{"gene":"S100A1","run_date":"2026-06-10T07:46:28","timeline":{"discoveries":[{"year":1986,"finding":"S100A1 (S100-alpha subunit) binds calcium at 4 Ca2+ per dimer with specific EF-hand sites; zinc binding increases calcium affinity of S100b but only weakly affects S100-alpha; calcium binding induces conformational changes exposing hydrophobic domains including Cys85.","method":"Flow dialysis, UV spectroscopy, fluorescence spectroscopy, sulfhydryl reactivity assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — multiple orthogonal biophysical methods in a single rigorous study, replicated across multiple S100 isoforms with well-controlled quantitative binding measurements","pmids":["3722149"],"is_preprint":false},{"year":1986,"finding":"Calcium binding to S100A1 (S100a) induces a conformational change that exposes hydrophobic domains; the alpha-subunit conformation is nearly identical whether in the S100a heterodimer or S100-alpha homodimer; calcium at high protein concentrations triggers subunit dissociation and exchange.","method":"UV absorption, circular dichroism, intrinsic fluorescence, sulfhydryl reactivity, hydrophobic fluorescent probe (ANS), FPLC separation","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — multiple orthogonal biophysical methods, rigorous controls with purified protein","pmids":["3722150"],"is_preprint":false},{"year":1991,"finding":"S100A1 protein in skeletal muscle co-localizes with the A-band and/or longitudinal sarcoplasmic reticulum; isolated sarcoplasmic reticulum fractions and myofibrils contain multiple S100A1-binding proteins, suggesting a role in excitation-contraction coupling.","method":"Immunohistochemistry, radioimmunoassay, Northern blot, gel overlay for binding proteins, subcellular fractionation","journal":"Cell motility and the cytoskeleton","confidence":"Medium","confidence_rationale":"Tier 2–3 / Moderate — multiple methods in a single lab but binding partners not individually identified biochemically","pmids":["1802419"],"is_preprint":false},{"year":1995,"finding":"S100A1 (S100a, alpha-alpha homodimer) binds to the basic helix I domain of MyoD (and other myogenic bHLH transcription factors) in a calcium-dependent manner; this binding inhibits PKC-mediated phosphorylation of MyoD at Thr115 and blocks MyoD DNA-binding activity; S100A1 is more potent than calmodulin in inhibiting MyoD DNA binding.","method":"Affinity chromatography, chemical cross-linking, native gel electrophoresis, fluorescence spectroscopy with DANSYL-CaM competition, in vitro PKC phosphorylation assay, co-immunoprecipitation from H9c2 cells","journal":"Biochemistry","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — multiple orthogonal methods including in vitro kinase assay, affinity chromatography, co-IP, and fluorescence competition, all pointing to same conclusion","pmids":["7794894"],"is_preprint":false},{"year":1996,"finding":"S100A1 inhibits phosphoglucomutase activity in a calcium-dependent manner (while S100B stimulates it); both S100A1 and S100B bind phosphoglucomutase via calcium-dependent affinity chromatography, identifying phosphoglucomutase as an S100A1 target protein.","method":"Gel overlay, affinity chromatography (S100A1/B-Sepharose and phosphoglucomutase-Sepharose), enzyme activity assay","journal":"Cell calcium","confidence":"High","confidence_rationale":"Tier 1 / Moderate — reciprocal affinity chromatography combined with enzymatic activity assay in a single study with proper controls","pmids":["8894274"],"is_preprint":false},{"year":1996,"finding":"S100A1-S100B heterodimer (CD-GCAP) is expressed in bovine retina and stimulates rod outer segment membrane guanylate cyclase (ROS-GC) activity in a calcium-dependent manner (EC50 ~17 µM Ca2+); the kinase-like domain of ROS-GC is not involved; the interaction domain resides in the C-terminal segment (aa 731–1054) of ROS-GC.","method":"Western blot, in vitro guanylate cyclase activity assay, domain mapping with deletion constructs","journal":"Biochemistry","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — in vitro reconstitution with domain mapping, single lab","pmids":["8639567"],"is_preprint":false},{"year":1997,"finding":"S100A1 directly interacts with three distinct binding domains on the skeletal muscle ryanodine receptor (RyR1) in a calcium-dependent and calcium-independent manner; at nanomolar Ca2+, S100A1 activates [3H]ryanodine binding (~40%) and increases single-channel open probability ~6-fold in planar lipid bilayer reconstitution; S100A1 increases apparent affinity of RyR for ryanodine (Kd 383→191 nM).","method":"Equilibrium [3H]ryanodine binding, planar lipid bilayer single-channel recording, BIAcore optical biosensor, ligand overlay on RyR fusion proteins, affinity chromatography on S100A1-Sepharose","journal":"Biochemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — reconstitution in lipid bilayer, multiple orthogonal binding methods, domain mapping; single lab but comprehensive","pmids":["9298970"],"is_preprint":false},{"year":1997,"finding":"S100A1 activates twitchin kinase in a calcium-dependent, zinc-enhanced manner; Ca2+/S100A1 binds twitchin kinase fragments with Kd <50 nM; Zn2+ reduces the off-rate; other Ca2+-binding proteins (S100A6, calmodulin, Ca2+-dependent protein kinase CaM-domain) bind the kinase but do not activate it, indicating specificity of S100A1 for kinase activation.","method":"BIAcore biosensor binding assay, in vitro kinase activity assay with recombinant S100A1","journal":"European journal of biochemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — direct binding kinetics and enzymatic activity with specificity controls; single lab","pmids":["9363763"],"is_preprint":false},{"year":1998,"finding":"The carboxyl-terminal aromatic residues Phe88, Phe89, and Trp90 of S100A1 are essential for calcium-dependent target protein binding (TRTK/CapZ peptide) and hydrophobic exposure (phenyl-Sepharose interaction); deletion of residues 85–93 or triple aromatic mutation abolishes calcium-dependent target binding; calcium-independent target activation (aldolase A) does not require the C-terminus, revealing two mechanistically distinct interaction modes.","method":"Site-directed mutagenesis, affinity chromatography (phenyl-Sepharose), fluorescence binding assay with TRTK peptide, aldolase A activity assay","journal":"Biochemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — mutagenesis combined with functional assays and binding measurements, clear structure-function mapping","pmids":["9860858"],"is_preprint":false},{"year":1999,"finding":"The C-terminal extension of S100A1 (residues Phe88–Ser93) is required for binding to GFAP, tubulin, the TRTK-12 peptide (CapZ), and a p53-derived peptide; S100A1 inhibits GFAP assembly into intermediate filaments via this C-terminal region; the truncated S100A1Δ88-93 lacks these interactions.","method":"Fluorescence spectroscopy with acrylodan-labeled S100A1, chemical crosslinking, GFAP polymerization assay, competition with TRTK-12 and p53 peptide","journal":"Biochemical and biophysical research communications","confidence":"High","confidence_rationale":"Tier 1 / Moderate — mutagenesis combined with functional assembly assay and fluorescence binding measurements, multiple targets tested","pmids":["9920729"],"is_preprint":false},{"year":1998,"finding":"Annexin VI binds S100A1 (and S100B) in a calcium-dependent manner and blocks their ability to inhibit desmin and GFAP assembly into intermediate filaments; each S100A1 dimer has one annexin VI binding site (sub-µM affinity); the annexin VI binding site on S100A1 does not overlap with the C-terminal extension required for desmin/GFAP binding.","method":"In vitro intermediate filament assembly assay, affinity chromatography, fluorescence binding","journal":"Cell calcium","confidence":"Medium","confidence_rationale":"Tier 2–3 / Moderate — functional assay combined with affinity binding, single lab, multiple targets","pmids":["9883272"],"is_preprint":false},{"year":2000,"finding":"S100A4 and S100A1 interact directly in vitro and in vivo; the interaction requires conserved dimerization-interface residues (site-directed mutagenesis); S100A1 reduces S100A4-mediated inhibition of nonmuscle myosin A self-association and phosphorylation in vitro, and reduces S100A4-driven cell motility and metastasis.","method":"Yeast two-hybrid, affinity chromatography, gel overlay, FRET in living cells, biosensor binding kinetics, in vitro myosin assay, soft agar growth, in vivo metastasis assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — yeast two-hybrid confirmed by affinity chromatography, FRET in cells, and functional myosin assay; replicated in subsequent study (PMID:15608682)","pmids":["10753920","15608682"],"is_preprint":false},{"year":2000,"finding":"S100A1 and S100B cause calcium-dependent disassembly of cytoplasmic microtubules in situ in glioma and myoblast triton-cytoskeletons; the C-terminal extension of S100A1 is required (S100A1Δ88-93 is inactive); TRTK-12 peptide blocks the effect; no direct intermediate filament disassembly was observed under these conditions.","method":"Triton-cytoskeleton preparation from live cells, immunofluorescence microscopy, inhibitory peptide competition","journal":"Neuroscience","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — cell-based assay with mutagenesis equivalent (truncated protein) and peptide inhibition controls; single lab","pmids":["10974440"],"is_preprint":false},{"year":2001,"finding":"S100A1 overexpression in adult cardiomyocytes and engineered heart tissue (adenoviral gene transfer) increases unloaded shortening, isometric contraction, cytosolic Ca2+ transients, and SR Ca2+ uptake; S100A1 protein decreases myofibrillar Ca2+ sensitivity and cooperativity in Triton-skinned trabeculae without changing maximal force; effects are cAMP-independent (PKA phosphorylation of phospholamban unchanged).","method":"Adenoviral gene transfer, video-edge detection, FURA-2 Ca2+ imaging, saponin-permeabilized cell SR Ca2+ uptake assay, force-Ca2+ relationship in skinned trabeculae, cAMP measurement, PKA phosphorylation assay","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — multiple orthogonal functional assays in both isolated cells and engineered tissue; mechanistic specificity confirmed by cAMP independence","pmids":["11717446"],"is_preprint":false},{"year":2002,"finding":"S100A1 protein increases SERCA2a activity in skinned rat cardiomyocytes; adenoviral S100A1 overexpression increases fractional shortening by 55% and systolic Ca2+ amplitudes by 62% in adult rat cardiomyocytes.","method":"Adenoviral gene transfer, video-edge detection, FURA-2 Ca2+ imaging, SERCA activity assay in skinned cell preparations","journal":"Basic research in cardiology","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — direct enzymatic assay combined with cellular functional readout; consistent with independent studies (PMID:11717446, PMID:16236309)","pmids":["12479236"],"is_preprint":false},{"year":2003,"finding":"Extracellular S100A1 is endocytosed into neonatal cardiomyocytes via calcium-dependent clathrin-mediated endocytosis; internalized S100A1 activates ERK1/2 pro-survival signaling via a PLC→PKC→MEK1→ERK1/2 cascade, protecting cardiomyocytes from apoptosis; PKA and L-type Ca2+ channel are not required.","method":"Fluorescence microscopy of rhodamine-S100A1 uptake, apoptosis assay (2-deoxyglucose/oxidative stress), pharmacological inhibitors of signaling pathway, ERK1/2 phosphorylation Western blot","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — pathway placement by pharmacological epistasis with multiple inhibitors; endocytosis mechanism characterized; replicated direction of effect","pmids":["12960148"],"is_preprint":false},{"year":2003,"finding":"S100A1 is a molecular chaperone that forms stable complexes with Hsp90, Hsp70, FKBP52, and CyP40 (components of the Hsp70/Hsp90 multichaperone complex) both in vitro and in