{"gene":"ABCB7","run_date":"2026-04-28T17:12:36","timeline":{"discoveries":[{"year":1997,"finding":"Yeast Atm1p (ABCB7 ortholog) localizes to the mitochondrial inner membrane and is required for mitochondrial iron homeostasis; deletion causes 30-fold accumulation of mitochondrial free iron, loss of heme-containing protein holoforms, and hypersensitivity to oxidative stress despite normal heme synthesis and transport.","method":"ATM1 gene disruption in yeast, cytochrome analysis, iron quantification, glutathione measurement, oxidative stress assays","journal":"FEBS letters","confidence":"High","confidence_rationale":"Tier 2 — clean KO with multiple orthogonal phenotypic readouts, foundational paper >200 citations","pmids":["9428742"],"is_preprint":false},{"year":1999,"finding":"Mitochondrial Atm1p (ABCB7 ortholog) performs an essential function specifically in the export of Fe/S cluster precursors from the mitochondrial matrix to the cytosol, enabling biogenesis of cytosolic Fe/S proteins; the matrix-localized cysteine desulfurase Nfs1p initiates this pathway by producing elemental sulfur.","method":"Yeast deletion mutants (Δatm1, Δnfs1), genetic complementation, Fe/S protein activity assays in mitochondrial and cytosolic fractions","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 2 — epistasis and compartment-specific Fe/S protein assays, replicated foundational paper >500 citations","pmids":["10406803"],"is_preprint":false},{"year":1998,"finding":"Human ABC7 (ABCB7) protein localizes to mitochondria and functionally complements yeast Δatm1 cells, restoring normal cytochrome levels, mitochondrial iron content, and glutathione levels, establishing it as the functional ortholog of yeast Atm1p.","method":"Immunostaining with specific antibody, yeast complementation assay, cytochrome analysis, iron and glutathione measurements","journal":"FEBS letters","confidence":"High","confidence_rationale":"Tier 2 — direct localization experiment with functional complementation, multiple orthogonal readouts","pmids":["9883897"],"is_preprint":false},{"year":1999,"finding":"A missense mutation I400M in the ABC7 gene (ABCB7), located in a predicted transmembrane segment, causes X-linked sideroblastic anemia with ataxia (XLSA/A); the corresponding mutation introduced into yeast ATM1 causes partial loss of function, and human wild-type ABC7 complements ATM1 deletion.","method":"Patient mutation screening, yeast complementation with wild-type and mutant protein, disease segregation analysis","journal":"Human molecular genetics","confidence":"High","confidence_rationale":"Tier 2 — disease mutation functionally validated by yeast complementation and loss-of-function assay","pmids":["10196363"],"is_preprint":false},{"year":2000,"finding":"A glutamate-to-lysine charge inversion mutation at residue E433 (E433K) of ABCB7 causes XLSA/A by impairing cytosolic Fe/S protein maturation; wild-type ABCB7 almost fully complements Δatm1 yeast, whereas E433K mutant protein has markedly reduced ability to support cytosolic Fe/S assembly.","method":"Patient mutation identification (G→A at nt 1305), yeast complementation of Δatm1 cells with wild-type vs. mutant ABCB7, Fe/S protein activity assays","journal":"Blood","confidence":"High","confidence_rationale":"Tier 1 — active-site/disease mutation with functional assay in orthologous system, multiple orthogonal methods","pmids":["11050011"],"is_preprint":false},{"year":2002,"finding":"ABCB7 physically interacts with the C-terminal iron-sulfur cluster-containing region of ferrochelatase (the last enzyme in heme biosynthesis); ABCB7 colocalizes with ferrochelatase in mitochondria, and its overexpression increases ferrochelatase activity and promotes heme production during erythroid differentiation.","method":"In vitro and in vivo pull-down assays, immunostaining colocalization, antisense oligonucleotide knockdown of heme measurement, stable overexpression in MEL cells","journal":"Blood","confidence":"High","confidence_rationale":"Tier 1–2 — reciprocal pull-down (in vitro and in vivo) plus functional rescue, replicated across multiple cell systems","pmids":["12480705"],"is_preprint":false},{"year":2004,"finding":"Atm1p (ABCB7 ortholog) functions as a homodimer; conserved Walker A and B motif