Affinage

STAC3

SH3 and cysteine-rich domain-containing protein 3 · UniProt Q96MF2

Length
364 aa
Mass
41.5 kDa
Annotated
2026-06-10
28 papers in source corpus 17 papers cited in narrative 17 extracted findings
Cross-family judge vs UniProt: Affinage preferred faithfulness: 6/6 claims corpus-supported (100%)

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

STAC3 is a skeletal muscle adapter protein that is an essential component of the excitation-contraction (EC) coupling machinery, linking sarcolemmal/T-tubule membrane depolarization to Ca2+ release from the sarcoplasmic reticulum (SR) (PMID:23736855, PMID:23818578). Genetic loss of STAC3 in zebrafish and mice abolishes EC coupling and causes perinatal-lethal paralysis, with the block residing upstream of RyR1, since the RyR agonist 4-chloro-m-cresol and caffeine still trigger SR Ca2+ release (PMID:23818578, PMID:27073615). Mechanistically, STAC3 docks onto the voltage sensor CaV1.1 through two interfaces: a C1-domain interaction with the CaV1.1 proximal C-terminus that is necessary and sufficient for channel functional expression and minimal EC coupling, and tandem SH3 domains that engage the CaV1.1 II-III loop to facilitate—but not absolutely require—coupling (PMID:28112192, PMID:32492370, PMID:40779452). Through these contacts STAC3 promotes CaV1.1 membrane trafficking and stability, determines the slow activation kinetics of CaV1.1 current, and specifically inhibits voltage-dependent (but not Ca2+-dependent) inactivation (PMID:28003463, PMID:29950399, PMID:36161458). The myopathy-causing W284S (W280S) variant preserves the STAC3-CaV1.1 interaction yet impairs conformational coupling to RyR1, placing its pathomechanism downstream of channel binding, and additional disease variants (F295L, K329N) disrupt II-III loop binding and EC coupling (PMID:27621462, PMID:30168660, PMID:32492370). Beyond EC coupling, STAC3 negatively regulates myoblast differentiation (PMID:24788338), is cleaved by calpain 1 in a Ca2+-dependent manner after eccentric contraction (PMID:34590910), and supports Leydig cell steroidogenesis via mitochondrial membrane potential and StAR processing (PMID:33409656).

Mechanistic history

Synthesis pass · year-by-year structured walk · 7 steps
  1. 2013 High

    Established that STAC3 is a previously unrecognized, dedicated component of skeletal muscle EC coupling rather than a generic signaling adapter.

    Evidence Zebrafish genetic screen plus electrophysiology, Ca2+ imaging and Co-IP; independently, a Stac3 knockout mouse with contractility assays and 4-chloro-m-cresol rescue

    PMID:23736855 PMID:23818578

    Open questions at the time
    • Did not define which CaV1.1 domains STAC3 engages
    • Molecular basis of coupling to RyR1 not resolved
  2. 2016 High

    Showed STAC3 acts upstream of RyR1 and is required for conformational coupling, distinguishing its role from simple channel trafficking and dissecting the W280S/W284S mutant defect.

    Evidence Stac3 KO myotube rescue with WT vs W280S, conditional postnatal KO mice with electrostimulation-vs-caffeine Ca2+ release comparison, patch-clamp and Ca2+ imaging

    PMID:27073615 PMID:27621462 PMID:28003463

    Open questions at the time
    • Structural interface with CaV1.1 not yet defined
    • How W280S uncouples binding from coupling unexplained
  3. 2017 Medium

    Localized the stable STAC3-CaV1.1 interaction to a binding pocket in the C1 domain and showed STAC3 triad incorporation can occur independently of CaV1.1.

