{"gene":"ABCB9","run_date":"2026-06-09T22:02:36","timeline":{"discoveries":[{"year":2000,"finding":"ABCB9 protein co-localizes with lysosomal markers LAMP1 and LAMP2 in transfected cells, establishing it as a lysosome-associated half ABC transporter with a predicted transmembrane domain and nucleotide-binding domain containing Walker motifs.","method":"Immunofluorescence co-localization with lysosomal markers in transfected cells; Northern analysis; phylogenetic analysis","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct co-localization experiment with lysosomal markers, single lab, multiple methods (Northern, transfection, co-localization)","pmids":["10748049"],"is_preprint":false},{"year":2004,"finding":"The N-terminal region (M1-S275) of ABCB9/TAPL is essential for localization to intracellular membranes; ABCB9 can interact with itself (homodimer) and with TAP1 and TAP2 via its M1-G75 region, as shown by co-localization of truncated GFP-fusion constructs with DsRed-tagged full-length TAPL or TAP1.","method":"Fluorescence protein-fusion co-expression and co-localization imaging; truncation analysis of GFP-tagged constructs","journal":"Biological & pharmaceutical bulletin","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — co-localization of fluorescent fusion proteins, single lab, multiple truncation constructs tested","pmids":["15577206"],"is_preprint":false},{"year":2003,"finding":"The ABCB9/TAPL gene consists of 12 exons on chromosome 12q23.34, produces at least three alternative splicing variants of exon 12 (12A, 12B, 12C) encoding shorter C-terminal isoforms, and its proximal promoter lacks a TATA-box but contains GC-box elements; a 60 bp upstream sequence with two GC-boxes confers basal promoter activity.","method":"3'RACE, genomic sequencing, luciferase promoter activity assay","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct promoter activity assay plus structural gene characterization, single lab","pmids":["13679046"],"is_preprint":false},{"year":2008,"finding":"ABCB9/TAPL binds ATP and ADP (but not AMP) in a Mg2+-dependent, pH-neutral manner and preferentially binds purine nucleotides over pyrimidines; chemical cross-linking established that TAPL forms a homodimer in membranes.","method":"ATP/ADP/AMP-agarose binding assay with competition; chemical cross-linking of insect cell-expressed TAPL","journal":"Biological & pharmaceutical bulletin","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vitro biochemical binding assay with nucleotide competition and cross-linking, single lab, two orthogonal methods","pmids":["18175933"],"is_preprint":false},{"year":2006,"finding":"The transport activity of ABCB9/TAPL (dependent on an intact Walker A ATP-binding motif) is required for conferring enhanced valinomycin sensitivity in yeast; a Walker A mutant that abolishes ATP binding eliminates this phenotype.","method":"Expression in yeast (BJ5457), valinomycin sensitivity assay, Walker A motif mutagenesis","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — active-site mutagenesis with functional readout, single lab","pmids":["16554024"],"is_preprint":false},{"year":2008,"finding":"The N-terminal transmembrane domain (Met1–Arg141) of ABCB9/TAPL contains the lysosomal sorting signal; the core domain (Arg141–Ala766) alone is distributed broadly in intracellular membranes but does not confer lysosomal targeting. Full-length TAPL and the core domain interact with each other, but N-terminal domain fragments alone do not associate.","method":"Co-immunoprecipitation of His6/Myc-tagged domain constructs; fluorescence microscopy of GFP-tagged truncations stably expressed in cells","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — domain dissection with co-IP and live imaging, single lab, two methods","pmids":["18952056"],"is_preprint":false},{"year":2011,"finding":"ABCB9/TAPL-GFP stably expressed in CHO-K1 cells co-sediments with lysosomal marker cathepsin D on Percoll gradients and co-localizes with LysoTracker but not MitoTracker, confirming lysosomal (not mitochondrial) localization. TAPL is resistant to cold non-ionic detergent and co-sediments with flotillin-1 on sucrose gradients, indicating localization to cholesterol-enriched lipid raft microdomains of lysosomal membranes; methyl-β-cyclodextrin treatment alters its distribution.","method":"Density gradient centrifugation, LysoTracker/MitoTracker co-localization, detergent resistance, methyl-β-cyclodextrin treatment, sucrose gradient fractionation","journal":"Biological & pharmaceutical bulletin","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal biochemical and imaging methods, single