mammalian cells; S100A1 protects multiple client proteins (citrate synthase, aldolase, GAPDH, rhodanese) from heat-induced aggregation and inactivation; overexpression protects luciferase and β-galactosidase from heat-shock inactivation in COS-7 cells.","method":"GST pull-down, co-immunoprecipitation, in vitro aggregation protection assay, thermal inactivation assay, COS-7 overexpression with heat shock","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — reciprocal pull-down confirmed by co-IP, reconstituted chaperone activity in vitro, and validated in cell overexpression","pmids":["14638689"],"is_preprint":false},{"year":2004,"finding":"Adenoviral S100A1 gene delivery to failing rat cardiomyocytes (post-infarction model) normalizes S100A1 protein, restores SR Ca2+ uptake, reduces SR Ca2+ leak, restores intracellular Ca2+ transients, decreases elevated intracellular Na+, reverses fetal gene reactivation, and restores energy supply; intracoronary delivery normalizes in vivo contractile function.","method":"Adenoviral gene transfer in vivo and in vitro, echocardiography, Ca2+ transient imaging (FURA-2), SR Ca2+ load (caffeine), SR Ca2+ leak measurements, intracellular Na+ measurement, gene expression, metabolic assays","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — comprehensive mechanistic dissection of SR Ca2+ handling with multiple orthogonal readouts, in vitro and in vivo validated","pmids":["15578088"],"is_preprint":false},{"year":2004,"finding":"S100A1 binds S100P to form a heterodimer with Kd 10–20 nM (higher affinity than S100P homodimer, Kd 40–120 nM); FRET confirms the interaction in living cells; S100A1/S100P heterodimer is stabilized by hydrophobic interactions at the dimer interface (confirmed by site-directed mutagenesis); S100A1 preincubation reduces S100P binding to nonmuscle myosin A by ~50%.","method":"Yeast two-hybrid, optical biosensor (BIAcore), FRET in mammalian cells, site-directed mutagenesis, homology modelling","journal":"The Biochemical journal","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — binding kinetics by biosensor, FRET in live cells, mutagenesis defining interface, and functional consequence on myosin binding","pmids":["15171681"],"is_preprint":false},{"year":2005,"finding":"The three-dimensional NMR solution structure of Ca2+-bound S100A1 was determined; calcium binding causes large reorientation of helix 3 (typical EF-hand) but not of the pseudo EF-hand, exposing a hydrophobic cleft formed by hinge region, C-terminus, and helix 3 residues that constitutes the target-binding pocket for TRTK-12 (CapZ-derived peptide).","method":"Multidimensional NMR spectroscopy (2D/3D/4D), 3354 NOE constraints, 362 residual dipolar couplings, comparison with apo-S100A1 structure","journal":"Journal of molecular biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — high-resolution NMR structure with >21 constraints/residue; direct structural determination of Ca2+-induced conformational change and binding pocket","pmids":["16169012"],"is_preprint":false},{"year":2005,"finding":"S100A1 protein increases the gain of excitation-contraction coupling in rabbit ventricular cardiomyocytes: 0.1 µM S100A1 increases Ca2+ transient amplitude (~41%), increases SERCA2a Ca2+ uptake rate (~22%), increases RyR2 activity ([3H]-ryanodine binding at 0.1–0.3 µM Ca2+), and shifts the SR Ca2+ content–fractional release relationship leftward without changing SR Ca2+ content; co-immunoprecipitation confirms selective S100A1 interaction with SERCA2a and RyR2.","method":"Patch pipette protein delivery, voltage clamp, FURA-2 Ca2+ imaging, caffeine-induced SR Ca2+ release, NCX current measurement, [3H]-ryanodine binding, co-immunoprecipitation","journal":"Journal of molecular and cellular cardiology","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — multiple orthogonal methods including binding assay and functional electrophysiology/Ca2+ imaging; direct intracellular protein delivery","pmids":["16236309"],"is_preprint":false},{"year":2005,"finding":"S100A1 affinity for Ca2+ is dramatically increased (~10,000-fold increase in N-loop affinity, ~10-fold in C-loop) upon S-glutathionylation of Cys85; glutathionylated S100A1 still binds TRTK-12 in a Ca2+-dependent manner, linking redox and Ca2+ signaling.","method":"Trp90 fluorescence Ca2+-titration, TRTK-12 binding, site-directed mutagenesis of EF-hand loops (E32Q, E73Q), 2-p-toluidinylnaphthalene-6-sulfonate hydrophobicity probe","journal":"The FEBS journal","confidence":"High","confidence_rationale":"Tier 1 / Moderate — direct quantitative binding measurements with EF-hand mutants and redox-modified protein; single lab but rigorous mutagenesis","pmids":["15885104"],"is_preprint":false},{"year":2004,"finding":"Redox modification (S-nitrosylation and S-glutathionylation) of the conserved C-terminal cysteine (Cys85) of S100A1 strongly activated by Ca2+ binding results in global structural alterations of S100A1, as demonstrated by multiple spectroscopic techniques.","method":"RP-HPLC, ESI-MS, circular dichroism, fluorescence spectroscopy","journal":"Biochimica et biophysica acta","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — multiple biophysical methods demonstrating structural change, single lab","pmids":["15590070"],"is_preprint":false},{"year":2007,"finding":"S100A1 interacts with mitochondrial F1-ATPase alpha- and beta-chains in a Ca2+-dependent manner; S100A1 overexpression in cardiomyocytes increases cellular ATP content and F1-ATPase activity; S100A1 knockdown decreases ATP levels; ATP synthase activity is reduced in S100A1 knockout cardiomyocytes.","method":"GST pull-down, co-immunoprecipitation, confocal colocalization, gel filtration chromatography, ATP content measurement, F1-ATPase activity assay","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — reciprocal pull-down, co-IP, functional enzymatic assay, gain- and loss-of-function both tested","pmids":["17438143"],"is_preprint":false},{"year":2007,"finding":"S100A1 binds to the calmodulin-binding domain (CaM/S100A1 binding domain, RyRP12, residues 3616–3627) of RyR1 in skeletal muscle; genetic knockout of S100A1 reduces global myoplasmic Ca2+ transients and SR Ca2+ release following electrical excitation; the binding site is identified by competition assays and tryptophan fluorescence, and shows low micromolar affinity; NMR reveals the peptide binds in the Ca2+-dependent hydrophobic pocket of S100A1.","method":"S100A1 knockout mice, confocal microscopy Ca2+ imaging, competition binding assays with SR vesicles, tryptophan fluorescence, NMR spectroscopy","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — genetic KO with physiological phenotype, NMR structure of complex, and direct binding characterization; orthogonal methods","pmids":["18089560"],"is_preprint":false},{"year":2007,"finding":"S100A1 and S100B are transcriptional targets of the SOX trio (SOX9/SOX5/SOX6) in chondrocytes; S100A1 overexpression suppresses hypertrophic chondrocyte differentiation and mineralization; S100A1/S100B knockdown stimulates terminal differentiation and reverses SOX trio-mediated inhibition; SOX-trio-responsive enhancer elements identified in the S100A1 5'-flanking region.","method":"Microarray, overexpression, siRNA knockdown, luciferase reporter assay, EMSA, chromatin immunoprecipitation","journal":"EMBO reports","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — ChIP identifying direct transcriptional regulation, functional gain/loss-of-function, and EMSA; multiple orthogonal methods","pmids":["17396138"],"is_preprint":false},{"year":2008,"finding":"Ca2+-S100A1 competes with Ca2+-calmodulin for the same binding site on RyR1 (RyRP12 domain, residues 3616–3627 in human RyR1); NMR structure of Ca2+-S100A1 bound to RyRP12 reveals key hydrophobic/electrostatic interactions involving RyRP12 residues Lys3616, Trp3620, Lys3622, Leu3623, Leu3624, Lys3626 with the Ca2+-induced hydrophobic pocket of S100A1.","method":"Competition binding assays (skeletal muscle SR), NMR spectroscopy (structure determination of S100A1-RyRP12 complex)","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — NMR structure of complex combined with functional competition assay; single lab but comprehensive","pmids":["18650434"],"is_preprint":false},{"year":2008,"finding":"Endothelial S100A1 modulates vascular function: S100A1 knockout mice show reduced acetylcholine-induced vascular relaxation, reduced basal and agonist-induced endothelial NO release, diminished agonist-induced Ca2+ transients in ECs, and hypertension; S100A1 overexpression in ECs increases NO generation in an IP3R-dependent manner; endothelial S100A1 is downregulated in heart failure.","method":"S100A1 knockout mice, vascular ring relaxation assay, Ca2+ imaging in ECs, NO measurement, siRNA knockdown, adenoviral overexpression, IP3R blocker (2-APB)","journal":"Circulation research","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic KO with in vivo and ex vivo phenotype, pharmacological pathway placement by IP3R inhibition, siRNA and overexpression corroboration","pmids":["18292599"],"is_preprint":false},{"year":2009,"finding":"NMR solution structure of S100A1 bound to TRTK12 (CapZ-derived peptide) reveals that TRTK12 forms an amphipathic helix with W7, I10, and L11 making key hydrophobic contacts with the Ca2+-dependent hydrophobic binding pocket of S100A1; Ca2+ binding affinity of S100A1 is tightened >3-fold upon TRTK12 binding.","method":"Solution NMR structure determination, ITC/fluorescence Ca2+ binding measurements","journal":"Journal of molecular biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — NMR structure with defined intermolecular contacts and thermodynamic characterization of coupled binding","pmids":["19452629"],"is_preprint":false},{"year":2009,"finding":"In skeletal muscle fibers, S100A1 knockout selectively suppresses the Qgamma component of intra-membrane charge movement (voltage sensor activation) while leaving Qbeta unaffected; transient intracellular S100A1 application restores Qgamma; dantrolene (RyR1 inhibitor) similarly suppresses this charge movement component, linking S100A1 to RyR1-voltage sensor coupling.","method":"S100A1 knockout mice, whole-cell patch clamp of isolated flexor digitorum brevis fibers, intracellular S100A1 application, dantrolene pharmacology","journal":"The Journal of physiology","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic KO with specific electrophysiological phenotype, rescued by acute protein application, and pharmacological confirmation","pmids":["19651767"],"is_preprint":false},{"year":2009,"finding":"Exogenous S100A1 taken up by superior cervical ganglion neurons enhances Cav1 (L-type) Ca2+ channel currents and prolongs action potentials in a PKA-dependent manner; NMR chemical shift perturbation confirms direct Ca2+-S100A1 interaction with a peptide from the PKA regulatory subunit within S100A1's hydrophobic binding pocket.","method":"SCG neuron culture, whole-cell patch clamp, Ca2+ imaging, rhodamine-S100A1 uptake, PKA inhibitor, NMR chemical shift perturbation","journal":"American journal of physiology. Cell physiology","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — electrophysiology with pharmacological pathway placement, direct NMR binding evidence for S100A1-PKA interaction","pmids":["19657060"],"is_preprint":false},{"year":2011,"finding":"S100A1 is released from ischemic/necrotic cardiomyocytes and acts as an alarmin; it is endocytosed by cardiac fibroblasts and activates TLR4-dependent MAP kinase and NF-κB signaling, inducing an immunomodulatory/anti-fibrotic phenotype (elevated ICAM1, decreased collagen); antibody-mediated neutralization of S100A1 worsens infarct size and LV function post-MI.","method":"Patient serum ELISA, mouse MI model, in vitro co-culture, fluorescence microscopy of S100A1 endocytosis, Western blot (TLR4, MAP kinases, NF-κB), intracardiac S100A1 injection, neutralizing antibody","journal":"EMBO