{"gene":"ATP2A1","run_date":"2026-06-09T22:02:44","timeline":{"discoveries":[{"year":1998,"finding":"Sarcolipin (SLN) co-localizes with SERCA1 in the ER membrane and regulates its activity: co-expression decreases apparent Ca2+ affinity of SERCA1 but stimulates maximal Ca2+ uptake rates (Vmax). The conserved C-terminal domain of SLN is critical for its function, and SLN and phospholamban (PLN) have different mechanisms of interaction with SERCA1 (additive regulatory effects when both co-expressed). Reduced SLN protein (40% decrease) in chronically stimulated fast-twitch muscle accounts for decreased SERCA1 activity.","method":"Co-expression in HEK-293T cells, immunohistochemistry, Ca2+ uptake assays, N- and C-terminal FLAG epitope tagging and mutagenesis, SR vesicle isolation from stimulated muscle","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — multiple orthogonal methods including mutagenesis, functional Ca2+ uptake assays, and in vivo muscle preparations; single lab but comprehensive mechanistic dissection","pmids":["9575189"],"is_preprint":false},{"year":1996,"finding":"Mutations in ATP2A1 (encoding SERCA1) cause Brody disease via autosomal recessive inheritance. Three mutations identified: one at the splice donor site of intron 3 and two leading to premature stop codons that truncate SERCA1 and delete essential functional domains, resulting in reduced Ca2+ uptake and Ca2+-ATPase activity in sarcoplasmic reticulum.","method":"Genetic linkage, mutation analysis of ATP2A1 gene, SR Ca2+ ATPase activity measurements in patient muscle","journal":"Nature genetics","confidence":"High","confidence_rationale":"Tier 2 / Strong — replicated across multiple families, combined genetic and biochemical evidence, foundational disease-gene paper","pmids":["8841193"],"is_preprint":false},{"year":2000,"finding":"The missense mutation Pro789Leu in SERCA1 (ATP2A1) causes Brody disease by producing near-complete loss of Ca2+ transport activity due to reduced Ca2+ affinity when expressed in HEK-293 cells. By contrast, Arg819Cys mutation showed near-normal Ca2+ transport activity and was not causal. This demonstrates the importance of functional testing for SERCA1 mutants.","method":"Site-directed mutagenesis, expression in HEK-293 cells, Ca2+ transport activity assay","journal":"Human genetics","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro functional reconstitution with mutagenesis in heterologous expression system, single lab","pmids":["10914677"],"is_preprint":false},{"year":1998,"finding":"Alanine-scanning mutagenesis of transmembrane helices M4, M5, M6, and M8 of SERCA1 revealed mutation-sensitive patches in M4, M5, and M6 but not M8. A six-residue motif (E/D)GLPA(T/V) in M4 and M6 and its counterpart in M5 are critical for Ca2+ binding. Site-directed disulfide mapping showed M4 and M6 associate as a right-handed coiled-coil, supporting a 'side-by-side' model for two Ca2+ binding sites.","method":"Alanine-scanning mutagenesis, site-directed disulfide mapping of transmembrane helices","journal":"Acta physiologica Scandinavica. Supplementum","confidence":"High","confidence_rationale":"Tier 1 / Moderate — systematic mutagenesis with structural cross-linking; comprehensive mechanistic study of Ca2+-binding domain","pmids":["9789547"],"is_preprint":false},{"year":2001,"finding":"Two SERCA1 splice variants (S1Ts) resulting from exon 4 and/or exon 11 splicing encode C-terminally truncated proteins with only one Ca2+-binding residue that cannot pump calcium. These S1T proteins: (1) localize to the ER membrane (co-localizing with SERCA2b); (2) form homodimers; (3) reduce ER Ca2+ concentration and reverse ER Ca2+ elevation caused by full-length SERCA1 or SERCA2b by increasing ER Ca2+ leakage (consistent with cation channel formation by S1T homodimers); (4) significantly induce apoptosis when overexpressed in liver-derived cells.","method":"Semi-quantitative RT-PCR, Western blot (including mildly denaturing conditions for dimer detection), confocal microscopy co-localization, ER-targeted aequorin (erAEQ) Ca2+ measurements, transfection, apoptosis assay","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (imaging, Ca2+ measurement, functional assay), mechanistically rigorous","pmids":["11402072"],"is_preprint":false},{"year":2000,"finding":"The HBV X gene promoter cis-activates chimeric HBV X/SERCA1 transcripts with splicing of SERCA1 exon 11, producing C-terminally truncated SERCA1 proteins that form dimers, localize to the ER, cause ER Ca2+ depletion, and induce cell death. These effects are attributable to the SERCA (not viral) moiety of the chimeric proteins.","method":"In vivo tumor analysis (HBV DNA integration), in vitro expression analysis, ER localization assay, Ca2+ measurement, cell viability assay","journal":"Oncogene","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple methods but single lab, mechanistic attribution supported by domain-specific analysis","pmids":["10871838"],"is_preprint":false},{"year":2008,"finding":"The truncated SERCA1 variant S1T localizes to ER-mitochondria microdomains, causes ER Ca2+ depletion via increased Ca2+ leak, increases the number of ER-mitochondria contact sites, inhibits mitochondria movements, and increases Ca2+ transfer to mitochondria, thereby activating the mitochondrial apoptotic pathway and amplifying ER stress through the PERK-eIF2α-ATF4-CHOP pathway. S1T knockdown prevents ER stress, mitochondrial Ca2+ overload, and apoptosis.","method":"siRNA knockdown, live-cell Ca2+ imaging, ER-mitochondria contact site quantification, mitochondria movement tracking, ER stress pathway analysis (Western blot for PERK, eIF2α, ATF4, CHOP), mitochondrial apoptosis assay","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods including loss-of-function with specific phenotypic readouts, pathway placement via ER stress markers","pmids":["19061639"],"is_preprint":false},{"year":2003,"finding":"Targeted disruption of ATP2A1 (SERCA1-null mice) reduces Ca2+ transport activity in diaphragm and skeletal muscle by 80% compared to wild-type. SERCA1-null mice show progressive cyanosis and respiratory failure shortly after birth due to impaired diaphragm muscle contractile function. No compensatory increases in other Ca2+ handling proteins are detected. SERCA1 expression is largely restricted to type II fibers predominating in mouse diaphragm.","method":"Gene targeting/knockout, immunohistochemistry, Ca2+ transport Vmax measurement, electrical stimulation contractility assay, mRNA/protein analysis of Ca2+ handling proteins","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean KO with defined physiological phenotype, quantitative biochemical confirmation, no compensatory response established","pmids":["12556521"],"is_preprint":false},{"year":2004,"finding":"In zebrafish, a loss-of-function mutation in atp2a1 (encoding SERCA1) causes the 'accordion' phenotype: bilateral trunk muscle co-contractions due to impaired muscle relaxation. In vivo Ca2+ imaging showed slower cytosolic Ca2+ decay in mutant muscle, confirming defective Ca2+ re-uptake into the SR as the mechanism.","method":"Forward genetic screen, positional cloning, in vivo muscle Ca2+ imaging, electrophysiology","journal":"Development (Cambridge, England)","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic loss-of-function with direct in vivo Ca2+ transient measurement as mechanistic readout","pmids":["15469975"],"is_preprint":false},{"year":2003,"finding":"Normal mode analysis of SERCA1 crystal structures (E1Ca2 and E2TG states) revealed that the N and A domains undergo the largest conformational movements during the transport cycle and behave as rigid bodies, while the P domain is highly flexible. Three low-frequency modes are sufficient to describe the E1Ca to E2TG transition, involving closure of the cytoplasmic headpiece and displacement of the L7-8 lumenal loop.","method":"Normal mode analysis of crystallographic structures (E1Ca2 and E2TG), DomainFinder dynamical domain analysis","journal":"Biophysical journal","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — computational analysis based on crystal structures; no experimental mutagenesis validation in this study","pmids":["14507684"],"is_preprint":false},{"year":2007,"finding":"MBNL1 binds to 'YGCU(U/G)Y' motifs downstream of SERCA1 exon 22 (specifically the 2nd and 3rd motifs in intron 22) and positively regulates exon 22 inclusion. In DM1, sequestration of MBNL1 into expanded CUG repeat DMPK mRNA causes exclusion of SERCA1 exon 22, producing aberrant SERCA1 transcripts that affect Ca2+ regulation in the sarcoplasmic reticulum.","method":"Exon trapping experiments, site-directed mutagenesis of MBNL1 binding motifs, overexpression of CUG repeat expansion","journal":"Human molecular genetics","confidence":"High","confidence_rationale":"Tier 2 / Moderate — direct exon trapping functional assay with mutagenesis of specific binding sites, mechanistic pathway placement","pmids":["17728322"],"is_preprint":false},{"year":2007,"finding":"The conserved C-terminal Tyr29 and Tyr31 residues of sarcolipin directly interact with SERCA1a at the luminal face. The peptide NAc-RSYQY representing this region binds SERCA1 and reduces Vmax for Ca2+ transport and inhibits ATP hydrolysis (IC50 ~200 µM). Native aromatic residues are essential for optimal inhibitory activity.","method":"Solid-state NMR (local protein dynamics), functional Ca2+ transport assays, peptide inhibition assays with SERCA1a in lipid bilayers","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — solid-state NMR structural data combined with functional inhibition assays; direct structural-functional correlation","pmids":["17616528"],"is_preprint":false},{"year":2003,"finding":"The N-terminal segment of SERCA1 (residues 1–211, containing transmembrane helices M1 and M2) contains an ER-retrieval signal. Chimeras containing the SERCA1 N-terminus localized to the ER, while those with the PMCA3 N-terminus escaped the ER. SERCA1 is maintained in the ER by a retrieval process (co-localization with ERGIC53).","method":"EGFP-tagged chimera expression in COS-7 cells, subcellular localization by confocal microscopy, co-localization with ER/Golgi intermediate compartment marker ERGIC53","journal":"The