lab","pmids":["21212514"],"is_preprint":false},{"year":2013,"finding":"miR-31 directly targets the 3'UTR of ABCB9 (validated by luciferase reporter assay) and suppresses its expression; inhibition of ABCB9 by miR-31 is required for cisplatin resistance and reduced apoptosis in NSCLC cells.","method":"Luciferase 3'UTR reporter assay, miR-31 overexpression/knockdown, ABCB9 expression analysis","journal":"Cancer letters","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct 3'UTR reporter assay plus functional rescue, single lab","pmids":["24099915"],"is_preprint":false},{"year":2016,"finding":"miR-24 directly binds the 3'UTR of ABCB9 (validated by reporter assay) and downregulates its expression, thereby reducing drug transport and increasing paclitaxel sensitivity in resistant breast cancer cells in vitro and in vivo.","method":"3'UTR luciferase reporter assay, miR-24 overexpression, ABCB9 knockdown, in vivo xenograft","journal":"Oncology letters","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct 3'UTR reporter assay, functional rescue in vitro and in vivo, single lab","pmids":["27895747"],"is_preprint":false}],"current_model":"ABCB9 (TAPL) is a half-type ABC transporter that homodimerizes and localizes to lysosomal lipid raft microdomains via an N-terminal sorting signal (Met1–Arg141); it binds purine nucleotides (ATP/ADP) in a Mg2+-dependent manner through its Walker A motif, which is required for its transport activity, and its expression is post-transcriptionally repressed by miR-31 and miR-24 targeting its 3'UTR, influencing drug resistance in cancer cells."},"narrative":{"mechanistic_narrative":"ABCB9 (TAPL) is a half-type ABC transporter that homodimerizes and functions in the membranes of lysosomes [PMID:10748049, PMID:18175933]. Its N-terminal transmembrane region (Met1–Arg141) carries a lysosomal sorting signal that directs the protein to lysosomal membranes, where it concentrates in cholesterol-enriched, detergent-resistant lipid raft microdomains together with flotillin-1; the core transporter domain alone lacks targeting information and distributes broadly across intracellular membranes [PMID:18952056, PMID:21212514]. The protein assembles as a homodimer in membranes and, through an N-terminal segment (M1–G75), can additionally associate with the peptide transporters TAP1 and TAP2 [PMID:15577206, PMID:18175933]. ABCB9 binds purine nucleotides ATP and ADP, but not AMP or pyrimidines, in a Mg2+-dependent, pH-neutral manner [PMID:18175933], and an intact Walker A ATP-binding motif is required for its transport activity, as a Walker A mutant abolishes the valinomycin-sensitivity phenotype it confers in yeast [PMID:16554024]. Expression of ABCB9 is post-transcriptionally repressed by miR-31 and miR-24, which directly target its 3'UTR; this repression modulates drug transport and contributes to cisplatin resistance in non-small-cell lung cancer and paclitaxel sensitivity in breast cancer cells [PMID:24099915, PMID:27895747]. The physiological transport substrate of ABCB9 has not been identified in the available corpus.","teleology":[{"year":2000,"claim":"Established the subcellular home of ABCB9, answering where a newly identified half ABC transporter acts by placing it at the lysosome.","evidence":"Immunofluorescence co-localization with LAMP1/LAMP2 in transfected cells, plus Northern and phylogenetic analysis","pmids":["10748049"],"confidence":"Medium","gaps":["No transport substrate identified","Functional transport activity not demonstrated","Co-localization only in overexpression context"]},{"year":2003,"claim":"Defined the gene architecture and transcriptional control of ABCB9, showing alternative splicing of exon 12 and a GC-box-driven, TATA-less promoter.","evidence":"3'RACE, genomic sequencing, and luciferase promoter activity assay","pmids":["13679046"],"confidence":"Medium","gaps":["Functional consequence of C-terminal splice isoforms unknown","Transcription factors binding the GC-boxes not identified"]},{"year":2004,"claim":"Mapped the N-terminal region as the determinant of intracellular membrane targeting and first showed self-association and interaction with TAP1/TAP2.","evidence":"Truncation analysis of GFP/DsRed fusion constructs by co-expression and co-localization imaging","pmids":["15577206"],"confidence":"Medium","gaps":["TAP1/TAP2 interaction shown only by co-localization, no biochemical complex isolation","Functional role of TAP association undefined"]},{"year":2006,"claim":"Demonstrated that ABCB9 is a functional transporter whose activity requires ATP binding, linking the Walker A motif to a measurable cellular phenotype.","evidence":"Heterologous