    Evidence FRAP in skeletal muscle triads with C1-domain mutagenesis and Co-IP; immunofluorescence in dysgenic (CaV1.1-null) myotubes; live imaging of DHPR transport in zebrafish nulls

    PMID:28112192 PMID:28697281 PMID:30071129

    Open questions at the time
    • Identity of the additional triad partner mediating CaV1.1-independent incorporation unknown
    • Single-lab FRAP findings
  4. 2018 Medium

    Demonstrated STAC3 enhances CaV1.1 trafficking and gating via the channel C-terminus and that myopathic mutations weaken this interaction, while patient-tissue work placed the W284S defect downstream of binding.

    Evidence Heterologous expression, patch-clamp, binding assays and mutagenesis; Xenopus oocyte cut-open voltage-clamp; Co-IP and Ca2+ imaging from patient muscle

    PMID:29386226 PMID:29950399 PMID:30168660

    Open questions at the time
    • Relationship between calmodulin and STAC3 C-terminal binding not fully resolved
    • Patient-tissue data limited to W284S
  5. 2020 High

    Provided the structural basis for STAC3 engagement of the CaV1.1 II-III loop via tandem SH3 domains and mapped multiple disease variants to this interface.

    Evidence X-ray crystallography of human STAC3 tandem SH3 domains, in vitro binding assays and EC coupling functional assays with F295L, K329N, W284S variants

    PMID:32492370

    Open questions at the time
    • Structure of the C1-CaV1.1 C-terminus interaction not determined
    • Full-length STAC3-channel complex architecture unresolved
  6. 2022 High

    Defined STAC3 as a determinant of CaV1.1 gating kinetics, specifically slowing activation and inhibiting voltage-dependent inactivation independently of Ca2+-dependent inactivation.

    Evidence Patch-clamp in CaV1.1/STAC3 double KO myotubes and HEK cells with STAC3-ETLAAA linker mutagenesis and Ba2+/Ca2+ recordings

    PMID:36161458

    Open questions at the time
    • Structural mechanism by which the linker region controls VDI unknown
    • Single-lab finding
  7. 2025 High

    Resolved the relative contributions of the two STAC3-CaV1.1 interfaces, establishing the C1-proximal C-terminus interaction as necessary and sufficient for minimal EC coupling and the II-III loop interaction as facilitating.

    Evidence Domain-specific rescue in CaV1.1/STAC3 double KO myotubes, patch-clamp, Ca2+ imaging, and patient mutation analysis deleting the II-III loop interaction domain

    PMID:40779452

    Open questions at the time
    • How the C1 interaction mechanistically transmits conformational coupling to RyR1 remains undefined

Open questions

Synthesis pass · forward-looking unresolved questions
  • The molecular basis by which STAC3 bridges CaV1.1 voltage sensing to RyR1 gating, and how its non-muscle role in Leydig cell steroidogenesis is mechanistically connected, remain open.
  • No structural model of a STAC3-CaV1.1-RyR1 coupling complex
  • Mitochondrial/StAR pathway link in steroidogenesis mechanistically unexplained
  • Physiological role of calpain cleavage of STAC3 not fully established

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0060090 molecular adaptor activity 5 GO:0098772 molecular function regulator activity 3 GO:0008092 cytoskeletal protein binding 2
Localization
GO:0005886 plasma membrane 2 GO:0005739 mitochondrion 1
Pathway
R-HSA-162582 Signal Transduction 3 R-HSA-397014 Muscle contraction 3
Partners
CACNA1SCALM1CAPN1RYR1
Complex memberships
skeletal muscle triad (CaV1.1/DHPR-RyR1 junction)

