{"gene":"STAC3","run_date":"2026-06-10T07:46:42","timeline":{"discoveries":[{"year":2013,"finding":"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.","method":"Zebrafish genetic screen, electrophysiology, Ca2+ imaging, immunocytochemistry, biochemistry (Co-IP)","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (electrophysiology, Ca2+ imaging, biochemistry) in zebrafish and replicated by independent lab same year (PMID:23818578)","pmids":["23736855"],"is_preprint":false},{"year":2013,"finding":"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.","method":"Stac3 knockout mouse, muscle contractility assays, 4-chloro-m-cresol rescue, Ca2+ imaging in cultured myotubes, immunofluorescence localization","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 / Strong — KO mouse with defined cellular phenotype, pharmacological rescue, Ca2+ imaging, replicated across labs","pmids":["23818578"],"is_preprint":false},{"year":2016,"finding":"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.","method":"Stac3 KO myotubes, rescue with WT or W280S Stac3, patch-clamp electrophysiology, Ca2+ imaging in tsA201 cells and myotubes","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — in vitro reconstitution in KO myotubes with mutagenesis, multiple orthogonal electrophysiology and Ca2+ imaging methods","pmids":["27621462"],"is_preprint":false},{"year":2016,"finding":"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.","method":"Electron microscopy, electrophysiology, dynamic Ca2+ imaging in zebrafish muscle fibers","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — multiple orthogonal methods (EM, electrophysiology, Ca2+ imaging) in zebrafish model","pmids":["28003463"],"is_preprint":false},{"year":2017,"finding":"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.","method":"FRAP (fluorescence recovery after photobleaching) in skeletal muscle triads, mutagenesis of C1 domain, Co-IP","journal":"Scientific reports","confidence":"High","confidence_rationale":"Tier 2 / Moderate — FRAP with functional mutagenesis and Co-IP; single lab but multiple orthogonal approaches","pmids":["28112192"],"is_preprint":false},{"year":2018,"finding":"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.","method":"Heterologous expression, electrophysiology (patch-clamp), biochemical binding assays, mutagenesis","journal":"The Journal of general physiology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — patch-clamp + binding assays with disease mutations, single lab","pmids":["29950399"],"is_preprint":false},{"year":2018,"finding":"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.","method":"Xenopus oocyte expression, cut-open oocyte voltage-clamp electrophysiology","journal":"The Journal of general physiology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — voltage-clamp electrophysiology with functional readout in Xenopus system, single lab","pmids":["29386226"],"is_preprint":false},{"year":2018,"finding":"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.","method":"Co-immunoprecipitation from patient muscle, immunofluorescence, Ca2+ imaging after KCl depolarization","journal":"Human mutation","confidence":"Medium","confidence_rationale":"Tier 2–3 / Moderate — Co-IP from patient tissue, Ca2+ imaging; multiple methods but limited to patient samples","pmids":["30168660"],"is_preprint":false},{"year":2018,"finding":"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.","method":"Immunofluorescence localization in dysgenic (CaV1.1-null) mouse myotubes and muscle fibers","journal":"Journal of cellular physiology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct localization experiment using genetic null model with functional consequence for complex assembly, single lab","pmids":["30071129"],"is_preprint":false},{"year":2020,"finding":"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.","method":"X-ray crystallography, in vitro binding assays, EC coupling functional assays in myotubes, mutagenesis","journal":"Structure (London, England : 1993)","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structure plus in vitro binding assays plus functional EC coupling assays with multiple disease variants","pmids":["32492370"],"is_preprint":false},{"year":2017,"finding":"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.","method":"Dynamic live imaging of fluorescently tagged DHPR in zebrafish muscle fibers, stac3 and DHPRβ null mutants","journal":"Traffic (Copenhagen, Denmark)","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — live imaging with genetic nulls, single lab, direct localization with functional consequence","pmids":["28697281"],"is_preprint":false},{"year":2022,"finding":"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.","method":"Patch-clamp electrophysiology in CaV1.1/STAC3 double KO myotubes and HEK