{"gene":"ABCB10","run_date":"2026-04-28T17:12:36","timeline":{"discoveries":[{"year":2013,"finding":"Crystal structures of ABCB10 in apo- and nucleotide-bound states reveal a classic exporter-fold ABC transporter in an open-inwards conformation; unexpectedly, ABCB10 adopts an open-inwards conformation even when complexed with non-hydrolysable ATP analogs (unlike other transporters that adopt open-outwards conformations with ATP), and a portal between two transmembrane helices is proposed to assist substrate entry into the binding cavity.","method":"X-ray crystallography with functional structural analysis; multiple ABCB10/ATP-analog complexes","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 — multiple crystal structures with nucleotide-bound complexes, rigorous structural validation","pmids":["23716676"],"is_preprint":false},{"year":2004,"finding":"ABCB10 contains an unusually long 105-amino acid mitochondrial targeting presequence (mTP); the central subdomain (aa 36-70) is sufficient for mitochondrial import, while the N-terminal subdomain participates in proper inner membrane import. Hydrophobic character of the mTP is required (L46Q/I47Q mutation greatly diminishes targeting). ABCB10 homodimerizes and homo-oligomerizes in the mitochondrial inner membrane as shown by mass spectrometry of chemically cross-linked immunoprecipitated protein.","method":"Mutagenesis of targeting sequence, subcellular fractionation/live imaging, mass spectrometry of cross-linked immunoprecipitated protein","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1-2 — mutagenesis plus MS validation, multiple orthogonal methods in one study","pmids":["15215243"],"is_preprint":false},{"year":2009,"finding":"ABCB10 physically interacts with mitoferrin-1 (Mfrn1/Slc25a37) in the mitochondrial inner membrane of erythroid cells, and this interaction stabilizes Mfrn1 protein, thereby enhancing Mfrn1-dependent mitochondrial iron importation. The binding domain maps to the N-terminus of Mfrn1.","method":"In vivo epitope-tagging affinity purification and mass spectrometry, co-immunoprecipitation/Western blot, transfection in heterologous COS7 cells, protein half-life assays","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 — reciprocal Co-IP, MS, functional iron import assay, replicated in multiple cell types","pmids":["19805291"],"is_preprint":false},{"year":2010,"finding":"Ferrochelatase (Fech), the terminal heme synthesis enzyme, forms an oligomeric complex with both mitoferrin-1 (Mfrn1) and ABCB10 in erythroid cells, physically integrating mitochondrial iron importation and heme biosynthesis.","method":"Affinity purification and mass spectrometry from stable MEL cell clones, immunoprecipitation/Western blot with endogenous and heterologous proteins in MEL and HEK293 cells","journal":"Blood","confidence":"High","confidence_rationale":"Tier 2 — reciprocal Co-IP with endogenous proteins plus MS, confirmed in two cell systems","pmids":["20427704"],"is_preprint":false},{"year":2019,"finding":"Dimeric ferrochelatase bridges ABCB7 and ABCB10 homodimers in an architecturally defined multiprotein complex required for heme biosynthesis; the interaction interfaces were mapped by chemical cross-linking, tandem mass spectrometry, and mutational analyses, with ferrochelatase binding near the nucleotide-binding domains of each ABC transporter.","method":"Chemical cross-linking, tandem mass spectrometry, mutational analysis, inducible knockdown cell lines","journal":"Haematologica","confidence":"High","confidence_rationale":"Tier 1-2 — cross-linking MS with mutational validation, interface mapping","pmids":["30765471"],"is_preprint":false},{"year":2012,"finding":"ABC-me/ABCB10 is essential for erythropoiesis in vivo: ABCB10-knockout mice die at embryonic day 12.5 with near-complete loss of primitive erythropoiesis; knockout erythroid precursors show increased mitochondrial superoxide production and protein carbonylation, and treatment with the SOD2 mimetic MnTBAP rescues survival and differentiation, placing ABCB10 upstream of oxidative stress-mediated apoptosis in erythroid development.","method":"Germline knockout mouse, in vivo and ex vivo erythroid differentiation assays, mitochondrial ROS measurement, antioxidant rescue experiments","journal":"Cell death and differentiation","confidence":"High","confidence_rationale":"Tier 2 — clean KO with specific phenotypic readout and mechanistic rescue, strong evidence","pmids":["22240895"],"is_preprint":false},{"year":2015,"finding":"Gly497 and Lys498 (Walker A), Glu624 (Walker B), and Gly602 (C-loop) in ABCB10 are required for proper ATP binding and hydrolysis. Oxidized glutathione (GSSG) stimulates ABCB10 ATPase activity without affecting ATP binding, while reduced glutathione (GSH) inhibits both ATP binding and hydrolysis; ABCB10 is glutathionylated at Cys547. Delta-aminolevulinic acid (dALA) does not alter ATP binding, excluding it as a direct substrate.","method":"8-azido-ATP photolabeling, site-directed mutagenesis, in vitro ATPase assays, mass spectrometry identification of glutathionylation site","journal":"PloS one","confidence":"High","confidence_rationale":"Tier 1 — in vitro ATPase assay with mutagenesis and MS identification of modification site","pmids":["26053025"],"is_preprint":false},{"year":2017,"finding":"ATPase activity of ABCB10 is necessary for hemoglobinization in erythroid MEL cells. Reduced ABCB10 does not cause protoporphyrin IX accumulation and does not affect ALA export from mitochondria, ruling out ALA as a transported substrate. ABCB10 silencing alters the heme biosynthesis transcriptional profile via Bach1-mediated repression, which can be partially rescued by overexpression of Alas2 or Gata1.","method":"shRNA knockdown in MEL cells, ATPase activity assays, succinylacetone inhibition of ALAD, metabolite measurements, transcriptional profiling, rescue experiments","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1-2 — multiple orthogonal functional assays, mechanistic pathway placement via epistasis","pmids":["28808058"],"is_preprint":false},{"year":2021,"finding":"ABCB10 is a mitochondrial biliverdin exporter: ABCB10 reconstituted into liposomes transports biliverdin, and ABCB10 deletion causes accumulation of biliverdin inside mitochondria. In obese mice, ABCB10-driven biliverdin export amplifies cytosolic bilirubin content, which inactivates PTP1B and elevates SREBP-1c, exacerbating insulin resistance and steatosis; restoration of cellular bilirubin in ABCB10 KO hepatocytes reverses improvements in mitochondrial function and PTP1B inactivation.","method":"Reconstitution of ABCB10 in liposomes with transport assay, ABCB10 hepatocyte-specific KO mice, metabolite measurements, rescue with bilirubin treatment","journal":"Science translational medicine","confidence":"High","confidence_rationale":"Tier 1 — direct reconstituted transport assay, KO mouse with mechanistic rescue, multiple orthogonal methods","pmids":["34011630"],"is_preprint":false},{"year":2020,"finding":"Zinc-mesoporphyrin stimulates ABCB10 ATPase activity (~70% increase) in purified ABCB10 reconstituted in lipid nanodiscs; this stimulation is specific to ABCB10 (not a bacterial ABC transporter control) and does not require typical heme regulatory motifs (cysteine-less ABCB10 also responds). Delta-aminolevulinic acid and glutathione do not activate ABCB10, further excluding them as direct substrates.","method":"Purified ABCB10 reconstituted in nanodiscs, in vitro ATPase assays with heme analogs and precursors","journal":"PloS one","confidence":"High","confidence_rationale":"Tier 1 — reconstituted in vitro ATPase assay with multiple control