{"gene":"MASP1","run_date":"2026-04-28T18:30:28","timeline":{"discoveries":[{"year":2001,"finding":"MASP-3 is generated through alternative splicing of the MASP-1/3 gene and associates with distinct MBL oligomers; larger MBL oligomers carry MASP-3 and MASP-2, while smaller oligomers carry MASP-1 and MAp19. MASP-3 downregulates C4 and C2 cleaving activity of MASP-2.","method":"Alternative splicing analysis, oligomer fractionation, functional complement activation assays","journal":"Immunity","confidence":"High","confidence_rationale":"Tier 2 — reciprocal biochemical fractionation + functional assays, highly cited foundational paper","pmids":["11485744"],"is_preprint":false},{"year":1999,"finding":"The MBL-MASP complex contains a 22 kDa protein (sMAP) that is a truncated form of MASP-2 generated by alternative polyadenylation, and sMAP associates with MASP-1 within the MBL complex.","method":"cDNA sequencing, protein biochemistry, Co-purification/Co-IP","journal":"International immunology","confidence":"High","confidence_rationale":"Tier 2 — direct binding demonstrated by co-purification, sequence confirmed by cDNA, replicated in subsequent work","pmids":["10330290"],"is_preprint":false},{"year":2009,"finding":"MAp44, an alternatively spliced product of the MASP1 gene sharing the first four domains with MASP-1 and MASP-3 plus 17 unique C-terminal residues, is found in serum at ~1.4 µg/ml and competes with MASP-2 for binding to MBL and ficolins, thereby inhibiting complement activation.","method":"Surface plasmon resonance (SPR), ELISA, complement activation assays, mRNA profiling","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 1-2 — SPR quantification of binding affinity + functional inhibition assay, multiple orthogonal methods","pmids":["19917686"],"is_preprint":false},{"year":2012,"finding":"In normal human serum, MASP-1 is the exclusive activator of MASP-2; MASP-2 cannot autoactivate under physiological conditions, and inhibition of MASP-1 prevents MASP-2 activation. MASP-1 also contributes ~60% of C2a generation for C3 convertase formation.","method":"Monospecific inhibitors against MASP-1 and MASP-2, complement activation assays in normal human serum","journal":"PNAS","confidence":"High","confidence_rationale":"Tier 1-2 — monospecific inhibitors with rigorous controls, replicated by multiple independent groups","pmids":["22691502"],"is_preprint":false},{"year":2008,"finding":"MASP-1 contributes to lectin pathway activation by promoting MASP-2 activation; MASP1/3-deficient mouse serum shows significantly lower C4 and C3 deposition on mannan, and activity is restored by adding recombinant MASP-1, which accelerates MASP-2 activation.","method":"Gene-targeted MASP1/3-knockout mice, C4/C3 deposition assays, reconstitution with recombinant MASP-1","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 2 — clean KO + reconstitution experiment, replicated by multiple labs","pmids":["18424734"],"is_preprint":false},{"year":2004,"finding":"MASP-1 has thrombin-like substrate specificity, cleaving Phe-Gly-Arg-AMC most rapidly among tested fluorescent amide substrates; MASP-1 is inhibited by C1 inhibitor and the thrombin inhibitor boroMpg (but not hirudin), whereas MASP-2 shows minimal amidolytic activity toward the same substrates.","method":"Fluorescent amide substrate cleavage assays with recombinant and serum-derived MASPs, inhibitor profiling","journal":"Molecular immunology","confidence":"High","confidence_rationale":"Tier 1 — direct in vitro enzymatic assay with multiple substrates and inhibitors","pmids":["14725788"],"is_preprint":false},{"year":2009,"finding":"MASP-1 activates Ca2+ signaling, NF-κB, and p38 MAPK pathways in cultured HUVECs through proteolytic cleavage of PAR4; MASP-2 had no such effect, and the proteolytic activity of MASP-1 is required for endothelial activation.","method":"Cell-based signaling assays, synthetic PAR peptide substrates, PAR4 agonist peptide, mRNA quantification, membrane PAR4 depletion assay","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods establishing PAR4 as the substrate, mechanistically validated","pmids":["19667088"],"is_preprint":false},{"year":2012,"finding":"MASP-1 activates factor XIII and cleaves fibrinogen and prothrombin in plasma-based systems; MASP-1 directly activates prothrombin and TAFI, and induces fibrin clot formation with altered clot structure.","method":"FXIII incorporation assay, specific activation product assays (F1+2, FPA, TAFIa), turbidimetric clotting assay, scanning electron microscopy","journal":"PloS one","confidence":"High","confidence_rationale":"Tier 1-2 — multiple in vitro biochemical assays with purified systems and plasma, replicated in subsequent work","pmids":["22536427"],"is_preprint":false},{"year":2008,"finding":"MASP-1 cleaves factor XIII A-chain and fibrinogen beta-chain at sites identical to thrombin, releases fibrinopeptide B (but not A), and drives cross-linked fibrinogen formation; thrombin turnover rate for factor XIII is ~650-fold faster than MASP-1.","method":"In vitro cleavage assays with recombinant MASP-1 and thrombin, SDS-PAGE, N-terminal sequencing","journal":"Biochimica et biophysica acta","confidence":"High","confidence_rationale":"Tier 1 — reconstituted in vitro with site-level resolution, replicated by other groups","pmids":["18456010"],"is_preprint":false},{"year":2011,"finding":"MASP-1 cleaves high-molecular-weight kininogen (HK) to release bradykinin; MASP-2 can also cleave HK but cannot release bradykinin. C1-inhibitor prevents HK cleavage by both MASPs.","method":"Differential gel electrophoresis (proteomic screen), SDS-PAGE, HPLC detection of bradykinin release","journal":"PloS one","confidence":"High","confidence_rationale":"Tier 1 — in vitro biochemical reconstitution confirmed by HPLC product detection, mechanistically characterized","pmids":["21625439"],"is_preprint":false},{"year":2012,"finding":"MASP-1 is essential for lectin pathway activation in a MASP-1/3-deficient patient; the alternative pathway functions normally in this patient and is unaffected by MASP-1/MASP-3 reconstitution. MASP-1 and MASP-2 can form co-complexes on MBL in serum, providing a structural basis for MASP-1-mediated transactivation of MASP-2.","method":"Patient with nonsense mutation in MASP1 gene, complement functional assays, reconstitution with recombinant MASPs, demonstration of MASP-1/MASP-2 co-complexes in serum","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 2 — human genetic loss-of-function combined with reconstitution and co-complex demonstration, independent validation","pmids":["22966085"],"is_preprint":false},{"year":2016,"finding":"MASP-3 is the exclusive activator of pro-factor D in resting blood; neither MASP-1 nor MASP-2 activates pro-factor D under resting physiological conditions, as demonstrated using specific evolved inhibitors against all three MASPs.","method":"Evolved monospecific MASP-1, MASP-2, and MASP-3 inhibitors, pro-factor D activation assays in resting blood","journal":"Scientific reports","confidence":"High","confidence_rationale":"Tier 1 — specific inhibitors for all three enzymes tested, rigorous kinetic analysis, replicated in subsequent studies","pmids":["27535802"],"is_preprint":false},{"year":2013,"finding":"Zymogen MASP-1 autoactivates ~3000-fold faster than zymogen MASP-2; both activated and proenzyme MASP-1 efficiently cleave proenzyme MASP-2, and MASP-1 also cleaves proenzyme MASP-3. Crystal structure of proenzyme MASP-1 at 2.5 Å explains the unusual activity of the zymogen.","method":"In vitro autoactivation kinetics with recombinant MASP-1/MASP-2 mutants (R448Q, S646A), crystal structure at 2.5 Å, synthetic substrate cleavage assays","journal":"Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — reconstitution + crystal structure + mutagenesis in a single study","pmids":["23386610"],"is_preprint":false},{"year":2012,"finding":"Both MASP-1 and MASP-2 are essential for lectin pathway activation; crystal structures of Michaelis-like complexes of MASP-1 and MASP-2 with substrate-like inhibitors at 1.28 Å resolution reveal plasticity of MASP-2 and explain enzyme-substrate interactions.","method":"Evolved monospecific inhibitors, lectin pathway functional assays, crystal structure determination (1.28 Å for