_count":32,"is_preprint":false},{"pmid":"29254242","id":"PMC_29254242","title":"A comprehensive genomic meta-analysis identifies confirmatory role of OBSCN gene in breast tumorigenesis.","date":"2017","source":"Oncotarget","url":"https://pubmed.ncbi.nlm.nih.gov/29254242","citation_count":29,"is_preprint":false},{"pmid":"33042279","id":"PMC_33042279","title":"Intracellular calcium current disorder and disease phenotype in OBSCN mutant iPSC-based cardiomyocytes in arrhythmogenic right ventricular cardiomyopathy.","date":"2020","source":"Theranostics","url":"https://pubmed.ncbi.nlm.nih.gov/33042279","citation_count":26,"is_preprint":false},{"pmid":"11080629","id":"PMC_11080629","title":"Structure of a PH domain from the C. elegans muscle protein UNC-89 suggests a novel function.","date":"2000","source":"Structure (London, England : 1993)","url":"https://pubmed.ncbi.nlm.nih.gov/11080629","citation_count":24,"is_preprint":false},{"pmid":"34957489","id":"PMC_34957489","title":"Bi-allelic loss-of-function OBSCN variants predispose individuals to severe recurrent rhabdomyolysis.","date":"2022","source":"Brain : a journal of neurology","url":"https://pubmed.ncbi.nlm.nih.gov/34957489","citation_count":20,"is_preprint":false},{"pmid":"36877839","id":"PMC_36877839","title":"OBSCN restoration via OBSCN-AS1 long-noncoding RNA CRISPR-targeting suppresses metastasis in triple-negative breast cancer.","date":"2023","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/36877839","citation_count":19,"is_preprint":false},{"pmid":"27009202","id":"PMC_27009202","title":"The SH3 domain of UNC-89 (obscurin) interacts with paramyosin, a coiled-coil protein, in Caenorhabditis elegans muscle.","date":"2016","source":"Molecular biology of the cell","url":"https://pubmed.ncbi.nlm.nih.gov/27009202","citation_count":18,"is_preprint":false},{"pmid":"34601892","id":"PMC_34601892","title":"Truncating Variants in OBSCN Gene Associated With Disease-Onset and Outcomes of Hypertrophic Cardiomyopathy.","date":"2021","source":"Circulation. Genomic and precision medicine","url":"https://pubmed.ncbi.nlm.nih.gov/34601892","citation_count":14,"is_preprint":false},{"pmid":"32645312","id":"PMC_32645312","title":"A Region of UNC-89 (Obscurin) Lying between Two Protein Kinase Domains Is a Highly Elastic Spring Required for Proper Sarcomere Organization.","date":"2020","source":"Journal of molecular biology","url":"https://pubmed.ncbi.nlm.nih.gov/32645312","citation_count":10,"is_preprint":false},{"pmid":"38159459","id":"PMC_38159459","title":"Novel OBSCN variants associated with a risk to exercise-intolerance and rhabdomyolysis.","date":"2023","source":"Neuromuscular disorders : NMD","url":"https://pubmed.ncbi.nlm.nih.gov/38159459","citation_count":8,"is_preprint":false},{"pmid":"22251166","id":"PMC_22251166","title":"Contribution of the OBSCN nonsynonymous variants to aspirin exacerbated respiratory disease susceptibility in Korean population.","date":"2012","source":"DNA and cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/22251166","citation_count":7,"is_preprint":false},{"pmid":"40025502","id":"PMC_40025502","title":"OBSCN undergoes extensive alternative splicing during human cardiac and skeletal muscle development.","date":"2025","source":"Skeletal muscle","url":"https://pubmed.ncbi.nlm.nih.gov/40025502","citation_count":4,"is_preprint":false},{"pmid":"40149008","id":"PMC_40149008","title":"Loss of OBSCN expression promotes bladder cancer progression but enhances the efficacy of PD-L1 inhibitors.","date":"2025","source":"Cell & bioscience","url":"https://pubmed.ncbi.nlm.nih.gov/40149008","citation_count":2,"is_preprint":false},{"pmid":"39420071","id":"PMC_39420071","title":"Protein kinase 2 of the giant sarcomeric protein UNC-89 regulates mitochondrial morphology and function.","date":"2024","source":"Communications biology","url":"https://pubmed.ncbi.nlm.nih.gov/39420071","citation_count":2,"is_preprint":false},{"pmid":"40813169","id":"PMC_40813169","title":"Rhabdomyolysis associated with OBSCN mutations: case report and mechanistic review.","date":"2025","source":"Neuromuscular disorders : NMD","url":"https://pubmed.ncbi.nlm.nih.gov/40813169","citation_count":1,"is_preprint":false},{"pmid":"40156064","id":"PMC_40156064","title":"Novel