compounds","pmids":["33253225"],"is_preprint":false},{"year":2023,"finding":"ABCB10 binds cardiolipin with significantly higher affinity than other phospholipids, with the first three cardiolipin binding events showing positive cooperativity suggestive of specific binding sites; cardiolipin regulates ABCB10 ATPase activity in a dose-dependent fashion.","method":"Native mass spectrometry for lipid binding, in vitro ATPase assays with various phospholipids","journal":"Biochemistry","confidence":"High","confidence_rationale":"Tier 1 — native MS binding quantification combined with functional ATPase assay","pmids":["37807693"],"is_preprint":false},{"year":2017,"finding":"ABCB10 expression is regulated by the transcription factor Nrf2 in blood-brain barrier endothelial cells: Nrf2 silencing suppresses ABCB10 protein, while Nrf2 activation by sulforaphane upregulates ABCB10. Conversely, ABCB10 knockdown induces Nrf2-driven antioxidant responses and elevates endothelial-monocyte adhesion.","method":"siRNA knockdown of Nrf2 and ABCB10 in human BBB endothelial cells, Western blot, sulforaphane treatment","journal":"Neuroscience letters","confidence":"Medium","confidence_rationale":"Tier 2-3 — single lab, siRNA experiments with functional readouts but no in vitro reconstitution","pmids":["28572033"],"is_preprint":false},{"year":2014,"finding":"ABCB10 transcription is regulated by E2F transcription factors: E2F2, E2F3, and E2F4 activate transcription from the ABCB10 promoter; E2F4 directly binds to ABCB10 promoter sites (confirmed by EMSA and ChIP), and silencing E2F factors reduces basal ABCB10 expression.","method":"Promoter cloning, luciferase reporter assay, EMSA, ChIP, siRNA knockdown of E2F factors","journal":"Genomics","confidence":"Medium","confidence_rationale":"Tier 2 — EMSA and ChIP confirm direct binding, functional reporter assays, single lab","pmids":["25220178"],"is_preprint":false},{"year":2019,"finding":"Mutant huntingtin (mtHtt) inhibits the mitochondrial unfolded protein response (UPRmt) by impairing ABCB10 mRNA stability; ABCB10 depletion reduces UPRmt markers HSP60, Clpp, and CHOP, and increases mitochondrial ROS and cell death, while ABCB10 overexpression rescues these phenotypes.","method":"HD mouse striatal cells and patient fibroblasts, siRNA knockdown, overexpression, mRNA stability assays, ROS measurement, Western blot","journal":"Biochimica et biophysica acta. Molecular basis of disease","confidence":"Medium","confidence_rationale":"Tier 2-3 — multiple cell models with gain/loss of function but no in vitro reconstitution of mRNA stability mechanism","pmids":["30802639"],"is_preprint":false},{"year":2017,"finding":"ABCB10 depletion in HepG2 cells upregulates ROS and ROS-detoxifying enzymes (SOD2, GSTA1, GSTA2, SESN3) and significantly decreases expression of UPRmt-related mitochondrial chaperones (HSPD1, DNAJA3) and protease LONP1, supporting a role for ABCB10 in UPRmt signaling similar to C. elegans HAF-1.","method":"siRNA knockdown in HepG2 cells, Western blot, ROS measurement, qPCR","journal":"Biochemical and biophysical research communications","confidence":"Low","confidence_rationale":"Tier 3 — single lab, single method category, no in vitro reconstitution","pmids":["28315685"],"is_preprint":false},{"year":2023,"finding":"Loss of Abcb10 in erythroid cells causes decreased cellular arginine levels, altered expression of amino acid transporters, and activation of the ATF4 nutrient stress pathway (increased eIF2α phosphorylation, upregulated ATF4 and targets CHOP, Chac1, Rars), with arginine supplementation improving proliferation and hemoglobinization in Abcb10-null cells.","method":"CRISPR/Cas9 deletion in MEL and K562 cells, metabolomic and transcriptional analyses, arginine supplementation rescue","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 — metabolomics plus transcriptomics plus functional rescue in two cell lines","pmids":["37269954"],"is_preprint":false},{"year":2021,"finding":"ABCB10 loss in CD4+ T cells impairs specific cytokine expression upon activation, reduces CD4+ cell numbers and Ag-specific memory formation in vivo, and disrupts the switch to aerobic glycolysis upon activation in Jurkat T cells; CD8+ T cells are less affected, indicating a cell-type-selective metabolic role.","method":"Conditional Abcb10 KO mice, in vivo viral infection model, CRISPR KO in Jurkat cells, cytokine assays, metabolic profiling","journal":"Journal of immunology","confidence":"Medium","confidence_rationale":"Tier 2 — KO mouse plus CRISPR in human cells with mechanistic metabolic readout, single lab","pmids":["34893527"],"is_preprint":false},{"year":2024,"finding":"Cardiomyocyte-specific deletion of Abcb10 causes progressive cardiac fibrosis and mitochondrial structural abnormalities, leading to lysosomal dysfunction (decreased NAD+ levels, Hif1α upregulation), accumulation of Fe2+ and lipid peroxides in lysosomes, and ferroptosis; iron chelator treatment suppresses lipid peroxidation, implicating lysosomal iron accumulation as the mechanistic driver.","method":"Cardiomyocyte-specific Abcb10 KO mouse, ABCB10 knockdown in HeLa cells, iron chelator treatment, ROS and lipid peroxide measurement, lysosomal morphology analysis","journal":"Bioscience reports","confidence":"Medium","confidence_rationale":"Tier 2 — conditional KO plus cell line KD with mechanistic rescue, single lab","pmids":["38655715"],"is_preprint":false},{"year":2024,"finding":"Induced deletion of Abcb10 in adult mouse hematopoietic stem cells (HSCs) causes increased erythroid progenitor numbers and decreased HSC number; Abcb10-deficient HSCs show excess mitochondrial iron accumulation and oxidative stress, with a skew toward erythroid-lineage differentiation, but no alteration in mitochondrial bioenergetic function.","method":"Inducible Abcb10 KO in adult mice, flow cytometry of bone marrow progenitors, mitochondrial iron and ROS measurement, in vivo iron chelator and antioxidant treatment","journal":"Experimental hematology","confidence":"Medium","confidence_rationale":"Tier 2 — conditional KO with specific cellular phenotype and mechanistic measurement, single lab","pmids":["38493949"],"is_preprint":false},{"year":2024,"finding":"Hepatocyte-specific ABCB10 gain-of-function in mice with alcoholic hepatitis increases the mitochondrial GSH/GSSG ratio and decreases hepatic 4-HNE protein adducts, reducing MPO gene expression and histone H3 citrullination (NET formation marker), demonstrating that ABCB10-mediated ROS reduction in hepatocytes mitigates neutrophilic inflammation.","method":"Hepatocyte-specific ABCB10 overexpression in alcoholic hepatitis mouse model, redox assays, MPO/NET markers, GSH/GSSG ratio","journal":"Redox biology","confidence":"Medium","confidence_rationale":"Tier 2 — gain-of-function in vivo with mechanistic redox readouts, single lab","pmids":["38290384"],"is_preprint":false},{"year":2021,"finding":"Beta-cell-specific deletion of Abcb10 protects mice from high-fat diet-induced hyperinsulinemia and insulin resistance by limiting beta-cell expansion; ABCB10 activity limits glucose-stimulated insulin secretion (GSIS) and H2O2-mediated signaling, and bilirubin treatment of ABCB10 KO islets reverses increased H2O2 and GSIS, placing bilirubin as the effector downstream of ABCB10.","method":"Beta-cell-specific Abcb10 KO mouse (Ins1Cre-Abcb10flox/flox), GSIS assays, H2O2 measurement, bilirubin rescue in isolated islets","journal":"Molecular metabolism","confidence":"Medium","confidence_rationale":"Tier 2 — conditional KO with mechanistic bilirubin rescue in islets, single lab","pmids":["34823065"],"is_preprint":false},{"year":2025,"finding":"Conserved transmembrane