Biochemical journal","confidence":"High","confidence_rationale":"Tier 2 / Moderate — direct localization experiment with systematic domain-swap chimeras, functional consequence for ER retention identified","pmids":["12585965"],"is_preprint":false},{"year":1995,"finding":"Phospholamban (PLN), when stably transfected into C2C12 fast-twitch skeletal muscle cells expressing endogenous SERCA1, inhibits SERCA1 activity by decreasing its Ca2+ affinity (apparent Km shifted from 0.27 to 0.41 µM) at low Ca2+ concentrations in the native membrane environment.","method":"Stable transfection of PLN into C2C12 myotubes, 45Ca2+-uptake assay over range of Ca2+ concentrations, Western blot, microsomal fractionation","journal":"Molecular and cellular biochemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — functional Ca2+ uptake assay in native membrane context, single lab","pmids":["7651372"],"is_preprint":false},{"year":2008,"finding":"A missense mutation in ATP2A1 exon 6 (c.491G>A; p.Arg164His) causes congenital pseudomyotonia in Chianina cattle by reducing SERCA1 activity by ~70%. Arg164 is a functionally important and strongly conserved residue of SERCA1.","method":"Linkage analysis, mutation analysis, SERCA1 ATPase activity measurement in SR membranes from affected cattle","journal":"Genomics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic and biochemical evidence in animal model, conserved residue identified as critical for function","pmids":["18786632"],"is_preprint":false},{"year":2008,"finding":"The Arg164His SERCA1 mutant (bovine pseudomyotonia) shows selective reduction of SERCA1 protein in SR membranes despite normal mRNA levels, without significant change in Ca2+-dependency of residual ATPase activity and without compensatory upregulation of SERCA2. The protein reduction (not catalytic deficiency) accounts for the reduced activity.","method":"Western blot, Northern blot, SERCA1 ATPase activity assay, Ca2+-dependency measurement, immunofluorescence","journal":"The American journal of pathology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — biochemical dissection of mechanism (protein quantity vs. catalytic defect), single lab","pmids":["19116366"],"is_preprint":false},{"year":2014,"finding":"The Arg164His SERCA1 mutant (Chianina pseudomyotonia) is degraded by the ubiquitin-proteasome system (UPS). Treatment with proteasome inhibitor MG132 rescues expression level and membrane localization of the mutant in a heterologous cellular model. The rescued mutant retains normal Ca2+ homeostasis maintenance ability. Ex vivo skeletal muscle fibers from affected animals confirmed these findings, indicating the mutation causes misfolding rather than catalytic inactivation.","method":"Proteasome inhibitor treatment (MG132), Western blot, immunofluorescence localization, Ca2+-sensitive aequorin probe in co-transfected cells, ex vivo adult muscle fiber analysis","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (pharmacological rescue, localization, functional Ca2+ assay), confirmed ex vivo","pmids":["25288803"],"is_preprint":false},{"year":2014,"finding":"Transcription factors Ebf3 and Ebf1 cooperate with MyoD to directly regulate Atp2a1 (SERCA1) expression in skeletal muscle. Ebf3 binds directly to the Atp2a1 promoter and synergizes with MyoD for Atp2a1 induction. In Ebf3-null mice, SERCA1 is downregulated in the diaphragm, causing impaired Ca2+ efflux-related muscle function; transgenic SERCA1 expression rescues this phenotype.","method":"ChIP (Ebf3 binding to Atp2a1 promoter), reporter assay (synergy with MyoD), knockout mouse analysis, transgenic rescue, Ca2+ efflux measurements","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 / Strong — direct promoter binding shown by ChIP, genetic rescue experiment, multiple orthogonal methods","pmids":["24786561"],"is_preprint":false},{"year":2015,"finding":"Small ankyrin 1 (sAnk1) interacts specifically with SERCA1 via its transmembrane domain and its cytoplasmic domain. This interaction is demonstrated in native SR vesicles from rabbit skeletal muscle and in transfected COS7 cells. sAnk1 co-expression reduces the apparent Ca2+ affinity of SERCA1 but the effect is smaller than sarcolipin. Replacement of all TM amino acids with leucines reduces binding ~2-fold and abolishes the effect on SERCA1 activity.","method":"Co-immunoprecipitation from native SR vesicles and transfected cells, anisotropy-based FRET (AFRET), ATPase activity assay, TM domain mutagenesis","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal co-IP, FRET, functional assay, mutagenesis; multiple orthogonal methods","pmids":["26405035"],"is_preprint":false},{"year":2017,"finding":"sAnk1 and SLN interact directly and form a three-protein complex with SERCA1 in the SR membrane. SLN promotes the interaction between sAnk1 and SERCA1. When sAnk1 and SLN are co-expressed with SERCA1, sAnk1 ablates SLN's inhibitory effect on SERCA1 activity. The sAnk1-SLN interaction does not require endogenous SERCA2.","method":"Co-immunoprecipitation, anisotropy-based FRET (AFRET), Ca2+-ATPase activity assay, co-transfection in COS7 cells","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal co-IP, FRET, functional enzyme assay; three-way complex characterized with multiple methods","pmids":["28487373"],"is_preprint":false},{"year":2015,"finding":"SERCA1a has approximately double the ATPase and Ca2+ uptake activity of SERCA1b when overexpressed in cells, despite similar affinities for ATP and Ca2+. SERCA1b is more sensitive to the inner microsomal environment. SERCA1b protein is highly expressed in DM1 muscle tissue, predominantly in fast-twitch fibers.","method":"Overexpression in cells, ATPase activity assay, Ca2+ uptake assay, Western blot, immunostaining","journal":"Biochimica et biophysica acta","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct functional comparison of two splice variants with enzyme activity assays, single lab","pmids":["26170059"],"is_preprint":false},{"year":2011,"finding":"4-aminoquinoline derivatives (NF1442 and NF1058) and clotrimazole inhibit SERCA1 by stabilizing an E2 state that interferes with Ca2+ binding and the E2→E1·Ca2 transition required for phosphoenzyme formation by ATP, but this E2 state retains the ability to form E2-P by reacting with Pi. This is mechanistically distinct from thapsigargin, which also inhibits Pi-dependent phosphorylation.","method":"Steady-state ATPase activity assay, single-cycle charge transfer measurement, sequential reaction kinetic characterization of phosphoenzyme formation","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — detailed mechanistic dissection of catalytic cycle states using multiple biochemical assays; defined mechanistic distinction from thapsigargin","pmids":["21914795"],"is_preprint":false},{"year":2003,"finding":"SERCA1 (RyR1/SERCA1 cross-talk): In heavy SR vesicles, SERCA1 ATPase catalytic activity is well coordinated to RyR1 activation/inactivation states. Ryanodine-induced Ca2+ channel leak activates SERCA1 in the absence of measurable bulk Ca2+ increase, suggesting SERCA1 pumps sense Ca2+ ions exiting RyR1 cytoplasmic openings. Conversely, RyR1 activation is dependent on SERCA1 activity; at threshold luminal Ca2+ load, RyR1-induced Ca2+ release produces transient reversal of SERCA1 catalytic activity.","method":"Synchronous fluorescence determination of extravesicular Ca2+ transients and catalytic activity in heavy SR membrane vesicles, ryanodine receptor pharmacology","journal":"Canadian journal of physiology and pharmacology","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — functional measurements in native membrane preparations, single lab, single method type","pmids":["12733821"],"is_preprint":false},{"year":2000,"finding":"The rat SERCA1 5' flanking region contains weight-bearing responsive elements. Specific CACC box at -1262 and a nearby E-box at -1248 are necessary and sufficient for transcriptional activation by muscle unloading. Both elements together are required to activate transcription; trimerized CACC sites alone are insufficient.","method":"In vivo somatic gene transfer into rat soleus muscle, deletion analysis of SERCA1 promoter/5' flank, mutagenesis of cis-elements, luciferase reporter assay","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — systematic deletion and mutagenesis of regulatory elements with in vivo reporter assay","pmids":["10811813"],"is_preprint":false},{"year":2018,"finding":"The ER-localized autophagy protein EPG-3/VMP1 regulates ER contacts with other organelles (phagophores, lipid droplets, mitochondria, endolysosomes) by activating SERCA (ATP2A/SERCA) calcium channel activity. Downstream, calmodulin (CALM) acts as a calcium effector controlling PIK3C3/VPS34 PI3-kinase activity to maintain ER contacts.","method":"Genetic epistasis in C. elegans, biochemical assays, live imaging of organelle contacts","journal":"Autophagy","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic epistasis with pathway placement; study addresses ATP2A/SERCA broadly and implicates SERCA activity in ER contact regulation","pmids":["29494262"],"is_preprint":false},{"year":2012,"finding":"PKC signaling regulates alternative splicing of SERCA1. PMA treatment regulates SERCA1 exon splicing in HEK293 cells; prolonged PMA (48h) normalizes SERCA1 splicing while short treatment (1.5h) promotes aberrant splicing. Both effects are abolished by PKC inhibitor Ro 31-8220. RNAi knockdown of PKCβII and PKCθ mimics prolonged PMA treatment (normalized splicing).","method":"PMA treatment, PKC inhibitor treatment, RNAi knockdown of PKC isoforms, RT-PCR splicing assay","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — pharmacological and RNAi epistasis placed PKC pathway in SERCA1 splicing regulation; single lab","pmids":["22609207"],"is_preprint":false},{"year":2025,"finding":"A novel small transmembrane protein MCARE (muscle-enriched Ca2+ regulator), predominantly expressed in fast-twitch muscles, enhances SERCA1 function by competitively inhibiting myoregulin (a muscle-specific micropeptide that suppresses SERCA1 activity). MCARE-mediated SERCA1 activation facilitates Ca2+ clearance from the cytoplasm and accelerates muscle relaxation. Mcare-deficient mice show muscular dystrophy-like