compound heterozygous OBSCN variants in Chinese children with congenital pulmonary airway malformation.","date":"2025","source":"Italian journal of pediatrics","url":"https://pubmed.ncbi.nlm.nih.gov/40156064","citation_count":1,"is_preprint":false},{"pmid":"41320670","id":"PMC_41320670","title":"Multi-Omics Analysis Reveals OBSCN as a Key Modulator of Tumor Microenvironment, Microbial Signatures and Clinical Outcomes in Gastric Cancer.","date":"2025","source":"MicrobiologyOpen","url":"https://pubmed.ncbi.nlm.nih.gov/41320670","citation_count":0,"is_preprint":false},{"pmid":"41530801","id":"PMC_41530801","title":"Novel GJC2 and OBSCN variants co-segregating in a Chinese primary lymphedema pedigree.","date":"2026","source":"Orphanet journal of rare diseases","url":"https://pubmed.ncbi.nlm.nih.gov/41530801","citation_count":0,"is_preprint":false},{"pmid":"40186404","id":"PMC_40186404","title":"Identification of Compound Heterozygous Variants in OBSCN Gene Associated With Rhabdomyolysis: A Case Report.","date":"2025","source":"Molecular genetics & genomic medicine","url":"https://pubmed.ncbi.nlm.nih.gov/40186404","citation_count":0,"is_preprint":false},{"pmid":"41226589","id":"PMC_41226589","title":"A Novel Germline Frameshift Variant in the Tumor Suppressor Gene OBSCN in a Melanoma Patient.","date":"2025","source":"International journal of molecular sciences","url":"https://pubmed.ncbi.nlm.nih.gov/41226589","citation_count":0,"is_preprint":false},{"pmid":"42068564","id":"PMC_42068564","title":"Co-Pathogenic Role of BRCA1 and OBSCN Deletions in Chinese Familial Breast Cancer: A Case Report.","date":"2026","source":"The American journal of case reports","url":"https://pubmed.ncbi.nlm.nih.gov/42068564","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":17330,"output_tokens":4210,"usd":0.05757,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":12108,"output_tokens":4152,"usd":0.08217,"stage2_stop_reason":"end_turn"},"total_usd":0.13974,"stage1_batch_id":"msgbatch_013a8chtv3AWyTqv4z4sEF4C","stage2_batch_id":"msgbatch_01AHsuW63vinsvuTgzmQ3n62","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1996,\n      \"finding\": \"C. elegans UNC-89 (ortholog of OBSCN) is a giant ~6,632 amino acid sarcomeric M-line protein composed of SH3, DH, PH, and multiple Ig domains; loss-of-function results in disorganized thick filaments and absence of M-lines, establishing UNC-89 as a structural component required for M-line assembly.\",\n      \"method\": \"Genetic cloning, sequencing, immunofluorescence microscopy, and immunoblot with polyclonal antiserum in unc-89 mutant nematodes\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — direct loss-of-function with defined sarcomeric phenotype plus immunolocalization, foundational paper independently confirmed by multiple subsequent studies\",\n      \"pmids\": [\"8603916\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"UNC-89 (obscurin ortholog) encodes at least four isoforms, three of which (UNC-89-B, -C, -D) contain two tandem protein kinase domains of the MLCK family (PK1 and PK2); homology modeling suggests PK2 is catalytically active and PK1 is inactive.\",\n      \"method\": \"cDNA cloning, isoform-specific RNAi, immunoblot with isoform-specific antibodies, homology modeling of kinase domains\",\n      \"journal\": \"Journal of molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (cloning, RNAi phenotype, antibody localization, structural modeling) in a single rigorous study; subsequently replicated\",\n      \"pmids\": [\"15313609\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"The tandem MLCK kinase domains of obscurin/UNC-89 define a novel subfamily conserved from C. elegans to vertebrates; phylogenetic analysis supports obscurin-MLCK as the vertebrate ortholog of UNC-89, with SPEG likely arising from obscurin-MLCK by gene duplication.\",\n      \"method\": \"Phylogenetic analysis of kinase domain sequences across species; conserved exon structure comparison\",\n      \"journal\": \"Development genes and evolution\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 4 / Moderate — computational/phylogenetic analysis replicated across multiple species but no direct biochemical experiment on the protein\",\n      \"pmids\": [\"15185077\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"The PH domain of UNC-89 (obscurin) adopts the canonical PH fold but has an unusual closed conformation with a deep hydrophobic pocket lined with negative charges, strongly negative overall electrostatic potential, and lacks association with inositol-1,4,5-triphosphate, suggesting it mediates protein-protein interactions rather than phospholipid binding.