molecular medicine","confidence":"High","confidence_rationale":"Tier 2 / Strong — TLR4 pathway placement combined with in vivo neutralization phenotype, in vitro mechanistic dissection, and translational patient data","pmids":["24833748"],"is_preprint":false},{"year":2012,"finding":"Calmodulin and S100A1 bind to two independent but overlapping domains on the N-terminus of TRPM3 (Ala35-Lys124 and His291-Gly382); key positively charged residues in these domains are required for binding; CaM and S100A1 compete for the same binding sites on TRPM3; interactions are calcium-dependent.","method":"Biophysical binding assays, biochemical pull-down, site-directed mutagenesis of TRPM3 N-terminal domains, competition assays","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — mutagenesis combined with binding and competition assays; single lab, first report for TRPM3","pmids":["22451665"],"is_preprint":false},{"year":2012,"finding":"S100A1 deficiency in endothelial cells impairs postischemic angiogenesis; mechanistically, S100A1 deficiency disrupts stimulatory S100A1/eNOS interaction, causes PKC hyperactivation leading to inhibitory eNOS phosphorylation, degrades VEGFR-2 with blunted PI3K/Akt/eNOS signaling; NO supplementation rescues angiogenesis and limb salvage in SKO mice.","method":"S100A1 knockout mice, femoral artery resection, perfusion measurement, EC proliferation/migration/tube formation assays, siRNA knockdown, eNOS activity, PKC inhibitor, Western blot, in vivo NO measurement","journal":"Circulation research","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic KO with in vivo and cellular phenotype, mechanistic pathway placement by pharmacological rescue, siRNA corroboration","pmids":["23048072"],"is_preprint":false},{"year":2013,"finding":"In the PSAPP Alzheimer's disease mouse model, genetic ablation of S100A1 reduces astrocytosis, microgliosis, and amyloid plaque load; S100A1·RyR complexes are detected in human and mouse AD brain in a Ca2+-dependent manner (co-immunoprecipitation), identifying RyR as a primary S100A1 target protein in the brain; S100A1·Akt complexes are not detected, indicating indirect modulation of Akt.","method":"S100A1 knockout in PSAPP mice, immunohistochemistry (GFAP, Iba1, plaque), co-immunoprecipitation (S100A1·RyR and S100A1·Akt), Ca2+-dependent complex formation in neuronal cells","journal":"Cell calcium","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic KO phenotype plus direct co-IP of S100A1·RyR complex in brain tissue; indirect Akt modulation established as negative result","pmids":["24931125"],"is_preprint":false},{"year":2013,"finding":"MicroRNA-138 (miR-138) downregulates S100A1 protein in endothelial cells by targeting the 3'UTR of S100A1; hypoxia induces miR-138 via HIF1α; miR-138-mediated reduction of S100A1 impairs tube formation and NO production; S100A1 adenoviral gene transfer rescues these defects.","method":"3'UTR luciferase reporter, miR-138 mimic/inhibitor transfection, HIF1α siRNA, IOX2 (prolyl-hydroxylase inhibitor), tube formation assay, NO measurement, adenoviral S100A1 rescue","journal":"PloS one","confidence":"High","confidence_rationale":"Tier 2 / Strong — 3'UTR reporter combined with miRNA mimic/inhibitor, HIF1α epistasis, and functional rescue by gene transfer","pmids":["24244340"],"is_preprint":false},{"year":2016,"finding":"At physiological concentrations, S100A1 does NOT compete with calmodulin for the same binding site on intact RyR1 or RyR2 (Ki for FRET-detected CaM displacement >10 µM); instead, high micromolar S100A1 alters the structural state of RyR-bound CaM (shifting to lower FRET orientation) without reducing CaM amount bound; CaM and S100A1 can concurrently bind and modulate RyR.","method":"FRET between donor-labeled FKBP12.6 and acceptor-labeled CaM on RyR in SR vesicles, time-resolved FRET, concentration-response with S100A1","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — FRET-based structural assay on native SR vesicles across two RyR isoforms; directly contradicts earlier competition model (PMID:18650434) with high-resolution methodology","pmids":["27226555"],"is_preprint":false},{"year":2011,"finding":"NMR solution structure of human apo-S100A1 (PDB 2L0P) was determined; backbone dynamics by 15N relaxation show that human apo-S100A1 is less mobile globally than bovine apo-S100A1 modified by disulfide at Cys85; secondary structure is nearly identical between the two forms.","method":"NMR spectroscopy, 15N magnetic relaxation","journal":"Journal of structural biology","confidence":"High","confidence_rationale":"Tier 1 / Moderate — direct NMR structure determination with dynamics; single lab","pmids":["21296671"],"is_preprint":false},{"year":2004,"finding":"S100A1 binds to synapsin I (dephosphorylated and phosphorylated forms) in nerve terminals, inhibiting synapsin-induced F-actin bundling and abolishing synapsin dimerization in a dose- and Ca2+-dependent manner, without affecting synapsin binding to F-actin, G-actin, or synaptic vesicles; S100A1 is present in the soluble fraction of isolated nerve endings and co-distributes with synapsin I in ~5–20% of nerve terminals.","method":"Subcellular fractionation, confocal microscopy, immunogold electron microscopy, in vitro F-actin bundling assay, synapsin dimerization assay","journal":"Journal of neurochemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — co-localization in nerve terminals plus in vitro functional assay dissecting mechanism; single lab","pmids":["15147519"],"is_preprint":false},{"year":2002,"finding":"Annexin VI and S100A1 form in vivo complexes (ANXA6/S100A1) in avian skeletal muscle, as shown by immunoprecipitation; both proteins co-localize at sarcolemma, sarcoplasmic reticulum membranes, and putative transverse tubules from embryonic day 18 onward; annexin V is not recovered in S100A1 immunoprecipitates.","method":"Confocal laser scanning microscopy, immunogold cytochemistry, Western blot, co-immunoprecipitation","journal":"Neuroscience","confidence":"Medium","confidence_rationale":"Tier 2–3 / Moderate — co-IP in tissue combined with confocal colocalization; single lab","pmids":["11801372"],"is_preprint":false},{"year":2005,"finding":"Extracellular S100A1 (1 µM) applied to embryonic mouse and neonatal rat ventricular cardiomyocytes rapidly translocates into cells and enhances L-type Ca2+ current density (~112%); this effect is PKA-dependent (blocked by PKA inhibitor) and associated with increased PKA activity; in vitro reconstitution assays show S100A1 enhances PKA activity; cAMP levels are unchanged.","method":"Whole-cell patch clamp, rhodamine-S100A1 fluorescence uptake, PKA activity assay, cAMP measurement, PKA inhibitor (PKI)","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 1–2 / Moderate — electrophysiology with pharmacological pathway placement and in vitro reconstitution; single lab","pmids":["16129693"],"is_preprint":false},{"year":2006,"finding":"S100A1 protein (0.1 µM) reduces Ca2+ spark frequency (~38%), amplitude (~14%), and duration (~18%) in resting permeabilized rabbit cardiomyocytes at diastolic Ca2+ (~150 nM) via its C-terminus (aa 75–94); the S100A1 C-terminal peptide mimics and blocks these effects, slightly increasing SR Ca2+ content; accessory RyR2 modulators (sorcin, FKBP12.6) stoichiometry is unaltered.","method":"Saponin-permeabilized cardiomyocytes, confocal Ca2+ spark imaging, S100A1-ct peptide competition, SR Ca2+ content measurement, co-immunoprecipitation","journal":"Cell calcium","confidence":"High","confidence_rationale":"Tier 2 / Strong — direct protein application with peptide competition defining the C-terminal domain, consistent with independent RyR2 findings","pmids":["16919727"],"is_preprint":false},{"year":2013,"finding":"Loss of CaM inhibition of RyR2 at diastolic Ca2+ (via single RyR2-L3591D mutation) also eliminates S100A1 regulation at both diastolic and systolic Ca2+ in single-channel measurements; Ryr2D/D mice develop cardiac hypertrophy and altered function, confirming that the RyR2 CaM/S100A1 binding domain is functionally important in vivo.","method":"Knock-in mouse (Ryr2D/D), single-channel planar lipid bilayer recording, echocardiography, heart weight/body weight ratio, ANP mRNA, transverse aortic constriction","journal":"American journal of physiology. Heart and circulatory physiology","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — knock-in mutagenesis with single-channel electrophysiology and in vivo cardiac phenotype","pmids":["23666671"],"is_preprint":false},{"year":2002,"finding":"S100A1 interaction with antiallergic drugs (olopatadine, amlexanox, cromolyn) is Ca2+-dependent; mutagenesis mapped the olopatadine-binding site to residues 76–85 of S100A1 and the amlexanox-binding site to residues 89–94; the two drug-binding sites are distinct and non-competitive; both drug sites overlap with the target protein-binding region at the S100A1 C-terminus.","method":"Affinity chromatography with drug-conjugated resin, site-directed mutagenesis, competition binding with target peptides","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — mutagenesis combined with affinity chromatography competition; single lab","pmids":["11944917"],"is_preprint":false}],"current_model":"S100A1 is a dimeric EF-hand Ca2+-sensor protein that undergoes Ca2+-induced conformational changes exposing a hydrophobic C-terminal binding pocket (defined by Phe88, Phe89, Trp90 and adjacent residues), through which it calcium-dependently engages a wide array of effectors including RyR1/RyR2 (activating SR Ca2+ release), SERCA2a (enhancing SR Ca2+ uptake), mitochondrial F1-ATPase (increasing ATP production), myofibrillar proteins (reducing Ca2+ sensitivity), endothelial NOS (stimulating NO production), Hsp70/Hsp90 chaperone complex components, twitchin kinase, MyoD, synapsin I, TRPM3, and annexin VI; Cys85 redox modifications (glutathionylation, S-nitrosylation) dramatically amplify Ca2+ affinity, linking redox and Ca2+ signaling; depletion of S100A1 in heart failure drives contractile dysfunction and adverse remodeling, while gene therapy restoring S100A1 rescues SR Ca2+ handling, energy homeostasis, and contractile performance in small and large animal models as well as in human failing cardiomyocytes."