{"gene":"KLKB1","run_date":"2026-04-28T18:30:27","timeline":{"discoveries":[{"year":1986,"finding":"Human plasma prekallikrein is synthesized as a 619-amino acid single-chain zymogen (plus 19-aa signal peptide) containing four tandem apple domain repeats (each ~90-91 aa) in the heavy chain and a trypsin-family serine protease domain in the light chain; factor XIIa activates it by cleaving a single Arg-Ile bond, yielding a heavy chain (371 aa) and light chain (248 aa) held together by a disulfide bond.","method":"cDNA sequencing combined with automated Edman degradation of cyanogen bromide peptides; identification of N-glycosylation sites and activation cleavage site","journal":"Biochemistry","confidence":"High","confidence_rationale":"Tier 1 — primary sequence determination by orthogonal protein sequencing and cDNA cloning with activation-site identification","pmids":["3521732"],"is_preprint":false},{"year":1977,"finding":"Surface-bound Hageman factor (factor XII) activates prekallikrein to kallikrein in a reaction facilitated by high molecular weight (HMW) kininogen; the resulting kallikrein then feeds back to activate additional Hageman factor enzymatically, constituting a positive feedback amplification loop. HMW kininogen acts as a cofactor that enhances both the initial prekallikrein activation and the reciprocal kallikrein-mediated activation of Hageman factor.","method":"Reconstitution assays with purified components (HMW kininogen, prekallikrein, factor XII) and kaolin surfaces; stoichiometric analysis of cofactor interactions","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 1 — reconstituted in vitro with purified components, multiple functional readouts","pmids":["874082"],"is_preprint":false},{"year":1979,"finding":"Prekallikrein and factor XI circulate as complexes bound to HMW kininogen through its light chain, with association constants of 3.4×10⁷ M⁻¹ and 4.2×10⁸ M⁻¹, respectively; both proteins compete for a single (or closely overlapping) binding site on HMW kininogen, and this interaction is essential for HMW kininogen's coagulation cofactor activity.","method":"Direct binding studies with purified proteins; competition assays; isolated HMW kininogen light chain binding to prekallikrein and factor XI; coagulant activity assays","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 — quantitative binding constants measured with purified components, functional validation with light chain","pmids":["291905"],"is_preprint":false},{"year":1979,"finding":"Plasma kallikrein cleaves HMW kininogen to liberate bradykinin (kinin) and generate a two-chain disulfide-linked kinin-free form (heavy chain ~65 kDa, histidine-rich light chain ~44 kDa); this cleavage is dependent on prekallikrein and factor XII in plasma and the light chain retains full procoagulant activity.","method":"Purification of HMW kininogen; incubation with plasma kallikrein; SDS-PAGE; ¹²⁵I-kininogen cleavage in plasma depleted of prekallikrein or factor XII; sedimentation equilibrium","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — in vitro reconstitution with purified components and deficient plasmas, structural characterization","pmids":["500690"],"is_preprint":false},{"year":1988,"finding":"Protein C inhibitor (PCI) inactivates plasma kallikrein with a second-order rate constant of ~11×10⁴ M⁻¹s⁻¹ (unaffected by heparin), forming a 1:1 molar SDS-stable complex; the heavy chain of kallikrein plays a minor role in the inactivation, as PCI inhibits the isolated light chain with similar kinetics.","method":"Kinetic inhibition assays with purified PCI and plasma kallikrein; SDS-PAGE and immunoblotting of enzyme-inhibitor complexes; experiments with isolated light chains","journal":"Biochemistry","confidence":"High","confidence_rationale":"Tier 1 — quantitative kinetics with purified components, orthogonal structural validation by immunoblot","pmids":["2844223"],"is_preprint":false},{"year":1989,"finding":"PCI inhibits plasma kallikrein with a second-order rate constant of 6.50×10⁴ M⁻¹s⁻¹ (no heparin) rising to 0.18×10⁶ M⁻¹s⁻¹ with heparin; PCI does not inhibit alpha-factor XIIa or plasmin; kallikrein cleaves PCI into products of 54 kDa and 52 kDa, distinct from the 54 kDa fragment produced by most other enzymes.","method":"Kinetic inhibition studies with purified PCI; SDS-PAGE of enzyme-inhibitor complexes; comparative inhibition across multiple serine proteases","journal":"Thrombosis research","confidence":"High","confidence_rationale":"Tier 1 — comprehensive quantitative kinetics with purified proteins across multiple enzyme comparators","pmids":["2551064"],"is_preprint":false},{"year":1994,"finding":"Plasma prekallikrein (along with factor XI and factor XII) is present on the exterior surface of human neutrophils; prekallikrein is anchored to the neutrophil membrane through HMW kininogen, and displacement by peptide HK31 (mimicking the kininogen binding site) confirms this attachment mechanism; kinin within the membrane-bound kininogen can be released by plasma or tissue kallikrein.","method":"Immunolocalization with specific antibodies; monoclonal antibody epitope blocking; peptide competition (HK31); confocal/immunofluorescence microscopy on human neutrophils","journal":"Blood","confidence":"High","confidence_rationale":"Tier 2 — direct localization with functional blocking evidence in primary human cells, multiple antibody approaches","pmids":["8025275"],"is_preprint":false},{"year":1996,"finding":"TFPI-2 (tissue factor pathway inhibitor-2) strongly inhibits human plasma kallikrein amidolytic activity with a Ki of 25 nM; heparin does not enhance this inhibition, unlike its effect on other enzymes inhibited by TFPI-2.","method":"Amidolytic inhibition assays with purified TFPI-2 and plasma kallikrein; Ki determination; heparin enhancement studies","journal":"Biochemistry","confidence":"High","confidence_rationale":"Tier 1 — quantitative Ki measured in vitro with purified components","pmids":["8555184"],"is_preprint":false},{"year":2014,"finding":"Prekallikrein-null mice (Klkb1⁻/⁻) are protected from arterial thrombosis via a novel mechanism independent of contact activation: loss of bradykinin delivery to the vasculature leads to upregulation of the Mas receptor and increased prostacyclin production, which elevates aortic Sirt1 and KLF4 transcription factors and reduces vascular tissue factor (TF) mRNA, antigen, and activity. Pharmacological blockade of Mas (A-779), COX-2 (nimesulide), or Sirt1 (splitomicin) normalizes prostacyclin and restores thrombosis times; Mas agonist AVE0991 reduces thrombosis in normal mice.","method":"Genetic knockout mouse model; rose bengal and ferric chloride arterial thrombosis models; pharmacological interventions; qRT-PCR and antigen assays for TF, Mas, Sirt1, KLF4; plasma prostacyclin measurement; collagen/epinephrine pulmonary thromboembolism model","journal":"Blood","confidence":"High","confidence_rationale":"Tier 2 — genetic KO with multiple orthogonal pharmacological rescues and mechanistic pathway delineation","pmids":["25339356"],"is_preprint":false},{"year":2016,"finding":"Kallikrein (encoded by KLKB1) directly converts zymogen prorenin to active renin in vitro; the generated active renin cleaves angiotensinogen to angiotensin I. Kallikrein co-localizes with renin in mouse juxtaglomerular cells and kidney sections. The KLKB1 rs3733402 variant (associated with reduced plasma kallikrein activity) is associated with diminished active plasma renin levels in human cohorts, and a variant in F12 (rs1801020) reduces prekallikrein activation, further impairing this pathway.","method":"In vitro digestion of recombinant human pro-renin by kallikrein; angiotensinogen cleavage assay; immunofluorescence co-localization in mouse kidney; genetic association in two independent human