symptoms (progressive muscle wasting, reduced strength, increased susceptibility to exercise-induced damage, rippling muscle contractions) in fast-twitch muscles.","method":"Knockout mouse model, Ca2+ clearance measurements, protein interaction studies, ATPase activity assays, competition assay with myoregulin","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic KO with defined phenotype, direct competitive inhibition mechanism established, multiple orthogonal methods","pmids":["41372236"],"is_preprint":false},{"year":2025,"finding":"The juxtamembrane region of sAnk1 cytoplasmic domain (residues K38, H39, H41) and hydrophobic residues R64-K73 mediate binding to SERCA1. The cytoplasmic domain alone (sAnk1(29-155)) does not inhibit SERCA1 Ca2+-ATPase activity, but the WT juxtamembrane sequence is required for the inhibitory activity of full-length sAnk1. Binding affinity of sAnk1(29-155) for SERCA1 is 444 nM by blot overlay.","method":"Site-directed mutagenesis, blot overlay binding affinity measurement, circular dichroism, ATPase activity assay, structural modeling","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — mutagenesis with functional readout, multiple structural and biochemical methods; single lab","pmids":["39863105"],"is_preprint":false},{"year":2025,"finding":"sAnk1 associates with phospholamban (PLN) and forms a three-way complex with PLN and SERCA1, as shown by co-IP and BiFC in COS7 cells and confirmed by AFRET. Unlike its effect on SLN inhibition, sAnk1 does not ablate PLN's inhibition of SERCA1 activity. Modeling suggests PLN binds SERCA1 first, then sAnk1 binds PLN; the interactions of PLN, SLN, and sAnk1 with SERCA1 are mechanistically distinct.","method":"Co-transfection, co-immunoprecipitation, bimolecular fluorescence complementation (BiFC), anisotropy-based FRET (AFRET), ATPase activity assay","journal":"Biochemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods for complex detection and functional characterization; single lab","pmids":["40998301"],"is_preprint":false},{"year":2025,"finding":"FAM134B short isoform (FAM134B-S), an ER-phagy receptor induced by statins via the mevalonate pathway and SREBPs, interacts with SERCA1 and promotes its autophagic degradation (SR-phagy). This degradation mechanism contributes to statin-associated muscle symptoms and myotoxicity. FAM134B plays a role in maintaining skeletal muscle integrity under both steady-state and statin-treated conditions in human iPS-derived myocytes and mice.","method":"Transcriptome analysis, protein-protein interaction studies (co-IP/pulldown), autophagy assays, knockdown/overexpression in iPS-derived myocytes and mice, pathway analysis (mevalonate pathway inhibition)","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct interaction between FAM134B-S and SERCA1 established, mechanistic pathway defined; preprint, not peer-reviewed","pmids":["bio_10.1101_2025.11.26.690680"],"is_preprint":true},{"year":2025,"finding":"CFTR correctors, particularly C17, rescue SERCA1 missense mutants (Brody myopathy/bovine pseudomyotonia) both in vitro and in vivo by counteracting premature proteasomal degradation of misfolded-but-catalytically-active SERCA1 mutant proteins. This identifies UPS-mediated degradation of misfolded SERCA1 as the shared pathogenetic mechanism with cystic fibrosis.","method":"CFTR corrector treatment in cellular and animal models, Western blot for SERCA1 rescue, Ca2+ homeostasis assays, in vivo bovine PMT model","journal":"Human molecular genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — pharmacological rescue in vitro and in vivo with mechanistic explanation; builds on prior UPS degradation findings","pmids":["41206505"],"is_preprint":false}],"current_model":"ATP2A1/SERCA1 is the fast-twitch skeletal muscle SR Ca2+-ATPase that pumps Ca2+ from the cytosol into the SR lumen to enable muscle relaxation; its activity is regulated by a network of transmembrane micropeptide regulators (sarcolipin, phospholamban, myoregulin, sAnk1, and MCARE) that modulate its Ca2+ affinity and/or Vmax, its ER localization is determined by an N-terminal retrieval signal (residues 1–211), its expression is transcriptionally co-activated by Ebf factors and MyoD, aberrant splicing of exon 22 driven by MBNL1 sequestration impairs function in myotonic dystrophy, truncated or misfolded SERCA1 variants (from disease mutations or alternative splicing) that reach the ER act as Ca2+ leak channels or are degraded by the ubiquitin-proteasome system, and pathogenic SERCA1 deficiency—causing Brody disease and animal pseudomyotonia phenotypes—leads to impaired cytosolic Ca2+ clearance, muscle relaxation failure, and downstream mitochondrial Ca2+ overload and apoptosis."},"narrative":{"mechanistic_narrative":"ATP2A1 encodes SERCA1, the fast-twitch skeletal muscle sarcoplasmic/endoplasmic reticulum Ca2+-ATPase that clears cytosolic Ca2+ into the SR lumen to drive muscle relaxation, as established by loss-of-function models in which SERCA1-null mice fail diaphragm contraction and zebrafish atp2a1 mutants show slowed cytosolic Ca2+ decay and sustained muscle co-contraction [PMID:12556521, PMID:15469975]. The pump cycles between E1Ca2 and E2 conformations through large rigid-body motions of its N and A domains, with a side-by-side pair of transmembrane Ca2+-binding sites built from M4, M5 and M6 helices [PMID:9789547, PMID:14507684]; pharmacological inhibitors such as 4-aminoquinolines and clotrimazole act by stabilizing an E2 state that blocks the E2→E1·Ca2 transition [PMID:21914795]. SERCA1 activity is tuned by a network of small transmembrane regulators—sarcolipin and phospholamban lower apparent Ca2+ affinity (sarcolipin additionally raising Vmax), small ankyrin 1 (sAnk1) binds SERCA1 directly and assembles three-way complexes that relieve sarcolipin inhibition, and the muscle-enriched micropeptide MCARE activates the pump by competitively antagonizing the inhibitor myoregulin [PMID:9575189, PMID:17616528, PMID:7651372, PMID:26405035, PMID:28487373, PMID:41372236]. Its ER residence is set by an N-terminal retrieval signal in residues 1–211, and its expression is driven by Ebf factors cooperating with MyoD [PMID:12585965, PMID:24786561]. Loss-of-function or misfolding mutations in ATP2A1 cause autosomal recessive Brody disease in humans and pseudomyotonia in cattle, with misfolded-but-catalytically-active mutants such as Arg164His cleared by the ubiquitin-proteasome system and rescuable by proteasome inhibition or CFTR correctors [PMID:8841193, PMID:10914677, PMID:18786632, PMID:25288803, PMID:41206505]. Aberrant SERCA1 splicing also generates pathology: MBNL1 sequestration in myotonic dystrophy excludes exon 22, and C-terminally truncated S1T variants that retain only partial Ca2+-binding residues form ER-localized leak channels at ER–mitochondria microdomains that deplete ER Ca2+, drive mitochondrial Ca2+ overload, ER stress, and apoptosis [PMID:11402072, PMID:19061639, PMID:17728322].","teleology":[{"year":1996,"claim":"Established that ATP2A1 is a disease gene, linking SERCA1 loss-of-function to a human muscle relaxation disorder and grounding its physiological role in SR Ca2+ uptake.","evidence":"Genetic linkage and mutation analysis of Brody disease families with SR Ca2+-ATPase activity measurements in patient muscle","pmids":["8841193"],"confidence":"High","gaps":["Did not resolve which mutations cause catalytic versus expression defects","No structural mechanism for individual mutations"]},{"year":1998,"claim":"Defined the structural basis of Ca2+ binding by mapping the transmembrane helices responsible for the two coordination sites, explaining how the pump captures cytosolic Ca2+.","evidence":"Alanine-scanning mutagenesis and site-directed disulfide cross-linking of M4–M6/M8 helices","pmids":["9789547"],"confidence":"High","gaps":["Coiled-coil model inferred from cross-linking, not full structure","Did not address conformational transitions during transport"]},{"year":1998,"claim":"Identified sarcolipin as a transmembrane regulator that modulates SERCA1 Ca2+ affinity and Vmax distinctly from phospholamban, opening the micropeptide regulatory network.","evidence":"Co-expression in HEK-293T cells, Ca2+ uptake assays, FLAG tagging and mutagenesis, SR vesicles from stimulated muscle","pmids":["9575189"],"confidence":"High","gaps":["Structural interface with SERCA1 not resolved here","Physiological stoichiometry in muscle not quantified"]},{"year":2000,"claim":"Demonstrated that disease-mutation phenotype depends on functional impact, distinguishing a causal affinity-disrupting mutation from a benign variant.","evidence":"Site-directed mutagenesis and Ca2+ transport assays of Pro789Leu and Arg819Cys in HEK-293 cells","pmids":["10914677"],"confidence":"High","gaps":["Did not address protein stability or folding of mutants","Limited to two variants"]},{"year":2001,"claim":"Revealed that truncated SERCA1 splice variants are not merely dead pumps but actively form ER Ca2+ leak channels that trigger apoptosis, establishing a gain-of-toxic-function mechanism.","evidence":"RT-PCR, dimer-detecting Western blot, confocal co-localization, ER-targeted aequorin Ca2+ measurements, apoptosis assays","pmids":["11402072"],"confidence":"High","gaps":["Channel structure of S1T homodimers not defined","Physiological relevance in muscle not established here"]},{"year":2003,"claim":"Provided the in vivo physiological proof that SERCA1 is essential for fast-twitch muscle relaxation and respiratory function with no compensatory redundancy.","evidence":"SERCA1-null mouse gene targeting, Ca2+ transport Vmax, contractility assays, Ca2+-handling protein profiling","pmids":["12556521"],"confidence":"High","gaps":["Did not test fiber-type-specific rescue","Mechanism of perinatal lethality limited to diaphragm phenotype"]},{"year":2003,"claim":"Located the ER-retrieval signal that confines SERCA1 to the ER/SR, explaining how the pump achieves its compartment-specific localization.","evidence":"EGFP chimera domain swaps in COS-7 cells with ERGIC53 co-localization","pmids":["12585965"],"confidence":"High","gaps":["Retrieval machinery/receptor not identified","Signal residues within 1–211 not narrowed"]},{"year":2003,"claim":"Modeled the conformational