},"narrative":{"mechanistic_narrative":"S100A1 is a dimeric EF-hand Ca2+-sensor that transduces intracellular Ca2+ signals into the regulation of muscle excitation-contraction coupling, energy metabolism, and vascular tone through Ca2+-dependent engagement of diverse effector proteins [PMID:3722149, PMID:16236309]. Each homodimer binds four Ca2+ via canonical and pseudo EF-hands; Ca2+ binding reorients helix 3 to expose a hydrophobic cleft formed by the hinge region, C-terminus, and helix 3 that serves as the target-binding pocket [PMID:16169012], with the C-terminal aromatic residues Phe88/Phe89/Trp90 being essential for Ca2+-dependent target engagement while a mechanistically distinct Ca2+-independent mode does not require this extension [PMID:9860858]. In striated muscle this pocket binds the calmodulin-binding domain of RyR1, activating SR Ca2+ release and channel open probability and supporting voltage-sensor coupling, as confirmed by genetic knockout phenotypes [PMID:9298970, PMID:18089560, PMID:19651767], while in cardiomyocytes S100A1 selectively interacts with both RyR2 and SERCA2a to raise the gain of excitation-contraction coupling, increasing Ca2+ transients and SR Ca2+ uptake while suppressing diastolic Ca2+ sparks via its C-terminus [PMID:16236309, PMID:16919727]. S100A1 also binds mitochondrial F1-ATPase to enhance ATP production [PMID:17438143] and reduces myofibrillar Ca2+ sensitivity, integrating contractile and energetic control [PMID:11717446]. Restoring S100A1 by gene transfer in failing cardiomyocytes normalizes SR Ca2+ handling, reduces SR Ca2+ leak, reverses fetal gene reactivation, and rescues contractile function in vivo [PMID:15578088]. Beyond muscle, endothelial S100A1 stimulates eNOS-dependent NO production to regulate vascular relaxation and postischemic angiogenesis [PMID:18292599, PMID:23048072], and extracellular S100A1 acts both as a pro-survival ligand internalized via clathrin-mediated endocytosis that activates PLC-PKC-MEK-ERK signaling [PMID:12960148] and as a released alarmin engaging TLR4 on cardiac fibroblasts [PMID:24833748]. The protein additionally functions as a Ca2+-regulated chaperone within the Hsp70/Hsp90 multichaperone complex [PMID:14638689] and binds cytoskeletal and regulatory targets including GFAP, tubulin, MyoD, synapsin I, and other S100 proteins [PMID:7794894, PMID:9920729, PMID:10753920, PMID:15608682]. Redox modification of Cys85 by glutathionylation or S-nitrosylation drives large structural changes and dramatically amplifies Ca2+ affinity, coupling redox state to Ca2+ sensing [PMID:15885104, PMID:15590070].","teleology":[{"year":1986,"claim":"Established that S100A1 is a genuine Ca2+ sensor whose ligand binding drives a conformational switch, defining the biophysical basis for downstream effector regulation.","evidence":"Flow dialysis and spectroscopy of purified S100-alpha measuring 4 Ca2+ per dimer and Ca2+-induced hydrophobic exposure of Cys85","pmids":["3722149","3722150"],"confidence":"High","gaps":["Did not identify physiological effector proteins","No atomic structure of the conformational change"]},{"year":1995,"claim":"Showed S100A1 can act as a Ca2+-dependent inhibitor of a transcription factor, broadening its role beyond a generic Ca2+ buffer to targeted protein regulation.","evidence":"Affinity chromatography, co-IP and in vitro PKC assays showing S100A1 binds MyoD helix I and blocks its phosphorylation and DNA binding","pmids":["7794894"],"confidence":"High","gaps":["In vivo relevance to myogenic differentiation not established","Cellular context where this regulation dominates unclear"]},{"year":1997,"claim":"Identified RyR1 as a direct S100A1 target, linking S100A1 to skeletal muscle SR Ca2+ release at the channel level.","evidence":"Lipid bilayer single-channel recording, [3H]ryanodine binding and biosensor mapping of three RyR1 binding domains","pmids":["9298970"],"confidence":"High","gaps":["Did not resolve binding stoichiometry on intact channel","Physiological consequence in muscle not yet tested genetically"]},{"year":1998,"claim":"Mapped the structural determinant of Ca2+-dependent target binding to C-terminal aromatic residues and revealed two distinct interaction modes.","evidence":"Site-directed mutagenesis of Phe88/Phe89/Trp90 with phenyl-Sepharose, TRTK peptide binding, and Ca2+-independent aldolase assays","pmids":["9860858"],"confidence":"High","gaps":["Structural basis of the Ca2+-independent mode not defined","Which physiological targets use each mode unknown"]},{"year":2001,"claim":"Demonstrated that S100A1 enhances cardiac contractility by improving SR Ca2+ handling, establishing its functional role in the heart.","evidence":"Adenoviral overexpression in cardiomyocytes and engineered tissue with Ca2+ imaging, SR uptake assays, and cAMP-independence controls","pmids":["11717446"],"confidence":"High","gaps":["Molecular targets mediating the effect not yet identified in this study","Relevance to failing myocardium not addressed"]},{"year":2003,"claim":"Revealed S100A1 functions as a Ca2+-regulated molecular chaperone, an activity distinct from its EC-coupling role.","evidence":"GST pull-down and co-IP with Hsp90/Hsp70/FKBP52/CyP40 plus in vitro client aggregation-protection assays","pmids":["14638689"],"confidence":"High","gaps":["Physiological client proteins in vivo not defined","Whether chaperone role intersects with cardiac function unknown"]},{"year":2004,"claim":"Established the therapeutic principle that restoring S100A1 reverses heart failure pathophysiology at the SR Ca2+-handling level.","evidence":"Adenoviral S100A1 delivery in a post-infarction rat model with echocardiography, Ca2+ transient, SR leak/load, and metabolic measurements","pmids":["15578088"],"confidence":"High","gaps":["Long-term durability of rescue not assessed","Large-animal translation not addressed in this study"]},{"year":2005,"claim":"Provided the atomic-resolution structure of Ca2+-bound S100A1, defining the target-binding pocket geometry.","evidence":"Multidimensional NMR solution structure with thousands of NOE constraints and RDCs versus apo-S100A1","pmids":["16169012"],"confidence":"High","gaps":["Bound-complex structures with physiological targets not yet solved here","Dynamics of pocket opening not quantified"]},{"year":2005,"claim":"Linked redox chemistry to Ca2+ sensing by showing Cys85 glutathionylation massively increases Ca2+ affinity.","evidence":"Trp90 fluorescence Ca2+ titration with EF-hand mutants and TRTK-12 binding on glutathionylated S100A1","pmids":["15885104","15590070"],"confidence":"High","gaps":["In vivo redox regulation of S100A1 not demonstrated","Reversibility kinetics under physiological conditions unclear"]},{"year":2007,"claim":"Connected S100A1 to cardiac energetics by identifying mitochondrial F1-ATPase as a direct target.","evidence":"Reciprocal pull-down, co-IP, colocalization, and ATP/F1-ATPase activity assays across gain- and loss-of-function","pmids":["17438143"],"confidence":"High","gaps":["Mechanism of ATPase stimulation not structurally defined","Contribution to whole-heart energetics not quantified"]},{"year":2007,"claim":"Confirmed RyR1 as a physiological S100A1 target in skeletal muscle and resolved the binding interface structurally.","evidence":"S100A1 knockout mice with Ca2+ imaging plus NMR of S100A1 bound to the RyR1 CaM-binding peptide","pmids":["18089560","18650434"],"confidence":"High","gaps":["Whether binding competes with CaM in situ unresolved at this stage","Stoichiometry on intact tetrameric channel unknown"]},{"year":2008,"claim":"Established S100A1 as a regulator of endothelial NO production and vascular tone, extending its role beyond muscle.","evidence":"S100A1 knockout mice with vascular relaxation, EC Ca2+ imaging, NO measurement, and IP3R-dependence pharmacology","pmids":["18292599"],"confidence":"High","gaps":["Direct S100A1-eNOS structural interaction not resolved here","Relative contribution versus IP3R-driven Ca2+ unclear"]},{"year":2011,"claim":"Revised the RyR regulation model, showing S100A1 and CaM can co-occupy and concurrently modulate the channel rather than strictly competing at physiological levels.","evidence":"Time-resolved FRET on native SR vesicles across RyR1 and RyR2 with S100A1 concentration-response","pmids":["27226555"],"confidence":"High","gaps":["Structural basis of the CaM conformational shift not defined","Functional output of dual occupancy on Ca2+ release not fully mapped"]},{"year":2014,"claim":"Defined an extracellular alarmin function whereby released S100A1 signals through TLR4 to shape post-infarction remodeling.","evidence":"Mouse MI model with neutralizing antibody, fibroblast co-culture, TLR4/NF-kB Western blots, and patient serum ELISA","pmids":["24833748"],"confidence":"High","gaps":["Direct S100A1-TLR4 binding not structurally shown","Balance between protective and adverse extracellular effects unclear"]},{"year":null,"claim":"How the many Ca2+-dependent S100A1 interactions are spatially and temporally prioritized within a single cell, and how redox state tunes this in vivo, remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No integrated model of target selection among competing effectors","In vivo redox regulation of Ca2+ affinity not demonstrated","Quantitative occupancy of competing targets in intact tissue unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140299","term_label":"molecular sensor activity","supporting_discovery_ids":[0,1,19]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[6,20,23,8]},{"term_id":"GO:0044183","term_label":"protein folding chaperone","supporting_discovery_ids":[16]},{"term_id":"GO:0008092","term_label":"cytoskeletal protein binding","supporting_discovery_ids":[9,12]},{"term_id":"GO:0140110","term_label":"transcription regulator activity","supporting_discovery_ids":[3]}],"localization":[{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[38,16]},{"term_id":"GO:0005783","term_label":"endoplasmic reticulum","supporting_discovery_ids":[2,39]},{"term_id":"GO:0005739","term_label":"mitochondrion","supporting_discovery_ids":[23]},{"term_id":"GO:0005576","term_label":"extracellular region","supporting_discovery_ids":[15,31]}],"pathway":[{"term_id":"R-HSA-397014","term_label":"Muscle contraction","supporting_discovery_ids":[13,20,24]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[15,27,30]},{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[23,4]},{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[16]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[31]}],"complexes":["Hsp70/Hsp90 multichaperone complex"],"partners":["RYR1","RYR2","ATP2A2","MYOD","ANXA6","HSP90","S100B","S100A4"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P23297","full_name":"Protein S100-A1","aliases":["S-100 protein alpha chain","S-100 protein subunit alpha","S100 calcium-binding protein A1"],"length_aa":94,"mass_kda":10.5,"function":"Small calcium binding protein that plays important roles in several biological processes such as Ca(2+) homeostasis, chondrocyte biology and cardiomyocyte regulation (PubMed:12804600). In response to an increase in intracellular Ca(2+) levels, binds calcium which triggers conformational changes (PubMed:23351007). These changes allow interactions with specific target proteins and modulate their activity (PubMed:22399290). Regulates a network in cardiomyocytes controlling sarcoplasmic reticulum Ca(2+) cycling and mitochondrial function through interaction with the ryanodine receptors RYR1 and RYR2, sarcoplasmic reticulum Ca(2+)-ATPase/ATP2A2 and mitochondrial F1-ATPase (PubMed:12804600). Facilitates diastolic Ca(2+) dissociation and myofilament mechanics in order to improve relaxation during diastole (PubMed:11717446)","subcellular_location":"Cytoplasm; Sarcoplasmic reticulum; Mitochondrion","url":"https://www.uniprot.org/uniprotkb/P23297/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/S100A1","classification":"Not Classified","n_dependent_lines":1,"n_total_lines":1208,"dependency_fraction":0.0008278145695364238},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/S100A1","total_profiled":1310},"omim":[{"mim_id":"617437","title":"S100 CALCIUM-BINDING PROTEIN A16; S100A16","url":"https://www.omim.org/entry/617437"},{"mim_id":"616284","title":"FILAGGRIN FAMILY MEMBER 2; FLG2","url":"https://www.omim.org/entry/616284"},{"mim_id":"610103","title":"S100 CALCIUM-BINDING PROTEIN, ZETA; S100Z","url":"https://www.omim.org/entry/610103"},{"mim_id":"604740","title":"SOLUTE CARRIER FAMILY 39 (ZINC TRANSPORTER), MEMBER 1; SLC39A1","url":"https://www.omim.org/entry/604740"},{"mim_id":"600353","title":"S100 CALCIUM-BINDING PROTEIN A7; S100A7","url":"https://www.omim.org/entry/600353"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Cytosol","reliability":"Supported"},{"location":"Nucleoplasm","reliability":"Additional"},{"location":"Golgi apparatus","reliability":"Additional"}],"tissue_specificity":"Group enriched","tissue_distribution":"Detected in all","driving_tissues":[{"tissue":"brain","ntpm":1266.4},{"tissue":"heart muscle","ntpm":2882.1},{"tissue":"skeletal muscle","ntpm":2868.7},{"tissue":"tongue","ntpm":4577.6}],"url":"https://www.proteinatlas.org/search/S100A1"},"hgnc":{"alias_symbol":["S100-alpha"],"prev_symbol":["S100A"]},"alphafold":{"accession":"P23297","domains":[{"cath_id":"1.10.238.10","chopping":"3-92","consensus_level":"high","plddt":84.0119,"start":3,"end":92}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P23297","model_url":"https://alphafold.ebi.ac.uk/files/AF-P23297-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P23297-F1-predicted_aligned_error_v6.png","plddt_mean":82.5},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=S100A1","jax_strain_url":"https://www.jax.org/strain/search?query=S100A1"},"sequence":{"accession":"P23297","fasta_url":"https://rest.uniprot.org/uniprotkb/P23297.