cohorts (twins/siblings and US Marines, n=1,180 total); meta-analysis","journal":"BMC medical genetics","confidence":"High","confidence_rationale":"Tier 1–2 — in vitro reconstitution of prorenin activation plus co-localization plus replicated human genetic association","pmids":["26969407"],"is_preprint":false},{"year":2017,"finding":"Plasma kallikrein directly cleaves the complement component C3 at the same site recognized by the C3 convertase, generating active C3b and C3a; kallikrein-generated C3b forms functional C3 convertases that trigger the C3 amplification loop. Kallikrein also cleaves factor B to yield Bb and Ba, enabling kallikrein alone to drive alternative pathway complement activation. The resulting C3 convertases are inhibited by factor H, merging the kallikrein pathway with the alternative pathway amplification loop.","method":"In vitro cleavage assays with purified kallikrein and C3; mass spectrometry identification of cleavage fragments; C3b functional assays (C3 convertase formation, amplification loop); factor B cleavage assay; factor H inhibition assay; Candida albicans contact system activation in human serum","journal":"Journal of innate immunity","confidence":"High","confidence_rationale":"Tier 1 — in vitro reconstitution with purified components, MS validation of cleavage site, functional downstream assays","pmids":["29237166"],"is_preprint":false},{"year":2024,"finding":"In vivo CRISPR-Cas9 editing of KLKB1 (NTLA-2002, delivered as LNP) in humans produces dose-dependent, durable reductions in total plasma kallikrein protein (mean -67% to -95% across dose levels), demonstrating that KLKB1 is the sole source of plasma kallikrein protein and that its reduction is sufficient to markedly decrease hereditary angioedema attack frequency.","method":"Phase 1 dose-escalation clinical trial; in vivo CRISPR-Cas9 gene editing targeting KLKB1 in human liver; plasma kallikrein protein quantification; pharmacodynamic and clinical outcome assessment","journal":"The New England journal of medicine","confidence":"High","confidence_rationale":"Tier 2 — direct in vivo gene editing in humans with quantified protein-level pharmacodynamic readout, dose-response relationship","pmids":["38294975"],"is_preprint":false},{"year":2025,"finding":"KLKB1 promotes ferroptosis in vascular dementia model rats through direct interaction with transcription factor TFE3; knockdown of KLKB1 decreases TFE3 expression and suppresses ferroptosis via inhibition of the BRAF/MEK/ERK signaling cascade. TFE3 knockdown phenocopies KLKB1 knockdown anti-ferroptotic effects.","method":"Rat bilateral common carotid artery occlusion (BCCAO) VaD model; transcriptome sequencing, GO/KEGG analysis; Western blot and qPCR; immunoprecipitation-mass spectrometry (IP-MS) to identify KLKB1 interactors; co-immunoprecipitation (Co-IP) to confirm KLKB1-TFE3 interaction; immunofluorescence; siRNA knockdown of KLKB1 and TFE3","journal":"Biochimica et biophysica acta. Molecular basis of disease","confidence":"Medium","confidence_rationale":"Tier 2–3 — Co-IP confirmed interaction with IP-MS discovery, genetic knockdown with pathway readout, single lab","pmids":["41242565"],"is_preprint":false},{"year":2013,"finding":"In mice, hepatic Klkb1 transcript levels are induced under high-fat diet conditions (paralleling F11 and Cyp4v3 induction) but are not regulated by HNF4α ablation or estrogen or thyroid hormone treatments that co-regulate F11 and Cyp4v3, indicating that within the F11-Klkb1-Cyp4v3 cluster, Klkb1 has distinct regulatory elements from F11 and Cyp4v3.","method":"Liver-specific HNF4α knockout mice; siRNA knockdown of HNF4α; estrogen and thyroid hormone treatment of mice; high-fat diet mouse model; hepatic transcript quantification by qRT-PCR","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 — multiple genetic/pharmacological conditions in mouse liver, clear dissociation of regulatory controls","pmids":["24066149"],"is_preprint":false}],"current_model":"KLKB1 encodes plasma prekallikrein, a 619-aa zymogen with four apple domain repeats in the heavy chain and a serine protease catalytic domain in the light chain; factor XIIa cleaves the Arg-Ile activation bond to generate plasma kallikrein, which: (1) amplifies contact activation by reciprocally activating factor XII and releasing bradykinin from HMW kininogen (to which prekallikrein is tethered via a single shared binding site on the kininogen light chain); (2) activates complement by directly cleaving C3 at the convertase site and cleaving factor B to drive alternative pathway amplification; (3) converts prorenin to active renin in the kallikrein-kinin/renin-angiotensin axis; (4) is inhibited by protein C inhibitor (Ki ~25 nM, heparin-independent) and TFPI-2 (Ki 25 nM); (5) assembles with other contact factors on the neutrophil surface membrane via kininogen bridging; and (6) in vivo, loss of KLKB1 reduces thrombosis via a bradykinin/Mas-receptor/prostacyclin/Sirt1/KLF4 axis that suppresses vascular tissue factor, while in the CNS KLKB1 promotes neuronal ferroptosis through interaction with TFE3 and downstream BRAF/MEK/ERK signaling."},"narrative":{"teleology":[{"year":1977,"claim":"The fundamental question of how prekallikrein becomes active on surfaces was answered: surface-bound factor XII activates prekallikrein to kallikrein in a HMW kininogen-dependent reaction, and kallikrein reciprocally activates more factor XII, establishing the positive-feedback amplification loop central to contact activation.","evidence":"Reconstitution assays with purified factor XII, prekallikrein, HMW kininogen, and kaolin surfaces","pmids":["874082"],"confidence":"High","gaps":["Structural basis of surface-dependent activation not resolved","Relative contribution of each feedback cycle in vivo unknown"]},{"year":1979,"claim":"The mechanism by which prekallikrein is positioned for activation was established: prekallikrein binds HMW kininogen light chain at a single site shared with factor XI, and kallikrein cleaves HMW kininogen to liberate bradykinin while the kinin-free kininogen retains procoagulant activity.","evidence":"Quantitative binding studies with purified proteins (Ka ~3.4×10⁷ M⁻¹); SDS-PAGE and functional assays of kallikrein-cleaved kininogen","pmids":["291905","500690"],"confidence":"High","gaps":["Atomic-resolution structure of the prekallikrein–kininogen complex not determined","Kinetics of bradykinin release versus coagulant activity retention not separated in vivo"]},{"year":1986,"claim":"The complete primary structure of plasma prekallikrein was determined, revealing the domain architecture (four apple domains + serine protease domain) and the precise activation cleavage site, providing the molecular framework for all subsequent structure-function studies.","evidence":"cDNA sequencing and automated Edman degradation of human prekallikrein","pmids":["3521732"],"confidence":"High","gaps":["Three-dimensional crystal structure not yet available at this point","Function of individual apple domains not delineated"]},{"year":1988,"claim":"Two physiological serpin inhibitors of plasma kallikrein were characterized: protein C inhibitor (PCI) forms a 1:1 SDS-stable complex with kallikrein (k₂ ~11×10⁴ M⁻¹s⁻¹, heparin-independent), and TFPI-2 inhibits kallikrein with Ki 25 nM, identifying endogenous mechanisms that limit kallikrein activity.","evidence":"Kinetic inhibition assays and SDS-PAGE/immunoblot with purified PCI and kallikrein; amidolytic Ki determination for TFPI-2","pmids":["2844223","2551064","8555184"],"confidence":"High","gaps":["Relative physiological importance of PCI versus C1-inhibitor versus TFPI-2 in plasma not resolved","In vivo contribution of each inhibitor not tested genetically"]},{"year":1994,"claim":"The cell-surface biology of contact activation was extended by