arginine residues R232 and R295 of ABCB10 are required for biliverdin-stimulated ATPase activity; mutation of these residues decreases stimulation by biliverdin and alters conformational equilibrium detected by LRET. Biliverdin dimethyl ester does not stimulate (and mesobiliverdin inhibits) ABCB10 ATPase, indicating specific complementarity between biliverdin functional groups and the substrate binding pocket. GDN detergent abolishes biliverdin-induced stimulation, suggesting it interferes with substrate binding.","method":"Site-directed mutagenesis of transmembrane arginines, in vitro ATPase assay with biliverdin analogs, Luminescence Resonance Energy Transfer (LRET) conformational assay","journal":"Protein science","confidence":"High","confidence_rationale":"Tier 1 — in vitro ATPase assay with mutagenesis and conformational probe, multiple substrate analogs tested","pmids":["41229075"],"is_preprint":false}],"current_model":"ABCB10 is a homodimeric ATP-binding cassette transporter embedded in the mitochondrial inner membrane that exports biliverdin to the cytosol (directly demonstrated by liposome reconstitution), where it is reduced to the ROS-scavenger bilirubin; it physically interacts with mitoferrin-1 and ferrochelatase to form a multiprotein complex that coordinates iron import and heme biosynthesis in erythroid cells, with its ATPase activity (regulated by cardiolipin, glutathione redox status, and conserved transmembrane arginines) being essential for hemoglobinization and protection against mitochondrial oxidative stress."},"narrative":{"teleology":[{"year":2004,"claim":"Establishing that ABCB10 is a mitochondrial inner-membrane homodimer resolved its subcellular location and oligomeric state, key prerequisites for understanding its transport function.","evidence":"Mutagenesis of the 105-aa mitochondrial targeting presequence, subcellular fractionation, and chemical cross-linking/mass spectrometry in mammalian cells","pmids":["15215243"],"confidence":"High","gaps":["Substrate identity unknown at this point","No functional transport assay performed","Mechanism of homodimerization interface unresolved"]},{"year":2009,"claim":"Identifying ABCB10 as a physical partner of mitoferrin-1 that stabilizes the iron importer linked ABCB10 to mitochondrial iron homeostasis and heme biosynthesis for the first time.","evidence":"Reciprocal co-immunoprecipitation and mass spectrometry in erythroid and COS7 cells, protein half-life measurements","pmids":["19805291"],"confidence":"High","gaps":["Whether ABCB10 ATPase activity is required for mitoferrin-1 stabilization was untested","No structural details of the interaction interface"]},{"year":2010,"claim":"Demonstrating that ferrochelatase joins the ABCB10–mitoferrin-1 complex expanded the model to a multiprotein assembly that physically couples iron import to protoporphyrin metallation.","evidence":"Affinity purification/MS and co-IP with endogenous proteins in MEL and HEK293 cells","pmids":["20427704"],"confidence":"High","gaps":["Stoichiometry and architecture of the complex unknown","Whether complex formation is regulated during differentiation untested"]},{"year":2012,"claim":"ABCB10 knockout mice dying at E12.5 with severe oxidative stress in erythroid precursors—rescued by a SOD2 mimetic—established ABCB10 as essential for erythropoiesis and placed it upstream of mitochondrial ROS.","evidence":"Germline Abcb10 KO mouse, ex vivo erythroid differentiation, mitochondrial superoxide measurement, MnTBAP rescue","pmids":["22240895"],"confidence":"High","gaps":["Transported substrate still unidentified","Whether the ROS phenotype reflects loss of heme synthesis vs. loss of a separate antioxidant mechanism was unresolved"]},{"year":2013,"claim":"Crystal structures in apo and nucleotide-bound states revealed an exporter fold with an unusual open-inward conformation even with ATP analogs, informing how substrate enters through a lateral portal.","evidence":"X-ray crystallography of multiple ABCB10–nucleotide-analog complexes","pmids":["23716676"],"confidence":"High","gaps":["No substrate-bound structure obtained","Portal-mediated entry remained a proposal without mutagenesis validation at this stage"]},{"year":2015,"claim":"Identifying Walker A/B and C-loop residues required for ATPase activity, and showing redox regulation via glutathionylation at Cys547, connected ABCB10's catalytic cycle to mitochondrial redox state while excluding δ-ALA as a substrate.","evidence":"Site-directed mutagenesis, 8-azido-ATP photolabeling, ATPase assays, MS identification of glutathionylation","pmids":["26053025"],"confidence":"High","gaps":["True transported substrate still unidentified","Physiological significance of GSSG stimulation not tested in cells"]},{"year":2017,"claim":"Showing that ABCB10 ATPase activity is required for hemoglobinization and that neither ALA nor protoporphyrin IX accumulates upon ABCB10 loss narrowed the substrate search and revealed downstream Bach1-mediated transcriptional consequences.","evidence":"shRNA knockdown in MEL cells, ATPase assays, metabolite quantification, transcriptional profiling with epistasis rescue","pmids":["28808058"],"confidence":"High","gaps":["Substrate identity still unknown","Whether Bach1 derepression is a direct or indirect effect of ABCB10 loss undetermined"]},{"year":2019,"claim":"Mapping the ferrochelatase-bridged ABCB10–ABCB7 complex architecture showed that ferrochelatase contacts the nucleotide-binding domains of both transporters, suggesting coordinated regulation of two ABC transporters at the heme synthesis step.","evidence":"Chemical cross-linking/tandem MS and mutational analysis in inducible knockdown cell lines","pmids":["30765471"],"confidence":"High","gaps":["Functional consequence of disrupting the ABCB10–ABCB7 bridge not fully characterized","Whether the complex exists in non-erythroid tissues unknown"]},{"year":2020,"claim":"Zinc-mesoporphyrin specifically stimulating ABCB10 ATPase in nanodiscs, while ALA and glutathione did not, provided the first biochemical evidence that a porphyrin-related molecule interacts with the substrate-binding site.","evidence":"Purified ABCB10 in lipid nanodiscs, ATPase assays with heme analogs and precursors","pmids":["33253225"],"confidence":"High","gaps":["Direct transport of the stimulating compound not shown","Identity of the physiological substrate not conclusively established"]},{"year":2021,"claim":"Reconstitution of ABCB10 in liposomes directly demonstrated biliverdin transport, and hepatocyte-specific KO showed mitochondrial biliverdin accumulation, definitively identifying the transported substrate after over a decade of investigation.","evidence":"Liposome reconstitution transport assay, hepatocyte-specific Abcb10 KO mice, metabolite measurements, bilirubin rescue","pmids":["34011630"],"confidence":"High","gaps":["Whether biliverdin is the sole substrate or one of several remains open","Structural basis of biliverdin recognition unknown"]},{"year":2021,"claim":"β-cell-specific ABCB10 deletion revealed that exported biliverdin/bilirubin modulates glucose-stimulated insulin secretion via H₂O₂ scavenging, extending ABCB10 function beyond erythropoiesis to metabolic signaling.","evidence":"Ins1Cre-Abcb10 KO mouse, GSIS assays, H₂O₂ measurement, bilirubin rescue in isolated islets","pmids":["34823065"],"confidence":"Medium","gaps":["Single lab finding not independently replicated","Relative contribution of biliverdin export vs. other ABCB10 functions in β-cells not dissected"]},{"year":2023,"claim":"Demonstrating cooperative, high-affinity cardiolipin binding that regulates ATPase activity identified a lipid-based