expression in yeast with valinomycin sensitivity assay and Walker A mutagenesis","pmids":["16554024"],"confidence":"Medium","gaps":["Endogenous substrate not identified","Phenotype is indirect (valinomycin sensitivity), not a direct transport measurement"]},{"year":2008,"claim":"Characterized the nucleotide specificity and oligomeric state, establishing ABCB9 as a homodimer that selectively binds purine nucleotides.","evidence":"ATP/ADP/AMP-agarose binding with competition and chemical cross-linking of insect-cell-expressed protein","pmids":["18175933"],"confidence":"Medium","gaps":["ATP hydrolysis kinetics not measured","Coupling of nucleotide binding to substrate transport not shown"]},{"year":2008,"claim":"Pinpointed the lysosomal sorting signal to the N-terminal transmembrane domain (Met1–Arg141) and showed the core domain interacts with full-length protein but lacks targeting.","evidence":"Co-immunoprecipitation of tagged domain constructs and fluorescence imaging of GFP-tagged truncations","pmids":["18952056"],"confidence":"Medium","gaps":["Sorting machinery recognizing the signal not identified","Structural basis of N-terminal/core interaction unknown"]},{"year":2011,"claim":"Refined the localization to cholesterol-rich lipid raft microdomains of the lysosomal membrane, distinguishing it from mitochondrial localization.","evidence":"Percoll/sucrose density gradients, LysoTracker/MitoTracker co-localization, detergent resistance, and methyl-β-cyclodextrin treatment in CHO-K1 cells","pmids":["21212514"],"confidence":"Medium","gaps":["Functional significance of raft localization for transport unknown","Performed in overexpressing stable lines"]},{"year":2016,"claim":"Established post-transcriptional control of ABCB9 by miR-31 and miR-24 and tied its expression to chemotherapy response in cancer cells.","evidence":"3'UTR luciferase reporter assays, miRNA over/under-expression, ABCB9 knockdown, and xenograft (miR-24)","pmids":["24099915","27895747"],"confidence":"Medium","gaps":["Direct drug substrate transported by ABCB9 not defined","Mechanism linking ABCB9 transport activity to apoptosis/resistance unresolved"]},{"year":null,"claim":"The endogenous physiological substrate of ABCB9 and the molecular link between its lysosomal transport activity and drug resistance remain undefined.","evidence":"No direct substrate identification or transport-coupled mechanism reported in the corpus","pmids":[],"confidence":"Medium","gaps":["No transport substrate identified","No structural model of the transporter","Physiological lysosomal function unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140657","term_label":"ATP-dependent activity","supporting_discovery_ids":[3,4]},{"term_id":"GO:0005215","term_label":"transporter activity","supporting_discovery_ids":[4]}],"localization":[{"term_id":"GO:0005764","term_label":"lysosome","supporting_discovery_ids":[0,6]}],"pathway":[{"term_id":"R-HSA-382551","term_label":"Transport of small molecules","supporting_discovery_ids":[4]}],"complexes":[],"partners":["TAP1","TAP2"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q9NP78","full_name":"ABC-type oligopeptide transporter ABCB9","aliases":["ATP-binding cassette sub-family B member 9","ATP-binding cassette transporter 9","ABC transporter 9 protein","hABCB9","TAP-like protein","TAPL"],"length_aa":766,"mass_kda":84.5,"function":"ATP-dependent low-affinity peptide transporter which translocates a broad spectrum of peptides from the cytosol to the lysosomal lumen for degradation (PubMed:15863492, PubMed:17977821, PubMed:18434309, PubMed:22641697, PubMed:25646430, PubMed:30353140, PubMed:30877195, PubMed:31417173). Displays a broad peptide length specificity from 6-mer up to at least 59-mer peptides with an optimum of 23-mers (PubMed:15863492, PubMed:25646430). Binds and transports smaller and larger peptides with the same affinity (PubMed:31417173). Favors positively charged, aromatic or hydrophobic residues in the N- and C-terminal positions whereas negatively charged residues as well as asparagine and methionine are not favored (PubMed:15863492, PubMed:17977821, PubMed:18434309)","subcellular_location":"Lysosome membrane","url":"https://www.uniprot.org/uniprotkb/Q9NP78/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/ABCB9","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/ABCB9","total_profiled":1310},"omim":[{"mim_id":"619109","title":"YIP1-INTERACTING FACTOR HOMOLOG B, MEMBRANE-TRAFFICKING PROTEIN; YIF1B","url":"https://www.omim.org/entry/619109"},{"mim_id":"605453","title":"ATP-BINDING CASSETTE, SUBFAMILY B, MEMBER 