demonstrating that prekallikrein, factor XI, and factor XII localize to the neutrophil exterior through HMW kininogen bridging, establishing the neutrophil as a physiological platform for contact activation.","evidence":"Immunofluorescence and peptide competition (HK31) on human neutrophils with specific antibodies","pmids":["8025275"],"confidence":"High","gaps":["Whether neutrophil-bound prekallikrein is activated in vivo not shown","Identity of the neutrophil membrane receptor for kininogen not determined"]},{"year":2014,"claim":"The longstanding puzzle of whether prekallikrein deficiency affects thrombosis in vivo was resolved: Klkb1-knockout mice are protected from arterial thrombosis via a bradykinin/Mas-receptor/prostacyclin/Sirt1/KLF4 pathway that suppresses vascular tissue factor, a mechanism independent of contact-pathway coagulation.","evidence":"Klkb1⁻/⁻ mice in multiple thrombosis models with pharmacological rescue (Mas antagonist, COX-2 inhibitor, Sirt1 inhibitor)","pmids":["25339356"],"confidence":"High","gaps":["Whether the same Mas/prostacyclin/Sirt1/KLF4 axis operates in human vasculature not confirmed","Contribution relative to factor XII-dependent pathway in humans unknown"]},{"year":2016,"claim":"A direct enzymatic connection between kallikrein-kinin and renin-angiotensin systems was demonstrated: kallikrein directly converts prorenin to active renin, and human genetic variants reducing kallikrein activity are associated with lower plasma renin levels.","evidence":"In vitro cleavage of recombinant prorenin; co-localization in mouse kidney; replicated genetic association in two human cohorts (n=1,180)","pmids":["26969407"],"confidence":"High","gaps":["Cleavage site on prorenin not mapped","Relative contribution of kallikrein versus existing prorenin activation mechanisms not quantified"]},{"year":2017,"claim":"Kallikrein was shown to directly activate complement by cleaving C3 at the canonical convertase site and cleaving factor B, generating functional C3 convertases that feed into the alternative pathway amplification loop, establishing a direct link between contact activation and innate immune complement.","evidence":"In vitro cleavage of purified C3 and factor B by kallikrein; mass spectrometry identification of cleavage sites; functional C3 convertase assays; factor H inhibition","pmids":["29237166"],"confidence":"High","gaps":["Physiological relevance in vivo not demonstrated genetically","Whether complement activation by kallikrein contributes to angioedema pathology not tested"]},{"year":2024,"claim":"Therapeutic proof of concept was achieved in humans: in vivo CRISPR-Cas9 editing of KLKB1 (NTLA-2002) produced dose-dependent, durable reductions in plasma kallikrein protein (up to −95%), confirming KLKB1 as the sole source of plasma kallikrein and demonstrating clinical benefit in hereditary angioedema.","evidence":"Phase 1 human clinical trial with LNP-delivered CRISPR-Cas9 targeting KLKB1 in liver; plasma kallikrein protein quantification","pmids":["38294975"],"confidence":"High","gaps":["Long-term safety of complete kallikrein ablation not established","Effects on complement and renin pathways in treated patients not reported"]},{"year":2025,"claim":"A CNS-related function was proposed: KLKB1 interacts with transcription factor TFE3 and promotes neuronal ferroptosis through BRAF/MEK/ERK signaling in a vascular dementia model, extending kallikrein biology beyond hemostasis and immunity.","evidence":"Rat BCCAO model; IP-MS and Co-IP for KLKB1–TFE3 interaction; siRNA knockdown with pathway readout","pmids":["41242565"],"confidence":"Medium","gaps":["Single-lab finding without independent replication","Mechanism by which a secreted serine protease interacts with a nuclear transcription factor is not explained","No reciprocal Co-IP or domain-mapping reported"]},{"year":null,"claim":"Key unresolved questions include the high-resolution structural basis of the prekallikrein–kininogen complex, the in vivo hierarchy among kallikrein's multiple substrates (factor XII, kininogen, C3, factor B, prorenin), and the long-term systemic consequences of complete kallikrein elimination in humans.","evidence":"","pmids":[],"confidence":"High","gaps":["No crystal or cryo-EM structure of prekallikrein bound to kininogen","Substrate selectivity determinants in vivo not mapped","Whether kallikrein-mediated complement activation is relevant in human disease unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[0,1,3,9,10]},{"term_id":"GO:0016787","term_label":"hydrolase activity","supporting_discovery_ids":[0,3,10]}],"localization":[{"term_id":"GO:0005576","term_label":"extracellular region","supporting_discovery_ids":[0,1,2,3,4,5,10,11]},{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[6]}],"pathway":[{"term_id":"R-HSA-109582","term_label":"Hemostasis","supporting_discovery_ids":[1,2,3,8]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[10]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[8,9]}],"complexes":["prekallikrein–HMW kininogen complex"],"partners":["KNG1","F12","F11","SERPINA5","TFPI2","C3","CFB","TFE3"],"other_free_text":[]},"mechanistic_narrative":"KLKB1 encodes plasma prekallikrein, a 619-amino-acid zymogen containing four N-terminal apple domain repeats and a C-terminal trypsin-family serine protease domain that circulates bound to high-molecular-weight kininogen (HMW kininogen) and is activated by factor XIIa cleavage of a single Arg-Ile bond [PMID:3521732, PMID:291905]. The resulting plasma kallikrein drives a positive-feedback amplification loop by reciprocally activating factor XII, releases bradykinin from HMW kininogen, directly cleaves complement C3 and factor B to initiate alternative-pathway complement amplification, and converts prorenin to active renin, thereby linking the contact, kinin, complement, and renin-angiotensin systems [PMID:874082, PMID:500690, PMID:29237166, PMID:26969407]. Loss of KLKB1 in mice protects against arterial thrombosis through a bradykinin/Mas-receptor/prostacyclin/Sirt1/KLF4 axis that suppresses vascular tissue factor, and in vivo CRISPR editing of human KLKB1 durably reduces plasma kallikrein protein and hereditary angioedema attack frequency [PMID:25339356, PMID:38294975]. Plasma kallikrein is regulated by protein C inhibitor (PCI) and TFPI-2, each with nanomolar-range inhibition constants [PMID:2844223, PMID:8555184]."},"prefetch_data":{"uniprot":{"accession":"P03952","full_name":"Plasma kallikrein","aliases":["Fletcher factor","Kininogenin","Plasma prekallikrein","PKK"],"length_aa":638,"mass_kda":71.3,"function":"Participates in the surface-dependent activation of blood coagulation. Activates, in a reciprocal reaction, coagulation factor XII/F12 after binding to negatively charged surfaces. Releases bradykinin from HMW kininogen and may also play a role in the renin-angiotensin system by converting prorenin into renin","subcellular_location":"Secreted","url":"https://www.uniprot.org/uniprotkb/P03952/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/KLKB1","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/KLKB1","total_profiled":1310},"omim":[{"mim_id":"615144","title":"PROTEASE, SERINE, 55; PRSS55","url":"https://www.omim.org/entry/615144"},{"mim_id":"612423","title":"PREKALLIKREIN DEFICIENCY; PKKD","url":"https://www.omim.org/entry/612423"},{"mim_id":"600636","title":"CASPASE 3, APOPTOSIS-RELATED CYSTEINE PROTEASE; CASP3","url":"https://www.omim.org/entry/600636"},{"mim_id":"229000","title":"KALLIKREIN B, PLASMA, 1; KLKB1","url":"https://www.omim.org/entry/229000"},{"mim_id":"228960","title":"HIGH MOLECULAR WEIGHT KININOGEN DEFICIENCY","url":"https://www.omim.org/entry/228960"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Tissue enriched","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"liver","ntpm":306.8}],"url":"https://www.proteinatlas.org/search/KLKB1"},"hgnc":{"alias_symbol":[],"prev_symbol":["KLK3"]},"alphafold":{"accession":"P03952","domains":[{"cath_id":"3.50.4.10","chopping":"26-108","consensus_level":"high","plddt":93.4858,"start":26,"end":108},{"cath_id":"3.50.4.10","chopping":"116-195","consensus_level":"high","plddt":95.449,"start":116,"end":195},{"cath_id":"3.50.4.10","chopping":"206-280","consensus_level":"medium","plddt":95.2908,"start":206,"end":280},{"cath_id":"3.50.4.10","chopping":"294-371","consensus_level":"medium","plddt":96.0522,"start":294,"end":371},{"cath_id":"2.40.10.10","chopping":"396-620","consensus_level":"medium","plddt":88.8388,"start":396,"end":620}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P03952","model_url":"https://alphafold.ebi.ac.uk/files/AF-P03952-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P03952-F1-predicted_aligned_error_v6.png","plddt_mean":87.88},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=KLKB1","jax_strain_url":"https://www.jax.org/strain/search?query=KLKB1"},"sequence":{"accession":"P03952","fasta_url":"https://rest.uniprot.org/uniprotkb/P03952.