MASP-2)","journal":"Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — crystal structures + specific inhibitors + functional assays, rigorous","pmids":["22511776"],"is_preprint":false},{"year":2015,"finding":"MASP-1 promotes clotting by directly activating prothrombin at three cleavage sites (R155, R271, R393), producing an alternative active thrombin species; MASP-1-induced clotting in whole blood and platelet-poor plasma is dependent on prothrombin.","method":"Thrombelastography, SDS-PAGE, N-terminal sequencing of cleavage products, prothrombin-depleted plasma","journal":"Molecular immunology","confidence":"High","confidence_rationale":"Tier 1 — in vitro reconstitution + site-level mapping + functional clotting assays","pmids":["25745807"],"is_preprint":false},{"year":2015,"finding":"MASP-1 activates prothrombin via two simultaneous pathways (cleaving R271 or R393 first), both requiring R320 cleavage and resulting in formation of active alternative thrombin species; R155 is not an important cleavage site for prothrombin activation.","method":"Arginine-to-glutamine prothrombin mutants (R271Q, R320Q, R393Q), active-site mutant S525A, SDS-PAGE, N-terminal sequencing, thrombelastography","journal":"PloS one","confidence":"High","confidence_rationale":"Tier 1 — multiple site-directed mutants + in vitro reconstitution + functional validation","pmids":["26645987"],"is_preprint":false},{"year":2010,"finding":"Collectin-11 (CL-K1) associates with MASP-1 and/or MASP-3 in plasma as demonstrated by co-purification and ELISA; CL-K1 also binds bacteria, fungi, and viruses.","method":"ELISA, co-purification, Western blotting, mass spectrometry","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods confirming MASP-1/CL-K1 interaction in plasma","pmids":["20956340"],"is_preprint":false},{"year":2012,"finding":"Collectin-11 associates with MASP-1, MASP-2, MASP-3, and MAP-1, and CL-11/MASP-2 complexes mediate C4b deposition on Candida albicans, defining CL-11 as the fifth lectin pathway recognition molecule.","method":"Protein interaction assays, C4b/C3b deposition assays on Candida albicans, depletion and reconstitution experiments","journal":"Journal of innate immunity","confidence":"High","confidence_rationale":"Tier 2 — depletion/reconstitution with functional complement readout","pmids":["23220946"],"is_preprint":false},{"year":2014,"finding":"MASP-1 induces IL-6 and IL-8 secretion (but not IL-1α, IL-1ra, TNFα, or MCP-1) from HUVECs through the p38 MAPK pathway, and conditioned supernatant activates neutrophil chemotaxis.","method":"Recombinant MASP-1 stimulation of HUVECs, cytokine ELISA, p38 MAPK pathway inhibition, neutrophil chemotaxis assay","journal":"PloS one","confidence":"High","confidence_rationale":"Tier 2 — mechanistic pathway identified with pharmacological inhibition and functional readout","pmids":["24489848"],"is_preprint":false},{"year":2014,"finding":"Serum MASP-1 in complex with MBL activates endothelial cells through the proteolytic activity of MASP-1; MASP-2, MASP-3, and non-enzymatic N-terminal domains of MASP-1/MASP-2 do not activate HUVECs, and a stable zymogen MASP-1 mutant is also inactive.","method":"Ca2+ signaling in HUVECs stimulated with MBL-MASP complexes, recombinant MASP fragments, zymogen MASP-1 mutant","journal":"Molecular immunology","confidence":"High","confidence_rationale":"Tier 2 — multiple controls including zymogen mutant establishing requirement for MASP-1 catalytic activity","pmids":["24472859"],"is_preprint":false},{"year":2013,"finding":"MASP-1 and MASP-2 form co-complexes on MBL and ficolins (despite not forming heterodimers directly); these co-complexes are present in serum and are functionally active in complement activation. MAp44 disrupts co-complexes, impairing MASP-2 transactivation.","method":"Native PAGE, size exclusion chromatography, functional complement assays, MBL/ficolin-mediated co-complex formation experiments","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 2 — co-complex formation demonstrated by multiple methods with functional validation","pmids":["23785123"],"is_preprint":false},{"year":2012,"finding":"Crystal structure of MAP-1 (MAp44) reveals a head-to-tail homodimer (~146 Å long); MAP-1 forms a calcium-dependent homodimer in solution and competes with all three MASPs for binding to MBL and ficolins, inhibiting lectin pathway activation.","method":"Crystal structure determination, multi-angle laser light scattering, surface plasmon resonance, C3/C9 deposition inhibition assays","journal":"Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — crystal structure + SPR binding + functional inhibition assays","pmids":["22854970"],"is_preprint":false},{"year":2014,"finding":"MASP-1 CUB1-EGF-CUB2 (D1-3) domains form tight Ca2+-dependent homodimers; MASP-1 and MASP-2 D1-3 domains can form heterodimers after dissociation-reassociation, and MASP-1:MASP-3 heterodimers readily exchange subunits even in the presence of Ca2+.","method":"Size exclusion chromatography, native PAGE, EDTA dissociation/recalcification reassociation experiments","journal":"Molecular immunology","confidence":"Medium","confidence_rationale":"Tier 2 — single lab, multiple methods, mechanistically informative","pmids":["24424083"],"is_preprint":false},{"year":2019,"finding":"MASP-1 directly increases endothelial permeability through PAR1-mediated Ca2+ mobilization, Rho-kinase-dependent MLC phosphorylation, cytoskeletal actin rearrangement, and disruption of interendothelial junctions; MASP-1 also up-regulates bradykinin B2 receptor expression in HUVECs.","method":"Real-time micro electric sensing (TEER), XperT permeability assay, Ca2+ imaging, MLC phosphorylation assay, microarray transcriptome analysis","journal":"Frontiers in immunology","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods establishing mechanism of permeability increase","pmids":["31130964"],"is_preprint":false},{"year":2016,"finding":"MASP-1 increases E-selectin expression on HUVECs (while decreasing ICAM-2), enhancing adhesion between endothelial cells and differentiated PLB-985 neutrophil model cells.","method":"Flow cytometry for adhesion molecule expression, cell adhesion assay with differentiated PLB-985 cells","journal":"Molecular immunology","confidence":"Medium","confidence_rationale":"Tier 2 — single lab, direct functional consequence of MASP-1 treatment measured","pmids":["27219453"],"is_preprint":false},{"year":2018,"finding":"MASP-1 enhances fibrin clot formation in a microvascular whole blood flow model; addition of selective MASP-1 inhibitor SGMI-1 delays clot formation, and complement activation by zymosan increases clotting in a MASP-1-dependent manner.","method":"Microfluidic endothelialized microchannel system, confocal microscopy real-time clot imaging, selective MASP-1 inhibitor SGMI-1","journal":"PloS one","confidence":"High","confidence_rationale":"Tier 2 — physiologically relevant flow model + selective inhibitor, functional readout","pmids":["29324883"],"is_preprint":false},{"year":2011,"finding":"Mutations in MASP1 cause 3MC syndrome; zebrafish morphants for MASP1 develop craniofacial abnormalities, and CL-K1 (encoded by COLEC11, a binding partner of MASP-1) serves as a guidance cue for neural crest cell migration.","method":"Homozygosity mapping, whole exome sequencing, Sanger sequencing, zebrafish morpholino knockdown","journal":"Nature genetics","confidence":"High","confidence_rationale":"Tier 2 — genetic loss-of-function in humans + zebrafish morphant phenotype, highly cited","pmids":["21258343"],"is_preprint":false},{"year":2022,"finding":"MASP-1-enriched small extracellular vesicles (EVs) released from hepatocytes activate hepatic stellate cells (HSCs) via p38 MAPK/ATF2 signaling to promote liver fibrosis; ARRB1 upregulates MASP1 expression in hepatocytes and increases EV release via Rab27A.","method":"Small EV purification, proteomic analysis, primary hepatocyte/HSC co-culture, p38 MAPK inhibition, CCl4 mouse model, siRNA knockdown","journal":"Hepatology","confidence":"Medium","confidence_rationale":"Tier 2 — multiple methods in vitro and in vivo, single lab","pmids":["35849032"],"is_preprint":false},{"year":2006,"finding":"MASP-1 cooperates with MASP-2 in C3 convertase generation via the MBL pathway; synergistic