9; ABCB9","url":"https://www.omim.org/entry/605453"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Vesicles","reliability":"Supported"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in all","driving_tissues":[{"tissue":"brain","ntpm":19.5},{"tissue":"testis","ntpm":17.1}],"url":"https://www.proteinatlas.org/search/ABCB9"},"hgnc":{"alias_symbol":["EST122234"],"prev_symbol":[]},"alphafold":{"accession":"Q9NP78","domains":[{"cath_id":"-","chopping":"2-138","consensus_level":"high","plddt":81.7895,"start":2,"end":138},{"cath_id":"1.20.1560.10","chopping":"171-483","consensus_level":"medium","plddt":91.5541,"start":171,"end":483},{"cath_id":"3.40.50.300","chopping":"503-743","consensus_level":"medium","plddt":90.3584,"start":503,"end":743}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9NP78","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9NP78-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9NP78-F1-predicted_aligned_error_v6.png","plddt_mean":85.44},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=ABCB9","jax_strain_url":"https://www.jax.org/strain/search?query=ABCB9"},"sequence":{"accession":"Q9NP78","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9NP78.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9NP78/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9NP78"}},"corpus_meta":[{"pmid":"24099915","id":"PMC_24099915","title":"MicroRNA-31 inhibits cisplatin-induced apoptosis in non-small cell lung cancer cells by regulating the drug transporter ABCB9.","date":"2013","source":"Cancer letters","url":"https://pubmed.ncbi.nlm.nih.gov/24099915","citation_count":120,"is_preprint":false},{"pmid":"10748049","id":"PMC_10748049","title":"Characterization of ABCB9, an ATP binding cassette protein associated with lysosomes.","date":"2000","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/10748049","citation_count":87,"is_preprint":false},{"pmid":"27895747","id":"PMC_27895747","title":"Overexpression of microRNA-24 increases the sensitivity to paclitaxel in drug-resistant breast carcinoma cell lines via targeting ABCB9.","date":"2016","source":"Oncology letters","url":"https://pubmed.ncbi.nlm.nih.gov/27895747","citation_count":34,"is_preprint":false},{"pmid":"13679046","id":"PMC_13679046","title":"Gene organization of human transporter associated with antigen processing-like (TAPL, ABCB9): analysis of alternative splicing variants and promoter activity.","date":"2003","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/13679046","citation_count":20,"is_preprint":false},{"pmid":"15577206","id":"PMC_15577206","title":"Membrane localization of transporter associated with antigen processing (TAP)-like (ABCB9) visualized in vivo with a fluorescence protein-fusion technique.","date":"2004","source":"Biological & pharmaceutical bulletin","url":"https://pubmed.ncbi.nlm.nih.gov/15577206","citation_count":19,"is_preprint":false},{"pmid":"18952056","id":"PMC_18952056","title":"Functional dissection of transmembrane domains of human TAP-like (ABCB9).","date":"2008","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/18952056","citation_count":17,"is_preprint":false},{"pmid":"14709908","id":"PMC_14709908","title":"The carboxyl terminal sequence of rat transporter associated with antigen processing (TAP)-like (ABCB9) is heterogeneous due to splicing of its mRNA.","date":"2004","source":"Biological & pharmaceutical bulletin","url":"https://pubmed.ncbi.nlm.nih.gov/14709908","citation_count":11,"is_preprint":false},{"pmid":"18175933","id":"PMC_18175933","title":"Biochemical characterization of transporter associated with antigen processing (TAP)-like (ABCB9) expressed in insect cells.","date":"2008","source":"Biological & pharmaceutical bulletin","url":"https://pubmed.ncbi.nlm.nih.gov/18175933","citation_count":11,"is_preprint":false},{"pmid":"16554024","id":"PMC_16554024","title":"Examination of drug resistance activity of human TAP-like (ABCB9) expressed in yeast.","date":"2006","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/16554024","citation_count":8,"is_preprint":false},{"pmid":"21212514","id":"PMC_21212514","title":"Transporter associated with antigen processing-like (ABCB9) stably expressed in Chinese hamster ovary-K1 cells is sorted to the microdomains of lysosomal membranes.","date":"2011","source":"Biological & pharmaceutical bulletin","url":"https://pubmed.ncbi.nlm.nih.gov/21212514","citation_count":4,"is_preprint":false},{"pmid":"27335633","id":"PMC_27335633","title":"Unexpected lack of specificity of a rabbit polyclonal TAP-L (ABCB9) antibody.","date":"2015","source":"F1000Research","url":"https://pubmed.ncbi.nlm.nih.gov/27335633","citation_count":1,"is_preprint":false},{"pmid":"36051605","id":"PMC_36051605","title":"ABCB9 