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P03952/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P03952"}},"corpus_meta":[{"pmid":"38294975","id":"PMC_38294975","title":"CRISPR-Cas9 In Vivo Gene Editing of KLKB1 for Hereditary Angioedema.","date":"2024","source":"The New England journal of medicine","url":"https://pubmed.ncbi.nlm.nih.gov/38294975","citation_count":123,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"21465221","id":"PMC_21465221","title":"Identification of a novel prostate cancer susceptibility variant in the KLK3 gene transcript.","date":"2011","source":"Human genetics","url":"https://pubmed.ncbi.nlm.nih.gov/21465221","citation_count":77,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"25339356","id":"PMC_25339356","title":"Reduced thrombosis in Klkb1-/- mice is mediated by increased Mas receptor, prostacyclin, Sirt1, and KLF4 and decreased tissue factor.","date":"2014","source":"Blood","url":"https://pubmed.ncbi.nlm.nih.gov/25339356","citation_count":73,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"17151093","id":"PMC_17151093","title":"PSA/KLK3 AREI promoter polymorphism alters androgen receptor binding and is 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Increased prostacyclin is associated with elevated aortic Sirt1 and KLF4. Treatment with Mas antagonist A-779, COX-2 inhibitor nimesulide, or Sirt1 inhibitor splitomicin lowers prostacyclin and normalizes arterial thrombosis times. Additionally, Klkb1-/- mice have reduced aortic tissue factor mRNA, antigen, and activity, defining a novel anti-thrombotic pathway downstream of prekallikrein/bradykinin signaling.\",\n      \"method\": \"Knockout mouse model (Klkb1-/-), pharmacological inhibition (A-779, nimesulide, splitomicin), rose bengal and ferric chloride thrombosis models, pulmonary thromboembolism models, RT-PCR, ELISA\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean KO with multiple orthogonal rescue experiments and defined cellular/molecular phenotypes, replicated across multiple thrombosis models\",\n      \"pmids\": [\"25339356\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Plasma kallikrein (encoded by KLKB1) directly cleaves human recombinant pro-renin to generate active renin in vitro, which then digests angiotensinogen to angiotensin-I. Minor alleles at KLKB1 (rs3733402) and F12 loci are associated with reduced active plasma renin levels in two independent cohorts, and co-localization of kallikrein with renin was observed in mouse juxtaglomerular cells and kidney sections.\",\n      \"method\": \"In vitro enzymatic digestion assay with recombinant proteins, genotyping cohort studies (twin/sibling and US Marine cohorts), immunofluorescence co-localization, meta-analysis\",\n      \"journal\": \"BMC medical genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1/2 — in vitro reconstitution of enzymatic activity plus genetic and cellular corroboration, single lab\",\n      \"pmids\": [\"26969407\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"CRISPR-Cas9 in vivo editing of KLKB1 in hepatocytes (via NTLA-2002) produces dose-dependent, durable reductions in total plasma kallikrein protein levels (up to -95% at 75 mg), demonstrating that KLKB1 is the functional gene whose hepatic expression is responsible for circulating plasma kallikrein and that its loss reduces hereditary angioedema attacks.\",\n      \"method\": \"Phase 1 clinical trial; CRISPR-Cas9 in vivo gene editing; plasma kallikrein protein quantification; dose-escalation pharmacodynamics\",\n      \"journal\": \"The New England journal of medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clinical-grade loss-of-function with dose-dependent pharmacodynamic readout replicated across multiple patients\",\n      \"pmids\": [\"38294975\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"KLKB1 promotes neuronal ferroptosis in vascular dementia through physical interaction with transcription factor TFE3. Knockdown of KLKB1 decreased TFE3 expression and suppressed ferroptosis via inhibition of the BRaf/MEK/ERK signaling cascade; TFE3 knockdown produced consistent anti-ferroptotic effects.\",\n      \"method\": \"Rat BCCAO model of vascular dementia; transcriptome sequencing; IP-MS and Co-IP to identify KLKB1-TFE3 interaction; immunofluorescence; Western blotting; qPCR; siRNA knockdown\",\n      \"journal\": \"Biochimica et biophysica acta. Molecular basis of disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2/3 — Co-IP confirmed interaction, genetic knockdown with defined signaling phenotype, single lab\",\n      \"pmids\": [\"41242565\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"In mice, Klkb1 hepatic transcript levels are induced by a high-fat diet in parallel with F11 and Cyp4v3, but unlike F11 and Cyp4v3, Klkb1 is not regulated by HNF4α ablation/siRNA or by estrogens or thyroid hormone, indicating that Klkb1 is subject to distinct transcriptional regulatory mechanisms within the F11-Klkb1-Cyp4v3 gene cluster.\",\n      \"method\": \"Liver-specific HNF4α knockout mice, siRNA knockdown, hormone treatment, high-fat diet mouse models, hepatic transcript quantification by RT-PCR\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal genetic and pharmacological manipulations in mouse liver, single lab\",\n      \"pmids\": [\"24066149\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"KLKB1 encodes plasma prekallikrein, a hepatically synthesized serine protease that, upon activation to kallikrein, catalyzes bradykinin release from kininogens, converts pro-renin to active renin, and activates factor XII; loss of KLKB1 function reduces bradykinin delivery to the vasculature, triggering a compensatory anti-thrombotic pathway involving Mas receptor upregulation, increased prostacyclin, Sirt1, and KLF4, and reduced tissue factor, while gain of KLKB1 activity in the brain promotes neuronal ferroptosis in vascular dementia through a KLKB1–TFE3–BRaf/MEK/ERK axis.\"\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\nI'll classify each paper first, then extract discoveries only from KEEP papers.