reconstitution with both MASP-1 and MASP-2 in MASP-depleted serum restores C3b deposition, dependent on C2 and C4 but not factor B.","method":"MASP-depleted serum reconstitution, C3b deposition assays, component-depleted sera","journal":"International immunology","confidence":"High","confidence_rationale":"Tier 2 — depletion/reconstitution with pathway-specific controls","pmids":["17182967"],"is_preprint":false},{"year":2002,"finding":"MASP-1/3 promoter is liver-specific and slightly upregulated by IL-1β; MASP-1/3 promoter activity is downregulated by IFN-γ and the stimulatory effect of IL-1β is abolished by IL-6—contrasting with C1s promoter which is strongly upregulated by IL-6.","method":"Reporter gene (luciferase) assays with 5'-flanking MASP-1/3 and MASP-2 gene constructs, cytokine stimulation","journal":"International immunology","confidence":"Medium","confidence_rationale":"Tier 2 — direct promoter functional characterization, single lab","pmids":["12356684"],"is_preprint":false},{"year":2020,"finding":"CRP binds monosodium urate (MSU) crystals and recruits complement proteases C1 and MASP-1 to the crystal surface, linking pattern recognition to complement activation at MSU crystals.","method":"Protein purification from human body fluids, CRP depletion from serum, complement fixation assays","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2-3 — biochemical identification of CRP-MASP-1 co-recruitment, single lab","pmids":["32286427"],"is_preprint":false},{"year":2022,"finding":"MASP-1/C1-INH complex levels are increased in serum during zymosan-induced complement activation and are elevated in COVID-19 patients, validating MASP-1/C1-INH complexes as markers of early lectin pathway activation; C1 esterase inhibitor (C1-INH) forms covalent complexes with active MASP-1.","method":"Sandwich ELISA, zymosan activation, COVID-19 patient cohort","journal":"Frontiers in immunology","confidence":"Medium","confidence_rationale":"Tier 2-3 — functional assay validation with clinical cohort, single lab for assay development","pmids":["36420270"],"is_preprint":false}],"current_model":"MASP-1 is a multifunctional serine protease of the complement lectin pathway that (1) acts as the principal initiator by rapidly autoactivating then transactivating MASP-2 within MBL/ficolin co-complexes; (2) cleaves C2 to contribute ~60% of C3 convertase formation; (3) activates coagulation factors including prothrombin, factor XIII, TAFI, and fibrinogen through thrombin-like specificity; (4) releases bradykinin from high-molecular-weight kininogen; (5) activates endothelial cells by cleaving PAR4 (and PAR1), triggering NF-κB/p38 MAPK signaling, cytokine release, neutrophil recruitment, E-selectin upregulation, and increased vascular permeability; and (6) along with MASP-3 (the exclusive pro-factor D activator in resting blood), is encoded by the alternatively spliced MASP1 gene that also produces MASP-3 and the regulatory inhibitor MAp44, with mutations in this gene causing 3MC syndrome through disruption of both complement activation and neural crest cell migration guidance."},"narrative":{"teleology":[{"year":1999,"claim":"Establishing that the MBL-associated complex contains multiple alternatively generated components—including sMAP (truncated MASP-2)—that co-associate with MASP-1, revealing the compositional complexity of the lectin pathway initiation complex.","evidence":"cDNA sequencing and co-purification from serum MBL complexes","pmids":["10330290"],"confidence":"High","gaps":["Stoichiometry of MASP-1/sMAP within MBL complexes undefined","Functional consequence of sMAP association with MASP-1 unclear"]},{"year":2001,"claim":"Discovery that the MASP1 gene generates MASP-3 by alternative splicing, and that MASP-3 associates with distinct (larger) MBL oligomers and downregulates MASP-2-mediated C4/C2 cleavage, revealing an intrinsic regulatory circuit encoded by the same gene.","evidence":"Alternative splicing analysis, MBL oligomer fractionation, and complement activation assays","pmids":["11485744"],"confidence":"High","gaps":["Physiological concentration and regulation of MASP-3 not determined","Mechanism of MASP-3 inhibition of MASP-2 activity not resolved"]},{"year":2004,"claim":"Defining MASP-1's substrate specificity as thrombin-like (preferring Phe-Gly-Arg), with inhibition by C1-inhibitor, established a biochemical basis for its dual complement/coagulation function.","evidence":"Fluorescent amide substrate profiling and inhibitor panel with recombinant and serum-derived MASP-1","pmids":["14725788"],"confidence":"High","gaps":["Natural macromolecular substrates beyond complement components not yet mapped","In vivo relevance of thrombin-like activity not demonstrated"]},{"year":2006,"claim":"Demonstrating that MASP-1 synergizes with MASP-2 for C3 convertase generation via C2 and C4 (but not factor B) established MASP-1 as a necessary amplifier rather than a redundant enzyme in the lectin pathway.","evidence":"MASP-depleted serum reconstitution with recombinant MASP-1 and MASP-2, C3b deposition on mannan","pmids":["17182967"],"confidence":"High","gaps":["Relative quantitative contribution of MASP-1 vs MASP-2 to C2 cleavage not measured","Mechanism of synergy (sequential or simultaneous) not resolved"]},{"year":2008,"claim":"Two independent lines of evidence—MASP1/3-knockout mice with impaired C4/C3 deposition rescued by recombinant MASP-1, and biochemical mapping of MASP-1 cleavage of factor XIII and fibrinogen at thrombin-identical sites—established MASP-1 as essential for both lectin pathway complement activation and cross-talk with coagulation.","evidence":"MASP1/3-KO mouse reconstitution (lectin pathway); in vitro cleavage with N-terminal sequencing (coagulation substrates)","pmids":["18424734","18456010"],"confidence":"High","gaps":["MASP-1 contribution to hemostasis in vivo not tested","MASP-3 loss confounds interpretation of KO mouse complement phenotype"]},{"year":2009,"claim":"Discovery that MASP-1 activates endothelial cells through proteolytic cleavage of PAR4, triggering Ca²⁺/NF-κB/p38 MAPK signaling, and that MAp44 (a third splice product of MASP1) competitively inhibits lectin pathway activation, revealed MASP-1's pro-inflammatory endothelial role and a built-in negative regulator.","evidence":"PAR4 agonist peptide controls, PAR4 surface depletion assay on HUVECs; SPR/ELISA/complement assays for MAp44","pmids":["19667088","19917686"],"confidence":"High","gaps":["PAR4 cleavage site on MASP-1 not mapped at residue level","In vivo relevance of MAp44 regulation not established"]},{"year":2011,"claim":"Identification of MASP1 mutations as the cause of 3MC syndrome, with zebrafish morphants recapitulating craniofacial defects and CL-K1 serving as a neural crest guidance cue, linked the MASP1 gene to developmental biology beyond innate immunity; separately, MASP-1 was shown to release bradykinin from HK, connecting it to the kinin system.","evidence":"Homozygosity mapping/exome sequencing in 3MC families, zebrafish morpholino knockdown; in vitro HK cleavage with HPLC bradykinin detection","pmids":["21258343","21625439"],"confidence":"High","gaps":["Which MASP1 splice product (MASP-1 vs MASP-3) mediates neural crest guidance not resolved","Bradykinin release by MASP-1 not confirmed in vivo"]},{"year":2012,"claim":"Convergent genetic and biochemical evidence—a MASP-1/3-deficient patient confirming MASP-1 as essential for lectin pathway activation, monospecific inhibitors proving MASP-1 is the exclusive MASP-2 activator contributing ~60% of C2 cleavage, and demonstration of MASP-1/MASP-2 co-complexes on MBL—solidified the mechanistic hierarchy of lectin pathway initiation.","evidence":"Human nonsense mutation reconstitution; monospecific inhibitors in normal serum; co-complex demonstration by native PAGE/SEC; crystal structures of MASP-1/MASP-2 Michaelis complexes","pmids":["22966085","22691502","23785123","22511776"],"confidence":"High","gaps":["Structure of the full MBL–MASP-1–MASP-2 ternary complex not solved","Mechanism of autoactivation signal initiation on pattern recognition molecules unknown"]},{"year":2013,"claim":"Crystal structure of proenzyme MASP-1 explained its ~3000-fold faster autoactivation relative to MASP-2 and showed that both zymogen and