regulatory mechanism consistent with ABCB10's mitochondrial inner-membrane localization.","evidence":"Native mass spectrometry quantification of lipid binding, in vitro ATPase assays with various phospholipids","pmids":["37807693"],"confidence":"High","gaps":["Cardiolipin binding sites not structurally mapped","Whether cardiolipin modulates biliverdin transport rates untested"]},{"year":2023,"claim":"ABCB10 deletion in erythroid cells causes arginine depletion and ATF4 nutrient-stress activation, revealing an unexpected metabolic consequence that contributes to the hemoglobinization defect.","evidence":"CRISPR KO in MEL and K562 cells, metabolomics, transcriptomics, arginine supplementation rescue","pmids":["37269954"],"confidence":"Medium","gaps":["Whether arginine depletion is a direct consequence of biliverdin accumulation or an independent effect is unknown","Mechanism linking ABCB10 loss to amino acid transporter changes unresolved"]},{"year":2024,"claim":"Cardiomyocyte-specific ABCB10 deletion causing lysosomal iron accumulation and ferroptosis extended the gene's protective role to cardiac tissue and linked it mechanistically to lysosomal integrity.","evidence":"Cardiomyocyte-specific Abcb10 KO mouse, iron chelator rescue, lipid peroxide and lysosomal morphology analysis","pmids":["38655715"],"confidence":"Medium","gaps":["How mitochondrial biliverdin export prevents lysosomal iron accumulation is mechanistically unclear","Not independently replicated"]},{"year":2025,"claim":"Identifying transmembrane arginines R232 and R295 as required for biliverdin-stimulated ATPase activity and conformational change provided the first residue-level understanding of substrate recognition in the transport cycle.","evidence":"Site-directed mutagenesis, ATPase assays with biliverdin analogs, LRET conformational monitoring","pmids":["41229075"],"confidence":"High","gaps":["No substrate-bound structure to confirm direct contact with R232/R295","Full transport cycle conformational dynamics not yet captured"]},{"year":null,"claim":"A substrate-bound structure of ABCB10, the complete transport cycle mechanism for biliverdin, and whether ABCB10 transports additional substrates remain unresolved.","evidence":"","pmids":[],"confidence":"High","gaps":["No cryo-EM or crystal structure with biliverdin bound","Whether cardiolipin regulation and glutathione redox sensing converge on a single conformational switch is unknown","Mechanism linking biliverdin accumulation to arginine depletion and ATF4 activation uncharacterized"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140657","term_label":"ATP-dependent activity","supporting_discovery_ids":[6,7,9,10,21]},{"term_id":"GO:0005215","term_label":"transporter activity","supporting_discovery_ids":[8,21]}],"localization":[{"term_id":"GO:0005739","term_label":"mitochondrion","supporting_discovery_ids":[0,1,2,5,8]}],"pathway":[{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[2,3,7,8]},{"term_id":"R-HSA-382551","term_label":"Transport of small molecules","supporting_discovery_ids":[8,21]},{"term_id":"R-HSA-8953897","term_label":"Cellular responses to stimuli","supporting_discovery_ids":[5,14,19]}],"complexes":["Mitoferrin-1–ABCB10–ferrochelatase–ABCB7 complex"],"partners":["SLC25A37","FECH","ABCB7"],"other_free_text":[]},"mechanistic_narrative":"ABCB10 is a homodimeric ATP-binding cassette transporter of the mitochondrial inner membrane that exports biliverdin to the cytosol and coordinates heme biosynthesis with mitochondrial iron import in erythroid and other cell types. Reconstitution in liposomes directly demonstrated biliverdin transport, and ABCB10 deletion causes mitochondrial biliverdin accumulation; in the cytosol, biliverdin is reduced to bilirubin, which acts as an antioxidant and modulates signaling through PTP1B inactivation and H₂O₂ scavenging [PMID:34011630, PMID:34823065]. ABCB10 physically associates with mitoferrin-1 and ferrochelatase in an oligomeric complex that couples mitochondrial iron uptake to heme synthesis, and its ATPase activity—stimulated by zinc-mesoporphyrin and biliverdin via conserved transmembrane arginines R232/R295, and regulated by cardiolipin binding and glutathione redox status—is essential for erythroid hemoglobinization [PMID:19805291, PMID:30765471, PMID:41229075, PMID:37807693, PMID:28808058]. Germline ABCB10 knockout causes embryonic lethality at E12.5 from failed primitive erythropoiesis driven by mitochondrial oxidative stress, and tissue-specific deletions reveal protective roles against ferroptosis in cardiomyocytes, metabolic dysfunction in hepatocytes and pancreatic β-cells, and impaired CD4⁺ T cell activation [PMID:22240895, PMID:38655715, PMID:34893527]."},"prefetch_data":{"uniprot":{"accession":"Q9NRK6","full_name":"ATP-binding cassette sub-family B member 10, mitochondrial","aliases":["ABC-mitochondrial erythroid protein","ABC-me protein","ATP-binding cassette transporter 10","ABC transporter 10 protein","Mitochondrial ATP-binding cassette 2","M-ABC2"],"length_aa":738,"mass_kda":79.1,"function":"ATP-dependent transporter located in the mitochondrial inner membrane that catalyzes the export of biliverdin from the mitochondrial matrix, and plays a crucial role in hemoglobin synthesis and antioxidative stress (PubMed:22085049, PubMed:28315685, PubMed:28808058, PubMed:34011630, PubMed:37041204). Participates in the early step of the heme biosynthetic process during insertion of iron into protoporphyrin IX (PPIX) (PubMed:22085049, PubMed:28808058). Involved in the stabilization of the iron transporter mitoferrin-1/SLC25A37 (By similarity). In addition may be involved in mitochondrial unfolded protein response (UPRmt) signaling pathway, although ABCB10 probably does not participate in peptide export from mitochondria (PubMed:28315685)","subcellular_location":"Mitochondrion inner membrane","url":"https://www.uniprot.org/uniprotkb/Q9NRK6/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/ABCB10","classification":"Not Classified","n_dependent_lines":137,"n_total_lines":1208,"dependency_fraction":0.11341059602649006},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/ABCB10","total_profiled":1310},"omim":[{"mim_id":"610387","title":"SOLUTE CARRIER FAMILY 25 (MITOCHONDRIAL IRON CARRIER), MEMBER 37; SLC25A37","url":"https://www.omim.org/entry/610387"},{"mim_id":"605454","title":"ATP-BINDING CASSETTE, SUBFAMILY B, MEMBER 10; ABCB10","url":"https://www.omim.org/entry/605454"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in all","driving_tissues":[{"tissue":"bone marrow","ntpm":56.7}],"url":"https://www.proteinatlas.org/search/ABCB10"},"hgnc":{"alias_symbol":["EST20237","M-ABC2","MTABC2"],"prev_symbol":[]},"alphafold":{"accession":"Q9NRK6","domains":[{"cath_id":"1.20.1560.10","chopping":"155-312_460-475","consensus_level":"medium","plddt":94.4132,"start":155,"end":475},{"cath_id":"3.40.50.300","chopping":"493-738","consensus_level":"medium","plddt":91.2014,"start":493,"end":738},{"cath_id":"1.10.287","chopping":"313-426","consensus_level":"medium","plddt":96.0382,"start":313,"end":426}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9NRK6","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9NRK6-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9NRK6-F1-predicted_aligned_error_v6.png","plddt_mean":80.69},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=ABCB10","jax_strain_url":"https://www.jax.org/strain/search?query=ABCB10"},"sequence":{"accession":"Q9NRK6","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9NRK6.