Evidence

Reading pass · 17 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2013 Stac3 is a novel component of the excitation-contraction (EC) coupling machinery in skeletal muscle; zebrafish stac3 mutants show defective EC coupling, and electrophysiological, Ca2+ imaging, immunocytochemical, and biochemical evidence demonstrates its participation in coupling membrane depolarization to SR Ca2+ release. Zebrafish genetic screen, electrophysiology, Ca2+ imaging, immunocytochemistry, biochemistry (Co-IP) Nature communications High 23736855
2013 STAC3 localizes to T-tubules and is essential for coupling membrane depolarization to Ca2+ release from the sarcoplasmic reticulum; Stac3 knockout mice are completely paralyzed and die perinatally. Application of the RyR agonist 4-chloro-m-cresol restored contractility, demonstrating the block is upstream of RyR1 and SR Ca2+ stores. Stac3 knockout mouse, muscle contractility assays, 4-chloro-m-cresol rescue, Ca2+ imaging in cultured myotubes, immunofluorescence localization Proceedings of the National Academy of Sciences of the United States of America High 23818578
2016 Stac3 is directly involved in conformational coupling between CaV1.1 and RyR1: it facilitates but is not absolutely required for membrane trafficking of CaV1.1, and the NAM mutation W280S partially restores Ca2+ currents but only marginally restores EC coupling Ca2+ release. Stac3 KO myotubes, rescue with WT or W280S Stac3, patch-clamp electrophysiology, Ca2+ imaging in tsA201 cells and myotubes Proceedings of the National Academy of Sciences of the United States of America High 27621462
2016 Stac3 regulates DHPR (CaV1.1) levels and functionality: stac3 mutant zebrafish myofibers show significantly reduced DHPR levels, functionality, and stability; NAM stac3 myofibers exhibit increased caffeine-induced Ca2+ release and increased SR luminal Ca2+, indicating altered RyR1 regulation. Electron microscopy, electrophysiology, dynamic Ca2+ imaging in zebrafish muscle fibers Proceedings of the National Academy of Sciences of the United States of America High 28003463
2017 STAC3 forms a stable interaction with CaV1.1 (the voltage sensor of EC coupling) through a protein-protein binding pocket in its C1 domain; mutation of two key residues in the C1 domain increases STAC3 turnover in triads. The NAM mutation (W284S) does not affect the stability of this STAC3-CaV1.1 interaction. FRAP (fluorescence recovery after photobleaching) in skeletal muscle triads, mutagenesis of C1 domain, Co-IP Scientific reports High 28112192
2018 Calmodulin and STAC3 independently enhance CaV1.1 channel trafficking and gating via interaction with the CaV1.1 carboxy terminus; myopathic STAC3 mutations weaken CaV1.1 C-terminal binding and diminish trafficking. Heterologous expression, electrophysiology (patch-clamp), biochemical binding assays, mutagenesis The Journal of general physiology Medium 29950399
2018 Co-expression of Stac3 dramatically increases plasma membrane expression of human CaV1.1 (with α2-δ1b and β1a subunits) in Xenopus oocytes, enabling functional analysis; Stac3 supports gating charge displacements sufficient to measure gating pore currents in HypoPP mutant channels. Xenopus oocyte expression, cut-open oocyte voltage-clamp electrophysiology The Journal of general physiology Medium 29386226
2018 The STAC3 p.W284S variant does not impair co-immunoprecipitation of STAC3 with CaV1.1 in patient and control muscle samples, and does not cause CaV1.1 sarcolemma mislocalization; instead, KCl-induced membrane depolarization leads to significantly reduced SR Ca2+ release, indicating the pathomechanism is downstream of the STAC3-CaV1.1 interaction. Co-immunoprecipitation from patient muscle, immunofluorescence, Ca2+ imaging after KCl depolarization Human mutation Medium 30168660