activated MASP-1 cleave proenzyme MASP-2 and MASP-3, providing the structural basis for the activation cascade hierarchy.","evidence":"2.5 Å crystal structure of proenzyme MASP-1, autoactivation kinetics with R448Q/S646A mutants","pmids":["23386610"],"confidence":"High","gaps":["How pattern recognition molecule binding triggers initial autoactivation event not structurally resolved","Rate of MASP-1-to-MASP-3 activation in vivo not determined"]},{"year":2015,"claim":"Detailed mapping of prothrombin activation by MASP-1 revealed two simultaneous cleavage pathways (R271-first and R393-first, both requiring R320), generating alternative active thrombin species, distinguishing MASP-1's coagulation mechanism from canonical thrombin generation.","evidence":"Arginine-to-glutamine prothrombin mutants, SDS-PAGE, N-terminal sequencing, thrombelastography","pmids":["25745807","26645987"],"confidence":"High","gaps":["Biological significance of alternative thrombin species not characterized","Whether MASP-1-generated thrombin has altered substrate preferences unknown"]},{"year":2016,"claim":"MASP-3 was identified as the exclusive activator of pro-factor D in resting blood (not MASP-1 or MASP-2), delineating functional specialization among MASP1 gene products: MASP-1 drives lectin pathway initiation while MASP-3 primes the alternative pathway.","evidence":"Evolved monospecific inhibitors for MASP-1, -2, -3 tested in pro-factor D activation assays in resting blood","pmids":["27535802"],"confidence":"High","gaps":["Whether MASP-1 can activate pro-factor D under inflammatory conditions not excluded","Regulatory mechanisms controlling MASP-3 activity in vivo unknown"]},{"year":2019,"claim":"MASP-1 was shown to increase endothelial permeability through PAR1-mediated Ca²⁺ mobilization and Rho-kinase/MLC phosphorylation, disrupting interendothelial junctions and upregulating bradykinin B2 receptor, revealing a second PAR substrate and a vascular leak mechanism.","evidence":"Real-time TEER measurement, XperT permeability assay, Ca²⁺ imaging, MLC phosphorylation, microarray on HUVECs","pmids":["31130964"],"confidence":"High","gaps":["Relative contribution of PAR1 vs PAR4 to MASP-1-driven endothelial responses not quantified","In vivo vascular permeability change by MASP-1 not demonstrated"]},{"year":null,"claim":"Key unresolved questions include: the structural basis of the full MBL/ficolin–MASP ternary complex; how pattern recognition molecule engagement triggers MASP-1 autoactivation; the in vivo significance of MASP-1's coagulation and kinin-generating activities; and which MASP1 splice product mediates the developmental functions disrupted in 3MC syndrome.","evidence":"","pmids":[],"confidence":"Medium","gaps":["Full ternary complex structure of lectin–MASP assemblies unsolved","In vivo contribution of MASP-1 to hemostasis vs complement not genetically dissected","Molecular mechanism linking MASP1 products to neural crest migration guidance uncharacterized"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[3,5,6,7,8,9,12,14,15,23]},{"term_id":"GO:0016787","term_label":"hydrolase activity","supporting_discovery_ids":[5,8,9]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[0,2,21]}],"localization":[{"term_id":"GO:0005576","term_label":"extracellular region","supporting_discovery_ids":[1,2,3,10,16,31]},{"term_id":"GO:0031410","term_label":"cytoplasmic vesicle","supporting_discovery_ids":[27]}],"pathway":[{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[3,4,10,13,20,28]},{"term_id":"R-HSA-109582","term_label":"Hemostasis","supporting_discovery_ids":[7,8,14,15,25]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[6,18,23]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[26]}],"complexes":["MBL-MASP complex","Ficolin-MASP complex","CL-K1-MASP complex"],"partners":["MBL2","MASP2","FCN1","COLEC11","SERPING1","F2","F13A1","FGB"],"other_free_text":[]},"mechanistic_narrative":"MASP1 encodes a multifunctional serine protease central to the complement lectin pathway, coagulation, endothelial inflammation, and developmental patterning; alternative splicing of the same gene produces MASP-1, MASP-3, and the regulatory inhibitor MAp44. MASP-1 rapidly autoactivates (~3000-fold faster than MASP-2) and serves as the exclusive physiological activator of MASP-2 within MBL/ficolin/collectin-11 co-complexes, also directly cleaving C2 to contribute approximately 60% of C3 convertase formation [PMID:22691502, PMID:23386610, PMID:23785123]. Beyond complement, MASP-1 exhibits thrombin-like activity—cleaving prothrombin, factor XIII, fibrinogen, and TAFI to promote coagulation, releasing bradykinin from high-molecular-weight kininogen, and activating endothelial cells via PAR4 (and PAR1) cleavage to trigger NF-κB/p38 MAPK signaling, cytokine secretion, neutrophil recruitment, E-selectin upregulation, and increased vascular permeability [PMID:22536427, PMID:21625439, PMID:19667088, PMID:31130964]. Mutations in MASP1 cause 3MC syndrome, a developmental disorder involving craniofacial abnormalities linked to disrupted neural crest cell migration guidance through the MASP-1/collectin-11 axis [PMID:21258343]."},"prefetch_data":{"uniprot":{"accession":"P48740","full_name":"Mannan-binding lectin serine protease 1","aliases":["Complement-activating component of Ra-reactive factor","Mannose-binding lectin-associated serine protease 1","MASP-1","Mannose-binding protein-associated serine protease","Ra-reactive factor serine protease p100","RaRF","Serine protease 5"],"length_aa":699,"mass_kda":79.2,"function":"Precursor of a serum protease that activates the complement pathway of the complement system, a cascade of proteins that leads to phagocytosis and breakdown of pathogens and signaling that strengthens the adaptive immune system Serine protease that activates the lectin pathway of the complement system, a cascade of proteins that leads to phagocytosis and breakdown of pathogens and signaling that strengthens the adaptive immune system (PubMed:10946292, PubMed:11527969, PubMed:12538697, PubMed:22691502, PubMed:22966085, PubMed:9087411). The lectin complement system is activated following association of lectins, such as MBL2, FCN1, FCN2 or FCN3, to carbohydrates on the pathogen surface (PubMed:22854970, PubMed:22966085, PubMed:23386610, PubMed:9087411). Following autoproteolytic processing in response to lectin-binding to pathogen carbohydrates, catalyzes cleavage and activation of MASP2, the next component of the lectin complement pathway (PubMed:22691502, PubMed:22966085, PubMed:23386610) Serine protease that activates the alternative pathway of the complement system, a cascade of proteins that leads to phagocytosis and breakdown of pathogens and signaling that strengthens the adaptive immune system (PubMed:20038603, PubMed:23792966, PubMed:27535802). The alternative complement pathway acts as an amplification loop that enhances other complement pathways (PubMed:27535802). Isoform MASP-3 specifically catalyzes cleavage and activation of factor D (CFD), the protease that initiates the alternative complement pathway (PubMed:20038603, PubMed:27535802)","subcellular_location":"Secreted","url":"https://www.uniprot.org/uniprotkb/P48740/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/MASP1","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1208,"dependency_fraction":0.