cells, STAC3-ETLAAA mutagenesis, combined Ca2+ recording","journal":"Journal of cellular physiology","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro mutagenesis with patch-clamp electrophysiology in KO rescue system, multiple ion carriers (Ca2+/Ba2+), single lab","pmids":["36161458"],"is_preprint":false},{"year":2021,"finding":"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.","method":"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":"Journal of applied physiology","confidence":"Medium","confidence_rationale":"Tier 2–3 / Moderate — pharmacological inhibitor experiment plus in vitro Ca2+ titration, single lab, mechanistically links calpain 1 as the protease","pmids":["34590910"],"is_preprint":false},{"year":2021,"finding":"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.","method":"Lentiviral in vivo knockdown in rat testis, TM3 Stac3-/- cell line, mitochondrial membrane potential assay, StAR processing western blot, testosterone ELISA","journal":"Cell and tissue research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — KO cell line plus in vivo knockdown with defined molecular readouts (StAR processing, mitochondrial potential), single lab","pmids":["33409656"],"is_preprint":false},{"year":2025,"finding":"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.","method":"Rescue experiments in CaV1.1/STAC3 double KO myotubes, patch-clamp electrophysiology, Ca2+ imaging, patient mutation analysis deleting the II-III loop interaction domain","journal":"JCI insight","confidence":"High","confidence_rationale":"Tier 1–2 / Moderate — KO rescue with domain-specific mutations, electrophysiology, Ca2+ imaging, validated by patient mutation; single lab","pmids":["40779452"],"is_preprint":false},{"year":2014,"finding":"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.","method":"siRNA knockdown and plasmid overexpression in C2C12 myoblasts, Stac3 KO mouse myoblast cultures, fusion index, myogenic marker expression (myogenin, MHC)","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — KO primary culture and OE/KD in C2C12 with multiple readouts, single lab","pmids":["24788338"],"is_preprint":false},{"year":2016,"finding":"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.","method":"Conditional KO mice (tamoxifen-inducible Cre-loxP), muscle contractile tests, Ca2+ imaging of single FDB myofibers, electrostimulation vs. caffeine comparison","journal":"Skeletal muscle","confidence":"High","confidence_rationale":"Tier 2 / Moderate — conditional KO with defined pharmacological dissection of EC coupling steps, multiple readouts, single lab","pmids":["27073615"],"is_preprint":false}],"current_model":"STAC3 is a skeletal muscle-specific adapter protein (containing C1 and tandem SH3 domains) that is an essential component of the excitation-contraction (EC) coupling machinery: it stably interacts with CaV1.1 via its C1 domain (proximal C-terminus interaction) and through its tandem SH3 domains with the CaV1.1 II-III loop, facilitating CaV1.1 membrane trafficking, determining the slow activation kinetics of CaV1.1 currents, specifically inhibiting voltage-dependent inactivation, and enabling conformational coupling between CaV1.1 and RyR1 for SR Ca2+ release; loss of STAC3 function (including the NAM-causing W284S mutation) impairs EC coupling and Ca2+ release, while STAC3 also negatively regulates myoblast differentiation and, unexpectedly, regulates Leydig cell steroidogenesis via mitochondrial membrane potential and StAR processing."},"narrative":{"mechanistic_narrative":"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].","teleology":[{"year":2013,"claim":"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","pmids":["23736855","23818578"],"confidence":"High","gaps":["Did not define which CaV1.1 domains STAC3 engages","Molecular basis of coupling to RyR1 not resolved"]},{"year":2016,"claim":"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","pmids":["27621462","28003463","27073615"],"confidence":"High","gaps":["Structural interface with CaV1.1 not yet defined","How W280S uncouples binding from coupling unexplained"]},{"year":2017,"claim":"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","pmids":["28112192","30071129","28697281"],"confidence":"Medium","gaps":["Identity of the additional triad partner mediating CaV1.1-independent incorporation unknown","Single-lab FRAP findings"]},{"year":2018,"claim":"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","pmids":["29950399","29386226","30168660"],"confidence":"Medium","gaps":["Relationship between calmodulin and STAC3 C-terminal binding not fully resolved","Patient-tissue data limited to W284S"]},{"year":2020,"claim":"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","pmids":["32492370"],"confidence":"High","gaps":["Structure of the C1-CaV1.1 C-terminus interaction