{"gene":"A1BG","run_date":"2026-04-28T17:12:36","timeline":{"discoveries":[{"year":1986,"finding":"A1BG (alpha-1-B glycoprotein) is a single polypeptide chain of 474 amino acid residues (Mr ~63,000) bearing five immunoglobulin-like domains, five intrachain disulfide bonds, and four N-linked oligosaccharides. Sequence analysis demonstrated internal duplication into five ~95-residue repeating structural domains, with significant homology to immunoglobulin variable regions and other members of the immunoglobulin supergene family (IgA receptor, secretory component), establishing A1BG as a member of the immunoglobulin superfamily.","method":"Complete amino acid sequence determination by protein sequencing; computational homology analysis","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 — complete primary structure determination with domain architecture characterization; foundational paper with >100 citations","pmids":["3458201"],"is_preprint":false},{"year":2004,"finding":"CRISP-3 (cysteine-rich secretory protein 3) is a specific, high-affinity ligand of A1BG in human plasma, forming a noncovalent 1:1 complex held together by strong electrostatic forces with a dissociation constant in the nanomolar range. A1BG-CRISP-3 complex formation in plasma was demonstrated by size-exclusion chromatography, immunoprecipitation, and surface plasmon resonance (SPR). The interaction is analogous to complexes between snake venom toxins and A1BG-like proteins in opossum plasma that inhibit venom metalloproteinases/myotoxins, suggesting A1BG may protect the circulation from harmful effects of free CRISP-3.","method":"Size-exclusion chromatography, immunoprecipitation, mass spectrometry identification of binding partner, surface plasmon resonance (SPR) with dissociation constant measurement","journal":"Biochemistry","confidence":"High","confidence_rationale":"Tier 1-2 — multiple orthogonal methods (SEC, co-IP, SPR with Kd determination) in a single rigorous study; 65 citations","pmids":["15461460"],"is_preprint":false},{"year":2024,"finding":"A1BG inhibits the sterol-binding and export function of CAP superfamily members (CRISP proteins). Coexpression of A1BG with CAP proteins in yeast abolished their sterol export function, and direct interaction between A1BG and CRISP2 inhibited sterol-binding in vitro. The interaction was mapped to the third of A1BG's five immunoglobulin-like domains. Importantly, the A1BG–CRISP2 interaction requires magnesium, indicating that Mg2+ coordination by conserved tetrad residues within the CAP domain is essential for stable complex formation.","method":"Yeast coexpression sterol export assay, in vitro sterol-binding assay, domain-mapping experiments, Mg2+-dependency studies","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1-2 — functional reconstitution in yeast + in vitro sterol-binding assay + domain mapping + mechanistic Mg2+ requirement, multiple orthogonal methods in one study","pmids":["39433128"],"is_preprint":false},{"year":2025,"finding":"Adipocyte-secreted A1BG promotes cisplatin resistance in osteosarcoma by directly interacting with NAMPT, stabilizing NAMPT protein, and increasing NAD+ production, which in turn enhances PARP1 activity and downstream DNA repair via the PARP1/ATM pathway. Depletion of A1BG in adipocytes restored cisplatin sensitivity, and recombinant A1BG enhanced resistance and promoted DNA repair. Pharmacological inhibition of NAMPT (FK886) or PARP1 (Olaparib) reversed adipocyte-conditioned medium-induced cisplatin resistance.","method":"Proteomic analysis of adipocyte-conditioned medium, A1BG knockdown and recombinant protein treatment, co-immunoprecipitation (A1BG–NAMPT direct interaction), NAD+ measurement, PARP1 activity assay, xenograft mouse models, patient-derived organoids","journal":"Advanced science (Weinheim, Baden-Wurttemberg, Germany)","confidence":"Medium","confidence_rationale":"Tier 2 — co-IP for A1BG-NAMPT interaction + functional rescue experiments + in vivo validation, but single lab study","pmids":["40560034"],"is_preprint":false},{"year":2025,"finding":"A1BG is required for maintaining ventricular structural integrity in a sex-specific manner: conditional knockout of A1bg in cardiomyocytes causes dilated cardiomyopathy (left ventricular dilation and wall thinning) in female but not male mice. Loss of A1BG disrupts intercalated disc architecture specifically in female cardiomyocytes (TEM) and dysregulates metabolic pathways including glucose-6-phosphate and acetyl-CoA metabolism. Mass spectrometry revealed sex-specific A1BG cardiac interactomes, suggesting the sex-differential phenotype is mediated through distinct protein interaction networks.","method":"Conditional A1bg knockout mouse (cardiomyocyte-specific), histology, electrocardiography, RNA-seq transcriptional profiling, transmission electron microscopy (intercalated disc analysis), western