\",\n      \"method\": \"Heteronuclear NMR structure determination; in vitro inositol-1,4,5-triphosphate binding assay\",\n      \"journal\": \"Structure\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — NMR structure with functional binding assay (negative result for phospholipid binding) in a single rigorous study\",\n      \"pmids\": [\"11080629\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"The DH-PH region of UNC-89 (obscurin) functions as a guanine nucleotide exchange factor that activates RHO-1 (C. elegans RhoA) but not CED-10 (Rac), MIG-2 (RhoG), or CDC-42 (Cdc42); partial knockdown of rho-1 phenocopies loss of the UNC-89 DH-PH region, placing this GEF activity upstream of RHO-1 in myosin thick filament organization.\",\n      \"method\": \"Yeast three-hybrid exchange activity assay; in vitro binding assay; RNAi knockdown of rho-1 with thick filament organization phenotype\",\n      \"journal\": \"Journal of molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — yeast three-hybrid functional assay plus in vitro binding plus genetic epistasis with defined phenotypic readout, multiple orthogonal methods\",\n      \"pmids\": [\"18801371\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"SCPL-1, a CTD-type protein phosphatase, is a binding partner for both PK1 and PK2 kinase domains of UNC-89 (obscurin); interaction requires the kinase domain plus adjacent Ig and Fn3 domains; SCPL-1 has phosphatase activity in vitro and localizes to the M-line and I-band; overexpression of SCPL-1 disorganizes UNC-89 at M-lines.\",\n      \"method\": \"Yeast two-hybrid screening; biochemical pull-down confirmation; in vitro phosphatase activity assay; immunofluorescence localization; RNAi knockdown\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — yeast two-hybrid confirmed by biochemical methods, in vitro enzymatic assay, and in vivo overexpression phenotype; multiple orthogonal approaches\",\n      \"pmids\": [\"18337465\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"LIM-9 (FHL) forms a complex with SCPL-1 and interacts with UNC-89 (obscurin) through its first kinase domain and the interkinase sequence; a ternary complex of UNC-89 kinase regions, SCPL-1, and LIM-9 was demonstrated; overexpression of SCPL-1 disorganizes UNC-89 at M-lines in vivo.\",\n      \"method\": \"Yeast two-hybrid; yeast three-hybrid ternary complex assay; biochemical pull-down; immunofluorescence with overexpression\",\n      \"journal\": \"Journal of molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal interactions confirmed biochemically and by yeast three-hybrid; in vivo functional consequence demonstrated by overexpression\",\n      \"pmids\": [\"19244614\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Large Ig domain-rich isoforms of UNC-89 (obscurin) are required for sarcomere organization, sarcoplasmic reticulum organization, and optimal calcium release during excitation-contraction coupling in C. elegans body wall muscle.\",\n      \"method\": \"Isoform-specific loss-of-function analysis; calcium imaging in vivo; electron and fluorescence microscopy of SR and sarcomere structure\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — isoform-specific loss-of-function with multiple cellular readouts (SR structure, sarcomere organization, calcium signaling)\",\n      \"pmids\": [\"22768340\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"UNC-89 (obscurin) interacts with the BTB-domain protein MEL-26 at sarcomeric M-lines; loss or gain of function of mel-26 disorganizes myosin thick filaments; UNC-89 normally inhibits the CUL-3/MEL-26 ubiquitin ligase complex toward its substrate MEI-1 (katanin), thereby regulating microtubule-severing activity in muscle.