not determined","Full-length STAC3-channel complex architecture unresolved"]},{"year":2022,"claim":"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","pmids":["36161458"],"confidence":"High","gaps":["Structural mechanism by which the linker region controls VDI unknown","Single-lab finding"]},{"year":2025,"claim":"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","pmids":["40779452"],"confidence":"High","gaps":["How the C1 interaction mechanistically transmits conformational coupling to RyR1 remains undefined"]},{"year":null,"claim":"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.","evidence":"","pmids":[],"confidence":"Medium","gaps":["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":{"molecular_activity":[{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[0,2,4,9,14]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[5,11,3]},{"term_id":"GO:0008092","term_label":"cytoskeletal protein binding","supporting_discovery_ids":[4,9]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[1,8]},{"term_id":"GO:0005739","term_label":"mitochondrion","supporting_discovery_ids":[13]}],"pathway":[{"term_id":"R-HSA-397014","term_label":"Muscle contraction","supporting_discovery_ids":[0,1,16]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[2,11,14]}],"complexes":["skeletal muscle triad (CaV1.1/DHPR-RyR1 junction)"],"partners":["CACNA1S","RYR1","CALM1","CAPN1"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q96MF2","full_name":"SH3 and cysteine-rich domain-containing protein 3","aliases":[],"length_aa":364,"mass_kda":41.5,"function":"Required for normal excitation-contraction coupling in skeletal muscle and for normal muscle contraction in response to membrane depolarization. Required for normal Ca(2+) release from the sarcplasmic reticulum, which ultimately leads to muscle contraction. Probably functions via its effects on muscle calcium channels (PubMed:23736855, PubMed:29078335). Increases CACNA1S channel activity, in addition to its role in enhancing the expression of CACNA1S at the cell membrane. Has a redundant role in promoting the expression of the calcium channel CACNA1S at the cell membrane (By similarity). Slows down the inactivation rate of the calcium channel CACNA1C (PubMed:29078335)","subcellular_location":"Cytoplasm; Cell membrane, sarcolemma; Cell membrane, sarcolemma, T-tubule","url":"https://www.uniprot.org/uniprotkb/Q96MF2/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/STAC3","classification":"Not Classified","n_dependent_lines":32,"n_total_lines":1208,"dependency_fraction":0.026490066225165563},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/STAC3","total_profiled":1310},"omim":[{"mim_id":"621356","title":"SH3 AND CYSTEINE-RICH DOMAINS 2; STAC2","url":"https://www.omim.org/entry/621356"},{"mim_id":"615521","title":"SH3 AND CYSTEINE-RICH DOMAINS 3; STAC3","url":"https://www.omim.org/entry/615521"},{"mim_id":"602317","title":"SH3 AND CYSTEINE-RICH DOMAINS 1; STAC1","url":"https://www.omim.org/entry/602317"},{"mim_id":"255995","title":"CONGENITAL MYOPATHY 13; CMYO13","url":"https://www.omim.org/entry/255995"},{"mim_id":"117000","title":"CONGENITAL MYOPATHY 1A, AUTOSOMAL DOMINANT, WITH SUSCEPTIBILITY TO MALIGNANT HYPERTHERMIA; CMYO1A","url":"https://www.omim.org/entry/117000"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Enhanced","locations":[{"location":"Nucleoplasm","reliability":"Enhanced"},{"location":"Cytosol","reliability":"Additional"}],"tissue_specificity":"Group enriched","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"skeletal muscle","ntpm":2168.8},{"tissue":"tongue","ntpm":1091.4}],"url":"https://www.proteinatlas.org/search/STAC3"},"hgnc":{"alias_symbol":["MGC2793"],"prev_symbol":[]},"alphafold":{"accession":"Q96MF2","domains":[{"cath_id":"3.30.60.20","chopping":"86-144","consensus_level":"medium","plddt":83.4898,"start":86,"end":144},{"cath_id":"2.30.30.40","chopping":"249-304","consensus_level":"high","plddt":91.8207,"start":249,"end":304},{"cath_id":"2.30.30.40","chopping":"308-362","consensus_level":"high","plddt":94.5387,"start":308,"end":362}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q96MF2","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q96MF2-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q96MF2-F1-predicted_aligned_error_v6.png","plddt_mean":69.25},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=STAC3","jax_strain_url":"https://www.jax.org/strain/search?query=STAC3"},"sequence":{"accession":"Q96MF2","fasta_url":"https://rest.uniprot.org/uniprotkb/Q96MF2.