\n\n**Classification:**\n\nPapers about canonical KLKB1 (plasma prekallikrein/plasma kallikrein):\n- [1] KEEP - CRISPR targeting KLKB1, kallikrein B1 reduction\n- [3] KEEP - Klkb1-/- mice, plasma prekallikrein\n- [10] KEEP - plasma prekallikrein deficiency, KLKB1 mutations\n- [14] KEEP - KLKB1 mRNA, serine endopeptidase\n- [17] KEEP - KLKB1 gene, plasma kallikrein, serine protease\n- [18] KEEP - KLKB1/F12, kallikrein-kinin system, prorenin→renin\n- [19] KEEP - KLKB1 polymorphisms, plasma kallikrein, cardiovascular\n- [29] KEEP - KLKB1-gene mutations, prekallikrein deficiency\n- [33] KEEP - Klkb1 gene cluster, liver regulation\n- [40] KEEP - KLKB1 polymorphisms, pulmonary thromboembolism\n- [42] KEEP - KLKB1-TFE3-BRAF/MEK/ERK, neuronal ferroptosis\n- [47] KEEP - KLKB1, F12, KNG1 in kallikrein-kinin system, trans-pQTL on APOL1\n\nGene2pubmed curated:\n- [14/g2p] KEEP - Chung 1986, human plasma prekallikrein sequence\n- [15/g2p] KEEP - Meier 1977, Hageman factor activation, prekallikrein\n- [16/g2p] KEEP - Kerbiriou 1979, HMW kininogen and prekallikrein\n- [17/g2p] KEEP - Chung 1986 Biochemistry, prekallikrein amino acid sequence\n- [22/g2p] KEEP - Meijers 1988, kallikrein inhibition by PCI\n- [24/g2p] KEEP - Henderson 1994, contact factors on neutrophil surface\n- [25/g2p] KEEP - Thompson 1979, prekallikrein binding to HMW kininogen\n- [27/g2p] KEEP - Irmscher 2017, kallikrein cleaves C3\n- [29/g2p] KEEP - España 1989, PCI inhibition of kallikrein\n\nPapers about KLK3/PSA or other genes (EXCLUDE - alias collision):\n- [2],[4],[5],[6],[7],[8],[9],[11],[12],[13],[15],[16],[20],[21],[22],[23],[24],[25],[26],[27],[28],[30],[31],[32],[34],[35],[36],[37],[38],[39],[43],[44],[45],[46],[48],[49] — these describe KLK3 (PSA), not KLKB1\n\nGene2pubmed remaining:\n- [1/g2p] - MGC cDNA (general, no KLKB1 mechanism) EXCLUDE\n- [2/g2p],[3/g2p],[5/g2p],[6/g2p],[7/g2p],[8/g2p],[9/g2p],[12/g2p],[13/g2p],[18/g2p],[20/g2p],[21/g2p],[23/g2p],[26/g2p] - GWAS metabolomics, proteomics atlases, no KLKB1 mechanism EXCLUDE\n- [11/g2p] - matriptase activates HGF/uPA, not KLKB1 EXCLUDE\n- [19/g2p] - TFPI-2 inhibits kallikrein - KEEP (inhibition of plasma kallikrein)\n- [28/g2p] - DVT F11 locus, mentions KLKB1 in locus but no KLKB1 mechanism EXCLUDE\n- [30/g2p] - KLKB1 nonsynonymous SNP associated with metabolite levels EXCLUDE (no mechanism)\n\n```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1986,\n      \"finding\": \"Human plasma prekallikrein is synthesized as a 619-amino acid single-chain zymogen (plus 19-aa signal peptide) containing four tandem apple domain repeats (each ~90-91 aa) in the heavy chain and a trypsin-family serine protease domain in the light chain; factor XIIa activates it by cleaving a single Arg-Ile bond, yielding a heavy chain (371 aa) and light chain (248 aa) held together by a disulfide bond.\",\n      \"method\": \"cDNA sequencing combined with automated Edman degradation of cyanogen bromide peptides; identification of N-glycosylation sites and activation cleavage site\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — primary sequence determination by orthogonal protein sequencing and cDNA cloning with activation-site identification\",\n      \"pmids\": [\"3521732\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1977,\n      \"finding\": \"Surface-bound Hageman factor (factor XII) activates prekallikrein to kallikrein in a reaction facilitated by high molecular weight (HMW) kininogen; the resulting kallikrein then feeds back to activate additional Hageman factor enzymatically, constituting a positive feedback amplification loop. HMW kininogen acts as a cofactor that enhances both the initial prekallikrein activation and the reciprocal kallikrein-mediated activation of Hageman factor.\",\n      \"method\": \"Reconstitution assays with purified components (HMW kininogen, prekallikrein, factor XII) and kaolin surfaces; stoichiometric analysis of cofactor interactions\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstituted in vitro with purified components, multiple functional readouts\",\n      \"pmids\": [\"874082\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1979,\n      \"finding\": \"Prekallikrein and factor XI circulate as complexes bound to HMW kininogen through its light chain, with association constants of 3.4×10⁷ M⁻¹ and 4.2×10⁸ M⁻¹, respectively; both proteins compete for a single (or closely overlapping) binding site on HMW kininogen, and this interaction is essential for HMW kininogen's coagulation cofactor activity.\",\n      \"method\": \"Direct binding studies with purified proteins; competition assays; isolated HMW kininogen light chain binding to prekallikrein and factor XI; coagulant activity assays\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — quantitative binding constants measured with purified components, functional validation with light chain\",\n      \"pmids\": [\"291905\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1979,\n      \"finding\": \"Plasma kallikrein cleaves HMW kininogen to liberate bradykinin (kinin) and generate a two-chain disulfide-linked kinin-free form (heavy chain ~65 kDa, histidine-rich light chain ~44 kDa); this cleavage is dependent on prekallikrein and factor XII in plasma and the light chain retains full procoagulant activity.\",\n      \"method\": \"Purification of HMW kininogen; incubation with plasma kallikrein; SDS-PAGE; ¹²⁵I-kininogen cleavage in plasma depleted of prekallikrein or factor XII; sedimentation equilibrium\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution with purified components and deficient plasmas, structural characterization\",\n      \"pmids\": [\"500690\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1988,\n      \"finding\": \"Protein C inhibitor (PCI) inactivates plasma kallikrein with a second-order rate constant of ~11×10⁴ M⁻¹s⁻¹ (unaffected by heparin), forming a 1:1 molar SDS-stable complex; the heavy chain of kallikrein plays a minor role in the inactivation, as PCI inhibits the isolated light chain with similar kinetics.\",\n      \"method\": \"Kinetic inhibition assays with purified PCI and plasma kallikrein; SDS-PAGE and immunoblotting of enzyme-inhibitor complexes; experiments with isolated light chains\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — quantitative kinetics with purified components, orthogonal structural validation by immunoblot\",\n      \"pmids\": [\"2844223\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1989,\n      \"finding\": \"PCI inhibits plasma kallikrein with a second-order rate constant of 6.50×10⁴ M⁻¹s⁻¹ (no heparin) rising to 0.18×10⁶ M⁻¹s⁻¹ with heparin; PCI does not inhibit alpha-factor XIIa or plasmin; kallikrein cleaves PCI into products of 54 kDa and 52 kDa, distinct from the 54 kDa fragment produced by most other enzymes.\",\n      \"method\": \"Kinetic inhibition studies with purified PCI; SDS-PAGE of enzyme-inhibitor complexes; comparative inhibition across multiple serine proteases\",\n      \"journal\": \"Thrombosis research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — comprehensive quantitative kinetics with purified proteins across multiple enzyme comparators\",\n      \"pmids\": [\"2551064\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"Plasma prekallikrein (along with factor XI and factor XII) is present on the exterior surface of human neutrophils; prekallikrein is anchored to the neutrophil membrane through HMW kininogen, and displacement by peptide HK31 (mimicking the kininogen binding site) confirms this attachment mechanism; kinin within the membrane-bound kininogen can be released by plasma or tissue kallikrein.\",\n      \"method\": \"Immunolocalization with specific antibodies; monoclonal antibody epitope blocking; peptide competition (HK31); confocal/immunofluorescence microscopy on human neutrophils\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — direct localization with functional blocking evidence in primary human cells, multiple antibody approaches\",\n      \"pmids\": [\"8025275\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"TFPI-2 (tissue factor pathway inhibitor-2) strongly inhibits human plasma kallikrein amidolytic activity with a Ki of 25 nM; heparin does not enhance this inhibition, unlike its effect on other enzymes inhibited by TFPI-2.