\",\n      \"method\": \"Yeast two-hybrid; co-immunoprecipitation; immunofluorescence colocalization; genetic epistasis with loss- and gain-of-function alleles; immunoblot for MEI-1 levels in unc-89 mutant\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — direct interaction confirmed by Co-IP, colocalization, and genetic epistasis with defined molecular mechanism (ubiquitin pathway inhibition)\",\n      \"pmids\": [\"22621901\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"The SH3 domain of UNC-89 (obscurin) directly binds paramyosin (a thick filament core protein) with a KD of ~1.1 μM; the interaction requires UNC-89's SH3 domain and residues 294–376 of paramyosin, which are α-helical and proline-free; loss of the SH3 domain causes paramyosin accumulations, and overexpression of the SH3 domain mislocalizes paramyosin.\",\n      \"method\": \"Yeast two-hybrid; in vitro binding assay with KD determination; immunofluorescence in unc-89 loss-of-function and SH3-overexpression animals; homology modeling\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — yeast two-hybrid confirmed by quantitative in vitro binding (KD), plus in vivo gain- and loss-of-function localization phenotypes\",\n      \"pmids\": [\"27009202\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"OBSCN mutations in human DCM patients are associated with haploinsufficiency: three samples with OBSCN mutations showed 45–72% of control obscurin immunoreactive protein levels compared to DCM samples without OBSCN mutations, establishing protein reduction as a mechanism by which OBSCN mutations contribute to DCM.\",\n      \"method\": \"Whole exon sequencing of explanted heart tissue; immunoblot quantification of obscurin protein levels in human myofibrils\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — immunoblot in human tissue with small sample size (n=3 mutant samples) but consistent with haploinsufficiency mechanism\",\n      \"pmids\": [\"26406308\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"The OBSCN p.Arg4444Trp variant, located in the Ig59 domain that binds titin ZIg9/ZIg10 at Z-disks, decreases titin binding affinity by approximately 15-fold, providing a structural mechanism by which this OBSCN variant may compromise myofibril stability.\",\n      \"method\": \"Structural modeling of the Ig58/Ig59 domain; quantitative binding assay comparing wild-type and mutant Ig59 binding to titin ZIg9/ZIg10\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct quantitative binding assay demonstrating reduced affinity; single study with defined molecular mechanism\",\n      \"pmids\": [\"29073160\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"The interkinase region of UNC-89 (obscurin), a 647-residue proline-rich sequence with low complexity between PK1 and PK2, behaves as an entropic spring (random coil) under single-molecule force spectroscopy; CRISPR/Cas9 deletion of 571 residues of this region causes severe sarcomere disorganization, defective locomotion, and reduced muscle force generation.\",\n      \"method\": \"Single-molecule force spectroscopy in vitro; CRISPR/Cas9 in-frame deletion in C. elegans; super-resolution microscopy; muscle force measurement\",\n      \"journal\": \"Journal of molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro single-molecule biophysics combined with CRISPR genetic deletion and multiple functional readouts in a single study\",\n      \"pmids\": [\"32645312\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"A frameshift mutation in OBSCN in an ARVC patient disrupts localization and decreases expression of its anchoring protein Ank1.5 in iPSC-derived cardiomyocytes, and is associated with increased L-type calcium currents, lipid accumulation, irregular Z-bands, and activation of adipogenesis pathways (PPARγ, C/EBPα, FABP4).\",\n      \"method\": \"iPSC differentiation into cardiomyocytes; transmission electron microscopy; immunofluorescence; electrophysiological recording; qRT-PCR; Western blotting\",\n      \"journal\": \"Theranostics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — iPSC-CM model with multiple orthogonal readouts but single patient/mutation studied\",\n      \"pmids\": [\"33042279\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Bi-allelic loss-of-function OBSCN variants cause reduced OBSCN expression and loss of obscurin protein in patient muscle; patient-derived myoblasts show greater depletion of sarcoplasmic reticulum Ca2+ content under starvation compared to controls, indicating impaired SR Ca2+ pumping/storage when obscurin is absent.