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q96MF2/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q96MF2"}},"corpus_meta":[{"pmid":"23736855","id":"PMC_23736855","title":"Stac3 is a component of the excitation-contraction coupling machinery and mutated in Native American myopathy.","date":"2013","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/23736855","citation_count":200,"is_preprint":false},{"pmid":"23818578","id":"PMC_23818578","title":"Skeletal muscle-specific T-tubule protein STAC3 mediates voltage-induced Ca2+ release and contractility.","date":"2013","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/23818578","citation_count":121,"is_preprint":false},{"pmid":"27621462","id":"PMC_27621462","title":"Stac3 has a direct role in skeletal muscle-type excitation-contraction coupling that is disrupted by a myopathy-causing mutation.","date":"2016","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/27621462","citation_count":69,"is_preprint":false},{"pmid":"30168660","id":"PMC_30168660","title":"STAC3 variants cause a congenital myopathy with distinctive dysmorphic features and malignant hyperthermia susceptibility.","date":"2018","source":"Human mutation","url":"https://pubmed.ncbi.nlm.nih.gov/30168660","citation_count":46,"is_preprint":false},{"pmid":"23076145","id":"PMC_23076145","title":"Stac3 is required for myotube formation and myogenic differentiation in vertebrate skeletal muscle.","date":"2012","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/23076145","citation_count":39,"is_preprint":false},{"pmid":"28003463","id":"PMC_28003463","title":"Congenital myopathy results from misregulation of a muscle Ca2+ channel by mutant Stac3.","date":"2016","source":"Proceedings of the National Academy of Sciences of the United States of 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the First Non-Amerindian Patient with Native American Myopathy.","date":"2017","source":"Neuropediatrics","url":"https://pubmed.ncbi.nlm.nih.gov/28411587","citation_count":30,"is_preprint":false},{"pmid":"24788338","id":"PMC_24788338","title":"Stac3 inhibits myoblast differentiation into myotubes.","date":"2014","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/24788338","citation_count":29,"is_preprint":false},{"pmid":"32492370","id":"PMC_32492370","title":"Multiple Sequence Variants in STAC3 Affect Interactions with CaV1.1 and Excitation-Contraction Coupling.","date":"2020","source":"Structure (London, England : 1993)","url":"https://pubmed.ncbi.nlm.nih.gov/32492370","citation_count":26,"is_preprint":false},{"pmid":"29950399","id":"PMC_29950399","title":"Duplex signaling by CaM and Stac3 enhances CaV1.1 function and provides insights into congenital myopathy.","date":"2018","source":"The Journal of general 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1985)","url":"https://pubmed.ncbi.nlm.nih.gov/34590910","citation_count":10,"is_preprint":false},{"pmid":"28697281","id":"PMC_28697281","title":"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.","date":"2017","source":"Traffic (Copenhagen, Denmark)","url":"https://pubmed.ncbi.nlm.nih.gov/28697281","citation_count":10,"is_preprint":false},{"pmid":"33409656","id":"PMC_33409656","title":"Testicular STAC3 regulates Leydig cell steroidogenesis through potentiating mitochondrial membrane potential and StAR processing.","date":"2021","source":"Cell and tissue research","url":"https://pubmed.ncbi.nlm.nih.gov/33409656","citation_count":8,"is_preprint":false},{"pmid":"38824262","id":"PMC_38824262","title":"STAC3 disorder: a common cause of congenital hypotonia in Southern African patients.","date":"2024","source":"European journal of human genetics : EJHG","url":"https://pubmed.ncbi.nlm.nih.gov/38824262","citation_count":5,"is_preprint":false},{"pmid":"27184118","id":"PMC_27184118","title":"Defective excitation-contraction coupling is partially responsible for impaired contractility in hindlimb muscles of Stac3 knockout mice.","date":"2016","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/27184118","citation_count":5,"is_preprint":false},{"pmid":"40779452","id":"PMC_40779452","title":"STAC3 binding to CaV1.1 II-III loop is nonessential but critically supports skeletal muscle excitation-contraction coupling.","date":"2025","source":"JCI insight","url":"https://pubmed.ncbi.nlm.nih.gov/40779452","citation_count":2,"is_preprint":false},{"pmid":"40262809","id":"PMC_40262809","title":"STAC3 gene congenital myopathy and malignant hyperthermia: a crossroads between neurology and anesthesia.","date":"2025","source":"Arquivos de neuro-psiquiatria","url":"https://pubmed.ncbi.nlm.nih.gov/40262809","citation_count":2,"is_preprint":false},{"pmid":"29467165","id":"PMC_29467165","title":"Improving the characterization of calcium channel gating pore currents with Stac3.","date":"2018","source":"The Journal of general physiology","url":"https://pubmed.ncbi.nlm.nih.gov/29467165","citation_count":2,"is_preprint":false},{"pmid":"32206505","id":"PMC_32206505","title":"Molecular characterization, tissue distribution, and functional analysis of the STAC3 gene in chicken.","date":"2020","source":"3 