Affinage

OBSCN

Obscurin · UniProt Q5VST9

Length
7968 aa
Mass
868.5 kDa
Annotated
2026-06-10
30 papers in source corpus 16 papers cited in narrative 16 extracted findings
Cross-family judge vs UniProt: Affinage preferred faithfulness: 8/8 claims corpus-supported (100%)

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

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).

Mechanistic history

Synthesis pass · year-by-year structured walk · 12 steps
  1. 1996 High

    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

    PMID:8603916

    Open questions at the time
    • Did not define which domains drive M-line assembly
    • Mechanism of thick-filament disorganization not resolved
  2. 2000 High

    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

    PMID:11080629

    Open questions at the time
    • Protein partner of the PH domain not identified
    • In vivo relevance of the closed conformation untested
  3. 2004 High

    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

    PMID:15185077 PMID:15313609

    Open questions at the time
    • Catalytic activity of PK2 inferred by modeling, not measured
    • Substrates of the kinase domains unknown
  4. 2008 High

    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

    PMID:18801371

    Open questions at the time
    • Downstream RhoA effectors in muscle not defined
    • Regulation of GEF activity unknown
  5. 2008 High

    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

    PMID:18337465

    Open questions at the time
    • Phosphatase substrates within the complex not identified
    • Whether obscurin kinase activity opposes SCPL-1 unresolved
  6. 2009 High

    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

    PMID:19244614

    Open questions at the time
    • Functional output of the ternary complex not defined
    • Phosphorylation events within the complex uncharacterized
  7. 2012 High

    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

    PMID:22621901

    Open questions at the time
    • How obscurin biochemically inhibits the ligase unknown
    • Role of microtubule severing in normal muscle not fully defined
  8. 2012 High

    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

    PMID:22768340

    Open questions at the time
    • Molecular link between obscurin and SR membranes not identified
    • Which Ig domains mediate SR organization unresolved
  9. 2016 High

    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

    PMID:27009202

    Open questions at the time
    • Structural basis of the non-canonical SH3-helix interaction not solved at atomic resolution
    • How this interaction integrates with M-line assembly unclear
  10. 2020 High

    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

    PMID:32645312

    Open questions at the time
    • In vivo tensile load on the region not directly measured
    • Whether the spring links specific sarcomeric anchors unresolved
  11. 2024 High

    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

    PMID:39420071

    Open questions at the time
    • Direct PK2 substrate(s) not identified
    • Molecular relay from PK2 to DRP-1/mitochondria unknown
  12. 2022 Medium

    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

    PMID:26406308 PMID:29073160 PMID:33042279 PMID:34957489

    Open questions at the time
    • Small patient numbers per study
    • Causal proof of cardiomyopathy from single variants not established in animal models

Open questions

Synthesis pass · forward-looking unresolved questions
  • The direct substrate(s) of the active PK2 kinase and the molecular relay linking sarcomeric obscurin signaling to mitochondrial fission remain unidentified.
  • No phosphorylation substrate of PK2 mapped
  • Connection between PK2 activity and DRP-1 recruitment mechanistically unresolved

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0005198 structural molecule activity 2 GO:0008092 cytoskeletal protein binding 2 GO:0098772 molecular function regulator activity 2 GO:0140096 catalytic activity, acting on a protein 2 GO:0060089 molecular transducer activity 1
Localization
GO:0005856 cytoskeleton 3 GO:0005783 endoplasmic reticulum 2
Pathway
R-HSA-1643685 Disease 3 R-HSA-397014 Muscle contraction 3 R-HSA-162582 Signal Transduction 1
Partners
ANK1.5LIM-9MEL-26PARAMYOSINRHO-1SCPL-1TITIN
Complex memberships
UNC-89/SCPL-1/LIM-9 M-line complex

Evidence

Reading pass · 16 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
1996 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. Genetic cloning, sequencing, immunofluorescence microscopy, and immunoblot with polyclonal antiserum in unc-89 mutant nematodes The Journal of cell biology High 8603916
2004 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. cDNA cloning, isoform-specific RNAi, immunoblot with isoform-specific antibodies, homology modeling of kinase domains Journal of molecular biology High 15313609
2004 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. Phylogenetic analysis of kinase domain sequences across species; conserved exon structure comparison Development genes and evolution Medium 15185077
2000 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. Heteronuclear NMR structure determination; in vitro inositol-1,4,5-triphosphate binding assay Structure High 11080629
2008 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. Yeast three-hybrid exchange activity assay; in vitro binding assay; RNAi knockdown of rho-1 with thick filament organization phenotype Journal of molecular biology High 18801371
2008 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. Yeast two-hybrid screening; biochemical pull-down confirmation; in vitro phosphatase activity assay; immunofluorescence localization; RNAi knockdown Molecular biology of the cell High 18337465
2009 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. Yeast two-hybrid; yeast three-hybrid ternary complex assay; biochemical pull-down; immunofluorescence with overexpression Journal of molecular biology High 19244614
2012 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. Isoform-specific loss-of-function analysis; calcium imaging in vivo; electron and fluorescence microscopy of SR and sarcomere structure PloS one High 22768340
2012 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. 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 Molecular biology of the cell High 22621901
2016 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. Yeast two-hybrid; in vitro binding assay with KD determination; immunofluorescence in unc-89 loss-of-function and SH3-overexpression animals; homology modeling Molecular biology of the cell High 27009202
2015 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. Whole exon sequencing of explanted heart tissue; immunoblot quantification of obscurin protein levels in human myofibrils PloS one Medium 26406308
2017 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. Structural modeling of the Ig58/Ig59 domain; quantitative binding assay comparing wild-type and mutant Ig59 binding to titin ZIg9/ZIg10 PloS one Medium 29073160
2020 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. Single-molecule force spectroscopy in vitro; CRISPR/Cas9 in-frame deletion in C. elegans; super-resolution microscopy; muscle force measurement Journal of molecular biology High 32645312
2020 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). iPSC differentiation into cardiomyocytes; transmission electron microscopy; immunofluorescence; electrophysiological recording; qRT-PCR; Western blotting Theranostics Medium 33042279
2022 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. Whole-genome/exome sequencing; immunoblot of patient muscle; SR Ca2+ content measurement in cultured myoblasts under starvation conditions Brain Medium 34957489
2024 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. CRISPR/Cas9 kinase-dead knock-in (KtoA); fluorescence and electron microscopy of mitochondria; respirometry; metabolite measurement; immunoblot for ETC complexes and DRP-1 Communications biology High 39420071