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9NRK6/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9NRK6"}},"corpus_meta":[{"pmid":"28744405","id":"PMC_28744405","title":"Circular RNA circ-ABCB10 promotes breast cancer proliferation and progression through sponging miR-1271.","date":"2017","source":"American journal of cancer research","url":"https://pubmed.ncbi.nlm.nih.gov/28744405","citation_count":305,"is_preprint":false},{"pmid":"23716676","id":"PMC_23716676","title":"Structures of ABCB10, a human ATP-binding cassette transporter in apo- and nucleotide-bound states.","date":"2013","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/23716676","citation_count":191,"is_preprint":false},{"pmid":"19805291","id":"PMC_19805291","title":"Abcb10 physically interacts with mitoferrin-1 (Slc25a37) to enhance its stability and function in the erythroid mitochondria.","date":"2009","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/19805291","citation_count":169,"is_preprint":false},{"pmid":"20427704","id":"PMC_20427704","title":"Ferrochelatase forms an oligomeric complex with mitoferrin-1 and Abcb10 for erythroid heme biosynthesis.","date":"2010","source":"Blood","url":"https://pubmed.ncbi.nlm.nih.gov/20427704","citation_count":128,"is_preprint":false},{"pmid":"32273769","id":"PMC_32273769","title":"Circ-ABCB10 Contributes to Paclitaxel Resistance in Breast Cancer Through Let-7a-5p/DUSP7 Axis.","date":"2020","source":"Cancer management and research","url":"https://pubmed.ncbi.nlm.nih.gov/32273769","citation_count":79,"is_preprint":false},{"pmid":"22884976","id":"PMC_22884976","title":"Mitochondrial ABC transporters function: the role of ABCB10 (ABC-me) as a novel player in cellular handling of reactive oxygen species.","date":"2012","source":"Biochimica et biophysica 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to assist substrate entry into the binding cavity.\",\n      \"method\": \"X-ray crystallography with functional structural analysis; multiple ABCB10/ATP-analog complexes\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — multiple crystal structures with nucleotide-bound complexes, rigorous structural validation\",\n      \"pmids\": [\"23716676\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"ABCB10 contains an unusually long 105-amino acid mitochondrial targeting presequence (mTP); the central subdomain (aa 36-70) is sufficient for mitochondrial import, while the N-terminal subdomain participates in proper inner membrane import. Hydrophobic character of the mTP is required (L46Q/I47Q mutation greatly diminishes targeting). ABCB10 homodimerizes and homo-oligomerizes in the mitochondrial inner membrane as shown by mass spectrometry of chemically cross-linked immunoprecipitated protein.\",\n      \"method\": \"Mutagenesis of targeting sequence, subcellular fractionation/live imaging, mass spectrometry of cross-linked immunoprecipitated protein\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — mutagenesis plus MS validation, multiple orthogonal methods in one study\",\n      \"pmids\": [\"15215243\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"ABCB10 physically interacts with mitoferrin-1 (Mfrn1/Slc25a37) in the mitochondrial inner membrane of erythroid cells, and this interaction stabilizes Mfrn1 protein, thereby enhancing Mfrn1-dependent mitochondrial iron importation. The binding domain maps to the N-terminus of Mfrn1.\",\n      \"method\": \"In vivo epitope-tagging affinity purification and mass spectrometry, co-immunoprecipitation/Western blot, transfection in heterologous COS7 cells, protein half-life assays\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP, MS, functional iron import assay, replicated in multiple cell types\",\n      \"pmids\": [\"19805291\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Ferrochelatase (Fech), the terminal heme synthesis enzyme, forms an oligomeric complex with both mitoferrin-1 (Mfrn1) and ABCB10 in erythroid cells, physically integrating mitochondrial iron importation and heme biosynthesis.\",\n      \"method\": \"Affinity purification and mass spectrometry from stable MEL cell clones, immunoprecipitation/Western blot with endogenous and heterologous proteins in MEL and HEK293 cells\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP with endogenous proteins plus MS, confirmed in two cell systems\",\n      \"pmids\": [\"20427704\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Dimeric ferrochelatase bridges ABCB7 and ABCB10 homodimers in an architecturally defined multiprotein complex required for heme biosynthesis; the interaction interfaces were mapped by chemical cross-linking, tandem mass spectrometry, and mutational analyses, with ferrochelatase binding near the nucleotide-binding domains of each ABC transporter.\",\n      \"method\": \"Chemical cross-linking, tandem mass spectrometry, mutational analysis, inducible knockdown cell lines\",\n      \"journal\": \"Haematologica\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — cross-linking MS with mutational validation, interface mapping\",\n      \"pmids\": [\"30765471\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"ABC-me/ABCB10 is essential for erythropoiesis in vivo: ABCB10-knockout mice die at embryonic day 12.5 with near-complete loss of primitive erythropoiesis; knockout erythroid precursors show increased mitochondrial superoxide production and protein carbonylation, and treatment with the SOD2 mimetic MnTBAP rescues survival and differentiation, placing ABCB10 upstream of oxidative stress-mediated apoptosis in erythroid development.\",\n      \"method\": \"Germline knockout mouse, in vivo and ex vivo erythroid differentiation assays, mitochondrial ROS measurement, antioxidant rescue experiments\",\n      \"journal\": \"Cell death and differentiation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean KO with specific phenotypic readout and mechanistic rescue, strong evidence\",\n      \"pmids\": [\"22240895\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Gly497 and Lys498 (Walker A), Glu624 (Walker B), and Gly602 (C-loop) in ABCB10 are required for proper ATP binding and hydrolysis. Oxidized glutathione (GSSG) stimulates ABCB10 ATPase activity without affecting ATP binding, while reduced glutathione (GSH) inhibits both ATP binding and hydrolysis; ABCB10 is glutathionylated at Cys547. Delta-aminolevulinic acid (dALA) does not alter ATP binding, excluding it as a direct substrate.\",\n      \"method\": \"8-azido-ATP photolabeling, site-directed mutagenesis, in vitro ATPase assays, mass spectrometry identification of glutathionylation site\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro ATPase assay with mutagenesis and MS identification of modification site\",\n      \"pmids\": [\"26053025\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"ATPase activity of ABCB10 is necessary for hemoglobinization in erythroid MEL cells. Reduced ABCB10 does not cause protoporphyrin IX accumulation and does not affect ALA export from mitochondria, ruling out ALA as a transported substrate. ABCB10 silencing alters the heme biosynthesis transcriptional profile via Bach1-mediated repression, which can be partially rescued by overexpression of Alas2 or Gata1.\",\n      \"method\": \"shRNA knockdown in MEL cells, ATPase activity assays, succinylacetone inhibition of ALAD, metabolite measurements, transcriptional profiling, rescue experiments\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple orthogonal functional assays, mechanistic pathway placement via epistasis\",\n      \"pmids\": [\"28808058\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"ABCB10 is a mitochondrial biliverdin exporter: ABCB10 reconstituted into liposomes transports biliverdin, and ABCB10 deletion causes accumulation of biliverdin inside mitochondria. In obese mice, ABCB10-driven biliverdin export amplifies cytosolic bilirubin content, which inactivates PTP1B and elevates SREBP-1c, exacerbating insulin resistance and steatosis; restoration of cellular bilirubin in ABCB10 KO hepatocytes reverses improvements in mitochondrial function and PTP1B inactivation.