mechanics of the transport cycle, identifying which domains move as rigid bodies during E1-to-E2 transitions.","evidence":"Normal mode analysis of E1Ca2 and E2TG crystal structures with dynamical domain decomposition","pmids":["14507684"],"confidence":"Medium","gaps":["Computational only, no experimental validation in this study","Did not capture regulator-bound states"]},{"year":2007,"claim":"Pinpointed the luminal sarcolipin residues that contact SERCA1 and inhibit turnover, giving residue-level resolution to micropeptide regulation.","evidence":"Solid-state NMR, peptide inhibition assays, Ca2+ transport assays with SERCA1a in lipid bilayers","pmids":["17616528"],"confidence":"High","gaps":["IC50 in the micromolar range may not reflect native affinity","Full-length interaction interface not mapped"]},{"year":2007,"claim":"Explained how SERCA1 splicing is disrupted in myotonic dystrophy by identifying MBNL1 as the direct exon-22 splicing activator that is titrated away by CUG repeats.","evidence":"Exon trapping with mutagenesis of MBNL1 binding motifs and CUG repeat overexpression","pmids":["17728322"],"confidence":"High","gaps":["Functional consequence of exon 22 exclusion on pump activity not measured here","Did not address other splice events"]},{"year":2008,"claim":"Extended the leak-channel toxic mechanism to ER–mitochondria signaling, showing truncated SERCA1 amplifies mitochondrial Ca2+ overload, ER stress and apoptosis.","evidence":"siRNA knockdown, live-cell Ca2+ imaging, ER-mitochondria contact quantification, PERK-eIF2α-ATF4-CHOP analysis","pmids":["19061639"],"confidence":"High","gaps":["In vivo muscle relevance of the contact-site mechanism not shown","Channel conductance properties not measured"]},{"year":2008,"claim":"Identified a conserved-residue missense mutation causing an animal pseudomyotonia phenotype, providing a naturally occurring model of SERCA1 deficiency.","evidence":"Linkage and mutation analysis with SR ATPase activity in Chianina cattle","pmids":["18786632"],"confidence":"Medium","gaps":["Mechanism of activity loss not yet defined at this stage","Single breed"]},{"year":2008,"claim":"Resolved that the Arg164His pseudomyotonia defect is loss of pump protein rather than catalytic incompetence, reframing the lesion as a stability problem.","evidence":"Western/Northern blot, ATPase and Ca2+-dependency assays, immunofluorescence in affected cattle muscle","pmids":["19116366"],"confidence":"Medium","gaps":["Degradation pathway not yet identified","Single lab"]},{"year":2014,"claim":"Demonstrated that the misfolded Arg164His SERCA1 is destroyed by the proteasome and pharmacologically rescuable, converting a structural lesion into a druggable target.","evidence":"MG132 proteasome inhibition, localization, aequorin Ca2+ assays, ex vivo muscle fibers","pmids":["25288803"],"confidence":"High","gaps":["Did not show clinical-grade rescue strategy","Generality across other Brody mutations not tested here"]},{"year":2014,"claim":"Established the transcriptional control of SERCA1, showing Ebf factors cooperate with MyoD at the Atp2a1 promoter to drive muscle expression with phenotypic rescue.","evidence":"ChIP of Ebf3 on Atp2a1 promoter, MyoD synergy reporter assays, Ebf3-null mice, transgenic SERCA1 rescue","pmids":["24786561"],"confidence":"High","gaps":["Fiber-type specificity of the regulatory circuit not fully resolved","Other upstream signals not mapped"]},{"year":2015,"claim":"Added small ankyrin 1 to the regulator network as a direct SERCA1 binder that lowers Ca2+ affinity, expanding the membrane regulatory repertoire beyond SLN/PLN.","evidence":"Co-IP from native SR and transfected cells, AFRET, ATPase assays, TM-domain mutagenesis","pmids":["26405035"],"confidence":"High","gaps":["Cytoplasmic-domain contribution not yet mapped","Physiological role in muscle Ca2+ handling not established"]},{"year":2015,"claim":"Showed SERCA1 splice variants differ functionally, with SERCA1a more active than SERCA1b and SERCA1b enriched in DM1 muscle, linking isoform choice to disease.","evidence":"Overexpression, ATPase and Ca2+ uptake assays, Western blot, immunostaining","pmids":["26170059"],"confidence":"Medium","gaps":["Structural basis of the activity difference unknown","Single lab"]},{"year":2017,"claim":"Defined a three-protein regulatory complex in which sAnk1 binds both SLN and SERCA1 and relieves SLN inhibition, revealing combinatorial control of the pump.","evidence":"Co-IP, AFRET, Ca2+-ATPase assays in COS7 cells","pmids":["28487373"],"confidence":"High","gaps":["Native-muscle stoichiometry of the complex not quantified","Structural arrangement inferred indirectly"]},{"year":2018,"claim":"Placed SERCA Ca2+ pumping within ER organelle-contact regulation, where VMP1 activates SERCA and calmodulin/VPS34 maintain inter-organelle contacts.","evidence":"Genetic epistasis in C. elegans, biochemical assays, live imaging of organelle contacts","pmids":["29494262"],"confidence":"Medium","gaps":["Addresses SERCA broadly, not ATP2A1-specific","Direct VMP1–SERCA biochemistry not shown"]},{"year":2025,"claim":"Refined the sAnk1 mechanism by mapping juxtamembrane and hydrophobic cytoplasmic residues required for binding and inhibition of SERCA1.","evidence":"Mutagenesis, blot-overlay affinity, circular dichroism, ATPase assays, modeling","pmids":["39863105"],"confidence":"Medium","gaps":["No high-resolution structure of the interface","Single lab"]},{"year":2025,"claim":"Distinguished how PLN versus SLN engage the sAnk1-containing complex, showing sAnk1 does not relieve PLN inhibition, indicating mechanistically distinct regulator modes.","evidence":"Co-IP, BiFC, AFRET, ATPase assays in COS7 cells","pmids":["40998301"],"confidence":"Medium","gaps":["Native assembly order not directly observed","Single lab"]},{"year":2025,"claim":"Identified MCARE as a positive regulator that activates SERCA1 by competitively antagonizing the inhibitor myoregulin, with loss causing dystrophy-like fast-twitch pathology.","evidence":"Knockout mice, Ca2+ clearance measurements, interaction and ATPase assays, myoregulin competition assay","pmids":["41372236"],"confidence":"High","gaps":["Structural basis of competition not resolved","Interplay with SLN/sAnk1 network not tested"]},{"year":2025,"claim":"Generalized UPS-mediated degradation of misfolded SERCA1 as a shared pathogenic mechanism and showed CFTR correctors rescue catalytically-active mutants in vivo.","evidence":"CFTR corrector treatment in cellular and bovine pseudomyotonia models, Western blot, Ca2+ homeostasis assays","pmids":["41206505"],"confidence":"Medium","gaps":["Human Brody disease efficacy not demonstrated","Long-term/in vivo durability not addressed"]},{"year":2025,"claim":"Linked SERCA1 to selective autophagic turnover (SR-phagy) via the ER-phagy receptor FAM134B-S, implicating regulated degradation in statin myotoxicity.","evidence":"Transcriptomics, co-IP/pulldown, autophagy assays, knockdown/overexpression in iPS myocytes and mice (preprint)","pmids":["bio_10.1101_2025.11.26.690680"],"confidence":"Medium","gaps":["Preprint, not peer-reviewed","Direct FAM134B-S binding interface on SERCA1 not mapped"]},{"year":null,"claim":"How the multiple micropeptide regulators (SLN, PLN, myoregulin, sAnk1, MCARE) are integrated stoichiometrically and spatially on a single SERCA1 pump in native fast-twitch SR remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No native-tissue structure of multi-regulator complexes","Quantitative regulator stoichiometry per pump unknown","Crosstalk between transcriptional, splicing, and degradative control not unified"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0005215","term_label":"transporter activity","supporting_discovery_ids":[7,8,1]},{"term_id":"GO:0140657","term_label":"ATP-dependent activity","supporting_discovery_ids":[2,11,21]},{"term_id":"GO:0016787","term_label":"hydrolase activity","supporting_discovery_ids":[11,18,20]}],"localization":[{"term_id":"GO:0005783","term_label":"endoplasmic reticulum","supporting_discovery_ids":[12,4,6]},{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[18,0]}],"pathway":[{"term_id":"R-HSA-397014","term_label":"Muscle contraction","supporting_discovery_ids":[7,8,26]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[1,2,14,30]},{"term_id":"R-HSA-382551","term_label":"Transport of small molecules","supporting_discovery_ids":[7,8]}],"complexes":["SERCA1-sarcolipin-sAnk1 complex","SERCA1-phospholamban-sAnk1 complex"],"partners":["SLN","PLN","SANK1","MCARE","MYOREGULIN","MBNL1","FAM134B"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"O14983","full_name":"Sarcoplasmic/endoplasmic reticulum calcium ATPase 1","aliases":["Calcium pump 1","Calcium-transporting ATPase sarcoplasmic reticulum type, fast twitch skeletal muscle isoform","Endoplasmic reticulum class 1/2 Ca(2+) ATPase"],"length_aa":1001,"mass_kda":110.3,"function":"Key regulator of striated muscle performance 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ARLN","url":"https://www.omim.org/entry/620530"},{"mim_id":"616246","title":"MYOREGULIN; MRLN","url":"https://www.omim.org/entry/616246"},{"mim_id":"616231","title":"MYOPATHY, VACUOLAR, WITH CASQ1 AGGREGATES; VMCQA","url":"https://www.omim.org/entry/616231"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Endoplasmic reticulum","reliability":"Approved"}],"tissue_specificity":"Group enriched","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"skeletal 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latipes) skeletal muscle tissue following cold challenge.","date":"2023","source":"Comparative biochemistry and physiology. 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The conserved C-terminal domain of SLN is critical for its function, and SLN and phospholamban (PLN) have different mechanisms of interaction with SERCA1 (additive regulatory effects when both co-expressed). Reduced SLN protein (40% decrease) in chronically stimulated fast-twitch muscle accounts for decreased SERCA1 activity.