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P23297/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P23297"}},"corpus_meta":[{"pmid":"3316838","id":"PMC_3316838","title":"Differential distribution of immunoreactive S100-alpha and S100-beta proteins in normal nonnervous human tissues.","date":"1987","source":"Laboratory investigation; a journal of technical methods and pathology","url":"https://pubmed.ncbi.nlm.nih.gov/3316838","citation_count":308,"is_preprint":false},{"pmid":"12460893","id":"PMC_12460893","title":"Gastric cancers overexpress S100A calcium-binding proteins.","date":"2002","source":"Cancer research","url":"https://pubmed.ncbi.nlm.nih.gov/12460893","citation_count":211,"is_preprint":false},{"pmid":"3722149","id":"PMC_3722149","title":"Ions binding to S100 proteins. 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zinc binding increases calcium affinity of S100b but only weakly affects S100-alpha; calcium binding induces conformational changes exposing hydrophobic domains including Cys85.\",\n      \"method\": \"Flow dialysis, UV spectroscopy, fluorescence spectroscopy, sulfhydryl reactivity assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — multiple orthogonal biophysical methods in a single rigorous study, replicated across multiple S100 isoforms with well-controlled quantitative binding measurements\",\n      \"pmids\": [\"3722149\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1986,\n      \"finding\": \"Calcium binding to S100A1 (S100a) induces a conformational change that exposes hydrophobic domains; the alpha-subunit conformation is nearly identical whether in the S100a heterodimer or S100-alpha homodimer; calcium at high protein concentrations triggers subunit dissociation and exchange.\",\n      \"method\": \"UV absorption, circular dichroism, intrinsic fluorescence, sulfhydryl reactivity, hydrophobic fluorescent probe (ANS), FPLC separation\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — multiple orthogonal biophysical methods, rigorous controls with purified protein\",\n      \"pmids\": [\"3722150\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1991,\n      \"finding\": \"S100A1 protein in skeletal muscle co-localizes with the A-band and/or longitudinal sarcoplasmic reticulum; isolated sarcoplasmic reticulum fractions and myofibrils contain multiple S100A1-binding proteins, suggesting a role in excitation-contraction coupling.\",\n      \"method\": \"Immunohistochemistry, radioimmunoassay, Northern blot, gel overlay for binding proteins, subcellular fractionation\",\n      \"journal\": \"Cell motility and the cytoskeleton\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Moderate — multiple methods in a single lab but binding partners not individually identified biochemically\",\n      \"pmids\": [\"1802419\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"S100A1 (S100a, alpha-alpha homodimer) binds to the basic helix I domain of MyoD (and other myogenic bHLH transcription factors) in a calcium-dependent manner; this binding inhibits PKC-mediated phosphorylation of MyoD at Thr115 and blocks MyoD DNA-binding activity; S100A1 is more potent than calmodulin in inhibiting MyoD DNA binding.\",\n      \"method\": \"Affinity chromatography, chemical cross-linking, native gel electrophoresis, fluorescence spectroscopy with DANSYL-CaM competition, in vitro PKC phosphorylation assay, co-immunoprecipitation from H9c2 cells\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — multiple orthogonal methods including in vitro kinase assay, affinity chromatography, co-IP, and fluorescence competition, all pointing to same conclusion\",\n      \"pmids\": [\"7794894\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"S100A1 inhibits phosphoglucomutase activity in a calcium-dependent manner (while S100B stimulates it); both S100A1 and S100B bind phosphoglucomutase via calcium-dependent affinity chromatography, identifying phosphoglucomutase as an S100A1 target protein.\",\n      \"method\": \"Gel overlay, affinity chromatography (S100A1/B-Sepharose and phosphoglucomutase-Sepharose), enzyme activity assay\",\n      \"journal\": \"Cell calcium\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — reciprocal affinity chromatography combined with enzymatic activity assay in a single study with proper controls\",\n      \"pmids\": [\"8894274\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"S100A1-S100B heterodimer (CD-GCAP) is expressed in bovine retina and stimulates rod outer segment membrane guanylate cyclase (ROS-GC) activity in a calcium-dependent manner (EC50 ~17 µM Ca2+); the kinase-like domain of ROS-GC is not involved; the interaction domain resides in the C-terminal segment (aa 731–1054) of ROS-GC.\",\n      \"method\": \"Western blot, in vitro guanylate cyclase activity assay, domain mapping with deletion constructs\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro reconstitution with domain mapping, single lab\",\n      \"pmids\": [\"8639567\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"S100A1 directly interacts with three distinct binding domains on the skeletal muscle ryanodine receptor (RyR1) in a calcium-dependent and calcium-independent manner; at nanomolar Ca2+, S100A1 activates [3H]ryanodine binding (~40%) and increases single-channel open probability ~6-fold in planar lipid bilayer reconstitution; S100A1 increases apparent affinity of RyR for ryanodine (Kd 383→191 nM).\",\n      \"method\": \"Equilibrium [3H]ryanodine binding, planar lipid bilayer single-channel recording, BIAcore optical biosensor, ligand overlay on RyR fusion proteins, affinity chromatography on S100A1-Sepharose\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — reconstitution in lipid bilayer, multiple orthogonal binding methods, domain mapping; single lab but comprehensive\",\n      \"pmids\": [\"9298970\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"S100A1 activates twitchin kinase in a calcium-dependent, zinc-enhanced manner; Ca2+/S100A1 binds twitchin kinase fragments with Kd <50 nM; Zn2+ reduces the off-rate; other Ca2+-binding proteins (S100A6, calmodulin, Ca2+-dependent protein kinase CaM-domain) bind the kinase but do not activate it, indicating specificity of S100A1 for kinase activation.\",\n      \"method\": \"BIAcore biosensor binding assay, in vitro kinase activity assay with recombinant S100A1\",\n      \"journal\": \"European journal of biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — direct binding kinetics and enzymatic activity with specificity controls; single lab\",\n      \"pmids\": [\"9363763\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"The carboxyl-terminal aromatic residues Phe88, Phe89, and Trp90 of S100A1 are essential for calcium-dependent target protein binding (TRTK/CapZ peptide) and hydrophobic exposure (phenyl-Sepharose interaction); deletion of residues 85–93 or triple aromatic mutation abolishes calcium-dependent target binding; calcium-independent target activation (aldolase A) does not require the C-terminus, revealing two mechanistically distinct interaction modes.\",\n      \"method\": \"Site-directed mutagenesis, affinity chromatography (phenyl-Sepharose), fluorescence binding assay with TRTK peptide, aldolase A activity assay\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — mutagenesis combined with functional assays and binding measurements, clear structure-function mapping\",\n      \"pmids\": [\"9860858\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"The C-terminal extension of S100A1 (residues Phe88–Ser93) is required for binding to GFAP, tubulin, the TRTK-12 peptide (CapZ), and a p53-derived peptide; S100A1 inhibits GFAP assembly into intermediate filaments via this C-terminal region; the truncated S100A1Δ88-93 lacks these interactions.\",\n      \"method\": \"Fluorescence spectroscopy with acrylodan-labeled S100A1, chemical crosslinking, GFAP polymerization assay, competition with TRTK-12 and p53 peptide\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — mutagenesis combined with functional assembly assay and fluorescence binding measurements, multiple targets tested\",\n      \"pmids\": [\"9920729\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"Annexin VI binds S100A1 (and S100B) in a calcium-dependent manner and blocks their ability to inhibit desmin and GFAP assembly into intermediate filaments; each S100A1 dimer has one annexin VI binding site (sub-µM affinity); the annexin VI binding site on S100A1 does not overlap with the C-terminal extension required for desmin/GFAP binding.\",\n      \"method\": \"In vitro intermediate filament assembly assay, affinity chromatography, fluorescence binding\",\n      \"journal\": \"Cell calcium\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Moderate — functional assay combined with affinity binding, single lab, multiple targets\",\n      \"pmids\": [\"9883272\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"S100A4 and S100A1 interact directly in vitro and in vivo; the interaction requires conserved dimerization-interface residues (site-directed mutagenesis); S100A1 reduces S100A4-mediated inhibition of nonmuscle myosin A self-association and phosphorylation in vitro, and reduces S100A4-driven cell motility and metastasis.\",\n      \"method\": \"Yeast two-hybrid, affinity chromatography, gel overlay, FRET in living cells, biosensor binding kinetics, in vitro myosin assay, soft agar growth, in vivo metastasis assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — yeast two-hybrid confirmed by affinity chromatography, FRET in cells, and functional myosin assay; replicated in subsequent study (PMID:15608682)\",\n      \"pmids\": [\"10753920\", \"15608682\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"S100A1 and S100B cause calcium-dependent disassembly of cytoplasmic microtubules in situ in glioma and myoblast triton-cytoskeletons; the C-terminal extension of S100A1 is required (S100A1Δ88-93 is inactive); TRTK-12 peptide blocks the effect; no direct intermediate filament disassembly was observed under these conditions.\",\n      \"method\": \"Triton-cytoskeleton preparation from live cells, immunofluorescence microscopy, inhibitory peptide competition\",\n      \"journal\": \"Neuroscience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — cell-based assay with mutagenesis equivalent (truncated protein) and peptide inhibition controls; single lab\",\n      \"pmids\": [\"10974440\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"S100A1 overexpression in adult cardiomyocytes and engineered heart tissue (adenoviral gene transfer) increases unloaded shortening, isometric contraction, cytosolic Ca2+ transients, and SR Ca2+ uptake; S100A1 protein decreases myofibrillar Ca2+ sensitivity and cooperativity in Triton-skinned trabeculae without changing maximal force; effects are cAMP-independent (PKA phosphorylation of phospholamban unchanged).\",\n      \"method\": \"Adenoviral gene transfer, video-edge detection, FURA-2 Ca2+ imaging, saponin-permeabilized cell SR Ca2+ uptake assay, force-Ca2+ relationship in skinned trabeculae, cAMP measurement, PKA phosphorylation assay\",\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 functional assays in both isolated cells and engineered tissue; mechanistic specificity confirmed by cAMP independence\",\n      \"pmids\": [\"11717446\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"S100A1 protein increases SERCA2a activity in skinned rat cardiomyocytes; adenoviral S100A1 overexpression increases fractional shortening by 55% and systolic Ca2+ amplitudes by 62% in adult rat cardiomyocytes.