blot, mass spectrometry interactome, immunohistochemistry","journal":"Biology of sex differences","confidence":"High","confidence_rationale":"Tier 2 — conditional KO with defined structural/functional phenotype, multiple orthogonal methods (TEM, RNA-seq, MS interactome, ECG), peer-reviewed","pmids":["40270023"],"is_preprint":false}],"current_model":"A1BG is a secreted plasma glycoprotein with five immunoglobulin-like domains that functions as a high-affinity binding partner for CRISP proteins (inhibiting their sterol-binding/export activity in a Mg2+-dependent manner), directly interacts with and stabilizes NAMPT to enhance NAD+ production and PARP1-mediated DNA repair (conferring cisplatin resistance), and is required for maintaining intercalated disc integrity and metabolic homeostasis in female cardiomyocytes, with its loss causing sex-specific dilated cardiomyopathy in mice."},"narrative":{"teleology":[{"year":1986,"claim":"Determination of the complete primary structure of A1BG established it as a five-immunoglobulin-domain member of the immunoglobulin superfamily, providing the first molecular framework for understanding its architecture but leaving its function entirely unknown.","evidence":"Complete amino acid sequencing and computational homology analysis of human plasma A1BG","pmids":["3458201"],"confidence":"High","gaps":["No binding partner or biological function identified","No information on tissue-specific expression or regulation"]},{"year":2004,"claim":"Identification of CRISP-3 as a nanomolar-affinity 1:1 binding partner of A1BG in plasma provided the first functional context — suggesting A1BG sequesters CRISP proteins — but the mechanistic consequence of this interaction was unknown.","evidence":"Size-exclusion chromatography, co-immunoprecipitation, and SPR with Kd measurement using human plasma proteins","pmids":["15461460"],"confidence":"High","gaps":["Functional consequence of CRISP-3 sequestration not demonstrated","Binding domain on A1BG not mapped","Whether A1BG interacts with other CRISP family members was untested"]},{"year":2024,"claim":"Reconstitution experiments demonstrated that A1BG directly inhibits CRISP-mediated sterol binding and export via an interaction requiring Mg²⁺ coordination, mapped to A1BG's third Ig-like domain, converting A1BG from a passive binding partner to an active functional inhibitor of CAP superfamily proteins.","evidence":"Yeast coexpression sterol export assay, in vitro sterol-binding assay, domain mapping, and Mg²⁺-dependency studies with A1BG and CRISP2","pmids":["39433128"],"confidence":"High","gaps":["Physiological relevance of CRISP sterol-export inhibition in mammalian systems not tested in vivo","Whether all five Ig-like domains contribute to other interactions is unknown","Structural basis of the Mg²⁺-dependent A1BG–CRISP interface not resolved"]},{"year":2025,"claim":"Discovery that adipocyte-secreted A1BG binds and stabilizes NAMPT to boost NAD⁺ production and PARP1-mediated DNA repair revealed a second major functional axis — paracrine metabolic signaling — distinct from CRISP inhibition.","evidence":"Co-immunoprecipitation of A1BG–NAMPT, NAD⁺ measurement, PARP1 activity assays, A1BG knockdown/recombinant rescue, xenograft models, and patient-derived organoids in osteosarcoma","pmids":["40560034"],"confidence":"Medium","gaps":["A1BG–NAMPT interaction demonstrated by co-IP in a single study; awaits independent validation and structural characterization","Whether A1BG–NAMPT interaction occurs outside the tumor microenvironment is untested","Relative contribution of A1BG to systemic NAD⁺ homeostasis is unknown"]},{"year":2025,"claim":"Cardiomyocyte-specific A1BG knockout revealed an unexpected cell-autonomous, sex-specific requirement for A1BG in maintaining intercalated disc integrity and metabolic homeostasis in the heart, establishing a tissue-specific in vivo function beyond its plasma roles.","evidence":"Conditional A1bg knockout in murine cardiomyocytes with echocardiography, TEM of intercalated discs, RNA-seq, and MS-based interactome profiling","pmids":["40270023"],"confidence":"High","gaps":["Molecular mechanism linking A1BG loss to intercalated disc disassembly not identified","Basis of the sex-specific phenotype (hormonal vs. chromosomal) is unresolved","Whether the cardiac function is mediated through CRISP or NAMPT interactions or novel partners is unknown"]},{"year":null,"claim":"A unifying model integrating A1BG's CRISP-inhibitory, NAMPT-stabilizing, and cardiac structural roles is lacking; it remains unknown whether these functions reflect a common molecular mechanism (e.g., protein stabilization via Ig-like domains) or independent activities in distinct compartments.","evidence":"","pmids":[],"confidence":"Low","gaps":["No high-resolution structure of A1BG alone or in complex with any partner","No comprehensive loss-of-function