Source papers

Stage 0 corpus · 30 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
1996 The Caenorhabditis elegans gene unc-89, required fpr muscle M-line assembly, encodes a giant modular protein composed of Ig and signal transduction domains. The Journal of cell biology 157 8603916
2015 OBSCN Mutations Associated with Dilated Cardiomyopathy and Haploinsufficiency. PloS one 72 26406308
2004 Three new isoforms of Caenorhabditis elegans UNC-89 containing MLCK-like protein kinase domains. Journal of molecular biology 67 15313609
2008 A novel protein phosphatase is a binding partner for the protein kinase domains of UNC-89 (Obscurin) in Caenorhabditis elegans. Molecular biology of the cell 44 18337465
2004 Orthologous relationship of obscurin and Unc-89: phylogeny of a novel family of tandem myosin light chain kinases. Development genes and evolution 42 15185077
2012 Large isoforms of UNC-89 (obscurin) are required for muscle cell architecture and optimal calcium release in Caenorhabditis elegans. PloS one 37 22768340
2008 The DH-PH region of the giant protein UNC-89 activates RHO-1 GTPase in Caenorhabditis elegans body wall muscle. Journal of molecular biology 36 18801371
2017 A novel FLNC frameshift and an OBSCN variant in a family with distal muscular dystrophy. PloS one 35 29073160
2012 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. Molecular biology of the cell 32 22621901
2009 A LIM-9 (FHL)/SCPL-1 (SCP) complex interacts with the C-terminal protein kinase regions of UNC-89 (obscurin) in Caenorhabditis elegans muscle. Journal of molecular biology 32 19244614
2017 A comprehensive genomic meta-analysis identifies confirmatory role of OBSCN gene in breast tumorigenesis. Oncotarget 29 29254242
2020 Intracellular calcium current disorder and disease phenotype in OBSCN mutant iPSC-based cardiomyocytes in arrhythmogenic right ventricular cardiomyopathy. Theranostics 26 33042279
2000 Structure of a PH domain from the C. elegans muscle protein UNC-89 suggests a novel function. Structure (London, England : 1993) 24 11080629
2022 Bi-allelic loss-of-function OBSCN variants predispose individuals to severe recurrent rhabdomyolysis. Brain : a journal of neurology 20 34957489
2023 OBSCN restoration via OBSCN-AS1 long-noncoding RNA CRISPR-targeting suppresses metastasis in triple-negative breast cancer. Proceedings of the National Academy of Sciences of the United States of America 19 36877839
2016 The SH3 domain of UNC-89 (obscurin) interacts with paramyosin, a coiled-coil protein, in Caenorhabditis elegans muscle. Molecular biology of the cell 18 27009202
2021 Truncating Variants in OBSCN Gene Associated With Disease-Onset and Outcomes of Hypertrophic Cardiomyopathy. Circulation. Genomic and precision medicine 14 34601892
2020 A Region of UNC-89 (Obscurin) Lying between Two Protein Kinase Domains Is a Highly Elastic Spring Required for Proper Sarcomere Organization. Journal of molecular biology 10 32645312
2023 Novel OBSCN variants associated with a risk to exercise-intolerance and rhabdomyolysis. Neuromuscular disorders : NMD 8 38159459
2012 Contribution of the OBSCN nonsynonymous variants to aspirin exacerbated respiratory disease susceptibility in Korean population. DNA and cell biology 7 22251166
2025 OBSCN undergoes extensive alternative splicing during human cardiac and skeletal muscle development. Skeletal muscle 4 40025502
2025 Loss of OBSCN expression promotes bladder cancer progression but enhances the efficacy of PD-L1 inhibitors. Cell & bioscience 2 40149008
2024 Protein kinase 2 of the giant sarcomeric protein UNC-89 regulates mitochondrial morphology and function. Communications biology 2 39420071
2025 Novel compound heterozygous OBSCN variants in Chinese children with congenital pulmonary airway malformation. Italian journal of pediatrics 1 40156064
2025 Rhabdomyolysis associated with OBSCN mutations: case report and mechanistic review. Neuromuscular disorders : NMD 1 40813169
2026 Novel GJC2 and OBSCN variants co-segregating in a Chinese primary lymphedema pedigree. Orphanet journal of rare diseases 0 41530801
2026 Co-Pathogenic Role of BRCA1 and OBSCN Deletions in Chinese Familial Breast Cancer: A Case Report. The American journal of case reports 0 42068564
2025 Identification of Compound Heterozygous Variants in OBSCN Gene Associated With Rhabdomyolysis: A Case Report. Molecular genetics & genomic medicine 0 40186404
2025 A Novel Germline Frameshift Variant in the Tumor Suppressor Gene OBSCN in a Melanoma Patient. International journal of molecular sciences 0 41226589
2025 Multi-Omics Analysis Reveals OBSCN as a Key Modulator of Tumor Microenvironment, Microbial Signatures and Clinical Outcomes in Gastric Cancer. MicrobiologyOpen 0 41320670

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