polymorphism rs61955196 is associated with schizophrenia in a Chinese Han population.","date":"2022","source":"World journal of psychiatry","url":"https://pubmed.ncbi.nlm.nih.gov/36051605","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":7380,"output_tokens":2180,"usd":0.02742,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":9173,"output_tokens":2585,"usd":0.055245,"stage2_stop_reason":"end_turn"},"total_usd":0.082665,"stage1_batch_id":"msgbatch_0179Z2pxRYBsXi2xADneafRw","stage2_batch_id":"msgbatch_01LaY9ZaVdgjWArcZo9eqQE5","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2000,\n      \"finding\": \"ABCB9 protein co-localizes with lysosomal markers LAMP1 and LAMP2 in transfected cells, establishing it as a lysosome-associated half ABC transporter with a predicted transmembrane domain and nucleotide-binding domain containing Walker motifs.\",\n      \"method\": \"Immunofluorescence co-localization with lysosomal markers in transfected cells; Northern analysis; phylogenetic analysis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct co-localization experiment with lysosomal markers, single lab, multiple methods (Northern, transfection, co-localization)\",\n      \"pmids\": [\"10748049\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"The N-terminal region (M1-S275) of ABCB9/TAPL is essential for localization to intracellular membranes; ABCB9 can interact with itself (homodimer) and with TAP1 and TAP2 via its M1-G75 region, as shown by co-localization of truncated GFP-fusion constructs with DsRed-tagged full-length TAPL or TAP1.\",\n      \"method\": \"Fluorescence protein-fusion co-expression and co-localization imaging; truncation analysis of GFP-tagged constructs\",\n      \"journal\": \"Biological & pharmaceutical bulletin\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — co-localization of fluorescent fusion proteins, single lab, multiple truncation constructs tested\",\n      \"pmids\": [\"15577206\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"The ABCB9/TAPL gene consists of 12 exons on chromosome 12q23.34, produces at least three alternative splicing variants of exon 12 (12A, 12B, 12C) encoding shorter C-terminal isoforms, and its proximal promoter lacks a TATA-box but contains GC-box elements; a 60 bp upstream sequence with two GC-boxes confers basal promoter activity.\",\n      \"method\": \"3'RACE, genomic sequencing, luciferase promoter activity assay\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct promoter activity assay plus structural gene characterization, single lab\",\n      \"pmids\": [\"13679046\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"ABCB9/TAPL binds ATP and ADP (but not AMP) in a Mg2+-dependent, pH-neutral manner and preferentially binds purine nucleotides over pyrimidines; chemical cross-linking established that TAPL forms a homodimer in membranes.\",\n      \"method\": \"ATP/ADP/AMP-agarose binding assay with competition; chemical cross-linking of insect cell-expressed TAPL\",\n      \"journal\": \"Biological & pharmaceutical bulletin\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vitro biochemical binding assay with nucleotide competition and cross-linking, single lab, two orthogonal methods\",\n      \"pmids\": [\"18175933\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"The transport activity of ABCB9/TAPL (dependent on an intact Walker A ATP-binding motif) is required for conferring enhanced valinomycin sensitivity in yeast; a Walker A mutant that abolishes ATP binding eliminates this phenotype.\",\n      \"method\": \"Expression in yeast (BJ5457), valinomycin sensitivity assay, Walker A motif mutagenesis\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — active-site mutagenesis with functional readout, single lab\",\n      \"pmids\": [\"16554024\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"The N-terminal transmembrane domain (Met1–Arg141) of ABCB9/TAPL contains the lysosomal sorting signal; the core domain (Arg141–Ala766) alone is distributed broadly in intracellular membranes but does not confer lysosomal targeting. Full-length TAPL and the core domain interact with each other, but N-terminal domain fragments alone do not associate.