2018 STAC3 incorporation into skeletal muscle triads occurs independently of the DHPR (CaV1.1): endogenous STAC3 incorporates into triads in the absence of DHPR in dysgenic mouse myotubes and muscle fibers, demonstrating STAC3 interacts with additional triad proteins. Immunofluorescence localization in dysgenic (CaV1.1-null) mouse myotubes and muscle fibers Journal of cellular physiology Medium 30071129
2020 Crystal structure of the human STAC3 tandem SH3 domains was resolved; STAC3 interacts with the CaV1.1 II-III loop through its tandem SH3 domains. Disease variants F295L and K329N (in addition to W284S) affect both CaV1.1 II-III loop binding and muscle EC coupling, highlighting the importance of both SH3 domains in CaV1.1 association. X-ray crystallography, in vitro binding assays, EC coupling functional assays in myotubes, mutagenesis Structure (London, England : 1993) High 32492370
2017 DHPR (CaV1.1) alpha subunit is transported along the longitudinal SR in a microtubule-independent mechanism prior to triad assembly; in Stac3-null zebrafish, DHPR transport in the SR membrane is altered, distinguishing the role of Stac3 from that of DHPRβ in DHPR trafficking. Dynamic live imaging of fluorescently tagged DHPR in zebrafish muscle fibers, stac3 and DHPRβ null mutants Traffic (Copenhagen, Denmark) Medium 28697281
2022 STAC3 determines the slow activation kinetics of CaV1.1 currents and specifically inhibits voltage-dependent inactivation (VDI) but not calcium-dependent inactivation (CDI) of CaV1.1. A linker-region triple mutation in STAC3 (ETLAAA) accelerated CaV1.1 current kinetics but did not increase CDI. Patch-clamp electrophysiology in CaV1.1/STAC3 double KO myotubes and HEK cells, STAC3-ETLAAA mutagenesis, combined Ca2+ recording Journal of cellular physiology High 36161458
2021 STAC3 undergoes Ca2+-dependent proteolysis by calpain 1 in skeletal muscle after damaging eccentric contractions; loss of full-length STAC3 is associated with force depression, and calpain inhibitor MDL-28170 prevents this proteolysis. In vitro Ca2+ exposure of muscle samples, calpain inhibitor MDL-28170, western blotting for full-length STAC3, in vivo eccentric contraction model in rat Journal of applied physiology Medium 34590910
2021 STAC3 is expressed in testicular Leydig cells and regulates steroidogenesis: STAC3 depletion attenuates mitochondrial membrane potential and StAR processing in db-cAMP-stimulated Leydig cells, reducing testosterone production and impairing male fertility. Lentiviral in vivo knockdown in rat testis, TM3 Stac3-/- cell line, mitochondrial membrane potential assay, StAR processing western blot, testosterone ELISA Cell and tissue research Medium 33409656
2025 STAC3 binding to the CaV1.1 II-III loop is not essential for EC coupling but plays a facilitating role; the interaction between STAC3 and the CaV1.1 proximal C-terminus is necessary and sufficient for CaV1.1 functional expression and minimal EC coupling. Rescue experiments in CaV1.1/STAC3 double KO myotubes, patch-clamp electrophysiology, Ca2+ imaging, patient mutation analysis deleting the II-III loop interaction domain JCI insight High 40779452
2014 Stac3 overexpression inhibits myoblast differentiation into myotubes and Stac3 knockdown promotes differentiation; Stac3 KO mouse myoblasts show accelerated differentiation into myotubes in culture, establishing an inhibitory role for endogenous Stac3 in myogenic differentiation. siRNA knockdown and plasmid overexpression in C2C12 myoblasts, Stac3 KO mouse myoblast cultures, fusion index, myogenic marker expression (myogenin, MHC) PloS one Medium 24788338
2016 Conditional postnatal Stac3 deletion in mice reduces electrostimulation-induced but not caffeine-induced Ca2+ release from the SR and maximal force output, confirming STAC3 acts upstream of RyR1 in EC coupling in postnatal muscle. Conditional KO mice (tamoxifen-inducible Cre-loxP), muscle contractile tests, Ca2+ imaging of single FDB myofibers, electrostimulation vs. caffeine comparison Skeletal muscle High 27073615