\",\n      \"method\": \"Co-expression in HEK-293T cells, immunohistochemistry, Ca2+ uptake assays, N- and C-terminal FLAG epitope tagging and mutagenesis, SR vesicle isolation from stimulated muscle\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — multiple orthogonal methods including mutagenesis, functional Ca2+ uptake assays, and in vivo muscle preparations; single lab but comprehensive mechanistic dissection\",\n      \"pmids\": [\"9575189\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"Mutations in ATP2A1 (encoding SERCA1) cause Brody disease via autosomal recessive inheritance. Three mutations identified: one at the splice donor site of intron 3 and two leading to premature stop codons that truncate SERCA1 and delete essential functional domains, resulting in reduced Ca2+ uptake and Ca2+-ATPase activity in sarcoplasmic reticulum.\",\n      \"method\": \"Genetic linkage, mutation analysis of ATP2A1 gene, SR Ca2+ ATPase activity measurements in patient muscle\",\n      \"journal\": \"Nature genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — replicated across multiple families, combined genetic and biochemical evidence, foundational disease-gene paper\",\n      \"pmids\": [\"8841193\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"The missense mutation Pro789Leu in SERCA1 (ATP2A1) causes Brody disease by producing near-complete loss of Ca2+ transport activity due to reduced Ca2+ affinity when expressed in HEK-293 cells. By contrast, Arg819Cys mutation showed near-normal Ca2+ transport activity and was not causal. This demonstrates the importance of functional testing for SERCA1 mutants.\",\n      \"method\": \"Site-directed mutagenesis, expression in HEK-293 cells, Ca2+ transport activity assay\",\n      \"journal\": \"Human genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro functional reconstitution with mutagenesis in heterologous expression system, single lab\",\n      \"pmids\": [\"10914677\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"Alanine-scanning mutagenesis of transmembrane helices M4, M5, M6, and M8 of SERCA1 revealed mutation-sensitive patches in M4, M5, and M6 but not M8. A six-residue motif (E/D)GLPA(T/V) in M4 and M6 and its counterpart in M5 are critical for Ca2+ binding. Site-directed disulfide mapping showed M4 and M6 associate as a right-handed coiled-coil, supporting a 'side-by-side' model for two Ca2+ binding sites.\",\n      \"method\": \"Alanine-scanning mutagenesis, site-directed disulfide mapping of transmembrane helices\",\n      \"journal\": \"Acta physiologica Scandinavica. Supplementum\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — systematic mutagenesis with structural cross-linking; comprehensive mechanistic study of Ca2+-binding domain\",\n      \"pmids\": [\"9789547\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"Two SERCA1 splice variants (S1Ts) resulting from exon 4 and/or exon 11 splicing encode C-terminally truncated proteins with only one Ca2+-binding residue that cannot pump calcium. These S1T proteins: (1) localize to the ER membrane (co-localizing with SERCA2b); (2) form homodimers; (3) reduce ER Ca2+ concentration and reverse ER Ca2+ elevation caused by full-length SERCA1 or SERCA2b by increasing ER Ca2+ leakage (consistent with cation channel formation by S1T homodimers); (4) significantly induce apoptosis when overexpressed in liver-derived cells.\",\n      \"method\": \"Semi-quantitative RT-PCR, Western blot (including mildly denaturing conditions for dimer detection), confocal microscopy co-localization, ER-targeted aequorin (erAEQ) Ca2+ measurements, transfection, apoptosis assay\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (imaging, Ca2+ measurement, functional assay), mechanistically rigorous\",\n      \"pmids\": [\"11402072\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"The HBV X gene promoter cis-activates chimeric HBV X/SERCA1 transcripts with splicing of SERCA1 exon 11, producing C-terminally truncated SERCA1 proteins that form dimers, localize to the ER, cause ER Ca2+ depletion, and induce cell death. These effects are attributable to the SERCA (not viral) moiety of the chimeric proteins.\",\n      \"method\": \"In vivo tumor analysis (HBV DNA integration), in vitro expression analysis, ER localization assay, Ca2+ measurement, cell viability assay\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple methods but single lab, mechanistic attribution supported by domain-specific analysis\",\n      \"pmids\": [\"10871838\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"The truncated SERCA1 variant S1T localizes to ER-mitochondria microdomains, causes ER Ca2+ depletion via increased Ca2+ leak, increases the number of ER-mitochondria contact sites, inhibits mitochondria movements, and increases Ca2+ transfer to mitochondria, thereby activating the mitochondrial apoptotic pathway and amplifying ER stress through the PERK-eIF2α-ATF4-CHOP pathway. S1T knockdown prevents ER stress, mitochondrial Ca2+ overload, and apoptosis.\",\n      \"method\": \"siRNA knockdown, live-cell Ca2+ imaging, ER-mitochondria contact site quantification, mitochondria movement tracking, ER stress pathway analysis (Western blot for PERK, eIF2α, ATF4, CHOP), mitochondrial apoptosis assay\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods including loss-of-function with specific phenotypic readouts, pathway placement via ER stress markers\",\n      \"pmids\": [\"19061639\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Targeted disruption of ATP2A1 (SERCA1-null mice) reduces Ca2+ transport activity in diaphragm and skeletal muscle by 80% compared to wild-type. SERCA1-null mice show progressive cyanosis and respiratory failure shortly after birth due to impaired diaphragm muscle contractile function. No compensatory increases in other Ca2+ handling proteins are detected. SERCA1 expression is largely restricted to type II fibers predominating in mouse diaphragm.\",\n      \"method\": \"Gene targeting/knockout, immunohistochemistry, Ca2+ transport Vmax measurement, electrical stimulation contractility assay, mRNA/protein analysis of Ca2+ handling proteins\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean KO with defined physiological phenotype, quantitative biochemical confirmation, no compensatory response established\",\n      \"pmids\": [\"12556521\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"In zebrafish, a loss-of-function mutation in atp2a1 (encoding SERCA1) causes the 'accordion' phenotype: bilateral trunk muscle co-contractions due to impaired muscle relaxation. In vivo Ca2+ imaging showed slower cytosolic Ca2+ decay in mutant muscle, confirming defective Ca2+ re-uptake into the SR as the mechanism.\",\n      \"method\": \"Forward genetic screen, positional cloning, in vivo muscle Ca2+ imaging, electrophysiology\",\n      \"journal\": \"Development (Cambridge, England)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic loss-of-function with direct in vivo Ca2+ transient measurement as mechanistic readout\",\n      \"pmids\": [\"15469975\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Normal mode analysis of SERCA1 crystal structures (E1Ca2 and E2TG states) revealed that the N and A domains undergo the largest conformational movements during the transport cycle and behave as rigid bodies, while the P domain is highly flexible. Three low-frequency modes are sufficient to describe the E1Ca to E2TG transition, involving closure of the cytoplasmic headpiece and displacement of the L7-8 lumenal loop.\",\n      \"method\": \"Normal mode analysis of crystallographic structures (E1Ca2 and E2TG), DomainFinder dynamical domain analysis\",\n      \"journal\": \"Biophysical journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — computational analysis based on crystal structures; no experimental mutagenesis validation in this study\",\n      \"pmids\": [\"14507684\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"MBNL1 binds to 'YGCU(U/G)Y' motifs downstream of SERCA1 exon 22 (specifically the 2nd and 3rd motifs in intron 22) and positively regulates exon 22 inclusion. In DM1, sequestration of MBNL1 into expanded CUG repeat DMPK mRNA causes exclusion of SERCA1 exon 22, producing aberrant SERCA1 transcripts that affect Ca2+ regulation in the sarcoplasmic reticulum.\",\n      \"method\": \"Exon trapping experiments, site-directed mutagenesis of MBNL1 binding motifs, overexpression of CUG repeat expansion\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct exon trapping functional assay with mutagenesis of specific binding sites, mechanistic pathway placement\",\n      \"pmids\": [\"17728322\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"The conserved C-terminal Tyr29 and Tyr31 residues of sarcolipin directly interact with SERCA1a at the luminal face. The peptide NAc-RSYQY representing this region binds SERCA1 and reduces Vmax for Ca2+ transport and inhibits ATP hydrolysis (IC50 ~200 µM). Native aromatic residues are essential for optimal inhibitory activity.\",\n      \"method\": \"Solid-state NMR (local protein dynamics), functional Ca2+ transport assays, peptide inhibition assays with SERCA1a in lipid bilayers\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — solid-state NMR structural data combined with functional inhibition assays; direct structural-functional correlation\",\n      \"pmids\": [\"17616528\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"The N-terminal segment of SERCA1 (residues 1–211, containing transmembrane helices M1 and M2) contains an ER-retrieval signal. Chimeras containing the SERCA1 N-terminus localized to the ER, while those with the PMCA3 N-terminus escaped the ER. SERCA1 is maintained in the ER by a retrieval process (co-localization with ERGIC53).\",\n      \"method\": \"EGFP-tagged chimera expression in COS-7 cells, subcellular localization by confocal microscopy, co-localization with ER/Golgi intermediate compartment marker ERGIC53\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct localization experiment with systematic domain-swap chimeras, functional consequence for ER retention identified\",\n      \"pmids\": [\"12585965\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"Phospholamban (PLN), when stably transfected into C2C12 fast-twitch skeletal muscle cells expressing endogenous SERCA1, inhibits SERCA1 activity by decreasing its Ca2+ affinity (apparent Km shifted from 0.27 to 0.41 µM) at low Ca2+ concentrations in the native membrane environment.