\",\n      \"method\": \"Whole-genome/exome sequencing; immunoblot of patient muscle; SR Ca2+ content measurement in cultured myoblasts under starvation conditions\",\n      \"journal\": \"Brain\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct measurement of SR Ca2+ function in patient-derived cells with confirmed protein loss; multiple patients but single lab\",\n      \"pmids\": [\"34957489\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"PK2 of UNC-89 (obscurin) is a catalytically active kinase domain; inactivation of PK2 (lysine-to-alanine mutation) does not affect sarcomere or SR organization but causes mitochondrial fragmentation associated with increased DRP-1 at mitochondria, increased ATP and glycolysis, altered electron transport chain complexes, increased complex I and decreased complex II basal respiration that cannot be uncoupled, and increased uncoupling protein UCP-4 levels, indicating PK2 signals from sarcomeres to mitochondria to regulate energy metabolism.\",\n      \"method\": \"CRISPR/Cas9 kinase-dead knock-in (KtoA); fluorescence and electron microscopy of mitochondria; respirometry; metabolite measurement; immunoblot for ETC complexes and DRP-1\",\n      \"journal\": \"Communications biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — precise catalytic-dead mutation with multiple orthogonal metabolic and morphological readouts, direct mechanistic link between PK2 activity and mitochondrial function\",\n      \"pmids\": [\"39420071\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"Obscurin (OBSCN/UNC-89) is a giant sarcomeric M-line and Z-disk scaffold protein whose N-terminal DH-PH region functions as a RhoA (RHO-1) GEF for myosin thick filament organization; its SH3 domain binds paramyosin, its Ig domains anchor it to titin at Z-disks, its elastic interkinase region acts as an entropic spring for sarcomere mechanics, its PK2 kinase domain is catalytically active and signals to mitochondria to regulate energy metabolism and morphology, its PK1 and PK2 domains interact with the phosphatase SCPL-1 and the LIM protein LIM-9 at M-lines, and it modulates CUL-3/MEL-26 ubiquitin ligase activity toward the microtubule-severing enzyme katanin; loss of obscurin disrupts SR organization and Ca2+ handling, and haploinsufficiency of OBSCN is linked to dilated and hypertrophic cardiomyopathy.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"Obscurin (OBSCN; C. elegans ortholog UNC-89) is a giant multidomain sarcomeric scaffold protein required for assembly and maintenance of the muscle contractile apparatus, particularly the M-line [#0]. Loss of function disorganizes myosin thick filaments and abolishes M-lines, establishing it as a structural organizer of the sarcomere [#0], and its large Ig-rich isoforms additionally organize the sarcoplasmic reticulum and support optimal Ca2+ release during excitation-contraction coupling [#7]. Obscurin engages multiple structural partners to build this architecture: its SH3 domain directly binds the thick-filament core protein paramyosin (KD ~1.1 μM), with SH3 loss causing paramyosin accumulations [#9], and an Ig domain (Ig59) anchors the protein at Z-disks by binding titin ZIg9/ZIg10 [#11]. Its N-terminal DH-PH module acts as a guanine nucleotide exchange factor specific for RHO-1/RhoA, placing obscurin upstream of RhoA in thick-filament organization; the PH domain adopts a closed, electronegative fold that mediates protein interactions rather than phosphoinositide binding [#3, #4]. The protein carries tandem MLCK-family kinase domains (PK1, inactive; PK2, catalytically active) separated by a 647-residue interkinase region that behaves as an entropic spring conferring sarcomere mechanical integrity [#1, #12]. The kinase region scaffolds a regulatory hub with the CTD-phosphatase SCPL-1 and the FHL/LIM protein LIM-9 at M-lines [#5, #6], while active PK2 transmits a signal from the sarcomere to mitochondria to control mitochondrial morphology and energy metabolism [#15]. Obscurin also restrains the CUL-3/MEL-26 ubiquitin ligase, limiting degradation of the microtubule-severing katanin MEI-1 to protect thick-filament organization [#8]. In humans, OBSCN haploinsufficiency and loss-of-function variants reduce obscurin protein and impair sarcomeric integrity and SR Ca2+ handling, linking the gene to dilated and arrhythmogenic cardiomyopathy and to a myopathy with defective SR Ca2+ storage [#10, #13, #14].