study in human genetics linking A1BG variants to disease","Relative importance of secreted versus cell-surface/intracellular A1BG pools is uncharacterized"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[1,2]},{"term_id":"GO:0140313","term_label":"molecular sequestering activity","supporting_discovery_ids":[1,2]}],"localization":[{"term_id":"GO:0005576","term_label":"extracellular region","supporting_discovery_ids":[0,1,3]}],"pathway":[{"term_id":"GO:0008289","term_label":"lipid binding","supporting_discovery_ids":[2]},{"term_id":"R-HSA-73894","term_label":"DNA Repair","supporting_discovery_ids":[3]}],"complexes":[],"partners":["CRISP3","CRISP2","NAMPT","PARP1"],"other_free_text":[]},"mechanistic_narrative":"A1BG is a secreted plasma glycoprotein of the immunoglobulin superfamily, composed of five immunoglobulin-like domains, that functions as a high-affinity inhibitor of cysteine-rich secretory proteins (CRISPs) and as a stabilizer of extracellular NAMPT to modulate NAD+ biosynthesis [PMID:3458201, PMID:15461460, PMID:39433128, PMID:40560034]. A1BG forms a nanomolar-affinity 1:1 complex with CRISP-3 in plasma and inhibits CRISP-mediated sterol binding and export through a Mg²⁺-dependent interaction mapped to its third immunoglobulin-like domain [PMID:15461460, PMID:39433128]. A1BG also directly binds and stabilizes NAMPT, increasing NAD⁺ production and enhancing PARP1-dependent DNA repair, thereby conferring cisplatin resistance in osteosarcoma [PMID:40560034]. Cardiomyocyte-specific loss of A1BG in female mice causes dilated cardiomyopathy with intercalated disc disruption and metabolic dysregulation, revealing a sex-specific structural role in the heart [PMID:40270023]."},"prefetch_data":{"uniprot":{"accession":"P04217","full_name":"Alpha-1B-glycoprotein","aliases":["Alpha-1-B glycoprotein"],"length_aa":495,"mass_kda":54.3,"function":"","subcellular_location":"Secreted","url":"https://www.uniprot.org/uniprotkb/P04217/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/A1BG","classification":"Not Classified","n_dependent_lines":1,"n_total_lines":1208,"dependency_fraction":0.0008278145695364238},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/A1BG","total_profiled":1310},"omim":[{"mim_id":"138670","title":"ALPHA-1-B-GLYCOPROTEIN; A1BG","url":"https://www.omim.org/entry/138670"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Tissue enriched","tissue_distribution":"Detected in single","driving_tissues":[{"tissue":"liver","ntpm":565.1}],"url":"https://www.proteinatlas.org/search/A1BG"},"hgnc":{"alias_symbol":[],"prev_symbol":[]},"alphafold":{"accession":"P04217","domains":[{"cath_id":"2.60.40.10","chopping":"29-109","consensus_level":"high","plddt":87.7098,"start":29,"end":109},{"cath_id":"2.60.40.10","chopping":"119-202","consensus_level":"high","plddt":86.7192,"start":119,"end":202},{"cath_id":"2.60.40","chopping":"210-293","consensus_level":"high","plddt":88.8673,"start":210,"end":293},{"cath_id":"2.60.40.10","chopping":"309-393","consensus_level":"high","plddt":90.3312,"start":309,"end":393},{"cath_id":"2.60.40.10","chopping":"403-492","consensus_level":"high","plddt":93.2188,"start":403,"end":492}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P04217","model_url":"https://alphafold.ebi.ac.uk/files/AF-P04217-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P04217-F1-predicted_aligned_error_v6.png","plddt_mean":86.44},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=A1BG","jax_strain_url":"https://www.jax.org/strain/search?query=A1BG"},"sequence":{"accession":"P04217","fasta_url":"https://rest.uniprot.org/uniprotkb/P04217.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P04217/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P04217"}},"corpus_meta":[{"pmid":"18706098","id":"PMC_18706098","title":"Proteomic 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Clinical applications","url":"https://pubmed.ncbi.nlm.nih.gov/21591266","citation_count":35,"is_preprint":false,"source_track":"gene2pubmed"}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":9661,"output_tokens":1156,"usd":0.023162},"stage2":{"model":"claude-opus-4-6","input_tokens":4360,"output_tokens":1569,"usd":0.091537},"total_usd":0.279596,"stage1_batch_id":"msgbatch_01TqNM6p6FsoMBT2jzQTwKBr","stage2_batch_id":"msgbatch_01Ya473eco8sTHbvRymQaU8o","note":"batch pricing = 50% of standard","round2_stage1":{"model":"claude-sonnet-4-6","input_tokens":22881,"output_tokens":2908,"usd":0.056132},"round2_rules_fired":"R3","round2_stage2":{"model":"claude-opus-4-6","input_tokens":5182,"output_tokens":1864,"usd":0.108765}},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2024,\n      \"finding\": \"A1BG directly interacts with CRISP2 (and other CAP superfamily members), and this interaction inhibits sterol-binding by CRISP proteins in vitro and abolishes their sterol export function in yeast. The interaction is mapped to the third of five immunoglobulin-like domains within A1BG and requires magnesium, indicating that Mg2+ coordination by conserved tetrad residues in the CAP domain is essential for stable complex formation.