\",\n      \"method\": \"Stable transfection of PLN into C2C12 myotubes, 45Ca2+-uptake assay over range of Ca2+ concentrations, Western blot, microsomal fractionation\",\n      \"journal\": \"Molecular and cellular biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional Ca2+ uptake assay in native membrane context, single lab\",\n      \"pmids\": [\"7651372\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"A missense mutation in ATP2A1 exon 6 (c.491G>A; p.Arg164His) causes congenital pseudomyotonia in Chianina cattle by reducing SERCA1 activity by ~70%. Arg164 is a functionally important and strongly conserved residue of SERCA1.\",\n      \"method\": \"Linkage analysis, mutation analysis, SERCA1 ATPase activity measurement in SR membranes from affected cattle\",\n      \"journal\": \"Genomics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic and biochemical evidence in animal model, conserved residue identified as critical for function\",\n      \"pmids\": [\"18786632\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"The Arg164His SERCA1 mutant (bovine pseudomyotonia) shows selective reduction of SERCA1 protein in SR membranes despite normal mRNA levels, without significant change in Ca2+-dependency of residual ATPase activity and without compensatory upregulation of SERCA2. The protein reduction (not catalytic deficiency) accounts for the reduced activity.\",\n      \"method\": \"Western blot, Northern blot, SERCA1 ATPase activity assay, Ca2+-dependency measurement, immunofluorescence\",\n      \"journal\": \"The American journal of pathology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — biochemical dissection of mechanism (protein quantity vs. catalytic defect), single lab\",\n      \"pmids\": [\"19116366\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"The Arg164His SERCA1 mutant (Chianina pseudomyotonia) is degraded by the ubiquitin-proteasome system (UPS). Treatment with proteasome inhibitor MG132 rescues expression level and membrane localization of the mutant in a heterologous cellular model. The rescued mutant retains normal Ca2+ homeostasis maintenance ability. Ex vivo skeletal muscle fibers from affected animals confirmed these findings, indicating the mutation causes misfolding rather than catalytic inactivation.\",\n      \"method\": \"Proteasome inhibitor treatment (MG132), Western blot, immunofluorescence localization, Ca2+-sensitive aequorin probe in co-transfected cells, ex vivo adult muscle fiber analysis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (pharmacological rescue, localization, functional Ca2+ assay), confirmed ex vivo\",\n      \"pmids\": [\"25288803\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Transcription factors Ebf3 and Ebf1 cooperate with MyoD to directly regulate Atp2a1 (SERCA1) expression in skeletal muscle. Ebf3 binds directly to the Atp2a1 promoter and synergizes with MyoD for Atp2a1 induction. In Ebf3-null mice, SERCA1 is downregulated in the diaphragm, causing impaired Ca2+ efflux-related muscle function; transgenic SERCA1 expression rescues this phenotype.\",\n      \"method\": \"ChIP (Ebf3 binding to Atp2a1 promoter), reporter assay (synergy with MyoD), knockout mouse analysis, transgenic rescue, Ca2+ efflux measurements\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — direct promoter binding shown by ChIP, genetic rescue experiment, multiple orthogonal methods\",\n      \"pmids\": [\"24786561\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Small ankyrin 1 (sAnk1) interacts specifically with SERCA1 via its transmembrane domain and its cytoplasmic domain. This interaction is demonstrated in native SR vesicles from rabbit skeletal muscle and in transfected COS7 cells. sAnk1 co-expression reduces the apparent Ca2+ affinity of SERCA1 but the effect is smaller than sarcolipin. Replacement of all TM amino acids with leucines reduces binding ~2-fold and abolishes the effect on SERCA1 activity.\",\n      \"method\": \"Co-immunoprecipitation from native SR vesicles and transfected cells, anisotropy-based FRET (AFRET), ATPase activity assay, TM domain mutagenesis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal co-IP, FRET, functional assay, mutagenesis; multiple orthogonal methods\",\n      \"pmids\": [\"26405035\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"sAnk1 and SLN interact directly and form a three-protein complex with SERCA1 in the SR membrane. SLN promotes the interaction between sAnk1 and SERCA1. When sAnk1 and SLN are co-expressed with SERCA1, sAnk1 ablates SLN's inhibitory effect on SERCA1 activity. The sAnk1-SLN interaction does not require endogenous SERCA2.\",\n      \"method\": \"Co-immunoprecipitation, anisotropy-based FRET (AFRET), Ca2+-ATPase activity assay, co-transfection in COS7 cells\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal co-IP, FRET, functional enzyme assay; three-way complex characterized with multiple methods\",\n      \"pmids\": [\"28487373\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"SERCA1a has approximately double the ATPase and Ca2+ uptake activity of SERCA1b when overexpressed in cells, despite similar affinities for ATP and Ca2+. SERCA1b is more sensitive to the inner microsomal environment. SERCA1b protein is highly expressed in DM1 muscle tissue, predominantly in fast-twitch fibers.\",\n      \"method\": \"Overexpression in cells, ATPase activity assay, Ca2+ uptake assay, Western blot, immunostaining\",\n      \"journal\": \"Biochimica et biophysica acta\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct functional comparison of two splice variants with enzyme activity assays, single lab\",\n      \"pmids\": [\"26170059\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"4-aminoquinoline derivatives (NF1442 and NF1058) and clotrimazole inhibit SERCA1 by stabilizing an E2 state that interferes with Ca2+ binding and the E2→E1·Ca2 transition required for phosphoenzyme formation by ATP, but this E2 state retains the ability to form E2-P by reacting with Pi. This is mechanistically distinct from thapsigargin, which also inhibits Pi-dependent phosphorylation.\",\n      \"method\": \"Steady-state ATPase activity assay, single-cycle charge transfer measurement, sequential reaction kinetic characterization of phosphoenzyme formation\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — detailed mechanistic dissection of catalytic cycle states using multiple biochemical assays; defined mechanistic distinction from thapsigargin\",\n      \"pmids\": [\"21914795\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"SERCA1 (RyR1/SERCA1 cross-talk): In heavy SR vesicles, SERCA1 ATPase catalytic activity is well coordinated to RyR1 activation/inactivation states. Ryanodine-induced Ca2+ channel leak activates SERCA1 in the absence of measurable bulk Ca2+ increase, suggesting SERCA1 pumps sense Ca2+ ions exiting RyR1 cytoplasmic openings. Conversely, RyR1 activation is dependent on SERCA1 activity; at threshold luminal Ca2+ load, RyR1-induced Ca2+ release produces transient reversal of SERCA1 catalytic activity.\",\n      \"method\": \"Synchronous fluorescence determination of extravesicular Ca2+ transients and catalytic activity in heavy SR membrane vesicles, ryanodine receptor pharmacology\",\n      \"journal\": \"Canadian journal of physiology and pharmacology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — functional measurements in native membrane preparations, single lab, single method type\",\n      \"pmids\": [\"12733821\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"The rat SERCA1 5' flanking region contains weight-bearing responsive elements. Specific CACC box at -1262 and a nearby E-box at -1248 are necessary and sufficient for transcriptional activation by muscle unloading. Both elements together are required to activate transcription; trimerized CACC sites alone are insufficient.\",\n      \"method\": \"In vivo somatic gene transfer into rat soleus muscle, deletion analysis of SERCA1 promoter/5' flank, mutagenesis of cis-elements, luciferase reporter assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — systematic deletion and mutagenesis of regulatory elements with in vivo reporter assay\",\n      \"pmids\": [\"10811813\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"The ER-localized autophagy protein EPG-3/VMP1 regulates ER contacts with other organelles (phagophores, lipid droplets, mitochondria, endolysosomes) by activating SERCA (ATP2A/SERCA) calcium channel activity. Downstream, calmodulin (CALM) acts as a calcium effector controlling PIK3C3/VPS34 PI3-kinase activity to maintain ER contacts.\",\n      \"method\": \"Genetic epistasis in C. elegans, biochemical assays, live imaging of organelle contacts\",\n      \"journal\": \"Autophagy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic epistasis with pathway placement; study addresses ATP2A/SERCA broadly and implicates SERCA activity in ER contact regulation\",\n      \"pmids\": [\"29494262\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"PKC signaling regulates alternative splicing of SERCA1. PMA treatment regulates SERCA1 exon splicing in HEK293 cells; prolonged PMA (48h) normalizes SERCA1 splicing while short treatment (1.5h) promotes aberrant splicing. Both effects are abolished by PKC inhibitor Ro 31-8220. RNAi knockdown of PKCβII and PKCθ mimics prolonged PMA treatment (normalized splicing).\",\n      \"method\": \"PMA treatment, PKC inhibitor treatment, RNAi knockdown of PKC isoforms, RT-PCR splicing assay\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — pharmacological and RNAi epistasis placed PKC pathway in SERCA1 splicing regulation; single lab\",\n      \"pmids\": [\"22609207\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"A novel small transmembrane protein MCARE (muscle-enriched Ca2+ regulator), predominantly expressed in fast-twitch muscles, enhances SERCA1 function by competitively inhibiting myoregulin (a muscle-specific micropeptide that suppresses SERCA1 activity). MCARE-mediated SERCA1 activation facilitates Ca2+ clearance from the cytoplasm and accelerates muscle relaxation. Mcare-deficient mice show muscular dystrophy-like symptoms (progressive muscle wasting, reduced strength, increased susceptibility to exercise-induced damage, rippling muscle contractions) in fast-twitch muscles.