\",\n      \"method\": \"Reconstitution of ABCB10 in liposomes with transport assay, ABCB10 hepatocyte-specific KO mice, metabolite measurements, rescue with bilirubin treatment\",\n      \"journal\": \"Science translational medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct reconstituted transport assay, KO mouse with mechanistic rescue, multiple orthogonal methods\",\n      \"pmids\": [\"34011630\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Zinc-mesoporphyrin stimulates ABCB10 ATPase activity (~70% increase) in purified ABCB10 reconstituted in lipid nanodiscs; this stimulation is specific to ABCB10 (not a bacterial ABC transporter control) and does not require typical heme regulatory motifs (cysteine-less ABCB10 also responds). Delta-aminolevulinic acid and glutathione do not activate ABCB10, further excluding them as direct substrates.\",\n      \"method\": \"Purified ABCB10 reconstituted in nanodiscs, in vitro ATPase assays with heme analogs and precursors\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstituted in vitro ATPase assay with multiple control compounds\",\n      \"pmids\": [\"33253225\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"ABCB10 binds cardiolipin with significantly higher affinity than other phospholipids, with the first three cardiolipin binding events showing positive cooperativity suggestive of specific binding sites; cardiolipin regulates ABCB10 ATPase activity in a dose-dependent fashion.\",\n      \"method\": \"Native mass spectrometry for lipid binding, in vitro ATPase assays with various phospholipids\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — native MS binding quantification combined with functional ATPase assay\",\n      \"pmids\": [\"37807693\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"ABCB10 expression is regulated by the transcription factor Nrf2 in blood-brain barrier endothelial cells: Nrf2 silencing suppresses ABCB10 protein, while Nrf2 activation by sulforaphane upregulates ABCB10. Conversely, ABCB10 knockdown induces Nrf2-driven antioxidant responses and elevates endothelial-monocyte adhesion.\",\n      \"method\": \"siRNA knockdown of Nrf2 and ABCB10 in human BBB endothelial cells, Western blot, sulforaphane treatment\",\n      \"journal\": \"Neuroscience letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — single lab, siRNA experiments with functional readouts but no in vitro reconstitution\",\n      \"pmids\": [\"28572033\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"ABCB10 transcription is regulated by E2F transcription factors: E2F2, E2F3, and E2F4 activate transcription from the ABCB10 promoter; E2F4 directly binds to ABCB10 promoter sites (confirmed by EMSA and ChIP), and silencing E2F factors reduces basal ABCB10 expression.\",\n      \"method\": \"Promoter cloning, luciferase reporter assay, EMSA, ChIP, siRNA knockdown of E2F factors\",\n      \"journal\": \"Genomics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — EMSA and ChIP confirm direct binding, functional reporter assays, single lab\",\n      \"pmids\": [\"25220178\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Mutant huntingtin (mtHtt) inhibits the mitochondrial unfolded protein response (UPRmt) by impairing ABCB10 mRNA stability; ABCB10 depletion reduces UPRmt markers HSP60, Clpp, and CHOP, and increases mitochondrial ROS and cell death, while ABCB10 overexpression rescues these phenotypes.\",\n      \"method\": \"HD mouse striatal cells and patient fibroblasts, siRNA knockdown, overexpression, mRNA stability assays, ROS measurement, Western blot\",\n      \"journal\": \"Biochimica et biophysica acta. Molecular basis of disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — multiple cell models with gain/loss of function but no in vitro reconstitution of mRNA stability mechanism\",\n      \"pmids\": [\"30802639\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"ABCB10 depletion in HepG2 cells upregulates ROS and ROS-detoxifying enzymes (SOD2, GSTA1, GSTA2, SESN3) and significantly decreases expression of UPRmt-related mitochondrial chaperones (HSPD1, DNAJA3) and protease LONP1, supporting a role for ABCB10 in UPRmt signaling similar to C. elegans HAF-1.\",\n      \"method\": \"siRNA knockdown in HepG2 cells, Western blot, ROS measurement, qPCR\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — single lab, single method category, no in vitro reconstitution\",\n      \"pmids\": [\"28315685\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Loss of Abcb10 in erythroid cells causes decreased cellular arginine levels, altered expression of amino acid transporters, and activation of the ATF4 nutrient stress pathway (increased eIF2α phosphorylation, upregulated ATF4 and targets CHOP, Chac1, Rars), with arginine supplementation improving proliferation and hemoglobinization in Abcb10-null cells.\",\n      \"method\": \"CRISPR/Cas9 deletion in MEL and K562 cells, metabolomic and transcriptional analyses, arginine supplementation rescue\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — metabolomics plus transcriptomics plus functional rescue in two cell lines\",\n      \"pmids\": [\"37269954\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"ABCB10 loss in CD4+ T cells impairs specific cytokine expression upon activation, reduces CD4+ cell numbers and Ag-specific memory formation in vivo, and disrupts the switch to aerobic glycolysis upon activation in Jurkat T cells; CD8+ T cells are less affected, indicating a cell-type-selective metabolic role.\",\n      \"method\": \"Conditional Abcb10 KO mice, in vivo viral infection model, CRISPR KO in Jurkat cells, cytokine assays, metabolic profiling\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — KO mouse plus CRISPR in human cells with mechanistic metabolic readout, single lab\",\n      \"pmids\": [\"34893527\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Cardiomyocyte-specific deletion of Abcb10 causes progressive cardiac fibrosis and mitochondrial structural abnormalities, leading to lysosomal dysfunction (decreased NAD+ levels, Hif1α upregulation), accumulation of Fe2+ and lipid peroxides in lysosomes, and ferroptosis; iron chelator treatment suppresses lipid peroxidation, implicating lysosomal iron accumulation as the mechanistic driver.\",\n      \"method\": \"Cardiomyocyte-specific Abcb10 KO mouse, ABCB10 knockdown in HeLa cells, iron chelator treatment, ROS and lipid peroxide measurement, lysosomal morphology analysis\",\n      \"journal\": \"Bioscience reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — conditional KO plus cell line KD with mechanistic rescue, single lab\",\n      \"pmids\": [\"38655715\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Induced deletion of Abcb10 in adult mouse hematopoietic stem cells (HSCs) causes increased erythroid progenitor numbers and decreased HSC number; Abcb10-deficient HSCs show excess mitochondrial iron accumulation and oxidative stress, with a skew toward erythroid-lineage differentiation, but no alteration in mitochondrial bioenergetic function.