\",\n      \"method\": \"Co-expression in yeast (sterol export assay), in vitro sterol-binding assay, domain-mapping experiments, reconstitution with recombinant proteins\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution with sterol-binding assay plus yeast functional assay and domain-mapping mutagenesis in a single study\",\n      \"pmids\": [\"39433128\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Secreted A1BG from adipocytes interacts directly with NAMPT, stabilizing it and increasing NAD+ production, which in turn enhances PARP1 activity and DNA repair via the PARP1/ATM pathway, thereby promoting cisplatin resistance in osteosarcoma cells.\",\n      \"method\": \"Proteomic analysis, co-immunoprecipitation (direct A1BG–NAMPT interaction), recombinant A1BG treatment, NAMPT/PARP1 inhibitor rescue experiments, A1BG depletion in adipocytes, diet-induced obesity mouse models, patient-derived organoids\",\n      \"journal\": \"Advanced science (Weinheim, Baden-Wurttemberg, Germany)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP identifying binding partner, recombinant protein rescue, multiple orthogonal functional assays including in vivo models\",\n      \"pmids\": [\"40560034\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Conditional knockout of A1BG specifically in cardiomyocytes causes dilated cardiomyopathy in female but not male mice, with left ventricular dilation, wall thinning, disruption of intercalated disc architecture (by TEM), and dysregulation of metabolic pathways (glucose-6-phosphate and acetyl-CoA metabolism). Mass spectrometry revealed sex-specific A1BG cardiac interactomes.\",\n      \"method\": \"Conditional A1bg knockout and Rosa26 knockin mouse models, histology, electrocardiography, RNA-seq, transmission electron microscopy, western blot, mass spectrometry, immunohistochemistry\",\n      \"journal\": \"Biology of sex differences\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean cardiomyocyte-specific KO with defined structural/functional phenotype, replicated across two publications (preprint and peer-reviewed), multiple orthogonal methods\",\n      \"pmids\": [\"40270023\", \"39070637\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Bioinformatic and comparative genomic analysis attributed A1BG to the leukocyte receptor cluster (LRC) in eutherian mammals, classifying it as an immunoglobulin-like domain-containing protein within this immune receptor gene family.\",\n      \"method\": \"Comprehensive bioinformatics analysis of LRC-related genes across mammalian genomes (eutherian, marsupial, monotreme)\",\n      \"journal\": \"Genome biology and evolution\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 4 — computational/bioinformatics only, no functional validation\",\n      \"pmids\": [\"31106814\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"A1BG is a secreted immunoglobulin-like domain glycoprotein that functions as an inhibitor of CAP-superfamily sterol-binding/export proteins (such as CRISP2) through direct Mg2+-dependent interaction with their CAP domain; in the tumor microenvironment it is secreted by adipocytes and binds NAMPT to stabilize it and boost NAD+/PARP1-mediated DNA repair, conferring cisplatin resistance; and in cardiomyocytes it is required in a sex-specific manner to maintain intercalated disc integrity and metabolic homeostasis, with its loss causing female-specific dilated cardiomyopathy.\"\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\nI'll classify each paper first, then extract discoveries only from KEPT papers.\n\n**Classification:**\n\n- [Retrieved 1] PMID:18706098 — KEEP (A1BG protein expression in pancreatic cancer, biomarker study — expression only, no mechanism) → EXCLUDE (no mechanistic finding)\n- [Retrieved 2] PMID:30556161 — EXCLUDE (case B: lncRNA A1BG-AS1, not the canonical protein)\n- [Retrieved 3] PMID:25009667 — KEEP (A1BG protein in CIN III, expression/biomarker only) → EXCLUDE (no mechanism)\n- [Retrieved 4] PMID:34885011 — KEEP (A1BG protein detection, biomarker/expression only) → EXCLUDE (no mechanism)\n- [Retrieved 5] PMID:38007504 — EXCLUDE (case B: lncRNA A1BG-AS1)\n- [Retrieved 6] PMID:34115333 — EXCLUDE (case B: lncRNA A1BG-AS1)\n- [Retrieved 7] PMID:38351022 — EXCLUDE (case B: lncRNA A1BG-AS1)\n- [Retrieved 8] PMID:37747800 — EXCLUDE (case B: lncRNA A1BG-AS1)\n- [Retrieved 9] PMID:31106814 — KEEP (bioinformatics analysis of A1BG gene in LRC evolution — computational only) → Low/Tier4\n- [Retrieved 10] PMID:40560034 — KEEP (A1BG protein mechanistic study: A1BG-NAMPT interaction, DNA repair)\n- [Retrieved 11] PMID:39433128 — KEEP (A1BG protein: sterol-binding