\",\n  \"teleology\": [\n    {\n      \"year\": 1996,\n      \"claim\": \"Established obscurin/UNC-89 as a structural component required for M-line assembly, answering whether this giant protein has a defined role in sarcomere architecture.\",\n      \"evidence\": \"Genetic cloning and immunolocalization in unc-89 loss-of-function nematodes\",\n      \"pmids\": [\"8603916\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not define which domains drive M-line assembly\", \"Mechanism of thick-filament disorganization not resolved\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Determined that the PH domain adopts a closed, electronegative fold lacking phosphoinositide binding, reframing it as a protein-interaction module rather than a lipid sensor.\",\n      \"evidence\": \"Heteronuclear NMR structure with in vitro inositol-triphosphate binding assay\",\n      \"pmids\": [\"11080629\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Protein partner of the PH domain not identified\", \"In vivo relevance of the closed conformation untested\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Defined the tandem MLCK-family kinase domains (PK1, PK2) and their isoform distribution, and placed obscurin-MLCK as the vertebrate ortholog of UNC-89, raising the question of catalytic function.\",\n      \"evidence\": \"cDNA/isoform cloning with RNAi and homology modeling; phylogenetic kinase-domain analysis across species\",\n      \"pmids\": [\"15313609\", \"15185077\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Catalytic activity of PK2 inferred by modeling, not measured\", \"Substrates of the kinase domains unknown\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Showed the DH-PH region is a RhoA-specific GEF acting upstream of RHO-1 in thick-filament organization, assigning a signaling function to obscurin's N-terminus.\",\n      \"evidence\": \"Yeast three-hybrid exchange assay, in vitro binding, and rho-1 RNAi epistasis\",\n      \"pmids\": [\"18801371\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Downstream RhoA effectors in muscle not defined\", \"Regulation of GEF activity unknown\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Identified the CTD-phosphatase SCPL-1 as a binding partner of both kinase domains and showed its overexpression disorganizes obscurin, establishing a kinase-phosphatase signaling module at the M-line.\",\n      \"evidence\": \"Yeast two-hybrid, pull-down, in vitro phosphatase assay, and overexpression localization in C. elegans\",\n      \"pmids\": [\"18337465\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Phosphatase substrates within the complex not identified\", \"Whether obscurin kinase activity opposes SCPL-1 unresolved\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Extended the M-line module by demonstrating a ternary complex of obscurin kinase regions, SCPL-1, and the LIM protein LIM-9, defining a multiprotein signaling scaffold.\",\n      \"evidence\": \"Yeast two- and three-hybrid, pull-down, and overexpression immunofluorescence\",\n      \"pmids\": [\"19244614\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional output of the ternary complex not defined\", \"Phosphorylation events within the complex uncharacterized\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Linked obscurin to ubiquitin-pathway regulation by showing it binds MEL-26 and inhibits CUL-3/MEL-26-mediated degradation of katanin MEI-1, connecting the sarcomere to microtubule-severing control.\",\n      \"evidence\": \"Yeast two-hybrid, Co-IP, colocalization, genetic epistasis, and MEI-1 immunoblot in unc-89 mutant\",\n      \"pmids\": [\"22621901\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How obscurin biochemically inhibits the ligase unknown\", \"Role of microtubule severing in normal muscle not fully defined\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Demonstrated that large Ig-rich isoforms organize the sarcoplasmic reticulum and support Ca2+ release, expanding obscurin's role beyond the contractile lattice to excitation-contraction coupling.