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/MASP1","total_profiled":1310},"omim":[{"mim_id":"613791","title":"MASP2 DEFICIENCY","url":"https://www.omim.org/entry/613791"},{"mim_id":"612502","title":"COLLECTIN 11; COLEC11","url":"https://www.omim.org/entry/612502"},{"mim_id":"606860","title":"COMPLEMENT COMPONENT 1 INHIBITOR; C1NH","url":"https://www.omim.org/entry/606860"},{"mim_id":"605102","title":"MANNAN-BINDING LECTIN SERINE PROTEASE 2; MASP2","url":"https://www.omim.org/entry/605102"},{"mim_id":"602228","title":"TRANSCRIPTION FACTOR 7-LIKE 2; TCF7L2","url":"https://www.omim.org/entry/602228"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Enhanced","locations":[{"location":"Nucleoplasm","reliability":"Enhanced"},{"location":"Cytosol","reliability":"Enhanced"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"cervix","ntpm":100.9},{"tissue":"heart muscle","ntpm":108.6},{"tissue":"liver","ntpm":171.6}],"url":"https://www.proteinatlas.org/search/MASP1"},"hgnc":{"alias_symbol":["MASP","Map44","MASP-3","MAP-1"],"prev_symbol":["CRARF","PRSS5"]},"alphafold":{"accession":"P48740","domains":[{"cath_id":"2.60.120.290","chopping":"21-140","consensus_level":"high","plddt":92.4643,"start":21,"end":140},{"cath_id":"2.60.120.290","chopping":"184-298","consensus_level":"medium","plddt":95.8408,"start":184,"end":298},{"cath_id":"2.10.70.10","chopping":"301-365","consensus_level":"medium","plddt":95.5078,"start":301,"end":365},{"cath_id":"2.10.70.10","chopping":"377-435","consensus_level":"medium","plddt":94.5271,"start":377,"end":435},{"cath_id":"2.40.10.10","chopping":"454-496_506-696","consensus_level":"medium","plddt":91.2106,"start":454,"end":696}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P48740","model_url":"https://alphafold.ebi.ac.uk/files/AF-P48740-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P48740-F1-predicted_aligned_error_v6.png","plddt_mean":90.44},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=MASP1","jax_strain_url":"https://www.jax.org/strain/search?query=MASP1"},"sequence":{"accession":"P48740","fasta_url":"https://rest.uniprot.org/uniprotkb/P48740.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P48740/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P48740"}},"corpus_meta":[{"pmid":"11485744","id":"PMC_11485744","title":"MASP-3 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MASP-3 downregulates C4 and C2 cleaving activity of MASP-2.\",\n      \"method\": \"Alternative splicing analysis, oligomer fractionation, functional complement activation assays\",\n      \"journal\": \"Immunity\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal biochemical fractionation + functional assays, highly cited foundational paper\",\n      \"pmids\": [\"11485744\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"The MBL-MASP complex contains a 22 kDa protein (sMAP) that is a truncated form of MASP-2 generated by alternative polyadenylation, and sMAP associates with MASP-1 within the MBL complex.\",\n      \"method\": \"cDNA sequencing, protein biochemistry, Co-purification/Co-IP\",\n      \"journal\": \"International immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — direct binding demonstrated by co-purification, sequence confirmed by cDNA, replicated in subsequent work\",\n      \"pmids\": [\"10330290\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"MAp44, an alternatively spliced product of the MASP1 gene sharing the first four domains with MASP-1 and MASP-3 plus 17 unique C-terminal residues, is found in serum at ~1.4 µg/ml and competes with MASP-2 for binding to MBL and ficolins, thereby inhibiting complement activation.\",\n      \"method\": \"Surface plasmon resonance (SPR), ELISA, complement activation assays, mRNA profiling\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — SPR quantification of binding affinity + functional inhibition assay, multiple orthogonal methods\",\n      \"pmids\": [\"19917686\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"In normal human serum, MASP-1 is the exclusive activator of MASP-2; MASP-2 cannot autoactivate under physiological conditions, and inhibition of MASP-1 prevents MASP-2 activation. MASP-1 also contributes ~60% of C2a generation for C3 convertase formation.\",\n      \"method\": \"Monospecific inhibitors against MASP-1 and MASP-2, complement activation assays in normal human serum\",\n      \"journal\": \"PNAS\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — monospecific inhibitors with rigorous controls, replicated by multiple independent groups\",\n      \"pmids\": [\"22691502\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"MASP-1 contributes to lectin pathway activation by promoting MASP-2 activation; MASP1/3-deficient mouse serum shows significantly lower C4 and C3 deposition on mannan, and activity is restored by adding recombinant MASP-1, which accelerates MASP-2 activation.\",\n      \"method\": \"Gene-targeted MASP1/3-knockout mice, C4/C3 deposition assays, reconstitution with recombinant MASP-1\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean KO + reconstitution experiment, replicated by multiple labs\",\n      \"pmids\": [\"18424734\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"MASP-1 has thrombin-like substrate specificity, cleaving Phe-Gly-Arg-AMC most rapidly among tested fluorescent amide substrates; MASP-1 is inhibited by C1 inhibitor and the thrombin inhibitor boroMpg (but not hirudin), whereas MASP-2 shows minimal amidolytic activity toward the same substrates.\",\n      \"method\": \"Fluorescent amide substrate cleavage assays with recombinant and serum-derived MASPs, inhibitor profiling\",\n      \"journal\": \"Molecular immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct in vitro enzymatic assay with multiple substrates and inhibitors\",\n      \"pmids\": [\"14725788\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"MASP-1 activates Ca2+ signaling, NF-κB, and p38 MAPK pathways in cultured HUVECs through proteolytic cleavage of PAR4; MASP-2 had no such effect, and the proteolytic activity of MASP-1 is required for endothelial activation.\",\n      \"method\": \"Cell-based signaling assays, synthetic PAR peptide substrates, PAR4 agonist peptide, mRNA quantification, membrane PAR4 depletion assay\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods establishing PAR4 as the substrate, mechanistically validated\",\n      \"pmids\": [\"19667088\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"MASP-1 activates factor XIII and cleaves fibrinogen and prothrombin in plasma-based systems; MASP-1 directly activates prothrombin and TAFI, and induces fibrin clot formation with altered clot structure.\",\n      \"method\": \"FXIII incorporation assay, specific activation product assays (F1+2, FPA, TAFIa), turbidimetric clotting assay, scanning electron microscopy\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple in vitro biochemical assays with purified systems and plasma, replicated in subsequent work\",\n      \"pmids\": [\"22536427\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"MASP-1 cleaves factor XIII A-chain and fibrinogen beta-chain at sites identical to thrombin, releases fibrinopeptide B (but not A), and drives cross-linked fibrinogen formation; thrombin turnover rate for factor XIII is ~650-fold faster than MASP-1.\",\n      \"method\": \"In vitro cleavage assays with recombinant MASP-1 and thrombin, SDS-PAGE, N-terminal sequencing\",\n      \"journal\": \"Biochimica et biophysica acta\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstituted in vitro with site-level resolution, replicated by other groups\",\n      \"pmids\": [\"18456010\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"MASP-1 cleaves high-molecular-weight kininogen (HK) to release bradykinin; MASP-2 can also cleave HK but cannot release bradykinin. C1-inhibitor prevents HK cleavage by both MASPs.\",\n      \"method\": \"Differential gel electrophoresis (proteomic screen), SDS-PAGE, HPLC detection of bradykinin release\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro biochemical reconstitution confirmed by HPLC product detection, mechanistically characterized\",\n      \"pmids\": [\"21625439\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"MASP-1 is essential for lectin pathway activation in a MASP-1/3-deficient patient; the alternative pathway functions normally in this patient and is unaffected by MASP-1/MASP-3 reconstitution. MASP-1 and MASP-2 can form co-complexes on MBL in serum, providing a structural basis for MASP-1-mediated transactivation of MASP-2.\",\n      \"method\": \"Patient with nonsense mutation in MASP1 gene, complement functional assays, reconstitution with recombinant MASPs, demonstration of MASP-1/MASP-2 co-complexes in serum\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — human genetic loss-of-function combined with reconstitution and co-complex demonstration, independent validation\",\n      \"pmids\": [\"22966085\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"MASP-3 is the exclusive activator of pro-factor D in resting blood; neither MASP-1 nor MASP-2 activates pro-factor D under resting physiological conditions, as demonstrated using specific evolved inhibitors against all three MASPs.