\",\n      \"method\": \"Inducible Abcb10 KO in adult mice, flow cytometry of bone marrow progenitors, mitochondrial iron and ROS measurement, in vivo iron chelator and antioxidant treatment\",\n      \"journal\": \"Experimental hematology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — conditional KO with specific cellular phenotype and mechanistic measurement, single lab\",\n      \"pmids\": [\"38493949\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Hepatocyte-specific ABCB10 gain-of-function in mice with alcoholic hepatitis increases the mitochondrial GSH/GSSG ratio and decreases hepatic 4-HNE protein adducts, reducing MPO gene expression and histone H3 citrullination (NET formation marker), demonstrating that ABCB10-mediated ROS reduction in hepatocytes mitigates neutrophilic inflammation.\",\n      \"method\": \"Hepatocyte-specific ABCB10 overexpression in alcoholic hepatitis mouse model, redox assays, MPO/NET markers, GSH/GSSG ratio\",\n      \"journal\": \"Redox biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — gain-of-function in vivo with mechanistic redox readouts, single lab\",\n      \"pmids\": [\"38290384\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Beta-cell-specific deletion of Abcb10 protects mice from high-fat diet-induced hyperinsulinemia and insulin resistance by limiting beta-cell expansion; ABCB10 activity limits glucose-stimulated insulin secretion (GSIS) and H2O2-mediated signaling, and bilirubin treatment of ABCB10 KO islets reverses increased H2O2 and GSIS, placing bilirubin as the effector downstream of ABCB10.\",\n      \"method\": \"Beta-cell-specific Abcb10 KO mouse (Ins1Cre-Abcb10flox/flox), GSIS assays, H2O2 measurement, bilirubin rescue in isolated islets\",\n      \"journal\": \"Molecular metabolism\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — conditional KO with mechanistic bilirubin rescue in islets, single lab\",\n      \"pmids\": [\"34823065\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Conserved transmembrane arginine residues R232 and R295 of ABCB10 are required for biliverdin-stimulated ATPase activity; mutation of these residues decreases stimulation by biliverdin and alters conformational equilibrium detected by LRET. Biliverdin dimethyl ester does not stimulate (and mesobiliverdin inhibits) ABCB10 ATPase, indicating specific complementarity between biliverdin functional groups and the substrate binding pocket. GDN detergent abolishes biliverdin-induced stimulation, suggesting it interferes with substrate binding.\",\n      \"method\": \"Site-directed mutagenesis of transmembrane arginines, in vitro ATPase assay with biliverdin analogs, Luminescence Resonance Energy Transfer (LRET) conformational assay\",\n      \"journal\": \"Protein science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro ATPase assay with mutagenesis and conformational probe, multiple substrate analogs tested\",\n      \"pmids\": [\"41229075\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"ABCB10 is a homodimeric ATP-binding cassette transporter embedded in the mitochondrial inner membrane that exports biliverdin to the cytosol (directly demonstrated by liposome reconstitution), where it is reduced to the ROS-scavenger bilirubin; it physically interacts with mitoferrin-1 and ferrochelatase to form a multiprotein complex that coordinates iron import and heme biosynthesis in erythroid cells, with its ATPase activity (regulated by cardiolipin, glutathione redox status, and conserved transmembrane arginines) being essential for hemoglobinization and protection against mitochondrial oxidative stress.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"ABCB10 is a homodimeric ATP-binding cassette transporter of the mitochondrial inner membrane that exports biliverdin to the cytosol and coordinates heme biosynthesis with mitochondrial iron import in erythroid and other cell types. Reconstitution in liposomes directly demonstrated biliverdin transport, and ABCB10 deletion causes mitochondrial biliverdin accumulation; in the cytosol, biliverdin is reduced to bilirubin, which acts as an antioxidant and modulates signaling through PTP1B inactivation and H₂O₂ scavenging [PMID:34011630, PMID:34823065]. ABCB10 physically associates with mitoferrin-1 and ferrochelatase in an oligomeric complex that couples mitochondrial iron uptake to heme synthesis, and its ATPase activity—stimulated by zinc-mesoporphyrin and biliverdin via conserved transmembrane arginines R232/R295, and regulated by cardiolipin binding and glutathione redox status—is essential for erythroid hemoglobinization [PMID:19805291, PMID:30765471, PMID:41229075, PMID:37807693, PMID:28808058]. Germline ABCB10 knockout causes embryonic lethality at E12.5 from failed primitive erythropoiesis driven by mitochondrial oxidative stress, and tissue-specific deletions reveal protective roles against ferroptosis in cardiomyocytes, metabolic dysfunction in hepatocytes and pancreatic β-cells, and impaired CD4⁺ T cell activation [PMID:22240895, PMID:38655715, PMID:34893527].\",\n  \"teleology\": [\n    {\n      \"year\": 2004,\n      \"claim\": \"Establishing that ABCB10 is a mitochondrial inner-membrane homodimer resolved its subcellular location and oligomeric state, key prerequisites for understanding its transport function.\",\n      \"evidence\": \"Mutagenesis of the 105-aa mitochondrial targeting presequence, subcellular fractionation, and chemical cross-linking/mass spectrometry in mammalian cells\",\n      \"pmids\": [\"15215243\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Substrate identity unknown at this point\", \"No functional transport assay performed\", \"Mechanism of homodimerization interface unresolved\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Identifying ABCB10 as a physical partner of mitoferrin-1 that stabilizes the iron importer linked ABCB10 to mitochondrial iron homeostasis and heme biosynthesis for the first time.\",\n      \"evidence\": \"Reciprocal co-immunoprecipitation and mass spectrometry in erythroid and COS7 cells, protein half-life measurements\",\n      \"pmids\": [\"19805291\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether ABCB10 ATPase activity is required for mitoferrin-1 stabilization was untested\", \"No structural details of the interaction interface\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Demonstrating that ferrochelatase joins the ABCB10–mitoferrin-1 complex expanded the model to a multiprotein assembly that physically couples iron import to protoporphyrin metallation.\",\n      \"evidence\": \"Affinity purification/MS and co-IP with endogenous proteins in MEL and HEK293 cells\",\n      \"pmids\": [\"20427704\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Stoichiometry and architecture of the complex unknown\", \"Whether complex formation is regulated during differentiation untested\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"ABCB10 knockout mice dying at E12.5 with severe oxidative stress in erythroid precursors—rescued by a SOD2 mimetic—established ABCB10 as essential for erythropoiesis and placed it upstream of mitochondrial ROS.\",\n      \"evidence\": \"Germline Abcb10 KO mouse, ex vivo erythroid differentiation, mitochondrial superoxide measurement, MnTBAP rescue\",\n      \"pmids\": [\"22240895\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Transported substrate still unidentified\", \"Whether the ROS phenotype reflects loss of heme synthesis vs. loss of a separate antioxidant mechanism was unresolved\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Crystal structures in apo and nucleotide-bound states revealed an exporter fold with an unusual open-inward conformation even with ATP analogs, informing how substrate enters through a lateral portal.