\",\n      \"method\": \"Knockout mouse model, Ca2+ clearance measurements, protein interaction studies, ATPase activity assays, competition assay with myoregulin\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic KO with defined phenotype, direct competitive inhibition mechanism established, multiple orthogonal methods\",\n      \"pmids\": [\"41372236\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"The juxtamembrane region of sAnk1 cytoplasmic domain (residues K38, H39, H41) and hydrophobic residues R64-K73 mediate binding to SERCA1. The cytoplasmic domain alone (sAnk1(29-155)) does not inhibit SERCA1 Ca2+-ATPase activity, but the WT juxtamembrane sequence is required for the inhibitory activity of full-length sAnk1. Binding affinity of sAnk1(29-155) for SERCA1 is 444 nM by blot overlay.\",\n      \"method\": \"Site-directed mutagenesis, blot overlay binding affinity measurement, circular dichroism, ATPase activity assay, structural modeling\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — mutagenesis with functional readout, multiple structural and biochemical methods; single lab\",\n      \"pmids\": [\"39863105\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"sAnk1 associates with phospholamban (PLN) and forms a three-way complex with PLN and SERCA1, as shown by co-IP and BiFC in COS7 cells and confirmed by AFRET. Unlike its effect on SLN inhibition, sAnk1 does not ablate PLN's inhibition of SERCA1 activity. Modeling suggests PLN binds SERCA1 first, then sAnk1 binds PLN; the interactions of PLN, SLN, and sAnk1 with SERCA1 are mechanistically distinct.\",\n      \"method\": \"Co-transfection, co-immunoprecipitation, bimolecular fluorescence complementation (BiFC), anisotropy-based FRET (AFRET), ATPase activity assay\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods for complex detection and functional characterization; single lab\",\n      \"pmids\": [\"40998301\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"FAM134B short isoform (FAM134B-S), an ER-phagy receptor induced by statins via the mevalonate pathway and SREBPs, interacts with SERCA1 and promotes its autophagic degradation (SR-phagy). This degradation mechanism contributes to statin-associated muscle symptoms and myotoxicity. FAM134B plays a role in maintaining skeletal muscle integrity under both steady-state and statin-treated conditions in human iPS-derived myocytes and mice.\",\n      \"method\": \"Transcriptome analysis, protein-protein interaction studies (co-IP/pulldown), autophagy assays, knockdown/overexpression in iPS-derived myocytes and mice, pathway analysis (mevalonate pathway inhibition)\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct interaction between FAM134B-S and SERCA1 established, mechanistic pathway defined; preprint, not peer-reviewed\",\n      \"pmids\": [\"bio_10.1101_2025.11.26.690680\"],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"CFTR correctors, particularly C17, rescue SERCA1 missense mutants (Brody myopathy/bovine pseudomyotonia) both in vitro and in vivo by counteracting premature proteasomal degradation of misfolded-but-catalytically-active SERCA1 mutant proteins. This identifies UPS-mediated degradation of misfolded SERCA1 as the shared pathogenetic mechanism with cystic fibrosis.\",\n      \"method\": \"CFTR corrector treatment in cellular and animal models, Western blot for SERCA1 rescue, Ca2+ homeostasis assays, in vivo bovine PMT model\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — pharmacological rescue in vitro and in vivo with mechanistic explanation; builds on prior UPS degradation findings\",\n      \"pmids\": [\"41206505\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"ATP2A1/SERCA1 is the fast-twitch skeletal muscle SR Ca2+-ATPase that pumps Ca2+ from the cytosol into the SR lumen to enable muscle relaxation; its activity is regulated by a network of transmembrane micropeptide regulators (sarcolipin, phospholamban, myoregulin, sAnk1, and MCARE) that modulate its Ca2+ affinity and/or Vmax, its ER localization is determined by an N-terminal retrieval signal (residues 1–211), its expression is transcriptionally co-activated by Ebf factors and MyoD, aberrant splicing of exon 22 driven by MBNL1 sequestration impairs function in myotonic dystrophy, truncated or misfolded SERCA1 variants (from disease mutations or alternative splicing) that reach the ER act as Ca2+ leak channels or are degraded by the ubiquitin-proteasome system, and pathogenic SERCA1 deficiency—causing Brody disease and animal pseudomyotonia phenotypes—leads to impaired cytosolic Ca2+ clearance, muscle relaxation failure, and downstream mitochondrial Ca2+ overload and apoptosis.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"ATP2A1 encodes SERCA1, the fast-twitch skeletal muscle sarcoplasmic/endoplasmic reticulum Ca2+-ATPase that clears cytosolic Ca2+ into the SR lumen to drive muscle relaxation, as established by loss-of-function models in which SERCA1-null mice fail diaphragm contraction and zebrafish atp2a1 mutants show slowed cytosolic Ca2+ decay and sustained muscle co-contraction [#7, #8]. The pump cycles between E1Ca2 and E2 conformations through large rigid-body motions of its N and A domains, with a side-by-side pair of transmembrane Ca2+-binding sites built from M4, M5 and M6 helices [#3, #9]; pharmacological inhibitors such as 4-aminoquinolines and clotrimazole act by stabilizing an E2 state that blocks the E2→E1·Ca2 transition [#21]. SERCA1 activity is tuned by a network of small transmembrane regulators—sarcolipin and phospholamban lower apparent Ca2+ affinity (sarcolipin additionally raising Vmax), small ankyrin 1 (sAnk1) binds SERCA1 directly and assembles three-way complexes that relieve sarcolipin inhibition, and the muscle-enriched micropeptide MCARE activates the pump by competitively antagonizing the inhibitor myoregulin [#0, #11, #13, #18, #19, #26]. Its ER residence is set by an N-terminal retrieval signal in residues 1–211, and its expression is driven by Ebf factors cooperating with MyoD [#12, #17]. Loss-of-function or misfolding mutations in ATP2A1 cause autosomal recessive Brody disease in humans and pseudomyotonia in cattle, with misfolded-but-catalytically-active mutants such as Arg164His cleared by the ubiquitin-proteasome system and rescuable by proteasome inhibition or CFTR correctors [#1, #2, #14, #16, #30]. Aberrant SERCA1 splicing also generates pathology: MBNL1 sequestration in myotonic dystrophy excludes exon 22, and C-terminally truncated S1T variants that retain only partial Ca2+-binding residues form ER-localized leak channels at ER–mitochondria microdomains that deplete ER Ca2+, drive mitochondrial Ca2+ overload, ER stress, and apoptosis [#4, #6, #10].\",\n  \"teleology\": [\n    {\n      \"year\": 1996,\n      \"claim\": \"Established that ATP2A1 is a disease gene, linking SERCA1 loss-of-function to a human muscle relaxation disorder and grounding its physiological role in SR Ca2+ uptake.\",\n      \"evidence\": \"Genetic linkage and mutation analysis of Brody disease families with SR Ca2+-ATPase activity measurements in patient muscle\",\n      \"pmids\": [\"8841193\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not resolve which mutations cause catalytic versus expression defects\", \"No structural mechanism for individual mutations\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"Defined the structural basis of Ca2+ binding by mapping the transmembrane helices responsible for the two coordination sites, explaining how the pump captures cytosolic Ca2+.\",\n      \"evidence\": \"Alanine-scanning mutagenesis and site-directed disulfide cross-linking of M4–M6/M8 helices\",\n      \"pmids\": [\"9789547\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Coiled-coil model inferred from cross-linking, not full structure\", \"Did not address conformational transitions during transport\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"Identified sarcolipin as a transmembrane regulator that modulates SERCA1 Ca2+ affinity and Vmax distinctly from phospholamban, opening the micropeptide regulatory network.\",\n      \"evidence\": \"Co-expression in HEK-293T cells, Ca2+ uptake assays, FLAG tagging and mutagenesis, SR vesicles from stimulated muscle\",\n      \"pmids\": [\"9575189\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural interface with SERCA1 not resolved here\", \"Physiological stoichiometry in muscle not quantified\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Demonstrated that disease-mutation phenotype depends on functional impact, distinguishing a causal affinity-disrupting mutation from a benign variant.\",\n      \"evidence\": \"Site-directed mutagenesis and Ca2+ transport assays of Pro789Leu and Arg819Cys in HEK-293 cells\",\n      \"pmids\": [\"10914677\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not address protein stability or folding of mutants\", \"Limited to two variants\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Revealed that truncated SERCA1 splice variants are not merely dead pumps but actively form ER Ca2+ leak channels that trigger apoptosis, establishing a gain-of-toxic-function mechanism.\",\n      \"evidence\": \"RT-PCR, dimer-detecting Western blot, confocal co-localization, ER-targeted aequorin Ca2+ measurements, apoptosis assays\",\n      \"pmids\": [\"11402072\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Channel structure of S1T homodimers not defined\", \"Physiological relevance in muscle not established here\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Provided the in vivo physiological proof that SERCA1 is essential for fast-twitch muscle relaxation and respiratory function with no compensatory redundancy.\",\n      \"evidence\": \"SERCA1-null mouse gene targeting, Ca2+ transport Vmax, contractility assays, Ca2+-handling protein profiling\",\n      \"pmids\": [\"12556521\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not test fiber-type-specific rescue\", \"Mechanism of perinatal lethality limited to diaphragm phenotype\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Located the ER-retrieval signal that confines SERCA1 to the ER/SR, explaining how the pump achieves its compartment-specific localization.