inhibition, CRISP2 interaction, Mg2+ requirement)\n- [Retrieved 12] PMID:7985993 — KEEP (A1BG polymorphism, population genetics — no mechanism)\n- [Retrieved 13] PMID:2591067 — KEEP (A1BG chromosomal assignment — no mechanism)\n- [Retrieved 14] PMID:39779214 — EXCLUDE (case B: lncRNA A1BG-AS1)\n- [Retrieved 15] PMID:39070637 — KEEP (PREPRINT: A1BG cardiac function, sex-specific KO)\n- [Retrieved 16] PMID:40270023 — KEEP (A1BG cardiac function, sex-specific KO, peer-reviewed)\n\n**Additional papers:**\n- PMID:22658674 — KEEP (mRNA interactome, A1BG identified as RBP — but this is HeLa proteome, A1BG detection only, no mechanistic finding for A1BG specifically)\n- PMID:12477932, 14702039, 15489334, 8889549 — cDNA sequencing projects, no A1BG mechanism\n- PMID:26186194, 28514442, 33961781 — BioPlex interactome screens; A1BG interactions detected\n- PMID:19056867, 23533145, 23376485 — proteomics detection of A1BG, no mechanism\n- PMID:3458201 — KEEP (amino acid sequence, immunoglobulin superfamily homology — foundational structural paper)\n- PMID:15221005 — hepatoblastoma expression profiling, no A1BG mechanism\n- PMID:22516433, 16502470 — proteomics detection, no A1BG mechanism\n- PMID:15461460 — KEEP (CRISP-3 binding partner identification, SPR, mechanistic)\n- PMID:21988832, 21900206 — interactome screens; A1BG interactions detected\n- PMID:16335952, 14760718 — glycoproteomics/N-glycosylation detection of A1BG, no mechanism\n- PMID:23418544 — KEEP (A1BG as autoantigen in RA — expression/biomarker, no mechanism)\n- PMID:27559042, 27068509 — ECM proteomics, A1BG detected, no mechanism\n- PMID:34732716 — SOX2/TRIM26/WWP2, not about A1BG\n- PMID:36138187 — NUDT21/CD19, not about A1BG\n- PMID:21591266 — KEEP (A1BG fragmentation in urine — biomarker, no mechanism)\n- PMID:21873635 — GO annotation, no specific A1BG mechanism\n- PMID:26186194/28514442/33961781 — BioPlex: A1BG listed as interactor but no specific mechanistic follow-up on A1BG itself\n\n```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1986,\n      \"finding\": \"A1BG (alpha-1-B glycoprotein) is a single polypeptide chain of 474 amino acid residues (Mr ~63,000) bearing five immunoglobulin-like domains, five intrachain disulfide bonds, and four N-linked oligosaccharides. Sequence analysis demonstrated internal duplication into five ~95-residue repeating structural domains, with significant homology to immunoglobulin variable regions and other members of the immunoglobulin supergene family (IgA receptor, secretory component), establishing A1BG as a member of the immunoglobulin superfamily.\",\n      \"method\": \"Complete amino acid sequence determination by protein sequencing; computational homology analysis\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — complete primary structure determination with domain architecture characterization; foundational paper with >100 citations\",\n      \"pmids\": [\"3458201\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"CRISP-3 (cysteine-rich secretory protein 3) is a specific, high-affinity ligand of A1BG in human plasma, forming a noncovalent 1:1 complex held together by strong electrostatic forces with a dissociation constant in the nanomolar range. A1BG-CRISP-3 complex formation in plasma was demonstrated by size-exclusion chromatography, immunoprecipitation, and surface plasmon resonance (SPR). The interaction is analogous to complexes between snake venom toxins and A1BG-like proteins in opossum plasma that inhibit venom metalloproteinases/myotoxins, suggesting A1BG may protect the circulation from harmful effects of free CRISP-3.\",\n      \"method\": \"Size-exclusion chromatography, immunoprecipitation, mass spectrometry identification of binding partner, surface plasmon resonance (SPR) with dissociation constant measurement\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple orthogonal methods (SEC, co-IP, SPR with Kd determination) in a single rigorous study; 65 citations\",\n      \"pmids\": [\"15461460\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"A1BG inhibits the sterol-binding and export function of CAP superfamily members (CRISP proteins). Coexpression of A1BG with CAP proteins in yeast abolished their sterol export function, and direct interaction between A1BG and CRISP2 inhibited sterol-binding in vitro. The interaction was mapped to the third of A1BG's five immunoglobulin-like domains. Importantly, the A1BG–CRISP2 interaction requires magnesium, indicating that Mg2+ coordination by conserved tetrad residues within the CAP domain is essential for stable complex formation.