\",\n      \"evidence\": \"X-ray crystallography of multiple ABCB10–nucleotide-analog complexes\",\n      \"pmids\": [\"23716676\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No substrate-bound structure obtained\", \"Portal-mediated entry remained a proposal without mutagenesis validation at this stage\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Identifying Walker A/B and C-loop residues required for ATPase activity, and showing redox regulation via glutathionylation at Cys547, connected ABCB10's catalytic cycle to mitochondrial redox state while excluding δ-ALA as a substrate.\",\n      \"evidence\": \"Site-directed mutagenesis, 8-azido-ATP photolabeling, ATPase assays, MS identification of glutathionylation\",\n      \"pmids\": [\"26053025\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"True transported substrate still unidentified\", \"Physiological significance of GSSG stimulation not tested in cells\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Showing that ABCB10 ATPase activity is required for hemoglobinization and that neither ALA nor protoporphyrin IX accumulates upon ABCB10 loss narrowed the substrate search and revealed downstream Bach1-mediated transcriptional consequences.\",\n      \"evidence\": \"shRNA knockdown in MEL cells, ATPase assays, metabolite quantification, transcriptional profiling with epistasis rescue\",\n      \"pmids\": [\"28808058\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Substrate identity still unknown\", \"Whether Bach1 derepression is a direct or indirect effect of ABCB10 loss undetermined\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Mapping the ferrochelatase-bridged ABCB10–ABCB7 complex architecture showed that ferrochelatase contacts the nucleotide-binding domains of both transporters, suggesting coordinated regulation of two ABC transporters at the heme synthesis step.\",\n      \"evidence\": \"Chemical cross-linking/tandem MS and mutational analysis in inducible knockdown cell lines\",\n      \"pmids\": [\"30765471\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional consequence of disrupting the ABCB10–ABCB7 bridge not fully characterized\", \"Whether the complex exists in non-erythroid tissues unknown\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Zinc-mesoporphyrin specifically stimulating ABCB10 ATPase in nanodiscs, while ALA and glutathione did not, provided the first biochemical evidence that a porphyrin-related molecule interacts with the substrate-binding site.\",\n      \"evidence\": \"Purified ABCB10 in lipid nanodiscs, ATPase assays with heme analogs and precursors\",\n      \"pmids\": [\"33253225\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct transport of the stimulating compound not shown\", \"Identity of the physiological substrate not conclusively established\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Reconstitution of ABCB10 in liposomes directly demonstrated biliverdin transport, and hepatocyte-specific KO showed mitochondrial biliverdin accumulation, definitively identifying the transported substrate after over a decade of investigation.\",\n      \"evidence\": \"Liposome reconstitution transport assay, hepatocyte-specific Abcb10 KO mice, metabolite measurements, bilirubin rescue\",\n      \"pmids\": [\"34011630\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether biliverdin is the sole substrate or one of several remains open\", \"Structural basis of biliverdin recognition unknown\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"β-cell-specific ABCB10 deletion revealed that exported biliverdin/bilirubin modulates glucose-stimulated insulin secretion via H₂O₂ scavenging, extending ABCB10 function beyond erythropoiesis to metabolic signaling.\",\n      \"evidence\": \"Ins1Cre-Abcb10 KO mouse, GSIS assays, H₂O₂ measurement, bilirubin rescue in isolated islets\",\n      \"pmids\": [\"34823065\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab finding not independently replicated\", \"Relative contribution of biliverdin export vs. other ABCB10 functions in β-cells not dissected\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Demonstrating cooperative, high-affinity cardiolipin binding that regulates ATPase activity identified a lipid-based regulatory mechanism consistent with ABCB10's mitochondrial inner-membrane localization.\",\n      \"evidence\": \"Native mass spectrometry quantification of lipid binding, in vitro ATPase assays with various phospholipids\",\n      \"pmids\": [\"37807693\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Cardiolipin binding sites not structurally mapped\", \"Whether cardiolipin modulates biliverdin transport rates untested\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"ABCB10 deletion in erythroid cells causes arginine depletion and ATF4 nutrient-stress activation, revealing an unexpected metabolic consequence that contributes to the hemoglobinization defect.\",\n      \"evidence\": \"CRISPR KO in MEL and K562 cells, metabolomics, transcriptomics, arginine supplementation rescue\",\n      \"pmids\": [\"37269954\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether arginine depletion is a direct consequence of biliverdin accumulation or an independent effect is unknown\", \"Mechanism linking ABCB10 loss to amino acid transporter changes unresolved\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Cardiomyocyte-specific ABCB10 deletion causing lysosomal iron accumulation and ferroptosis extended the gene's protective role to cardiac tissue and linked it mechanistically to lysosomal integrity.\",\n      \"evidence\": \"Cardiomyocyte-specific Abcb10 KO mouse, iron chelator rescue, lipid peroxide and lysosomal morphology analysis\",\n      \"pmids\": [\"38655715\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"How mitochondrial biliverdin export prevents lysosomal iron accumulation is mechanistically unclear\", \"Not independently replicated\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Identifying transmembrane arginines R232 and R295 as required for biliverdin-stimulated ATPase activity and conformational change provided the first residue-level understanding of substrate recognition in the transport cycle.\",\n      \"evidence\": \"Site-directed mutagenesis, ATPase assays with biliverdin analogs, LRET conformational monitoring\",\n      \"pmids\": [\"41229075\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No substrate-bound structure to confirm direct contact with R232/R295\", \"Full transport cycle conformational dynamics not yet captured\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"A substrate-bound structure of ABCB10, the complete transport cycle mechanism for biliverdin, and whether ABCB10 transports additional substrates remain unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No cryo-EM or crystal structure with biliverdin bound\", \"Whether cardiolipin regulation and glutathione redox sensing converge on a single conformational switch is unknown\", \"Mechanism linking biliverdin accumulation to arginine depletion and ATF4 activation uncharacterized\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140657\", \"supporting_discovery_ids\": [6, 7, 9, 10, 21]},\n      {\"term_id\": \"GO:0005215\", \"supporting_discovery_ids\": [8, 21]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005739\", \"supporting_discovery_ids\": [0, 1, 2, 5, 8]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [2, 3, 7, 8]},\n      {\"term_id\": \"R-HSA-382551\", \"supporting_discovery_ids\": [8, 21]},\n      {\"term_id\": \"R-HSA-8953897\", \"supporting_discovery_ids\": [5, 14, 19]}\n    ],\n    \"complexes\": [\n      \"Mitoferrin-1–ABCB10–ferrochelatase–ABCB7 complex\"\n    ],\n    \"partners\": [\n      \"SLC25A37\",\n      \"FECH\",\n      \"ABCB7\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}