\",\n      \"method\": \"Co-immunoprecipitation of His6/Myc-tagged domain constructs; fluorescence microscopy of GFP-tagged truncations stably expressed in cells\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — domain dissection with co-IP and live imaging, single lab, two methods\",\n      \"pmids\": [\"18952056\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"ABCB9/TAPL-GFP stably expressed in CHO-K1 cells co-sediments with lysosomal marker cathepsin D on Percoll gradients and co-localizes with LysoTracker but not MitoTracker, confirming lysosomal (not mitochondrial) localization. TAPL is resistant to cold non-ionic detergent and co-sediments with flotillin-1 on sucrose gradients, indicating localization to cholesterol-enriched lipid raft microdomains of lysosomal membranes; methyl-β-cyclodextrin treatment alters its distribution.\",\n      \"method\": \"Density gradient centrifugation, LysoTracker/MitoTracker co-localization, detergent resistance, methyl-β-cyclodextrin treatment, sucrose gradient fractionation\",\n      \"journal\": \"Biological & pharmaceutical bulletin\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal biochemical and imaging methods, single lab\",\n      \"pmids\": [\"21212514\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"miR-31 directly targets the 3'UTR of ABCB9 (validated by luciferase reporter assay) and suppresses its expression; inhibition of ABCB9 by miR-31 is required for cisplatin resistance and reduced apoptosis in NSCLC cells.\",\n      \"method\": \"Luciferase 3'UTR reporter assay, miR-31 overexpression/knockdown, ABCB9 expression analysis\",\n      \"journal\": \"Cancer letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct 3'UTR reporter assay plus functional rescue, single lab\",\n      \"pmids\": [\"24099915\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"miR-24 directly binds the 3'UTR of ABCB9 (validated by reporter assay) and downregulates its expression, thereby reducing drug transport and increasing paclitaxel sensitivity in resistant breast cancer cells in vitro and in vivo.\",\n      \"method\": \"3'UTR luciferase reporter assay, miR-24 overexpression, ABCB9 knockdown, in vivo xenograft\",\n      \"journal\": \"Oncology letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct 3'UTR reporter assay, functional rescue in vitro and in vivo, single lab\",\n      \"pmids\": [\"27895747\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"ABCB9 (TAPL) is a half-type ABC transporter that homodimerizes and localizes to lysosomal lipid raft microdomains via an N-terminal sorting signal (Met1–Arg141); it binds purine nucleotides (ATP/ADP) in a Mg2+-dependent manner through its Walker A motif, which is required for its transport activity, and its expression is post-transcriptionally repressed by miR-31 and miR-24 targeting its 3'UTR, influencing drug resistance in cancer cells.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"ABCB9 (TAPL) is a half-type ABC transporter that homodimerizes and functions in the membranes of lysosomes [#0, #3]. Its N-terminal transmembrane region (Met1–Arg141) carries a lysosomal sorting signal that directs the protein to lysosomal membranes, where it concentrates in cholesterol-enriched, detergent-resistant lipid raft microdomains together with flotillin-1; the core transporter domain alone lacks targeting information and distributes broadly across intracellular membranes [#5, #6]. The protein assembles as a homodimer in membranes and, through an N-terminal segment (M1–G75), can additionally associate with the peptide transporters TAP1 and TAP2 [#1, #3]. ABCB9 binds purine nucleotides ATP and ADP, but not AMP or pyrimidines, in a Mg2+-dependent, pH-neutral manner [#3], and an intact Walker A ATP-binding motif is required for its transport activity, as a Walker A mutant abolishes the valinomycin-sensitivity phenotype it confers in yeast [#4]. Expression of ABCB9 is post-transcriptionally repressed by miR-31 and miR-24, which directly target its 3'UTR; this repression modulates drug transport and contributes to cisplatin resistance in non-small-cell lung cancer and paclitaxel sensitivity in breast cancer cells [#7, #8]. The physiological transport substrate of ABCB9 has not been identified in the available corpus.\",\n  \"teleology\": [\n    {\n      \"year\": 2000,\n      \"claim\": \"Established the subcellular home of ABCB9, answering where a newly identified half ABC transporter acts by placing it at the lysosome.\",\n      \"evidence\": \"Immunofluorescence co-localization with LAMP1/LAMP2 in transfected cells, plus Northern and phylogenetic analysis\",\n      \"pmids\": [\"10748049\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No transport substrate identified\", \"Functional transport activity not demonstrated\", \"Co-localization only in overexpression context\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Defined the gene architecture and transcriptional control of ABCB9, showing alternative splicing of exon 12 and a GC-box-driven, TATA-less promoter.