\",\n      \"method\": \"Evolved monospecific MASP-1, MASP-2, and MASP-3 inhibitors, pro-factor D activation assays in resting blood\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — specific inhibitors for all three enzymes tested, rigorous kinetic analysis, replicated in subsequent studies\",\n      \"pmids\": [\"27535802\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Zymogen MASP-1 autoactivates ~3000-fold faster than zymogen MASP-2; both activated and proenzyme MASP-1 efficiently cleave proenzyme MASP-2, and MASP-1 also cleaves proenzyme MASP-3. Crystal structure of proenzyme MASP-1 at 2.5 Å explains the unusual activity of the zymogen.\",\n      \"method\": \"In vitro autoactivation kinetics with recombinant MASP-1/MASP-2 mutants (R448Q, S646A), crystal structure at 2.5 Å, synthetic substrate cleavage assays\",\n      \"journal\": \"Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstitution + crystal structure + mutagenesis in a single study\",\n      \"pmids\": [\"23386610\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Both MASP-1 and MASP-2 are essential for lectin pathway activation; crystal structures of Michaelis-like complexes of MASP-1 and MASP-2 with substrate-like inhibitors at 1.28 Å resolution reveal plasticity of MASP-2 and explain enzyme-substrate interactions.\",\n      \"method\": \"Evolved monospecific inhibitors, lectin pathway functional assays, crystal structure determination (1.28 Å for MASP-2)\",\n      \"journal\": \"Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structures + specific inhibitors + functional assays, rigorous\",\n      \"pmids\": [\"22511776\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"MASP-1 promotes clotting by directly activating prothrombin at three cleavage sites (R155, R271, R393), producing an alternative active thrombin species; MASP-1-induced clotting in whole blood and platelet-poor plasma is dependent on prothrombin.\",\n      \"method\": \"Thrombelastography, SDS-PAGE, N-terminal sequencing of cleavage products, prothrombin-depleted plasma\",\n      \"journal\": \"Molecular immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution + site-level mapping + functional clotting assays\",\n      \"pmids\": [\"25745807\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"MASP-1 activates prothrombin via two simultaneous pathways (cleaving R271 or R393 first), both requiring R320 cleavage and resulting in formation of active alternative thrombin species; R155 is not an important cleavage site for prothrombin activation.\",\n      \"method\": \"Arginine-to-glutamine prothrombin mutants (R271Q, R320Q, R393Q), active-site mutant S525A, SDS-PAGE, N-terminal sequencing, thrombelastography\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — multiple site-directed mutants + in vitro reconstitution + functional validation\",\n      \"pmids\": [\"26645987\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Collectin-11 (CL-K1) associates with MASP-1 and/or MASP-3 in plasma as demonstrated by co-purification and ELISA; CL-K1 also binds bacteria, fungi, and viruses.\",\n      \"method\": \"ELISA, co-purification, Western blotting, mass spectrometry\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods confirming MASP-1/CL-K1 interaction in plasma\",\n      \"pmids\": [\"20956340\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Collectin-11 associates with MASP-1, MASP-2, MASP-3, and MAP-1, and CL-11/MASP-2 complexes mediate C4b deposition on Candida albicans, defining CL-11 as the fifth lectin pathway recognition molecule.\",\n      \"method\": \"Protein interaction assays, C4b/C3b deposition assays on Candida albicans, depletion and reconstitution experiments\",\n      \"journal\": \"Journal of innate immunity\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — depletion/reconstitution with functional complement readout\",\n      \"pmids\": [\"23220946\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"MASP-1 induces IL-6 and IL-8 secretion (but not IL-1α, IL-1ra, TNFα, or MCP-1) from HUVECs through the p38 MAPK pathway, and conditioned supernatant activates neutrophil chemotaxis.\",\n      \"method\": \"Recombinant MASP-1 stimulation of HUVECs, cytokine ELISA, p38 MAPK pathway inhibition, neutrophil chemotaxis assay\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — mechanistic pathway identified with pharmacological inhibition and functional readout\",\n      \"pmids\": [\"24489848\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Serum MASP-1 in complex with MBL activates endothelial cells through the proteolytic activity of MASP-1; MASP-2, MASP-3, and non-enzymatic N-terminal domains of MASP-1/MASP-2 do not activate HUVECs, and a stable zymogen MASP-1 mutant is also inactive.\",\n      \"method\": \"Ca2+ signaling in HUVECs stimulated with MBL-MASP complexes, recombinant MASP fragments, zymogen MASP-1 mutant\",\n      \"journal\": \"Molecular immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple controls including zymogen mutant establishing requirement for MASP-1 catalytic activity\",\n      \"pmids\": [\"24472859\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"MASP-1 and MASP-2 form co-complexes on MBL and ficolins (despite not forming heterodimers directly); these co-complexes are present in serum and are functionally active in complement activation. MAp44 disrupts co-complexes, impairing MASP-2 transactivation.\",\n      \"method\": \"Native PAGE, size exclusion chromatography, functional complement assays, MBL/ficolin-mediated co-complex formation experiments\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — co-complex formation demonstrated by multiple methods with functional validation\",\n      \"pmids\": [\"23785123\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Crystal structure of MAP-1 (MAp44) reveals a head-to-tail homodimer (~146 Å long); MAP-1 forms a calcium-dependent homodimer in solution and competes with all three MASPs for binding to MBL and ficolins, inhibiting lectin pathway activation.\",\n      \"method\": \"Crystal structure determination, multi-angle laser light scattering, surface plasmon resonance, C3/C9 deposition inhibition assays\",\n      \"journal\": \"Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure + SPR binding + functional inhibition assays\",\n      \"pmids\": [\"22854970\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"MASP-1 CUB1-EGF-CUB2 (D1-3) domains form tight Ca2+-dependent homodimers; MASP-1 and MASP-2 D1-3 domains can form heterodimers after dissociation-reassociation, and MASP-1:MASP-3 heterodimers readily exchange subunits even in the presence of Ca2+.\",\n      \"method\": \"Size exclusion chromatography, native PAGE, EDTA dissociation/recalcification reassociation experiments\",\n      \"journal\": \"Molecular immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — single lab, multiple methods, mechanistically informative\",\n      \"pmids\": [\"24424083\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"MASP-1 directly increases endothelial permeability through PAR1-mediated Ca2+ mobilization, Rho-kinase-dependent MLC phosphorylation, cytoskeletal actin rearrangement, and disruption of interendothelial junctions; MASP-1 also up-regulates bradykinin B2 receptor expression in HUVECs.\",\n      \"method\": \"Real-time micro electric sensing (TEER), XperT permeability assay, Ca2+ imaging, MLC phosphorylation assay, microarray transcriptome analysis\",\n      \"journal\": \"Frontiers in immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods establishing mechanism of permeability increase\",\n      \"pmids\": [\"31130964\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"MASP-1 increases E-selectin expression on HUVECs (while decreasing ICAM-2), enhancing adhesion between endothelial cells and differentiated PLB-985 neutrophil model cells.\",\n      \"method\": \"Flow cytometry for adhesion molecule expression, cell adhesion assay with differentiated PLB-985 cells\",\n      \"journal\": \"Molecular immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — single lab, direct functional consequence of MASP-1 treatment measured\",\n      \"pmids\": [\"27219453\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"MASP-1 enhances fibrin clot formation in a microvascular whole blood flow model; addition of selective MASP-1 inhibitor SGMI-1 delays clot formation, and complement activation by zymosan increases clotting in a MASP-1-dependent manner.