\",\n      \"method\": \"Yeast coexpression sterol export assay, in vitro sterol-binding assay, domain-mapping experiments, Mg2+-dependency studies\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — functional reconstitution in yeast + in vitro sterol-binding assay + domain mapping + mechanistic Mg2+ requirement, multiple orthogonal methods in one study\",\n      \"pmids\": [\"39433128\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Adipocyte-secreted A1BG promotes cisplatin resistance in osteosarcoma by directly interacting with NAMPT, stabilizing NAMPT protein, and increasing NAD+ production, which in turn enhances PARP1 activity and downstream DNA repair via the PARP1/ATM pathway. Depletion of A1BG in adipocytes restored cisplatin sensitivity, and recombinant A1BG enhanced resistance and promoted DNA repair. Pharmacological inhibition of NAMPT (FK886) or PARP1 (Olaparib) reversed adipocyte-conditioned medium-induced cisplatin resistance.\",\n      \"method\": \"Proteomic analysis of adipocyte-conditioned medium, A1BG knockdown and recombinant protein treatment, co-immunoprecipitation (A1BG–NAMPT direct interaction), NAD+ measurement, PARP1 activity assay, xenograft mouse models, patient-derived organoids\",\n      \"journal\": \"Advanced science (Weinheim, Baden-Wurttemberg, Germany)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — co-IP for A1BG-NAMPT interaction + functional rescue experiments + in vivo validation, but single lab study\",\n      \"pmids\": [\"40560034\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"A1BG is required for maintaining ventricular structural integrity in a sex-specific manner: conditional knockout of A1bg in cardiomyocytes causes dilated cardiomyopathy (left ventricular dilation and wall thinning) in female but not male mice. Loss of A1BG disrupts intercalated disc architecture specifically in female cardiomyocytes (TEM) and dysregulates metabolic pathways including glucose-6-phosphate and acetyl-CoA metabolism. Mass spectrometry revealed sex-specific A1BG cardiac interactomes, suggesting the sex-differential phenotype is mediated through distinct protein interaction networks.\",\n      \"method\": \"Conditional A1bg knockout mouse (cardiomyocyte-specific), histology, electrocardiography, RNA-seq transcriptional profiling, transmission electron microscopy (intercalated disc analysis), western blot, mass spectrometry interactome, immunohistochemistry\",\n      \"journal\": \"Biology of sex differences\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — conditional KO with defined structural/functional phenotype, multiple orthogonal methods (TEM, RNA-seq, MS interactome, ECG), peer-reviewed\",\n      \"pmids\": [\"40270023\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"A1BG is a secreted plasma glycoprotein with five immunoglobulin-like domains that functions as a high-affinity binding partner for CRISP proteins (inhibiting their sterol-binding/export activity in a Mg2+-dependent manner), directly interacts with and stabilizes NAMPT to enhance NAD+ production and PARP1-mediated DNA repair (conferring cisplatin resistance), and is required for maintaining intercalated disc integrity and metabolic homeostasis in female cardiomyocytes, with its loss causing sex-specific dilated cardiomyopathy in mice.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"A1BG is a secreted glycoprotein containing five immunoglobulin-like domains that functions as a direct inhibitor of CAP-superfamily cysteine-rich secretory proteins: its third Ig-like domain engages the CAP domain of CRISP2 in a Mg²⁺-dependent manner, blocking sterol binding and abolishing sterol export [PMID:39433128]. In the tumor microenvironment, adipocyte-secreted A1BG binds and stabilizes extracellular NAMPT, elevating NAD⁺ levels and enhancing PARP1/ATM-mediated DNA repair, thereby conferring cisplatin resistance in osteosarcoma [PMID:40560034]. Cardiomyocyte-specific deletion of A1BG causes female-selective dilated cardiomyopathy with intercalated disc disruption and metabolic dysregulation, revealing a sex-dependent structural role in the heart [PMID:40270023].\",\n  \"teleology\": [\n    {\n      \"year\": 2019,\n      \"claim\": \"Whether A1BG belongs to a recognizable immune receptor gene family was clarified by assigning it to the leukocyte receptor cluster (LRC) based on comparative genomics, providing an evolutionary framework but no functional mechanism.\",\n      \"evidence\": \"Bioinformatic analysis of LRC-related genes across mammalian genomes\",\n      \"pmids\": [\"31106814\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"Purely computational — no experimental validation of immune receptor function\",\n        \"No functional assay linking A1BG to immune signaling\",\n        \"Does not address non-immune roles\"\n      ]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"The long-standing question of what A1BG binds and inhibits was resolved by demonstrating that it directly engages the CAP domain of CRISP proteins via its third Ig-like domain in a Mg²⁺-dependent manner, blocking sterol binding and export — establishing A1BG as an endogenous inhibitor of CAP-superfamily sterol-transport activity.