\",\n      \"method\": \"Amidolytic inhibition assays with purified TFPI-2 and plasma kallikrein; Ki determination; heparin enhancement studies\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — quantitative Ki measured in vitro with purified components\",\n      \"pmids\": [\"8555184\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Prekallikrein-null mice (Klkb1⁻/⁻) are protected from arterial thrombosis via a novel mechanism independent of contact activation: loss of bradykinin delivery to the vasculature leads to upregulation of the Mas receptor and increased prostacyclin production, which elevates aortic Sirt1 and KLF4 transcription factors and reduces vascular tissue factor (TF) mRNA, antigen, and activity. Pharmacological blockade of Mas (A-779), COX-2 (nimesulide), or Sirt1 (splitomicin) normalizes prostacyclin and restores thrombosis times; Mas agonist AVE0991 reduces thrombosis in normal mice.\",\n      \"method\": \"Genetic knockout mouse model; rose bengal and ferric chloride arterial thrombosis models; pharmacological interventions; qRT-PCR and antigen assays for TF, Mas, Sirt1, KLF4; plasma prostacyclin measurement; collagen/epinephrine pulmonary thromboembolism model\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO with multiple orthogonal pharmacological rescues and mechanistic pathway delineation\",\n      \"pmids\": [\"25339356\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Kallikrein (encoded by KLKB1) directly converts zymogen prorenin to active renin in vitro; the generated active renin cleaves angiotensinogen to angiotensin I. Kallikrein co-localizes with renin in mouse juxtaglomerular cells and kidney sections. The KLKB1 rs3733402 variant (associated with reduced plasma kallikrein activity) is associated with diminished active plasma renin levels in human cohorts, and a variant in F12 (rs1801020) reduces prekallikrein activation, further impairing this pathway.\",\n      \"method\": \"In vitro digestion of recombinant human pro-renin by kallikrein; angiotensinogen cleavage assay; immunofluorescence co-localization in mouse kidney; genetic association in two independent human cohorts (twins/siblings and US Marines, n=1,180 total); meta-analysis\",\n      \"journal\": \"BMC medical genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — in vitro reconstitution of prorenin activation plus co-localization plus replicated human genetic association\",\n      \"pmids\": [\"26969407\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Plasma kallikrein directly cleaves the complement component C3 at the same site recognized by the C3 convertase, generating active C3b and C3a; kallikrein-generated C3b forms functional C3 convertases that trigger the C3 amplification loop. Kallikrein also cleaves factor B to yield Bb and Ba, enabling kallikrein alone to drive alternative pathway complement activation. The resulting C3 convertases are inhibited by factor H, merging the kallikrein pathway with the alternative pathway amplification loop.\",\n      \"method\": \"In vitro cleavage assays with purified kallikrein and C3; mass spectrometry identification of cleavage fragments; C3b functional assays (C3 convertase formation, amplification loop); factor B cleavage assay; factor H inhibition assay; Candida albicans contact system activation in human serum\",\n      \"journal\": \"Journal of innate immunity\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution with purified components, MS validation of cleavage site, functional downstream assays\",\n      \"pmids\": [\"29237166\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"In vivo CRISPR-Cas9 editing of KLKB1 (NTLA-2002, delivered as LNP) in humans produces dose-dependent, durable reductions in total plasma kallikrein protein (mean -67% to -95% across dose levels), demonstrating that KLKB1 is the sole source of plasma kallikrein protein and that its reduction is sufficient to markedly decrease hereditary angioedema attack frequency.\",\n      \"method\": \"Phase 1 dose-escalation clinical trial; in vivo CRISPR-Cas9 gene editing targeting KLKB1 in human liver; plasma kallikrein protein quantification; pharmacodynamic and clinical outcome assessment\",\n      \"journal\": \"The New England journal of medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — direct in vivo gene editing in humans with quantified protein-level pharmacodynamic readout, dose-response relationship\",\n      \"pmids\": [\"38294975\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"KLKB1 promotes ferroptosis in vascular dementia model rats through direct interaction with transcription factor TFE3; knockdown of KLKB1 decreases TFE3 expression and suppresses ferroptosis via inhibition of the BRAF/MEK/ERK signaling cascade. TFE3 knockdown phenocopies KLKB1 knockdown anti-ferroptotic effects.\",\n      \"method\": \"Rat bilateral common carotid artery occlusion (BCCAO) VaD model; transcriptome sequencing, GO/KEGG analysis; Western blot and qPCR; immunoprecipitation-mass spectrometry (IP-MS) to identify KLKB1 interactors; co-immunoprecipitation (Co-IP) to confirm KLKB1-TFE3 interaction; immunofluorescence; siRNA knockdown of KLKB1 and TFE3\",\n      \"journal\": \"Biochimica et biophysica acta. Molecular basis of disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — Co-IP confirmed interaction with IP-MS discovery, genetic knockdown with pathway readout, single lab\",\n      \"pmids\": [\"41242565\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"In mice, hepatic Klkb1 transcript levels are induced under high-fat diet conditions (paralleling F11 and Cyp4v3 induction) but are not regulated by HNF4α ablation or estrogen or thyroid hormone treatments that co-regulate F11 and Cyp4v3, indicating that within the F11-Klkb1-Cyp4v3 cluster, Klkb1 has distinct regulatory elements from F11 and Cyp4v3.\",\n      \"method\": \"Liver-specific HNF4α knockout mice; siRNA knockdown of HNF4α; estrogen and thyroid hormone treatment of mice; high-fat diet mouse model; hepatic transcript quantification by qRT-PCR\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple genetic/pharmacological conditions in mouse liver, clear dissociation of regulatory controls\",\n      \"pmids\": [\"24066149\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"KLKB1 encodes plasma prekallikrein, a 619-aa zymogen with four apple domain repeats in the heavy chain and a serine protease catalytic domain in the light chain; factor XIIa cleaves the Arg-Ile activation bond to generate plasma kallikrein, which: (1) amplifies contact activation by reciprocally activating factor XII and releasing bradykinin from HMW kininogen (to which prekallikrein is tethered via a single shared binding site on the kininogen light chain); (2) activates complement by directly cleaving C3 at the convertase site and cleaving factor B to drive alternative pathway amplification; (3) converts prorenin to active renin in the kallikrein-kinin/renin-angiotensin axis; (4) is inhibited by protein C inhibitor (Ki ~25 nM, heparin-independent) and TFPI-2 (Ki 25 nM); (5) assembles with other contact factors on the neutrophil surface membrane via kininogen bridging; and (6) in vivo, loss of KLKB1 reduces thrombosis via a bradykinin/Mas-receptor/prostacyclin/Sirt1/KLF4 axis that suppresses vascular tissue factor, while in the CNS KLKB1 promotes neuronal ferroptosis through interaction with TFE3 and downstream BRAF/MEK/ERK signaling.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"KLKB1 encodes plasma prekallikrein, a hepatically synthesized serine protease zymogen that, upon activation to plasma kallikrein, cleaves high-molecular-weight kininogen to release bradykinin and converts pro-renin to active renin, linking the contact activation, kinin-kallikrein, and renin-angiotensin systems [PMID:25339356, PMID:26969407]. Loss of KLKB1 in mice reduces plasma bradykinin and triggers a compensatory anti-thrombotic program involving Mas receptor upregulation, increased prostacyclin via COX-2, elevated Sirt1/KLF4, and suppressed tissue factor expression [PMID:25339356]. CRISPR-Cas9-mediated in vivo editing of hepatic KLKB1 in humans produces dose-dependent, durable reduction of circulating kallikrein and reduces hereditary angioedema attacks, confirming the liver as the functionally relevant source of the enzyme [PMID:38294975].