\",\n      \"method\": \"Adenoviral gene transfer, video-edge detection, FURA-2 Ca2+ imaging, SERCA activity assay in skinned cell preparations\",\n      \"journal\": \"Basic research in cardiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — direct enzymatic assay combined with cellular functional readout; consistent with independent studies (PMID:11717446, PMID:16236309)\",\n      \"pmids\": [\"12479236\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Extracellular S100A1 is endocytosed into neonatal cardiomyocytes via calcium-dependent clathrin-mediated endocytosis; internalized S100A1 activates ERK1/2 pro-survival signaling via a PLC→PKC→MEK1→ERK1/2 cascade, protecting cardiomyocytes from apoptosis; PKA and L-type Ca2+ channel are not required.\",\n      \"method\": \"Fluorescence microscopy of rhodamine-S100A1 uptake, apoptosis assay (2-deoxyglucose/oxidative stress), pharmacological inhibitors of signaling pathway, ERK1/2 phosphorylation Western blot\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — pathway placement by pharmacological epistasis with multiple inhibitors; endocytosis mechanism characterized; replicated direction of effect\",\n      \"pmids\": [\"12960148\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"S100A1 is a molecular chaperone that forms stable complexes with Hsp90, Hsp70, FKBP52, and CyP40 (components of the Hsp70/Hsp90 multichaperone complex) both in vitro and in mammalian cells; S100A1 protects multiple client proteins (citrate synthase, aldolase, GAPDH, rhodanese) from heat-induced aggregation and inactivation; overexpression protects luciferase and β-galactosidase from heat-shock inactivation in COS-7 cells.\",\n      \"method\": \"GST pull-down, co-immunoprecipitation, in vitro aggregation protection assay, thermal inactivation assay, COS-7 overexpression with heat shock\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — reciprocal pull-down confirmed by co-IP, reconstituted chaperone activity in vitro, and validated in cell overexpression\",\n      \"pmids\": [\"14638689\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Adenoviral S100A1 gene delivery to failing rat cardiomyocytes (post-infarction model) normalizes S100A1 protein, restores SR Ca2+ uptake, reduces SR Ca2+ leak, restores intracellular Ca2+ transients, decreases elevated intracellular Na+, reverses fetal gene reactivation, and restores energy supply; intracoronary delivery normalizes in vivo contractile function.\",\n      \"method\": \"Adenoviral gene transfer in vivo and in vitro, echocardiography, Ca2+ transient imaging (FURA-2), SR Ca2+ load (caffeine), SR Ca2+ leak measurements, intracellular Na+ measurement, gene expression, metabolic assays\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — comprehensive mechanistic dissection of SR Ca2+ handling with multiple orthogonal readouts, in vitro and in vivo validated\",\n      \"pmids\": [\"15578088\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"S100A1 binds S100P to form a heterodimer with Kd 10–20 nM (higher affinity than S100P homodimer, Kd 40–120 nM); FRET confirms the interaction in living cells; S100A1/S100P heterodimer is stabilized by hydrophobic interactions at the dimer interface (confirmed by site-directed mutagenesis); S100A1 preincubation reduces S100P binding to nonmuscle myosin A by ~50%.\",\n      \"method\": \"Yeast two-hybrid, optical biosensor (BIAcore), FRET in mammalian cells, site-directed mutagenesis, homology modelling\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — binding kinetics by biosensor, FRET in live cells, mutagenesis defining interface, and functional consequence on myosin binding\",\n      \"pmids\": [\"15171681\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"The three-dimensional NMR solution structure of Ca2+-bound S100A1 was determined; calcium binding causes large reorientation of helix 3 (typical EF-hand) but not of the pseudo EF-hand, exposing a hydrophobic cleft formed by hinge region, C-terminus, and helix 3 residues that constitutes the target-binding pocket for TRTK-12 (CapZ-derived peptide).\",\n      \"method\": \"Multidimensional NMR spectroscopy (2D/3D/4D), 3354 NOE constraints, 362 residual dipolar couplings, comparison with apo-S100A1 structure\",\n      \"journal\": \"Journal of molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — high-resolution NMR structure with >21 constraints/residue; direct structural determination of Ca2+-induced conformational change and binding pocket\",\n      \"pmids\": [\"16169012\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"S100A1 protein increases the gain of excitation-contraction coupling in rabbit ventricular cardiomyocytes: 0.1 µM S100A1 increases Ca2+ transient amplitude (~41%), increases SERCA2a Ca2+ uptake rate (~22%), increases RyR2 activity ([3H]-ryanodine binding at 0.1–0.3 µM Ca2+), and shifts the SR Ca2+ content–fractional release relationship leftward without changing SR Ca2+ content; co-immunoprecipitation confirms selective S100A1 interaction with SERCA2a and RyR2.\",\n      \"method\": \"Patch pipette protein delivery, voltage clamp, FURA-2 Ca2+ imaging, caffeine-induced SR Ca2+ release, NCX current measurement, [3H]-ryanodine binding, co-immunoprecipitation\",\n      \"journal\": \"Journal of molecular and cellular cardiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — multiple orthogonal methods including binding assay and functional electrophysiology/Ca2+ imaging; direct intracellular protein delivery\",\n      \"pmids\": [\"16236309\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"S100A1 affinity for Ca2+ is dramatically increased (~10,000-fold increase in N-loop affinity, ~10-fold in C-loop) upon S-glutathionylation of Cys85; glutathionylated S100A1 still binds TRTK-12 in a Ca2+-dependent manner, linking redox and Ca2+ signaling.\",\n      \"method\": \"Trp90 fluorescence Ca2+-titration, TRTK-12 binding, site-directed mutagenesis of EF-hand loops (E32Q, E73Q), 2-p-toluidinylnaphthalene-6-sulfonate hydrophobicity probe\",\n      \"journal\": \"The FEBS journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — direct quantitative binding measurements with EF-hand mutants and redox-modified protein; single lab but rigorous mutagenesis\",\n      \"pmids\": [\"15885104\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Redox modification (S-nitrosylation and S-glutathionylation) of the conserved C-terminal cysteine (Cys85) of S100A1 strongly activated by Ca2+ binding results in global structural alterations of S100A1, as demonstrated by multiple spectroscopic techniques.\",\n      \"method\": \"RP-HPLC, ESI-MS, circular dichroism, fluorescence spectroscopy\",\n      \"journal\": \"Biochimica et biophysica acta\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — multiple biophysical methods demonstrating structural change, single lab\",\n      \"pmids\": [\"15590070\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"S100A1 interacts with mitochondrial F1-ATPase alpha- and beta-chains in a Ca2+-dependent manner; S100A1 overexpression in cardiomyocytes increases cellular ATP content and F1-ATPase activity; S100A1 knockdown decreases ATP levels; ATP synthase activity is reduced in S100A1 knockout cardiomyocytes.\",\n      \"method\": \"GST pull-down, co-immunoprecipitation, confocal colocalization, gel filtration chromatography, ATP content measurement, F1-ATPase activity assay\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — reciprocal pull-down, co-IP, functional enzymatic assay, gain- and loss-of-function both tested\",\n      \"pmids\": [\"17438143\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"S100A1 binds to the calmodulin-binding domain (CaM/S100A1 binding domain, RyRP12, residues 3616–3627) of RyR1 in skeletal muscle; genetic knockout of S100A1 reduces global myoplasmic Ca2+ transients and SR Ca2+ release following electrical excitation; the binding site is identified by competition assays and tryptophan fluorescence, and shows low micromolar affinity; NMR reveals the peptide binds in the Ca2+-dependent hydrophobic pocket of S100A1.\",\n      \"method\": \"S100A1 knockout mice, confocal microscopy Ca2+ imaging, competition binding assays with SR vesicles, tryptophan fluorescence, NMR spectroscopy\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — genetic KO with physiological phenotype, NMR structure of complex, and direct binding characterization; orthogonal methods\",\n      \"pmids\": [\"18089560\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"S100A1 and S100B are transcriptional targets of the SOX trio (SOX9/SOX5/SOX6) in chondrocytes; S100A1 overexpression suppresses hypertrophic chondrocyte differentiation and mineralization; S100A1/S100B knockdown stimulates terminal differentiation and reverses SOX trio-mediated inhibition; SOX-trio-responsive enhancer elements identified in the S100A1 5'-flanking region.\",\n      \"method\": \"Microarray, overexpression, siRNA knockdown, luciferase reporter assay, EMSA, chromatin immunoprecipitation\",\n      \"journal\": \"EMBO reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — ChIP identifying direct transcriptional regulation, functional gain/loss-of-function, and EMSA; multiple orthogonal methods\",\n      \"pmids\": [\"17396138\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Ca2+-S100A1 competes with Ca2+-calmodulin for the same binding site on RyR1 (RyRP12 domain, residues 3616–3627 in human RyR1); NMR structure of Ca2+-S100A1 bound to RyRP12 reveals key hydrophobic/electrostatic interactions involving RyRP12 residues Lys3616, Trp3620, Lys3622, Leu3623, Leu3624, Lys3626 with the Ca2+-induced hydrophobic pocket of S100A1.\",\n      \"method\": \"Competition binding assays (skeletal muscle SR), NMR spectroscopy (structure determination of S100A1-RyRP12 complex)\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — NMR structure of complex combined with functional competition assay; single lab but comprehensive\",\n      \"pmids\": [\"18650434\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Endothelial S100A1 modulates vascular function: S100A1 knockout mice show reduced acetylcholine-induced vascular relaxation, reduced basal and agonist-induced endothelial NO release, diminished agonist-induced Ca2+ transients in ECs, and hypertension; S100A1 overexpression in ECs increases NO generation in an IP3R-dependent manner; endothelial S100A1 is downregulated in heart failure.\",\n      \"method\": \"S100A1 knockout mice, vascular ring relaxation assay, Ca2+ imaging in ECs, NO measurement, siRNA knockdown, adenoviral overexpression, IP3R blocker (2-APB)\",\n      \"journal\": \"Circulation research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic KO with in vivo and ex vivo phenotype, pharmacological pathway placement by IP3R inhibition, siRNA and overexpression corroboration\",\n      \"pmids\": [\"18292599\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"NMR solution structure of S100A1 bound to TRTK12 (CapZ-derived peptide) reveals that TRTK12 forms an amphipathic helix with W7, I10, and L11 making key hydrophobic contacts with the Ca2+-dependent hydrophobic binding pocket of S100A1; Ca2+ binding affinity of S100A1 is tightened >3-fold upon TRTK12 binding.\",\n      \"method\": \"Solution NMR structure determination, ITC/fluorescence Ca2+ binding measurements\",\n      \"journal\": \"Journal of molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — NMR structure with defined intermolecular contacts and thermodynamic characterization of coupled binding\",\n      \"pmids\": [\"19452629\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"In skeletal muscle fibers, S100A1 knockout selectively suppresses the Qgamma component of intra-membrane charge movement (voltage sensor activation) while leaving Qbeta unaffected; transient intracellular S100A1 application restores Qgamma; dantrolene (RyR1 inhibitor) similarly suppresses this charge movement component, linking S100A1 to RyR1-voltage sensor coupling.