Source papers

Stage 0 corpus · 28 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2013 Stac3 is a component of the excitation-contraction coupling machinery and mutated in Native American myopathy. Nature communications 200 23736855
2013 Skeletal muscle-specific T-tubule protein STAC3 mediates voltage-induced Ca2+ release and contractility. Proceedings of the National Academy of Sciences of the United States of America 121 23818578
2016 Stac3 has a direct role in skeletal muscle-type excitation-contraction coupling that is disrupted by a myopathy-causing mutation. Proceedings of the National Academy of Sciences of the United States of America 69 27621462
2018 STAC3 variants cause a congenital myopathy with distinctive dysmorphic features and malignant hyperthermia susceptibility. Human mutation 46 30168660
2016 Congenital myopathy results from misregulation of a muscle Ca2+ channel by mutant Stac3. Proceedings of the National Academy of Sciences of the United States of America 39 28003463
2012 Stac3 is required for myotube formation and myogenic differentiation in vertebrate skeletal muscle. The Journal of biological chemistry 39 23076145
2017 STAC3 stably interacts through its C1 domain with CaV1.1 in skeletal muscle triads. Scientific reports 34 28112192
2013 Stac3 is a novel regulator of skeletal muscle development in mice. PloS one 31 23626854
2018 Stac3 enhances expression of human CaV1.1 in Xenopus oocytes and reveals gating pore currents in HypoPP mutant channels. The Journal of general physiology 30 29386226
2017 Novel STAC3 Mutations in the First Non-Amerindian Patient with Native American Myopathy. Neuropediatrics 30 28411587
2014 Stac3 inhibits myoblast differentiation into myotubes. PloS one 29 24788338
2020 Multiple Sequence Variants in STAC3 Affect Interactions with CaV1.1 and Excitation-Contraction Coupling. Structure (London, England : 1993) 26 32492370
2018 Duplex signaling by CaM and Stac3 enhances CaV1.1 function and provides insights into congenital myopathy. The Journal of general physiology 18 29950399
2016 The SH3 and cysteine-rich domain 3 (Stac3) gene is important to growth, fiber composition, and calcium release from the sarcoplasmic reticulum in postnatal skeletal muscle. Skeletal muscle 17 27073615
2018 STAC3 incorporation into skeletal muscle triads occurs independent of the dihydropyridine receptor. Journal of cellular physiology 13 30071129
2014 Identification of the STAC3 gene as a skeletal muscle-specifically expressed gene and a novel regulator of satellite cell differentiation in cattle. Journal of animal science 12 24948655
2022 STAC3 related congenital myopathy: A case series of seven Comorian patients. European journal of medical genetics 10 36030003
2022 STAC3 determines the slow activation kinetics of CaV 1.1 currents and inhibits its voltage-dependent inactivation. Journal of cellular physiology 10 36161458
2021 Preconditioning contractions prevent prolonged force depression and Ca2+-dependent proteolysis of STAC3 after damaging eccentric contractions. Journal of applied physiology (Bethesda, Md. : 1985) 10 34590910
2017 Transport of the alpha subunit of the voltage gated L-type calcium channel through the sarcoplasmic reticulum occurs prior to localization to triads and requires the beta subunit but not Stac3 in skeletal muscles. Traffic (Copenhagen, Denmark) 10 28697281
2021 Testicular STAC3 regulates Leydig cell steroidogenesis through potentiating mitochondrial membrane potential and StAR processing. Cell and tissue research 8 33409656
2024 STAC3 disorder: a common cause of congenital hypotonia in Southern African patients. European journal of human genetics : EJHG 5 38824262
2016 Defective excitation-contraction coupling is partially responsible for impaired contractility in hindlimb muscles of Stac3 knockout mice. Scientific reports 5 27184118
2025 STAC3 gene congenital myopathy and malignant hyperthermia: a crossroads between neurology and anesthesia. Arquivos de neuro-psiquiatria 2 40262809
2025 STAC3 binding to CaV1.1 II-III loop is nonessential but critically supports skeletal muscle excitation-contraction coupling. JCI insight 2 40779452
2018 Improving the characterization of calcium channel gating pore currents with Stac3. The Journal of general physiology 2 29467165
2020 Molecular characterization, tissue distribution, and functional analysis of the STAC3 gene in chicken. 3 Biotech 1 32206505
2024 Early life lipid overload in Native American Myopathy is phenocopied by stac3 knockout in zebrafish. Gene 0 39592070

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