\",\n      \"method\": \"Microfluidic endothelialized microchannel system, confocal microscopy real-time clot imaging, selective MASP-1 inhibitor SGMI-1\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — physiologically relevant flow model + selective inhibitor, functional readout\",\n      \"pmids\": [\"29324883\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Mutations in MASP1 cause 3MC syndrome; zebrafish morphants for MASP1 develop craniofacial abnormalities, and CL-K1 (encoded by COLEC11, a binding partner of MASP-1) serves as a guidance cue for neural crest cell migration.\",\n      \"method\": \"Homozygosity mapping, whole exome sequencing, Sanger sequencing, zebrafish morpholino knockdown\",\n      \"journal\": \"Nature genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic loss-of-function in humans + zebrafish morphant phenotype, highly cited\",\n      \"pmids\": [\"21258343\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"MASP-1-enriched small extracellular vesicles (EVs) released from hepatocytes activate hepatic stellate cells (HSCs) via p38 MAPK/ATF2 signaling to promote liver fibrosis; ARRB1 upregulates MASP1 expression in hepatocytes and increases EV release via Rab27A.\",\n      \"method\": \"Small EV purification, proteomic analysis, primary hepatocyte/HSC co-culture, p38 MAPK inhibition, CCl4 mouse model, siRNA knockdown\",\n      \"journal\": \"Hepatology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple methods in vitro and in vivo, single lab\",\n      \"pmids\": [\"35849032\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"MASP-1 cooperates with MASP-2 in C3 convertase generation via the MBL pathway; synergistic reconstitution with both MASP-1 and MASP-2 in MASP-depleted serum restores C3b deposition, dependent on C2 and C4 but not factor B.\",\n      \"method\": \"MASP-depleted serum reconstitution, C3b deposition assays, component-depleted sera\",\n      \"journal\": \"International immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — depletion/reconstitution with pathway-specific controls\",\n      \"pmids\": [\"17182967\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"MASP-1/3 promoter is liver-specific and slightly upregulated by IL-1β; MASP-1/3 promoter activity is downregulated by IFN-γ and the stimulatory effect of IL-1β is abolished by IL-6—contrasting with C1s promoter which is strongly upregulated by IL-6.\",\n      \"method\": \"Reporter gene (luciferase) assays with 5'-flanking MASP-1/3 and MASP-2 gene constructs, cytokine stimulation\",\n      \"journal\": \"International immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct promoter functional characterization, single lab\",\n      \"pmids\": [\"12356684\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"CRP binds monosodium urate (MSU) crystals and recruits complement proteases C1 and MASP-1 to the crystal surface, linking pattern recognition to complement activation at MSU crystals.\",\n      \"method\": \"Protein purification from human body fluids, CRP depletion from serum, complement fixation assays\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — biochemical identification of CRP-MASP-1 co-recruitment, single lab\",\n      \"pmids\": [\"32286427\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"MASP-1/C1-INH complex levels are increased in serum during zymosan-induced complement activation and are elevated in COVID-19 patients, validating MASP-1/C1-INH complexes as markers of early lectin pathway activation; C1 esterase inhibitor (C1-INH) forms covalent complexes with active MASP-1.\",\n      \"method\": \"Sandwich ELISA, zymosan activation, COVID-19 patient cohort\",\n      \"journal\": \"Frontiers in immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — functional assay validation with clinical cohort, single lab for assay development\",\n      \"pmids\": [\"36420270\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"MASP-1 is a multifunctional serine protease of the complement lectin pathway that (1) acts as the principal initiator by rapidly autoactivating then transactivating MASP-2 within MBL/ficolin co-complexes; (2) cleaves C2 to contribute ~60% of C3 convertase formation; (3) activates coagulation factors including prothrombin, factor XIII, TAFI, and fibrinogen through thrombin-like specificity; (4) releases bradykinin from high-molecular-weight kininogen; (5) activates endothelial cells by cleaving PAR4 (and PAR1), triggering NF-κB/p38 MAPK signaling, cytokine release, neutrophil recruitment, E-selectin upregulation, and increased vascular permeability; and (6) along with MASP-3 (the exclusive pro-factor D activator in resting blood), is encoded by the alternatively spliced MASP1 gene that also produces MASP-3 and the regulatory inhibitor MAp44, with mutations in this gene causing 3MC syndrome through disruption of both complement activation and neural crest cell migration guidance.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"MASP1 encodes a multifunctional serine protease central to the complement lectin pathway, coagulation, endothelial inflammation, and developmental patterning; alternative splicing of the same gene produces MASP-1, MASP-3, and the regulatory inhibitor MAp44. MASP-1 rapidly autoactivates (~3000-fold faster than MASP-2) and serves as the exclusive physiological activator of MASP-2 within MBL/ficolin/collectin-11 co-complexes, also directly cleaving C2 to contribute approximately 60% of C3 convertase formation [PMID:22691502, PMID:23386610, PMID:23785123]. Beyond complement, MASP-1 exhibits thrombin-like activity—cleaving prothrombin, factor XIII, fibrinogen, and TAFI to promote coagulation, releasing bradykinin from high-molecular-weight kininogen, and activating endothelial cells via PAR4 (and PAR1) cleavage to trigger NF-κB/p38 MAPK signaling, cytokine secretion, neutrophil recruitment, E-selectin upregulation, and increased vascular permeability [PMID:22536427, PMID:21625439, PMID:19667088, PMID:31130964]. Mutations in MASP1 cause 3MC syndrome, a developmental disorder involving craniofacial abnormalities linked to disrupted neural crest cell migration guidance through the MASP-1/collectin-11 axis [PMID:21258343].\",\n  \"teleology\": [\n    {\n      \"year\": 1999,\n      \"claim\": \"Establishing that the MBL-associated complex contains multiple alternatively generated components—including sMAP (truncated MASP-2)—that co-associate with MASP-1, revealing the compositional complexity of the lectin pathway initiation complex.\",\n      \"evidence\": \"cDNA sequencing and co-purification from serum MBL complexes\",\n      \"pmids\": [\"10330290\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Stoichiometry of MASP-1/sMAP within MBL complexes undefined\", \"Functional consequence of sMAP association with MASP-1 unclear\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Discovery that the MASP1 gene generates MASP-3 by alternative splicing, and that MASP-3 associates with distinct (larger) MBL oligomers and downregulates MASP-2-mediated C4/C2 cleavage, revealing an intrinsic regulatory circuit encoded by the same gene.\",\n      \"evidence\": \"Alternative splicing analysis, MBL oligomer fractionation, and complement activation assays\",\n      \"pmids\": [\"11485744\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Physiological concentration and regulation of MASP-3 not determined\", \"Mechanism of MASP-3 inhibition of MASP-2 activity not resolved\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Defining MASP-1's substrate specificity as thrombin-like (preferring Phe-Gly-Arg), with inhibition by C1-inhibitor, established a biochemical basis for its dual complement/coagulation function.\",\n      \"evidence\": \"Fluorescent amide substrate profiling and inhibitor panel with recombinant and serum-derived MASP-1\",\n      \"pmids\": [\"14725788\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Natural macromolecular substrates beyond complement components not yet mapped\", \"In vivo relevance of thrombin-like activity not demonstrated\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Demonstrating that MASP-1 synergizes with MASP-2 for C3 convertase generation via C2 and C4 (but not factor B) established MASP-1 as a necessary amplifier rather than a redundant enzyme in the lectin pathway.