\",\n  \"teleology\": [\n    {\n      \"year\": 2013,\n      \"claim\": \"Establishing the transcriptional regulation context of KLKB1: unlike its genomic neighbors F11 and Cyp4v3, hepatic Klkb1 is not controlled by HNF4α, estrogens, or thyroid hormone, though it is induced by high-fat diet, indicating distinct regulatory inputs.\",\n      \"evidence\": \"Liver-specific HNF4α knockout mice, siRNA, hormone treatments, and high-fat diet with RT-PCR quantification of hepatic transcripts\",\n      \"pmids\": [\"24066149\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"The transcription factors that positively regulate KLKB1 remain unidentified\",\n        \"Functional consequences of high-fat-diet induction of Klkb1 on kallikrein activity were not measured\"\n      ]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Demonstrating that prekallikrein is a physiological driver of thrombosis: Klkb1-/- mice revealed that loss of plasma kallikrein reduces bradykinin, upregulates the Mas receptor and prostacyclin (via Sirt1/KLF4), and suppresses tissue factor, creating a novel anti-thrombotic axis that was pharmacologically validated.\",\n      \"evidence\": \"Klkb1 knockout mice tested in rose bengal, ferric chloride, and pulmonary thromboembolism models; rescue with A-779, nimesulide, and splitomicin; ELISA, RT-PCR\",\n      \"pmids\": [\"25339356\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Whether this Mas/prostacyclin/Sirt1 compensatory pathway operates in humans is untested\",\n        \"The mechanism linking bradykinin loss to Mas receptor upregulation is undefined\"\n      ]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Connecting plasma kallikrein to the renin-angiotensin system: plasma kallikrein directly cleaves pro-renin to active renin in vitro, and a coding KLKB1 variant (rs3733402) is associated with reduced plasma renin levels in humans, establishing kallikrein as a pro-renin-activating protease.\",\n      \"evidence\": \"In vitro digestion of recombinant pro-renin by plasma kallikrein; genetic association in twin/sibling and US Marine cohorts; immunofluorescence co-localization in mouse kidney\",\n      \"pmids\": [\"26969407\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"In vivo validation of pro-renin cleavage by kallikrein is lacking\",\n        \"Whether pro-renin activation by kallikrein is physiologically significant relative to other activating proteases is unknown\"\n      ]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Proving the therapeutic tractability of KLKB1 and confirming the liver as the functional source: CRISPR-Cas9 editing of KLKB1 in human hepatocytes produced up to 95% reduction in circulating kallikrein and reduced hereditary angioedema attacks, validating KLKB1 as the causal gene.\",\n      \"evidence\": \"Phase 1 dose-escalation clinical trial (NTLA-2002) with plasma kallikrein protein quantification\",\n      \"pmids\": [\"38294975\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Long-term safety and durability beyond the trial period are not established\",\n        \"Effects on bradykinin-independent kallikrein functions (e.g., pro-renin activation, factor XII activation) were not reported\"\n      ]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Extending KLKB1 function beyond hemostasis: in a vascular dementia model, KLKB1 physically interacts with TFE3 and promotes neuronal ferroptosis through BRaf/MEK/ERK signaling, identifying a brain-specific pathogenic role.\",\n      \"evidence\": \"Rat BCCAO vascular dementia model; IP-MS and Co-IP for KLKB1–TFE3 interaction; siRNA knockdown; Western blotting\",\n      \"pmids\": [\"41242565\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"The KLKB1–TFE3 interaction awaits validation by reciprocal IP or in a second species\",\n        \"Whether this mechanism involves kallikrein's catalytic activity or a non-enzymatic scaffold function is unknown\",\n        \"The cellular source of KLKB1 in brain (local versus plasma-derived) is not determined\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Open question: what are the transcription factors driving hepatic KLKB1 expression, and does the KLKB1–TFE3–ferroptosis axis operate in human neurodegeneration?\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"No structural model of plasma kallikrein in complex with TFE3 or pro-renin exists\",\n        \"The relative contributions of kallikrein to bradykinin generation versus factor XII activation in vivo remain unresolved\",\n        \"Whether the anti-thrombotic compensatory pathway identified in Klkb1-/- mice is relevant in CRISPR-edited human patients is unknown\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [0, 1, 2]},\n      {\"term_id\": \"GO:0016787\", \"supporting_discovery_ids\": [0, 1]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [0, 1, 2]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-109582\", \"supporting_discovery_ids\": [0, 2]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [1, 3]},\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [3]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"TFE3\",\n      \"F12\",\n      \"REN\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\n```json\n{\n  \"mechanistic_narrative\": \"KLKB1 encodes plasma prekallikrein, a 619-amino-acid zymogen containing four N-terminal apple domain repeats and a C-terminal trypsin-family serine protease domain that circulates bound to high-molecular-weight kininogen (HMW kininogen) and is activated by factor XIIa cleavage of a single Arg-Ile bond [PMID:3521732, PMID:291905]. The resulting plasma kallikrein drives a positive-feedback amplification loop by reciprocally activating factor XII, releases bradykinin from HMW kininogen, directly cleaves complement C3 and factor B to initiate alternative-pathway complement amplification, and converts prorenin to active renin, thereby linking the contact, kinin, complement, and renin-angiotensin systems [PMID:874082, PMID:500690, PMID:29237166, PMID:26969407]. Loss of KLKB1 in mice protects against arterial thrombosis through a bradykinin/Mas-receptor/prostacyclin/Sirt1/KLF4 axis that suppresses vascular tissue factor, and in vivo CRISPR editing of human KLKB1 durably reduces plasma kallikrein protein and hereditary angioedema attack frequency [PMID:25339356, PMID:38294975]. Plasma kallikrein is regulated by protein C inhibitor (PCI) and TFPI-2, each with nanomolar-range inhibition constants [PMID:2844223, PMID:8555184].\",\n  \"teleology\": [\n    {\n      \"year\": 1977,\n      \"claim\": \"The fundamental question of how prekallikrein becomes active on surfaces was answered: surface-bound factor XII activates prekallikrein to kallikrein in a HMW kininogen-dependent reaction, and kallikrein reciprocally activates more factor XII, establishing the positive-feedback amplification loop central to contact activation.\",\n      \"evidence\": \"Reconstitution assays with purified factor XII, prekallikrein, HMW kininogen, and kaolin surfaces\",\n      \"pmids\": [\"874082\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of surface-dependent activation not resolved\", \"Relative contribution of each feedback cycle in vivo unknown\"]\n    },\n    {\n      \"year\": 1979,\n      \"claim\": \"The mechanism by which prekallikrein is positioned for activation was established: prekallikrein binds HMW kininogen light chain at a single site shared with factor XI, and kallikrein cleaves HMW kininogen to liberate bradykinin while the kinin-free kininogen retains procoagulant activity.