Biotech","url":"https://pubmed.ncbi.nlm.nih.gov/32206505","citation_count":1,"is_preprint":false},{"pmid":"39592070","id":"PMC_39592070","title":"Early life lipid overload in Native American Myopathy is phenocopied by stac3 knockout in zebrafish.","date":"2024","source":"Gene","url":"https://pubmed.ncbi.nlm.nih.gov/39592070","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":15231,"output_tokens":4215,"usd":0.054459,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":12123,"output_tokens":3073,"usd":0.06872,"stage2_stop_reason":"end_turn"},"total_usd":0.123179,"stage1_batch_id":"msgbatch_013LWZZT6MWaqB9qyTSeQBmU","stage2_batch_id":"msgbatch_0194ZzQaTGNpruoNJBbEMbt3","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2013,\n      \"finding\": \"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.\",\n      \"method\": \"Zebrafish genetic screen, electrophysiology, Ca2+ imaging, immunocytochemistry, biochemistry (Co-IP)\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (electrophysiology, Ca2+ imaging, biochemistry) in zebrafish and replicated by independent lab same year (PMID:23818578)\",\n      \"pmids\": [\"23736855\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"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.\",\n      \"method\": \"Stac3 knockout mouse, muscle contractility assays, 4-chloro-m-cresol rescue, Ca2+ imaging in cultured myotubes, immunofluorescence localization\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — KO mouse with defined cellular phenotype, pharmacological rescue, Ca2+ imaging, replicated across labs\",\n      \"pmids\": [\"23818578\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"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.\",\n      \"method\": \"Stac3 KO myotubes, rescue with WT or W280S Stac3, patch-clamp electrophysiology, Ca2+ imaging in tsA201 cells and myotubes\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — in vitro reconstitution in KO myotubes with mutagenesis, multiple orthogonal electrophysiology and Ca2+ imaging methods\",\n      \"pmids\": [\"27621462\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"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.\",\n      \"method\": \"Electron microscopy, electrophysiology, dynamic Ca2+ imaging in zebrafish muscle fibers\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — multiple orthogonal methods (EM, electrophysiology, Ca2+ imaging) in zebrafish model\",\n      \"pmids\": [\"28003463\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"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.\",\n      \"method\": \"FRAP (fluorescence recovery after photobleaching) in skeletal muscle triads, mutagenesis of C1 domain, Co-IP\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — FRAP with functional mutagenesis and Co-IP; single lab but multiple orthogonal approaches\",\n      \"pmids\": [\"28112192\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"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.\",\n      \"method\": \"Heterologous expression, electrophysiology (patch-clamp), biochemical binding assays, mutagenesis\",\n      \"journal\": \"The Journal of general physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — patch-clamp + binding assays with disease mutations, single lab\",\n      \"pmids\": [\"29950399\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"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.\",\n      \"method\": \"Xenopus oocyte expression, cut-open oocyte voltage-clamp electrophysiology\",\n      \"journal\": \"The Journal of general physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — voltage-clamp electrophysiology with functional readout in Xenopus system, single lab\",\n      \"pmids\": [\"29386226\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"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.\",\n      \"method\": \"Co-immunoprecipitation from patient muscle, immunofluorescence, Ca2+ imaging after KCl depolarization\",\n      \"journal\": \"Human mutation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Moderate — Co-IP from patient tissue, Ca2+ imaging; multiple methods but limited to patient samples\",\n      \"pmids\": [\"30168660\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"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.\",\n      \"method\": \"Immunofluorescence localization in dysgenic (CaV1.1-null) mouse myotubes and muscle fibers\",\n      \"journal\": \"Journal of cellular physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct localization experiment using genetic null model with functional consequence for complex assembly, single lab\",\n      \"pmids\": [\"30071129\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"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.