\",\n      \"evidence\": \"In vitro sterol-binding assays with recombinant proteins, co-expression sterol export assay in yeast, domain-mapping and mutagenesis\",\n      \"pmids\": [\"39433128\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Physiological sterol substrates and tissues where this inhibition matters in vivo remain undefined\",\n        \"Whether A1BG inhibits all CAP-superfamily members with equal potency is untested in mammalian cells\",\n        \"No structural model of the A1BG–CRISP2 complex at atomic resolution\"\n      ]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"A1BG was shown to act as a paracrine factor secreted by adipocytes that stabilizes NAMPT and boosts NAD⁺/PARP1-dependent DNA repair, answering how obesity-associated signals promote chemoresistance in osteosarcoma.\",\n      \"evidence\": \"Co-immunoprecipitation, recombinant A1BG rescue, NAMPT/PARP1 inhibitor experiments, diet-induced obesity mouse model, patient-derived organoids\",\n      \"pmids\": [\"40560034\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Whether A1BG–NAMPT interaction is Ig-domain-mediated like the CRISP interaction is unknown\",\n        \"Relevance to other tumor types or non-neoplastic NAD⁺ biology not examined\",\n        \"Mechanism of NAMPT stabilization (e.g., protection from degradation vs. conformational effect) not defined\"\n      ]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"A cardiomyocyte-intrinsic, sex-specific requirement for A1BG was established: its conditional deletion causes dilated cardiomyopathy only in female mice, with intercalated disc disruption and metabolic pathway dysregulation, revealing an unexpected structural/metabolic role in the heart.\",\n      \"evidence\": \"Cardiomyocyte-specific conditional knockout mice, echocardiography, TEM, RNA-seq, mass spectrometry interactome, histology\",\n      \"pmids\": [\"40270023\", \"39070637\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Molecular basis of the sex specificity (hormonal vs. genetic) is undetermined\",\n        \"Direct cardiac binding partners responsible for intercalated disc maintenance are not identified\",\n        \"Whether human A1BG loss-of-function variants cause cardiomyopathy is untested\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How A1BG's multiple binding activities — CRISP inhibition, NAMPT stabilization, and intercalated disc maintenance — are coordinated across tissues, and what structural features determine partner selectivity, remain central unresolved questions.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"No unified structural model explaining how one protein engages such diverse partners\",\n        \"In vivo physiological relevance of CRISP inhibition in mammalian tissues not demonstrated\",\n        \"Sex-specific cardiac interactome partners identified by mass spectrometry await functional validation\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [0]},\n      {\"term_id\": \"GO:0044183\", \"supporting_discovery_ids\": [1]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [0, 1]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0008289\", \"supporting_discovery_ids\": [0]},\n      {\"term_id\": \"R-HSA-73894\", \"supporting_discovery_ids\": [1]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [1, 2]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"CRISP2\",\n      \"NAMPT\",\n      \"PARP1\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\n```json\n{\n  \"mechanistic_narrative\": \"A1BG is a secreted plasma glycoprotein of the immunoglobulin superfamily, composed of five immunoglobulin-like domains, that functions as a high-affinity inhibitor of cysteine-rich secretory proteins (CRISPs) and as a stabilizer of extracellular NAMPT to modulate NAD+ biosynthesis [PMID:3458201, PMID:15461460, PMID:39433128, PMID:40560034]. A1BG forms a nanomolar-affinity 1:1 complex with CRISP-3 in plasma and inhibits CRISP-mediated sterol binding and export through a Mg²⁺-dependent interaction mapped to its third immunoglobulin-like domain [PMID:15461460, PMID:39433128]. A1BG also directly binds and stabilizes NAMPT, increasing NAD⁺ production and enhancing PARP1-dependent DNA repair, thereby conferring cisplatin resistance in osteosarcoma [PMID:40560034]. Cardiomyocyte-specific loss of A1BG in female mice causes dilated cardiomyopathy with intercalated disc disruption and metabolic dysregulation, revealing a sex-specific structural role in the heart [PMID:40270023].\",\n  \"teleology\": [\n    {\n      \"year\": 1986,\n      \"claim\": \"Determination of the complete primary structure of A1BG established it as a five-immunoglobulin-domain member of the immunoglobulin superfamily, providing the first molecular framework for understanding its architecture but leaving its function entirely unknown.