\",\n      \"method\": \"S100A1 knockout mice, whole-cell patch clamp of isolated flexor digitorum brevis fibers, intracellular S100A1 application, dantrolene pharmacology\",\n      \"journal\": \"The Journal of physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic KO with specific electrophysiological phenotype, rescued by acute protein application, and pharmacological confirmation\",\n      \"pmids\": [\"19651767\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Exogenous S100A1 taken up by superior cervical ganglion neurons enhances Cav1 (L-type) Ca2+ channel currents and prolongs action potentials in a PKA-dependent manner; NMR chemical shift perturbation confirms direct Ca2+-S100A1 interaction with a peptide from the PKA regulatory subunit within S100A1's hydrophobic binding pocket.\",\n      \"method\": \"SCG neuron culture, whole-cell patch clamp, Ca2+ imaging, rhodamine-S100A1 uptake, PKA inhibitor, NMR chemical shift perturbation\",\n      \"journal\": \"American journal of physiology. Cell physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — electrophysiology with pharmacological pathway placement, direct NMR binding evidence for S100A1-PKA interaction\",\n      \"pmids\": [\"19657060\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"S100A1 is released from ischemic/necrotic cardiomyocytes and acts as an alarmin; it is endocytosed by cardiac fibroblasts and activates TLR4-dependent MAP kinase and NF-κB signaling, inducing an immunomodulatory/anti-fibrotic phenotype (elevated ICAM1, decreased collagen); antibody-mediated neutralization of S100A1 worsens infarct size and LV function post-MI.\",\n      \"method\": \"Patient serum ELISA, mouse MI model, in vitro co-culture, fluorescence microscopy of S100A1 endocytosis, Western blot (TLR4, MAP kinases, NF-κB), intracardiac S100A1 injection, neutralizing antibody\",\n      \"journal\": \"EMBO molecular medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — TLR4 pathway placement combined with in vivo neutralization phenotype, in vitro mechanistic dissection, and translational patient data\",\n      \"pmids\": [\"24833748\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Calmodulin and S100A1 bind to two independent but overlapping domains on the N-terminus of TRPM3 (Ala35-Lys124 and His291-Gly382); key positively charged residues in these domains are required for binding; CaM and S100A1 compete for the same binding sites on TRPM3; interactions are calcium-dependent.\",\n      \"method\": \"Biophysical binding assays, biochemical pull-down, site-directed mutagenesis of TRPM3 N-terminal domains, competition assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — mutagenesis combined with binding and competition assays; single lab, first report for TRPM3\",\n      \"pmids\": [\"22451665\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"S100A1 deficiency in endothelial cells impairs postischemic angiogenesis; mechanistically, S100A1 deficiency disrupts stimulatory S100A1/eNOS interaction, causes PKC hyperactivation leading to inhibitory eNOS phosphorylation, degrades VEGFR-2 with blunted PI3K/Akt/eNOS signaling; NO supplementation rescues angiogenesis and limb salvage in SKO mice.\",\n      \"method\": \"S100A1 knockout mice, femoral artery resection, perfusion measurement, EC proliferation/migration/tube formation assays, siRNA knockdown, eNOS activity, PKC inhibitor, Western blot, in vivo NO measurement\",\n      \"journal\": \"Circulation research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic KO with in vivo and cellular phenotype, mechanistic pathway placement by pharmacological rescue, siRNA corroboration\",\n      \"pmids\": [\"23048072\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"In the PSAPP Alzheimer's disease mouse model, genetic ablation of S100A1 reduces astrocytosis, microgliosis, and amyloid plaque load; S100A1·RyR complexes are detected in human and mouse AD brain in a Ca2+-dependent manner (co-immunoprecipitation), identifying RyR as a primary S100A1 target protein in the brain; S100A1·Akt complexes are not detected, indicating indirect modulation of Akt.\",\n      \"method\": \"S100A1 knockout in PSAPP mice, immunohistochemistry (GFAP, Iba1, plaque), co-immunoprecipitation (S100A1·RyR and S100A1·Akt), Ca2+-dependent complex formation in neuronal cells\",\n      \"journal\": \"Cell calcium\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic KO phenotype plus direct co-IP of S100A1·RyR complex in brain tissue; indirect Akt modulation established as negative result\",\n      \"pmids\": [\"24931125\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"MicroRNA-138 (miR-138) downregulates S100A1 protein in endothelial cells by targeting the 3'UTR of S100A1; hypoxia induces miR-138 via HIF1α; miR-138-mediated reduction of S100A1 impairs tube formation and NO production; S100A1 adenoviral gene transfer rescues these defects.\",\n      \"method\": \"3'UTR luciferase reporter, miR-138 mimic/inhibitor transfection, HIF1α siRNA, IOX2 (prolyl-hydroxylase inhibitor), tube formation assay, NO measurement, adenoviral S100A1 rescue\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — 3'UTR reporter combined with miRNA mimic/inhibitor, HIF1α epistasis, and functional rescue by gene transfer\",\n      \"pmids\": [\"24244340\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"At physiological concentrations, S100A1 does NOT compete with calmodulin for the same binding site on intact RyR1 or RyR2 (Ki for FRET-detected CaM displacement >10 µM); instead, high micromolar S100A1 alters the structural state of RyR-bound CaM (shifting to lower FRET orientation) without reducing CaM amount bound; CaM and S100A1 can concurrently bind and modulate RyR.\",\n      \"method\": \"FRET between donor-labeled FKBP12.6 and acceptor-labeled CaM on RyR in SR vesicles, time-resolved FRET, concentration-response with S100A1\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — FRET-based structural assay on native SR vesicles across two RyR isoforms; directly contradicts earlier competition model (PMID:18650434) with high-resolution methodology\",\n      \"pmids\": [\"27226555\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"NMR solution structure of human apo-S100A1 (PDB 2L0P) was determined; backbone dynamics by 15N relaxation show that human apo-S100A1 is less mobile globally than bovine apo-S100A1 modified by disulfide at Cys85; secondary structure is nearly identical between the two forms.\",\n      \"method\": \"NMR spectroscopy, 15N magnetic relaxation\",\n      \"journal\": \"Journal of structural biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — direct NMR structure determination with dynamics; single lab\",\n      \"pmids\": [\"21296671\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"S100A1 binds to synapsin I (dephosphorylated and phosphorylated forms) in nerve terminals, inhibiting synapsin-induced F-actin bundling and abolishing synapsin dimerization in a dose- and Ca2+-dependent manner, without affecting synapsin binding to F-actin, G-actin, or synaptic vesicles; S100A1 is present in the soluble fraction of isolated nerve endings and co-distributes with synapsin I in ~5–20% of nerve terminals.\",\n      \"method\": \"Subcellular fractionation, confocal microscopy, immunogold electron microscopy, in vitro F-actin bundling assay, synapsin dimerization assay\",\n      \"journal\": \"Journal of neurochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — co-localization in nerve terminals plus in vitro functional assay dissecting mechanism; single lab\",\n      \"pmids\": [\"15147519\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"Annexin VI and S100A1 form in vivo complexes (ANXA6/S100A1) in avian skeletal muscle, as shown by immunoprecipitation; both proteins co-localize at sarcolemma, sarcoplasmic reticulum membranes, and putative transverse tubules from embryonic day 18 onward; annexin V is not recovered in S100A1 immunoprecipitates.\",\n      \"method\": \"Confocal laser scanning microscopy, immunogold cytochemistry, Western blot, co-immunoprecipitation\",\n      \"journal\": \"Neuroscience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Moderate — co-IP in tissue combined with confocal colocalization; single lab\",\n      \"pmids\": [\"11801372\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Extracellular S100A1 (1 µM) applied to embryonic mouse and neonatal rat ventricular cardiomyocytes rapidly translocates into cells and enhances L-type Ca2+ current density (~112%); this effect is PKA-dependent (blocked by PKA inhibitor) and associated with increased PKA activity; in vitro reconstitution assays show S100A1 enhances PKA activity; cAMP levels are unchanged.\",\n      \"method\": \"Whole-cell patch clamp, rhodamine-S100A1 fluorescence uptake, PKA activity assay, cAMP measurement, PKA inhibitor (PKI)\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — electrophysiology with pharmacological pathway placement and in vitro reconstitution; single lab\",\n      \"pmids\": [\"16129693\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"S100A1 protein (0.1 µM) reduces Ca2+ spark frequency (~38%), amplitude (~14%), and duration (~18%) in resting permeabilized rabbit cardiomyocytes at diastolic Ca2+ (~150 nM) via its C-terminus (aa 75–94); the S100A1 C-terminal peptide mimics and blocks these effects, slightly increasing SR Ca2+ content; accessory RyR2 modulators (sorcin, FKBP12.6) stoichiometry is unaltered.\",\n      \"method\": \"Saponin-permeabilized cardiomyocytes, confocal Ca2+ spark imaging, S100A1-ct peptide competition, SR Ca2+ content measurement, co-immunoprecipitation\",\n      \"journal\": \"Cell calcium\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — direct protein application with peptide competition defining the C-terminal domain, consistent with independent RyR2 findings\",\n      \"pmids\": [\"16919727\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Loss of CaM inhibition of RyR2 at diastolic Ca2+ (via single RyR2-L3591D mutation) also eliminates S100A1 regulation at both diastolic and systolic Ca2+ in single-channel measurements; Ryr2D/D mice develop cardiac hypertrophy and altered function, confirming that the RyR2 CaM/S100A1 binding domain is functionally important in vivo.\",\n      \"method\": \"Knock-in mouse (Ryr2D/D), single-channel planar lipid bilayer recording, echocardiography, heart weight/body weight ratio, ANP mRNA, transverse aortic constriction\",\n      \"journal\": \"American journal of physiology. Heart and circulatory physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — knock-in mutagenesis with single-channel electrophysiology and in vivo cardiac phenotype\",\n      \"pmids\": [\"23666671\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"S100A1 interaction with antiallergic drugs (olopatadine, amlexanox, cromolyn) is Ca2+-dependent; mutagenesis mapped the olopatadine-binding site to residues 76–85 of S100A1 and the amlexanox-binding site to residues 89–94; the two drug-binding sites are distinct and non-competitive; both drug sites overlap with the target protein-binding region at the S100A1 C-terminus.\",\n      \"method\": \"Affinity chromatography with drug-conjugated resin, site-directed mutagenesis, competition binding with target peptides\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — mutagenesis combined with affinity chromatography competition; single lab\",\n      \"pmids\": [\"11944917\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"S100A1 is a dimeric EF-hand Ca2+-sensor protein that undergoes Ca2+-induced conformational changes exposing a hydrophobic C-terminal binding pocket (defined by Phe88, Phe89, Trp90 and adjacent residues), through which it calcium-dependently engages a wide array of effectors including RyR1/RyR2 (activating SR Ca2+ release), SERCA2a (enhancing SR Ca2+ uptake), mitochondrial F1-ATPase (increasing ATP production), myofibrillar proteins (reducing Ca2+ sensitivity), endothelial NOS (stimulating NO production), Hsp70/Hsp90 chaperone complex components, twitchin kinase, MyoD, synapsin I, TRPM3, and annexin VI; Cys85 redox modifications (glutathionylation, S-nitrosylation) dramatically amplify Ca2+ affinity, linking redox and Ca2+ signaling; depletion of S100A1 in heart failure drives contractile dysfunction and adverse remodeling, while gene therapy restoring S100A1 rescues SR Ca2+ handling, energy homeostasis, and contractile performance in small and large animal models as well as in human failing cardiomyocytes.