\",\n      \"method\": \"X-ray crystallography, in vitro binding assays, EC coupling functional assays in myotubes, mutagenesis\",\n      \"journal\": \"Structure (London, England : 1993)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structure plus in vitro binding assays plus functional EC coupling assays with multiple disease variants\",\n      \"pmids\": [\"32492370\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"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.\",\n      \"method\": \"Dynamic live imaging of fluorescently tagged DHPR in zebrafish muscle fibers, stac3 and DHPRβ null mutants\",\n      \"journal\": \"Traffic (Copenhagen, Denmark)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — live imaging with genetic nulls, single lab, direct localization with functional consequence\",\n      \"pmids\": [\"28697281\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"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.\",\n      \"method\": \"Patch-clamp electrophysiology in CaV1.1/STAC3 double KO myotubes and HEK cells, STAC3-ETLAAA mutagenesis, combined Ca2+ recording\",\n      \"journal\": \"Journal of cellular physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro mutagenesis with patch-clamp electrophysiology in KO rescue system, multiple ion carriers (Ca2+/Ba2+), single lab\",\n      \"pmids\": [\"36161458\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"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.\",\n      \"method\": \"In vitro Ca2+ exposure of muscle samples, calpain inhibitor MDL-28170, western blotting for full-length STAC3, in vivo eccentric contraction model in rat\",\n      \"journal\": \"Journal of applied physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Moderate — pharmacological inhibitor experiment plus in vitro Ca2+ titration, single lab, mechanistically links calpain 1 as the protease\",\n      \"pmids\": [\"34590910\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"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.\",\n      \"method\": \"Lentiviral in vivo knockdown in rat testis, TM3 Stac3-/- cell line, mitochondrial membrane potential assay, StAR processing western blot, testosterone ELISA\",\n      \"journal\": \"Cell and tissue research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — KO cell line plus in vivo knockdown with defined molecular readouts (StAR processing, mitochondrial potential), single lab\",\n      \"pmids\": [\"33409656\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"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.\",\n      \"method\": \"Rescue experiments in CaV1.1/STAC3 double KO myotubes, patch-clamp electrophysiology, Ca2+ imaging, patient mutation analysis deleting the II-III loop interaction domain\",\n      \"journal\": \"JCI insight\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — KO rescue with domain-specific mutations, electrophysiology, Ca2+ imaging, validated by patient mutation; single lab\",\n      \"pmids\": [\"40779452\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"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.\",\n      \"method\": \"siRNA knockdown and plasmid overexpression in C2C12 myoblasts, Stac3 KO mouse myoblast cultures, fusion index, myogenic marker expression (myogenin, MHC)\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — KO primary culture and OE/KD in C2C12 with multiple readouts, single lab\",\n      \"pmids\": [\"24788338\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"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.\",\n      \"method\": \"Conditional KO mice (tamoxifen-inducible Cre-loxP), muscle contractile tests, Ca2+ imaging of single FDB myofibers, electrostimulation vs. caffeine comparison\",\n      \"journal\": \"Skeletal muscle\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — conditional KO with defined pharmacological dissection of EC coupling steps, multiple readouts, single lab\",\n      \"pmids\": [\"27073615\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"STAC3 is a skeletal muscle-specific adapter protein (containing C1 and tandem SH3 domains) that is an essential component of the excitation-contraction (EC) coupling machinery: it stably interacts with CaV1.1 via its C1 domain (proximal C-terminus interaction) and through its tandem SH3 domains with the CaV1.1 II-III loop, facilitating CaV1.1 membrane trafficking, determining the slow activation kinetics of CaV1.1 currents, specifically inhibiting voltage-dependent inactivation, and enabling conformational coupling between CaV1.1 and RyR1 for SR Ca2+ release; loss of STAC3 function (including the NAM-causing W284S mutation) impairs EC coupling and Ca2+ release, while STAC3 also negatively regulates myoblast differentiation and, unexpectedly, regulates Leydig cell steroidogenesis via mitochondrial membrane potential and StAR processing.