\",\n      \"evidence\": \"3'RACE, genomic sequencing, and luciferase promoter activity assay\",\n      \"pmids\": [\"13679046\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional consequence of C-terminal splice isoforms unknown\", \"Transcription factors binding the GC-boxes not identified\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Mapped the N-terminal region as the determinant of intracellular membrane targeting and first showed self-association and interaction with TAP1/TAP2.\",\n      \"evidence\": \"Truncation analysis of GFP/DsRed fusion constructs by co-expression and co-localization imaging\",\n      \"pmids\": [\"15577206\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"TAP1/TAP2 interaction shown only by co-localization, no biochemical complex isolation\", \"Functional role of TAP association undefined\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Demonstrated that ABCB9 is a functional transporter whose activity requires ATP binding, linking the Walker A motif to a measurable cellular phenotype.\",\n      \"evidence\": \"Heterologous expression in yeast with valinomycin sensitivity assay and Walker A mutagenesis\",\n      \"pmids\": [\"16554024\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Endogenous substrate not identified\", \"Phenotype is indirect (valinomycin sensitivity), not a direct transport measurement\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Characterized the nucleotide specificity and oligomeric state, establishing ABCB9 as a homodimer that selectively binds purine nucleotides.\",\n      \"evidence\": \"ATP/ADP/AMP-agarose binding with competition and chemical cross-linking of insect-cell-expressed protein\",\n      \"pmids\": [\"18175933\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"ATP hydrolysis kinetics not measured\", \"Coupling of nucleotide binding to substrate transport not shown\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Pinpointed the lysosomal sorting signal to the N-terminal transmembrane domain (Met1–Arg141) and showed the core domain interacts with full-length protein but lacks targeting.\",\n      \"evidence\": \"Co-immunoprecipitation of tagged domain constructs and fluorescence imaging of GFP-tagged truncations\",\n      \"pmids\": [\"18952056\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Sorting machinery recognizing the signal not identified\", \"Structural basis of N-terminal/core interaction unknown\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Refined the localization to cholesterol-rich lipid raft microdomains of the lysosomal membrane, distinguishing it from mitochondrial localization.\",\n      \"evidence\": \"Percoll/sucrose density gradients, LysoTracker/MitoTracker co-localization, detergent resistance, and methyl-β-cyclodextrin treatment in CHO-K1 cells\",\n      \"pmids\": [\"21212514\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional significance of raft localization for transport unknown\", \"Performed in overexpressing stable lines\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Established post-transcriptional control of ABCB9 by miR-31 and miR-24 and tied its expression to chemotherapy response in cancer cells.\",\n      \"evidence\": \"3'UTR luciferase reporter assays, miRNA over/under-expression, ABCB9 knockdown, and xenograft (miR-24)\",\n      \"pmids\": [\"24099915\", \"27895747\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct drug substrate transported by ABCB9 not defined\", \"Mechanism linking ABCB9 transport activity to apoptosis/resistance unresolved\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The endogenous physiological substrate of ABCB9 and the molecular link between its lysosomal transport activity and drug resistance remain undefined.\",\n      \"evidence\": \"No direct substrate identification or transport-coupled mechanism reported in the corpus\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No transport substrate identified\", \"No structural model of the transporter\", \"Physiological lysosomal function unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140657\", \"supporting_discovery_ids\": [3, 4]},\n      {\"term_id\": \"GO:0005215\", \"supporting_discovery_ids\": [4]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005764\", \"supporting_discovery_ids\": [0, 6]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-382551\", \"supporting_discovery_ids\": [4]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"TAP1\", \"TAP2\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"tie","faith_supported":5,"faith_total":5,"faith_pct":100.0}}