\",\n      \"evidence\": \"Isoform-specific loss-of-function with in vivo calcium imaging and ultrastructural microscopy\",\n      \"pmids\": [\"22768340\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular link between obscurin and SR membranes not identified\", \"Which Ig domains mediate SR organization unresolved\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Established a direct, quantitative SH3-paramyosin interaction required for paramyosin localization, identifying a specific thick-filament binding mechanism.\",\n      \"evidence\": \"Yeast two-hybrid, in vitro KD determination, and gain/loss-of-function localization in C. elegans\",\n      \"pmids\": [\"27009202\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of the non-canonical SH3-helix interaction not solved at atomic resolution\", \"How this interaction integrates with M-line assembly unclear\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Showed the interkinase region is an entropic spring whose deletion severely disorganizes sarcomeres and reduces force, assigning a mechanical function to this low-complexity sequence.\",\n      \"evidence\": \"Single-molecule force spectroscopy, CRISPR/Cas9 in-frame deletion, super-resolution microscopy, and force measurement\",\n      \"pmids\": [\"32645312\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo tensile load on the region not directly measured\", \"Whether the spring links specific sarcomeric anchors unresolved\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Demonstrated that PK2 is catalytically active and signals from the sarcomere to mitochondria to control fission and energy metabolism, separating obscurin's kinase signaling from its structural functions.\",\n      \"evidence\": \"CRISPR/Cas9 kinase-dead knock-in with mitochondrial imaging, respirometry, metabolite assays, and ETC/DRP-1 immunoblots in C. elegans\",\n      \"pmids\": [\"39420071\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct PK2 substrate(s) not identified\", \"Molecular relay from PK2 to DRP-1/mitochondria unknown\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Connected obscurin loss to human disease by showing bi-allelic loss-of-function variants deplete obscurin and impair SR Ca2+ storage in patient muscle and myoblasts, and that cardiac variants reduce protein or partner localization.\",\n      \"evidence\": \"Human sequencing with immunoblot and SR Ca2+ measurements; iPSC-cardiomyocyte modeling of an ARVC frameshift; haploinsufficiency quantification and titin-binding affinity assay\",\n      \"pmids\": [\"34957489\", \"33042279\", \"26406308\", \"29073160\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Small patient numbers per study\", \"Causal proof of cardiomyopathy from single variants not established in animal models\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The direct substrate(s) of the active PK2 kinase and the molecular relay linking sarcomeric obscurin signaling to mitochondrial fission remain unidentified.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No phosphorylation substrate of PK2 mapped\", \"Connection between PK2 activity and DRP-1 recruitment mechanistically unresolved\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [1, 15]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [4, 8]},\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [0, 7]},\n      {\"term_id\": \"GO:0008092\", \"supporting_discovery_ids\": [9, 11]},\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [4]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005856\", \"supporting_discovery_ids\": [0, 8, 9]},\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [7, 14]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-397014\", \"supporting_discovery_ids\": [0, 7, 12]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [4]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [10, 13, 14]}\n    ],\n    \"complexes\": [\"UNC-89/SCPL-1/LIM-9 M-line complex\"],\n    \"partners\": [\"paramyosin\", \"titin\", \"SCPL-1\", \"LIM-9\", \"MEL-26\", \"RHO-1\", \"Ank1.5\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":8,"faith_total":8,"faith_pct":100.0}}