\",\n      \"evidence\": \"MASP-depleted serum reconstitution with recombinant MASP-1 and MASP-2, C3b deposition on mannan\",\n      \"pmids\": [\"17182967\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relative quantitative contribution of MASP-1 vs MASP-2 to C2 cleavage not measured\", \"Mechanism of synergy (sequential or simultaneous) not resolved\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Two independent lines of evidence—MASP1/3-knockout mice with impaired C4/C3 deposition rescued by recombinant MASP-1, and biochemical mapping of MASP-1 cleavage of factor XIII and fibrinogen at thrombin-identical sites—established MASP-1 as essential for both lectin pathway complement activation and cross-talk with coagulation.\",\n      \"evidence\": \"MASP1/3-KO mouse reconstitution (lectin pathway); in vitro cleavage with N-terminal sequencing (coagulation substrates)\",\n      \"pmids\": [\"18424734\", \"18456010\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"MASP-1 contribution to hemostasis in vivo not tested\", \"MASP-3 loss confounds interpretation of KO mouse complement phenotype\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Discovery that MASP-1 activates endothelial cells through proteolytic cleavage of PAR4, triggering Ca²⁺/NF-κB/p38 MAPK signaling, and that MAp44 (a third splice product of MASP1) competitively inhibits lectin pathway activation, revealed MASP-1's pro-inflammatory endothelial role and a built-in negative regulator.\",\n      \"evidence\": \"PAR4 agonist peptide controls, PAR4 surface depletion assay on HUVECs; SPR/ELISA/complement assays for MAp44\",\n      \"pmids\": [\"19667088\", \"19917686\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"PAR4 cleavage site on MASP-1 not mapped at residue level\", \"In vivo relevance of MAp44 regulation not established\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Identification of MASP1 mutations as the cause of 3MC syndrome, with zebrafish morphants recapitulating craniofacial defects and CL-K1 serving as a neural crest guidance cue, linked the MASP1 gene to developmental biology beyond innate immunity; separately, MASP-1 was shown to release bradykinin from HK, connecting it to the kinin system.\",\n      \"evidence\": \"Homozygosity mapping/exome sequencing in 3MC families, zebrafish morpholino knockdown; in vitro HK cleavage with HPLC bradykinin detection\",\n      \"pmids\": [\"21258343\", \"21625439\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Which MASP1 splice product (MASP-1 vs MASP-3) mediates neural crest guidance not resolved\", \"Bradykinin release by MASP-1 not confirmed in vivo\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Convergent genetic and biochemical evidence—a MASP-1/3-deficient patient confirming MASP-1 as essential for lectin pathway activation, monospecific inhibitors proving MASP-1 is the exclusive MASP-2 activator contributing ~60% of C2 cleavage, and demonstration of MASP-1/MASP-2 co-complexes on MBL—solidified the mechanistic hierarchy of lectin pathway initiation.\",\n      \"evidence\": \"Human nonsense mutation reconstitution; monospecific inhibitors in normal serum; co-complex demonstration by native PAGE/SEC; crystal structures of MASP-1/MASP-2 Michaelis complexes\",\n      \"pmids\": [\"22966085\", \"22691502\", \"23785123\", \"22511776\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structure of the full MBL–MASP-1–MASP-2 ternary complex not solved\", \"Mechanism of autoactivation signal initiation on pattern recognition molecules unknown\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Crystal structure of proenzyme MASP-1 explained its ~3000-fold faster autoactivation relative to MASP-2 and showed that both zymogen and activated MASP-1 cleave proenzyme MASP-2 and MASP-3, providing the structural basis for the activation cascade hierarchy.\",\n      \"evidence\": \"2.5 Å crystal structure of proenzyme MASP-1, autoactivation kinetics with R448Q/S646A mutants\",\n      \"pmids\": [\"23386610\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How pattern recognition molecule binding triggers initial autoactivation event not structurally resolved\", \"Rate of MASP-1-to-MASP-3 activation in vivo not determined\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Detailed mapping of prothrombin activation by MASP-1 revealed two simultaneous cleavage pathways (R271-first and R393-first, both requiring R320), generating alternative active thrombin species, distinguishing MASP-1's coagulation mechanism from canonical thrombin generation.\",\n      \"evidence\": \"Arginine-to-glutamine prothrombin mutants, SDS-PAGE, N-terminal sequencing, thrombelastography\",\n      \"pmids\": [\"25745807\", \"26645987\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Biological significance of alternative thrombin species not characterized\", \"Whether MASP-1-generated thrombin has altered substrate preferences unknown\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"MASP-3 was identified as the exclusive activator of pro-factor D in resting blood (not MASP-1 or MASP-2), delineating functional specialization among MASP1 gene products: MASP-1 drives lectin pathway initiation while MASP-3 primes the alternative pathway.\",\n      \"evidence\": \"Evolved monospecific inhibitors for MASP-1, -2, -3 tested in pro-factor D activation assays in resting blood\",\n      \"pmids\": [\"27535802\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether MASP-1 can activate pro-factor D under inflammatory conditions not excluded\", \"Regulatory mechanisms controlling MASP-3 activity in vivo unknown\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"MASP-1 was shown to increase endothelial permeability through PAR1-mediated Ca²⁺ mobilization and Rho-kinase/MLC phosphorylation, disrupting interendothelial junctions and upregulating bradykinin B2 receptor, revealing a second PAR substrate and a vascular leak mechanism.\",\n      \"evidence\": \"Real-time TEER measurement, XperT permeability assay, Ca²⁺ imaging, MLC phosphorylation, microarray on HUVECs\",\n      \"pmids\": [\"31130964\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relative contribution of PAR1 vs PAR4 to MASP-1-driven endothelial responses not quantified\", \"In vivo vascular permeability change by MASP-1 not demonstrated\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include: the structural basis of the full MBL/ficolin–MASP ternary complex; how pattern recognition molecule engagement triggers MASP-1 autoactivation; the in vivo significance of MASP-1's coagulation and kinin-generating activities; and which MASP1 splice product mediates the developmental functions disrupted in 3MC syndrome.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Full ternary complex structure of lectin–MASP assemblies unsolved\", \"In vivo contribution of MASP-1 to hemostasis vs complement not genetically dissected\", \"Molecular mechanism linking MASP1 products to neural crest migration guidance uncharacterized\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [3, 5, 6, 7, 8, 9, 12, 14, 15, 23]},\n      {\"term_id\": \"GO:0016787\", \"supporting_discovery_ids\": [5, 8, 9]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [0, 2, 21]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [1, 2, 3, 10, 16, 31]},\n      {\"term_id\": \"GO:0031410\", \"supporting_discovery_ids\": [27]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [3, 4, 10, 13, 20, 28]},\n      {\"term_id\": \"R-HSA-109582\", \"supporting_discovery_ids\": [7, 8, 14, 15, 25]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [6, 18, 23]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [26]}\n    ],\n    \"complexes\": [\n      \"MBL-MASP complex\",\n      \"Ficolin-MASP complex\",\n      \"CL-K1-MASP complex\"\n    ],\n    \"partners\": [\n      \"MBL2\",\n      \"MASP2\",\n      \"FCN1\",\n      \"COLEC11\",\n      \"SERPING1\",\n      \"F2\",\n      \"F13A1\",\n      \"FGB\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}