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"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) [#0, #1]. 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 [#1, #16]. 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 [#4, #9, #14]. 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 [#3, #5, #11]. 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 [#2, #7, #9]. Beyond EC coupling, STAC3 negatively regulates myoblast differentiation [#15], is cleaved by calpain 1 in a Ca2+-dependent manner after eccentric contraction [#12], and supports Leydig cell steroidogenesis via mitochondrial membrane potential and StAR processing [#13].\",\n  \"teleology\": [\n    {\n      \"year\": 2013,\n      \"claim\": \"Established that STAC3 is a previously unrecognized, dedicated component of skeletal muscle EC coupling rather than a generic signaling adapter.\",\n      \"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\",\n      \"pmids\": [\"23736855\", \"23818578\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not define which CaV1.1 domains STAC3 engages\", \"Molecular basis of coupling to RyR1 not resolved\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"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.\",\n      \"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\",\n      \"pmids\": [\"27621462\", \"28003463\", \"27073615\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural interface with CaV1.1 not yet defined\", \"How W280S uncouples binding from coupling unexplained\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"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.\",\n      \"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\",\n      \"pmids\": [\"28112192\", \"30071129\", \"28697281\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Identity of the additional triad partner mediating CaV1.1-independent incorporation unknown\", \"Single-lab FRAP findings\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"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.\",\n      \"evidence\": \"Heterologous expression, patch-clamp, binding assays and mutagenesis; Xenopus oocyte cut-open voltage-clamp; Co-IP and Ca2+ imaging from patient muscle\",\n      \"pmids\": [\"29950399\", \"29386226\", \"30168660\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Relationship between calmodulin and STAC3 C-terminal binding not fully resolved\", \"Patient-tissue data limited to W284S\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"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.\",\n      \"evidence\": \"X-ray crystallography of human STAC3 tandem SH3 domains, in vitro binding assays and EC coupling functional assays with F295L, K329N, W284S variants\",\n      \"pmids\": [\"32492370\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structure of the C1-CaV1.1 C-terminus interaction not determined\", \"Full-length STAC3-channel complex architecture unresolved\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Defined STAC3 as a determinant of CaV1.1 gating kinetics, specifically slowing activation and inhibiting voltage-dependent inactivation independently of Ca2+-dependent inactivation.\",\n      \"evidence\": \"Patch-clamp in CaV1.1/STAC3 double KO myotubes and HEK cells with STAC3-ETLAAA linker mutagenesis and Ba2+/Ca2+ recordings\",\n      \"pmids\": [\"36161458\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural mechanism by which the linker region controls VDI unknown\", \"Single-lab finding\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"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.\",\n      \"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\",\n      \"pmids\": [\"40779452\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How the C1 interaction mechanistically transmits conformational coupling to RyR1 remains undefined\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"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.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"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\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [0, 2, 4, 9, 14]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [5, 11, 3]},\n      {\"term_id\": \"GO:0008092\", \"supporting_discovery_ids\": [4, 9]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [1, 8]},\n      {\"term_id\": \"GO:0005739\", \"supporting_discovery_ids\": [13]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-397014\", \"supporting_discovery_ids\": [0, 1, 16]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [2, 11, 14]}\n    ],\n    \"complexes\": [\"skeletal muscle triad (CaV1.1/DHPR-RyR1 junction)\"],\n    \"partners\": [\"CACNA1S\", \"RYR1\", \"CALM1\", \"CAPN1\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}