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"S100A1 is a dimeric EF-hand Ca2+-sensor that transduces intracellular Ca2+ signals into the regulation of muscle excitation-contraction coupling, energy metabolism, and vascular tone through Ca2+-dependent engagement of diverse effector proteins [#0, #20]. Each homodimer binds four Ca2+ via canonical and pseudo EF-hands; Ca2+ binding reorients helix 3 to expose a hydrophobic cleft formed by the hinge region, C-terminus, and helix 3 that serves as the target-binding pocket [#19], with the C-terminal aromatic residues Phe88/Phe89/Trp90 being essential for Ca2+-dependent target engagement while a mechanistically distinct Ca2+-independent mode does not require this extension [#8]. In striated muscle this pocket binds the calmodulin-binding domain of RyR1, activating SR Ca2+ release and channel open probability and supporting voltage-sensor coupling, as confirmed by genetic knockout phenotypes [#6, #24, #29], while in cardiomyocytes S100A1 selectively interacts with both RyR2 and SERCA2a to raise the gain of excitation-contraction coupling, increasing Ca2+ transients and SR Ca2+ uptake while suppressing diastolic Ca2+ sparks via its C-terminus [#20, #41]. S100A1 also binds mitochondrial F1-ATPase to enhance ATP production [#23] and reduces myofibrillar Ca2+ sensitivity, integrating contractile and energetic control [#13]. Restoring S100A1 by gene transfer in failing cardiomyocytes normalizes SR Ca2+ handling, reduces SR Ca2+ leak, reverses fetal gene reactivation, and rescues contractile function in vivo [#17]. Beyond muscle, endothelial S100A1 stimulates eNOS-dependent NO production to regulate vascular relaxation and postischemic angiogenesis [#27, #33], and extracellular S100A1 acts both as a pro-survival ligand internalized via clathrin-mediated endocytosis that activates PLC-PKC-MEK-ERK signaling [#15] and as a released alarmin engaging TLR4 on cardiac fibroblasts [#31]. The protein additionally functions as a Ca2+-regulated chaperone within the Hsp70/Hsp90 multichaperone complex [#16] and binds cytoskeletal and regulatory targets including GFAP, tubulin, MyoD, synapsin I, and other S100 proteins [#3, #9, #11]. Redox modification of Cys85 by glutathionylation or S-nitrosylation drives large structural changes and dramatically amplifies Ca2+ affinity, coupling redox state to Ca2+ sensing [#21, #22].\",\n  \"teleology\": [\n    {\n      \"year\": 1986,\n      \"claim\": \"Established that S100A1 is a genuine Ca2+ sensor whose ligand binding drives a conformational switch, defining the biophysical basis for downstream effector regulation.\",\n      \"evidence\": \"Flow dialysis and spectroscopy of purified S100-alpha measuring 4 Ca2+ per dimer and Ca2+-induced hydrophobic exposure of Cys85\",\n      \"pmids\": [\"3722149\", \"3722150\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not identify physiological effector proteins\", \"No atomic structure of the conformational change\"]\n    },\n    {\n      \"year\": 1995,\n      \"claim\": \"Showed S100A1 can act as a Ca2+-dependent inhibitor of a transcription factor, broadening its role beyond a generic Ca2+ buffer to targeted protein regulation.\",\n      \"evidence\": \"Affinity chromatography, co-IP and in vitro PKC assays showing S100A1 binds MyoD helix I and blocks its phosphorylation and DNA binding\",\n      \"pmids\": [\"7794894\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo relevance to myogenic differentiation not established\", \"Cellular context where this regulation dominates unclear\"]\n    },\n    {\n      \"year\": 1997,\n      \"claim\": \"Identified RyR1 as a direct S100A1 target, linking S100A1 to skeletal muscle SR Ca2+ release at the channel level.\",\n      \"evidence\": \"Lipid bilayer single-channel recording, [3H]ryanodine binding and biosensor mapping of three RyR1 binding domains\",\n      \"pmids\": [\"9298970\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not resolve binding stoichiometry on intact channel\", \"Physiological consequence in muscle not yet tested genetically\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"Mapped the structural determinant of Ca2+-dependent target binding to C-terminal aromatic residues and revealed two distinct interaction modes.\",\n      \"evidence\": \"Site-directed mutagenesis of Phe88/Phe89/Trp90 with phenyl-Sepharose, TRTK peptide binding, and Ca2+-independent aldolase assays\",\n      \"pmids\": [\"9860858\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of the Ca2+-independent mode not defined\", \"Which physiological targets use each mode unknown\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Demonstrated that S100A1 enhances cardiac contractility by improving SR Ca2+ handling, establishing its functional role in the heart.\",\n      \"evidence\": \"Adenoviral overexpression in cardiomyocytes and engineered tissue with Ca2+ imaging, SR uptake assays, and cAMP-independence controls\",\n      \"pmids\": [\"11717446\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular targets mediating the effect not yet identified in this study\", \"Relevance to failing myocardium not addressed\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Revealed S100A1 functions as a Ca2+-regulated molecular chaperone, an activity distinct from its EC-coupling role.\",\n      \"evidence\": \"GST pull-down and co-IP with Hsp90/Hsp70/FKBP52/CyP40 plus in vitro client aggregation-protection assays\",\n      \"pmids\": [\"14638689\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Physiological client proteins in vivo not defined\", \"Whether chaperone role intersects with cardiac function unknown\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Established the therapeutic principle that restoring S100A1 reverses heart failure pathophysiology at the SR Ca2+-handling level.\",\n      \"evidence\": \"Adenoviral S100A1 delivery in a post-infarction rat model with echocardiography, Ca2+ transient, SR leak/load, and metabolic measurements\",\n      \"pmids\": [\"15578088\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Long-term durability of rescue not assessed\", \"Large-animal translation not addressed in this study\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Provided the atomic-resolution structure of Ca2+-bound S100A1, defining the target-binding pocket geometry.\",\n      \"evidence\": \"Multidimensional NMR solution structure with thousands of NOE constraints and RDCs versus apo-S100A1\",\n      \"pmids\": [\"16169012\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Bound-complex structures with physiological targets not yet solved here\", \"Dynamics of pocket opening not quantified\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Linked redox chemistry to Ca2+ sensing by showing Cys85 glutathionylation massively increases Ca2+ affinity.\",\n      \"evidence\": \"Trp90 fluorescence Ca2+ titration with EF-hand mutants and TRTK-12 binding on glutathionylated S100A1\",\n      \"pmids\": [\"15885104\", \"15590070\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo redox regulation of S100A1 not demonstrated\", \"Reversibility kinetics under physiological conditions unclear\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Connected S100A1 to cardiac energetics by identifying mitochondrial F1-ATPase as a direct target.\",\n      \"evidence\": \"Reciprocal pull-down, co-IP, colocalization, and ATP/F1-ATPase activity assays across gain- and loss-of-function\",\n      \"pmids\": [\"17438143\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism of ATPase stimulation not structurally defined\", \"Contribution to whole-heart energetics not quantified\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Confirmed RyR1 as a physiological S100A1 target in skeletal muscle and resolved the binding interface structurally.\",\n      \"evidence\": \"S100A1 knockout mice with Ca2+ imaging plus NMR of S100A1 bound to the RyR1 CaM-binding peptide\",\n      \"pmids\": [\"18089560\", \"18650434\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether binding competes with CaM in situ unresolved at this stage\", \"Stoichiometry on intact tetrameric channel unknown\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Established S100A1 as a regulator of endothelial NO production and vascular tone, extending its role beyond muscle.\",\n      \"evidence\": \"S100A1 knockout mice with vascular relaxation, EC Ca2+ imaging, NO measurement, and IP3R-dependence pharmacology\",\n      \"pmids\": [\"18292599\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct S100A1-eNOS structural interaction not resolved here\", \"Relative contribution versus IP3R-driven Ca2+ unclear\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Revised the RyR regulation model, showing S100A1 and CaM can co-occupy and concurrently modulate the channel rather than strictly competing at physiological levels.\",\n      \"evidence\": \"Time-resolved FRET on native SR vesicles across RyR1 and RyR2 with S100A1 concentration-response\",\n      \"pmids\": [\"27226555\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of the CaM conformational shift not defined\", \"Functional output of dual occupancy on Ca2+ release not fully mapped\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Defined an extracellular alarmin function whereby released S100A1 signals through TLR4 to shape post-infarction remodeling.\",\n      \"evidence\": \"Mouse MI model with neutralizing antibody, fibroblast co-culture, TLR4/NF-kB Western blots, and patient serum ELISA\",\n      \"pmids\": [\"24833748\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct S100A1-TLR4 binding not structurally shown\", \"Balance between protective and adverse extracellular effects unclear\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How the many Ca2+-dependent S100A1 interactions are spatially and temporally prioritized within a single cell, and how redox state tunes this in vivo, remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No integrated model of target selection among competing effectors\", \"In vivo redox regulation of Ca2+ affinity not demonstrated\", \"Quantitative occupancy of competing targets in intact tissue unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140299\", \"supporting_discovery_ids\": [0, 1, 19]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [6, 20, 23, 8]},\n      {\"term_id\": \"GO:0044183\", \"supporting_discovery_ids\": [16]},\n      {\"term_id\": \"GO:0008092\", \"supporting_discovery_ids\": [9, 12]},\n      {\"term_id\": \"GO:0140110\", \"supporting_discovery_ids\": [3]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [38, 16]},\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [2, 39]},\n      {\"term_id\": \"GO:0005739\", \"supporting_discovery_ids\": [23]},\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [15, 31]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-397014\", \"supporting_discovery_ids\": [13, 20, 24]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [15, 27, 30]},\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [23, 4]},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [16]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [31]}\n    ],\n    \"complexes\": [\"Hsp70/Hsp90 multichaperone complex\"],\n    \"partners\": [\"RYR1\", \"RYR2\", \"ATP2A2\", \"MyoD\", \"ANXA6\", \"HSP90\", \"S100B\", \"S100A4\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":8,"faith_total":8,"faith_pct":100.0}}