\",\n      \"evidence\": \"EGFP chimera domain swaps in COS-7 cells with ERGIC53 co-localization\",\n      \"pmids\": [\"12585965\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Retrieval machinery/receptor not identified\", \"Signal residues within 1–211 not narrowed\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Modeled the conformational mechanics of the transport cycle, identifying which domains move as rigid bodies during E1-to-E2 transitions.\",\n      \"evidence\": \"Normal mode analysis of E1Ca2 and E2TG crystal structures with dynamical domain decomposition\",\n      \"pmids\": [\"14507684\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Computational only, no experimental validation in this study\", \"Did not capture regulator-bound states\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Pinpointed the luminal sarcolipin residues that contact SERCA1 and inhibit turnover, giving residue-level resolution to micropeptide regulation.\",\n      \"evidence\": \"Solid-state NMR, peptide inhibition assays, Ca2+ transport assays with SERCA1a in lipid bilayers\",\n      \"pmids\": [\"17616528\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"IC50 in the micromolar range may not reflect native affinity\", \"Full-length interaction interface not mapped\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Explained how SERCA1 splicing is disrupted in myotonic dystrophy by identifying MBNL1 as the direct exon-22 splicing activator that is titrated away by CUG repeats.\",\n      \"evidence\": \"Exon trapping with mutagenesis of MBNL1 binding motifs and CUG repeat overexpression\",\n      \"pmids\": [\"17728322\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional consequence of exon 22 exclusion on pump activity not measured here\", \"Did not address other splice events\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Extended the leak-channel toxic mechanism to ER–mitochondria signaling, showing truncated SERCA1 amplifies mitochondrial Ca2+ overload, ER stress and apoptosis.\",\n      \"evidence\": \"siRNA knockdown, live-cell Ca2+ imaging, ER-mitochondria contact quantification, PERK-eIF2α-ATF4-CHOP analysis\",\n      \"pmids\": [\"19061639\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo muscle relevance of the contact-site mechanism not shown\", \"Channel conductance properties not measured\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Identified a conserved-residue missense mutation causing an animal pseudomyotonia phenotype, providing a naturally occurring model of SERCA1 deficiency.\",\n      \"evidence\": \"Linkage and mutation analysis with SR ATPase activity in Chianina cattle\",\n      \"pmids\": [\"18786632\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism of activity loss not yet defined at this stage\", \"Single breed\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Resolved that the Arg164His pseudomyotonia defect is loss of pump protein rather than catalytic incompetence, reframing the lesion as a stability problem.\",\n      \"evidence\": \"Western/Northern blot, ATPase and Ca2+-dependency assays, immunofluorescence in affected cattle muscle\",\n      \"pmids\": [\"19116366\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Degradation pathway not yet identified\", \"Single lab\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Demonstrated that the misfolded Arg164His SERCA1 is destroyed by the proteasome and pharmacologically rescuable, converting a structural lesion into a druggable target.\",\n      \"evidence\": \"MG132 proteasome inhibition, localization, aequorin Ca2+ assays, ex vivo muscle fibers\",\n      \"pmids\": [\"25288803\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not show clinical-grade rescue strategy\", \"Generality across other Brody mutations not tested here\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Established the transcriptional control of SERCA1, showing Ebf factors cooperate with MyoD at the Atp2a1 promoter to drive muscle expression with phenotypic rescue.\",\n      \"evidence\": \"ChIP of Ebf3 on Atp2a1 promoter, MyoD synergy reporter assays, Ebf3-null mice, transgenic SERCA1 rescue\",\n      \"pmids\": [\"24786561\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Fiber-type specificity of the regulatory circuit not fully resolved\", \"Other upstream signals not mapped\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Added small ankyrin 1 to the regulator network as a direct SERCA1 binder that lowers Ca2+ affinity, expanding the membrane regulatory repertoire beyond SLN/PLN.\",\n      \"evidence\": \"Co-IP from native SR and transfected cells, AFRET, ATPase assays, TM-domain mutagenesis\",\n      \"pmids\": [\"26405035\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Cytoplasmic-domain contribution not yet mapped\", \"Physiological role in muscle Ca2+ handling not established\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Showed SERCA1 splice variants differ functionally, with SERCA1a more active than SERCA1b and SERCA1b enriched in DM1 muscle, linking isoform choice to disease.\",\n      \"evidence\": \"Overexpression, ATPase and Ca2+ uptake assays, Western blot, immunostaining\",\n      \"pmids\": [\"26170059\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Structural basis of the activity difference unknown\", \"Single lab\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Defined a three-protein regulatory complex in which sAnk1 binds both SLN and SERCA1 and relieves SLN inhibition, revealing combinatorial control of the pump.\",\n      \"evidence\": \"Co-IP, AFRET, Ca2+-ATPase assays in COS7 cells\",\n      \"pmids\": [\"28487373\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Native-muscle stoichiometry of the complex not quantified\", \"Structural arrangement inferred indirectly\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Placed SERCA Ca2+ pumping within ER organelle-contact regulation, where VMP1 activates SERCA and calmodulin/VPS34 maintain inter-organelle contacts.\",\n      \"evidence\": \"Genetic epistasis in C. elegans, biochemical assays, live imaging of organelle contacts\",\n      \"pmids\": [\"29494262\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Addresses SERCA broadly, not ATP2A1-specific\", \"Direct VMP1–SERCA biochemistry not shown\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Refined the sAnk1 mechanism by mapping juxtamembrane and hydrophobic cytoplasmic residues required for binding and inhibition of SERCA1.\",\n      \"evidence\": \"Mutagenesis, blot-overlay affinity, circular dichroism, ATPase assays, modeling\",\n      \"pmids\": [\"39863105\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No high-resolution structure of the interface\", \"Single lab\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Distinguished how PLN versus SLN engage the sAnk1-containing complex, showing sAnk1 does not relieve PLN inhibition, indicating mechanistically distinct regulator modes.\",\n      \"evidence\": \"Co-IP, BiFC, AFRET, ATPase assays in COS7 cells\",\n      \"pmids\": [\"40998301\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Native assembly order not directly observed\", \"Single lab\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Identified MCARE as a positive regulator that activates SERCA1 by competitively antagonizing the inhibitor myoregulin, with loss causing dystrophy-like fast-twitch pathology.\",\n      \"evidence\": \"Knockout mice, Ca2+ clearance measurements, interaction and ATPase assays, myoregulin competition assay\",\n      \"pmids\": [\"41372236\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of competition not resolved\", \"Interplay with SLN/sAnk1 network not tested\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Generalized UPS-mediated degradation of misfolded SERCA1 as a shared pathogenic mechanism and showed CFTR correctors rescue catalytically-active mutants in vivo.\",\n      \"evidence\": \"CFTR corrector treatment in cellular and bovine pseudomyotonia models, Western blot, Ca2+ homeostasis assays\",\n      \"pmids\": [\"41206505\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Human Brody disease efficacy not demonstrated\", \"Long-term/in vivo durability not addressed\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Linked SERCA1 to selective autophagic turnover (SR-phagy) via the ER-phagy receptor FAM134B-S, implicating regulated degradation in statin myotoxicity.\",\n      \"evidence\": \"Transcriptomics, co-IP/pulldown, autophagy assays, knockdown/overexpression in iPS myocytes and mice (preprint)\",\n      \"pmids\": [\"bio_10.1101_2025.11.26.690680\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Preprint, not peer-reviewed\", \"Direct FAM134B-S binding interface on SERCA1 not mapped\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How the multiple micropeptide regulators (SLN, PLN, myoregulin, sAnk1, MCARE) are integrated stoichiometrically and spatially on a single SERCA1 pump in native fast-twitch SR remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No native-tissue structure of multi-regulator complexes\", \"Quantitative regulator stoichiometry per pump unknown\", \"Crosstalk between transcriptional, splicing, and degradative control not unified\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0005215\", \"supporting_discovery_ids\": [7, 8, 1]},\n      {\"term_id\": \"GO:0140657\", \"supporting_discovery_ids\": [2, 11, 21]},\n      {\"term_id\": \"GO:0016787\", \"supporting_discovery_ids\": [11, 18, 20]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [12, 4, 6]},\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [18, 0]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-397014\", \"supporting_discovery_ids\": [7, 8, 26]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [1, 2, 14, 30]},\n      {\"term_id\": \"R-HSA-382551\", \"supporting_discovery_ids\": [7, 8]}\n    ],\n    \"complexes\": [\n      \"SERCA1-sarcolipin-sAnk1 complex\",\n      \"SERCA1-phospholamban-sAnk1 complex\"\n    ],\n    \"partners\": [\n      \"SLN\",\n      \"PLN\",\n      \"sAnk1\",\n      \"MCARE\",\n      \"MYOREGULIN\",\n      \"MBNL1\",\n      \"FAM134B\"\n    ],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}