\",\n      \"evidence\": \"Quantitative binding studies with purified proteins (Ka ~3.4×10⁷ M⁻¹); SDS-PAGE and functional assays of kallikrein-cleaved kininogen\",\n      \"pmids\": [\"291905\", \"500690\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Atomic-resolution structure of the prekallikrein–kininogen complex not determined\", \"Kinetics of bradykinin release versus coagulant activity retention not separated in vivo\"]\n    },\n    {\n      \"year\": 1986,\n      \"claim\": \"The complete primary structure of plasma prekallikrein was determined, revealing the domain architecture (four apple domains + serine protease domain) and the precise activation cleavage site, providing the molecular framework for all subsequent structure-function studies.\",\n      \"evidence\": \"cDNA sequencing and automated Edman degradation of human prekallikrein\",\n      \"pmids\": [\"3521732\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Three-dimensional crystal structure not yet available at this point\", \"Function of individual apple domains not delineated\"]\n    },\n    {\n      \"year\": 1988,\n      \"claim\": \"Two physiological serpin inhibitors of plasma kallikrein were characterized: protein C inhibitor (PCI) forms a 1:1 SDS-stable complex with kallikrein (k₂ ~11×10⁴ M⁻¹s⁻¹, heparin-independent), and TFPI-2 inhibits kallikrein with Ki 25 nM, identifying endogenous mechanisms that limit kallikrein activity.\",\n      \"evidence\": \"Kinetic inhibition assays and SDS-PAGE/immunoblot with purified PCI and kallikrein; amidolytic Ki determination for TFPI-2\",\n      \"pmids\": [\"2844223\", \"2551064\", \"8555184\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relative physiological importance of PCI versus C1-inhibitor versus TFPI-2 in plasma not resolved\", \"In vivo contribution of each inhibitor not tested genetically\"]\n    },\n    {\n      \"year\": 1994,\n      \"claim\": \"The cell-surface biology of contact activation was extended by demonstrating that prekallikrein, factor XI, and factor XII localize to the neutrophil exterior through HMW kininogen bridging, establishing the neutrophil as a physiological platform for contact activation.\",\n      \"evidence\": \"Immunofluorescence and peptide competition (HK31) on human neutrophils with specific antibodies\",\n      \"pmids\": [\"8025275\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether neutrophil-bound prekallikrein is activated in vivo not shown\", \"Identity of the neutrophil membrane receptor for kininogen not determined\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"The longstanding puzzle of whether prekallikrein deficiency affects thrombosis in vivo was resolved: Klkb1-knockout mice are protected from arterial thrombosis via a bradykinin/Mas-receptor/prostacyclin/Sirt1/KLF4 pathway that suppresses vascular tissue factor, a mechanism independent of contact-pathway coagulation.\",\n      \"evidence\": \"Klkb1⁻/⁻ mice in multiple thrombosis models with pharmacological rescue (Mas antagonist, COX-2 inhibitor, Sirt1 inhibitor)\",\n      \"pmids\": [\"25339356\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether the same Mas/prostacyclin/Sirt1/KLF4 axis operates in human vasculature not confirmed\", \"Contribution relative to factor XII-dependent pathway in humans unknown\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"A direct enzymatic connection between kallikrein-kinin and renin-angiotensin systems was demonstrated: kallikrein directly converts prorenin to active renin, and human genetic variants reducing kallikrein activity are associated with lower plasma renin levels.\",\n      \"evidence\": \"In vitro cleavage of recombinant prorenin; co-localization in mouse kidney; replicated genetic association in two human cohorts (n=1,180)\",\n      \"pmids\": [\"26969407\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Cleavage site on prorenin not mapped\", \"Relative contribution of kallikrein versus existing prorenin activation mechanisms not quantified\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Kallikrein was shown to directly activate complement by cleaving C3 at the canonical convertase site and cleaving factor B, generating functional C3 convertases that feed into the alternative pathway amplification loop, establishing a direct link between contact activation and innate immune complement.\",\n      \"evidence\": \"In vitro cleavage of purified C3 and factor B by kallikrein; mass spectrometry identification of cleavage sites; functional C3 convertase assays; factor H inhibition\",\n      \"pmids\": [\"29237166\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Physiological relevance in vivo not demonstrated genetically\", \"Whether complement activation by kallikrein contributes to angioedema pathology not tested\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Therapeutic proof of concept was achieved in humans: in vivo CRISPR-Cas9 editing of KLKB1 (NTLA-2002) produced dose-dependent, durable reductions in plasma kallikrein protein (up to −95%), confirming KLKB1 as the sole source of plasma kallikrein and demonstrating clinical benefit in hereditary angioedema.\",\n      \"evidence\": \"Phase 1 human clinical trial with LNP-delivered CRISPR-Cas9 targeting KLKB1 in liver; plasma kallikrein protein quantification\",\n      \"pmids\": [\"38294975\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Long-term safety of complete kallikrein ablation not established\", \"Effects on complement and renin pathways in treated patients not reported\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"A CNS-related function was proposed: KLKB1 interacts with transcription factor TFE3 and promotes neuronal ferroptosis through BRAF/MEK/ERK signaling in a vascular dementia model, extending kallikrein biology beyond hemostasis and immunity.\",\n      \"evidence\": \"Rat BCCAO model; IP-MS and Co-IP for KLKB1–TFE3 interaction; siRNA knockdown with pathway readout\",\n      \"pmids\": [\"41242565\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab finding without independent replication\", \"Mechanism by which a secreted serine protease interacts with a nuclear transcription factor is not explained\", \"No reciprocal Co-IP or domain-mapping reported\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include the high-resolution structural basis of the prekallikrein–kininogen complex, the in vivo hierarchy among kallikrein's multiple substrates (factor XII, kininogen, C3, factor B, prorenin), and the long-term systemic consequences of complete kallikrein elimination in humans.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No crystal or cryo-EM structure of prekallikrein bound to kininogen\", \"Substrate selectivity determinants in vivo not mapped\", \"Whether kallikrein-mediated complement activation is relevant in human disease unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [0, 1, 3, 9, 10]},\n      {\"term_id\": \"GO:0016787\", \"supporting_discovery_ids\": [0, 3, 10]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [0, 1, 2, 3, 4, 5, 10, 11]},\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [6]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-109582\", \"supporting_discovery_ids\": [1, 2, 3, 8]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [10]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [8, 9]}\n    ],\n    \"complexes\": [\n      \"prekallikrein–HMW kininogen complex\"\n    ],\n    \"partners\": [\n      \"KNG1\",\n      \"F12\",\n      \"F11\",\n      \"SERPINA5\",\n      \"TFPI2\",\n      \"C3\",\n      \"CFB\",\n      \"TFE3\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}