\",\n      \"evidence\": \"Complete amino acid sequencing and computational homology analysis of human plasma A1BG\",\n      \"pmids\": [\"3458201\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"No binding partner or biological function identified\",\n        \"No information on tissue-specific expression or regulation\"\n      ]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Identification of CRISP-3 as a nanomolar-affinity 1:1 binding partner of A1BG in plasma provided the first functional context — suggesting A1BG sequesters CRISP proteins — but the mechanistic consequence of this interaction was unknown.\",\n      \"evidence\": \"Size-exclusion chromatography, co-immunoprecipitation, and SPR with Kd measurement using human plasma proteins\",\n      \"pmids\": [\"15461460\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Functional consequence of CRISP-3 sequestration not demonstrated\",\n        \"Binding domain on A1BG not mapped\",\n        \"Whether A1BG interacts with other CRISP family members was untested\"\n      ]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Reconstitution experiments demonstrated that A1BG directly inhibits CRISP-mediated sterol binding and export via an interaction requiring Mg²⁺ coordination, mapped to A1BG's third Ig-like domain, converting A1BG from a passive binding partner to an active functional inhibitor of CAP superfamily proteins.\",\n      \"evidence\": \"Yeast coexpression sterol export assay, in vitro sterol-binding assay, domain mapping, and Mg²⁺-dependency studies with A1BG and CRISP2\",\n      \"pmids\": [\"39433128\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Physiological relevance of CRISP sterol-export inhibition in mammalian systems not tested in vivo\",\n        \"Whether all five Ig-like domains contribute to other interactions is unknown\",\n        \"Structural basis of the Mg²⁺-dependent A1BG–CRISP interface not resolved\"\n      ]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Discovery that adipocyte-secreted A1BG binds and stabilizes NAMPT to boost NAD⁺ production and PARP1-mediated DNA repair revealed a second major functional axis — paracrine metabolic signaling — distinct from CRISP inhibition.\",\n      \"evidence\": \"Co-immunoprecipitation of A1BG–NAMPT, NAD⁺ measurement, PARP1 activity assays, A1BG knockdown/recombinant rescue, xenograft models, and patient-derived organoids in osteosarcoma\",\n      \"pmids\": [\"40560034\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"A1BG–NAMPT interaction demonstrated by co-IP in a single study; awaits independent validation and structural characterization\",\n        \"Whether A1BG–NAMPT interaction occurs outside the tumor microenvironment is untested\",\n        \"Relative contribution of A1BG to systemic NAD⁺ homeostasis is unknown\"\n      ]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Cardiomyocyte-specific A1BG knockout revealed an unexpected cell-autonomous, sex-specific requirement for A1BG in maintaining intercalated disc integrity and metabolic homeostasis in the heart, establishing a tissue-specific in vivo function beyond its plasma roles.\",\n      \"evidence\": \"Conditional A1bg knockout in murine cardiomyocytes with echocardiography, TEM of intercalated discs, RNA-seq, and MS-based interactome profiling\",\n      \"pmids\": [\"40270023\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Molecular mechanism linking A1BG loss to intercalated disc disassembly not identified\",\n        \"Basis of the sex-specific phenotype (hormonal vs. chromosomal) is unresolved\",\n        \"Whether the cardiac function is mediated through CRISP or NAMPT interactions or novel partners is unknown\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"A unifying model integrating A1BG's CRISP-inhibitory, NAMPT-stabilizing, and cardiac structural roles is lacking; it remains unknown whether these functions reflect a common molecular mechanism (e.g., protein stabilization via Ig-like domains) or independent activities in distinct compartments.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"No high-resolution structure of A1BG alone or in complex with any partner\",\n        \"No comprehensive loss-of-function study in human genetics linking A1BG variants to disease\",\n        \"Relative importance of secreted versus cell-surface/intracellular A1BG pools is uncharacterized\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [1, 2]},\n      {\"term_id\": \"GO:0140313\", \"supporting_discovery_ids\": [1, 2]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [0, 1, 3]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0008289\", \"supporting_discovery_ids\": [2]},\n      {\"term_id\": \"R-HSA-73894\", \"supporting_discovery_ids\": [3]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"CRISP3\",\n      \"CRISP2\",\n      \"NAMPT\",\n      \"PARP1\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}