residues required for ATP binding and hydrolysis are essential for Atm1p function, and ATP binding is important for homodimerization.","method":"In vivo yeast mutagenesis of Walker A/B motifs, dimerization analysis","journal":"FEBS letters","confidence":"Medium","confidence_rationale":"Tier 2 — mutagenesis with functional and dimerization readouts, single lab","pmids":["15225610"],"is_preprint":false},{"year":2006,"finding":"Mouse Abcb7 is essential in extra-embryonic tissues and in numerous cell types; conditional hepatic deletion impairs cytosolic Fe/S cluster assembly, causing loss of IRP1 regulation, dysregulation of iron regulatory protein 1 activity, and hepatocyte iron metabolic disturbance without lethality.","method":"Inducible Cre/loxP deletion of Abcb7 exons 9–10, X-chromosome inactivation assays, tissue-specific deletions, IRP1 activity assay, iron metabolism studies","journal":"Human molecular genetics","confidence":"High","confidence_rationale":"Tier 2 — conditional KO with multiple defined cellular and molecular phenotypes, replicated across tissues","pmids":["16467350"],"is_preprint":false},{"year":2006,"finding":"siRNA silencing of ABCB7 in HeLa cells causes ~6-fold mitochondrial iron accumulation, reduced cytosolic aconitase (IRP1) activity, increased protoporphyrin IX, and reduced mitochondrial superoxide dismutase 2 activity, supporting a role for ABCB7 in transferring iron from mitochondria to cytosol and maturing cytosolic Fe/S enzymes.","method":"Sequential siRNA transfection, iron quantification (mitochondrial fractionation), aconitase activity assay, SOD2 activity assay, H2O2 sensitivity assay","journal":"Blood","confidence":"High","confidence_rationale":"Tier 2 — knockdown with multiple orthogonal biochemical readouts","pmids":["17192393"],"is_preprint":false},{"year":2006,"finding":"Abcb7 is essential for hematopoiesis; partial loss-of-function mutations directly or indirectly inhibit heme biosynthesis, causing the sideroblastic anemia phenotype of XLSA/A.","method":"Conditional Abcb7 deletion in hematopoietic cells (mouse model), heme biosynthesis assays","journal":"Blood","confidence":"High","confidence_rationale":"Tier 2 — tissue-specific KO with defined hematopoietic phenotype","pmids":["17192398"],"is_preprint":false},{"year":2006,"finding":"Purified Atm1p (ABCB7 ortholog) reconstituted into proteoliposomes exhibits stable ATPase activity (Km ~0.1 mM, turnover ~127 min⁻¹) that is inhibited by vanadate; this ATPase activity is specifically stimulated 3–5-fold by thiol-containing compounds, particularly cysteine thiols in peptides, suggesting the physiological substrate contains multiple sulfhydryl groups.","method":"E. coli expression and purification of Atm1p, reconstitution into proteoliposomes, in vitro ATPase activity assay with substrate panel, vanadate inhibition","journal":"Molecular membrane biology","confidence":"High","confidence_rationale":"Tier 1 — in vitro reconstitution with biochemical characterization and substrate screening","pmids":["16754360"],"is_preprint":false},{"year":2008,"finding":"abcb7 mutation in medaka fish causes abnormal iron metabolism in erythrocytes and lipid accumulation in the liver, with dysregulation of iron and lipid metabolism gene expression, revealing a role for Abcb7 in liver development and function.","method":"Positional cloning, mutagenesis screen, microarray gene expression, in situ hybridization in medaka","journal":"Development, growth & differentiation","confidence":"Medium","confidence_rationale":"Tier 2 — vertebrate KO model with defined phenotype, single lab","pmids":["19046159"],"is_preprint":false},{"year":2011,"finding":"Loss of C. elegans abtm-1 (ABCB7 ortholog) causes accumulation of ferric iron, increased oxidative stress, and embryonic morphogenetic defects with premature cell death; DAF-16/FOXO nuclear accumulation and SOD-3 upregulation extend lifespan in abtm-1 mutants.","method":"C. elegans mutant and RNAi, ferric iron staining, oxidative stress assays, DAF-16::GFP localization, SOD-3 expression, lifespan assay","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 — ortholog KO with multiple readouts, single lab","pmids":["21464130"],"is_preprint":false},{"year":2014,"finding":"Glutathione-complexed [2Fe-2S] cluster significantly stimulates the ATPase activity of an ABCB7-type transporter (KD ~68 μM in proteoliposome-bound form), identifying the glutathione-coordinated Fe/S cluster as a likely natural substrate; a substrate-binding site was identified on a structural model of the active transporter.","method":"ATPase stimulation assay in solution and proteoliposome-bound forms, structural modeling, KD determination","journal":"Chemical communications (Cambridge, England)","confidence":"High","confidence_rationale":"Tier 1 — in vitro reconstitution with substrate-stimulated ATPase assay and structural model","pmids":["24584132"],"is_preprint":false},{"year":2015,"finding":"The glutathione-coordinated [2Fe-2S] cluster is a viable physiological substrate for mitochondrial ABCB7/Atm1p transport, demonstrated by quantitative flow cytometry and colorimetric assays of metal translocation in proteoliposomes.","method":"Flow cytometry, colorimetric metal translocation assay, proteoliposome reconstitution","journal":"Chemical communications (Cambridge, England)","confidence":"High","confidence_rationale":"Tier 1 — direct transport assay in reconstituted proteoliposomes with two orthogonal detection methods","pmids":["25556595"],"is_preprint":false},{"year":2016,"finding":"Mutant SF3B1 causes aberrant splicing of ABCB7 via usage of an alternative 3' splice site, generating a premature termination codon; the aberrantly spliced ABCB7 mRNA is degraded by nonsense-mediated decay (NMD), leading to ABCB7 downregulation and mitochondrial iron accumulation in MDS with ring sideroblasts.","method":"RNA sequencing, CRISPR/Cas9-generated SF3B1 mutant cell line, NMD inhibitor (cycloheximide) treatment, RT-PCR splice variant analysis","journal":"Leukemia","confidence":"High","confidence_rationale":"Tier 2 — mechanism defined by multiple orthogonal methods including CRISPR model and NMD inhibition","pmids":["27211273"],"is_preprint":false},{"year":2019,"finding":"ABCB7 forms a defined multiprotein complex with dimeric ferrochelatase and ABCB10 homodimers; ferrochelatase physically bridges ABCB7 and ABCB10 by binding near the nucleotide-binding domains of each transporter. Knockdown of ABCB7 preferentially depletes mitochondrial Fe/S proteins before causing cytosolic Fe/S defects, activates IRP1/2, upregulates mitoferrin-1, and causes defective heme biosynthesis via translational repression of ALAS2 and decreased ferrochelatase stability.","method":"Inducible ABCB7-knockdown cell lines, chemical crosslinking, tandem mass spectrometry, mutational analysis, iron distribution assays, IRP activity, hemoglobinization measurement","journal":"Haematologica","confidence":"High","confidence_rationale":"Tier 1–2 — crosslinking MS with mutational mapping of complex interfaces plus multiple functional readouts","pmids":["30765471"],"is_preprint":false},{"year":2019,"finding":"ABCB7 knockdown in cardiomyocytes (H9C2 cells) increases ROS, ferritin and transferrin receptor expression, and iron overload in both mitochondria and cytoplasm; ABCB7 was found to interact with mitochondrial complexes IV and V. ABCB7 overexpression rescues these changes in pressure-overload cardiac hypertrophy.","method":"ABCB7 siRNA knockdown in H9C2 cells, ABCB7 overexpression rescue, angiotensin II stimulation, ROS measurement, iron quantification, co-immunoprecipitation with mitochondrial complexes IV and V","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2–3 — KD/OE with rescue and Co-IP, single lab","pmids":["31511561"],"is_preprint":false},{"year":2019,"finding":"ABCB7 reduces mitochondrial reactive oxygen species to suppress non-apoptotic cell death, and promotes HIF1α accumulation (independent of hypoxia) by controlling intracellular iron homeostasis, which suppresses apoptosis via inhibition of leucine zipper downregulated in cancer 1 (LDOC1) and maintenance of NF-κB signaling.","method":"ABCB7 knockdown and overexpression in cancer cells, mitochondrial ROS measurement, HIF1α and LDOC1 protein quantification, NF-κB signaling assays, flow cytometry for cell death","journal":"Oncogene","confidence":"Medium","confidence_rationale":"Tier 2–3 — mechanistic pathway placement with multiple readouts, single lab","pmids":["31772327"],"is_preprint":false},{"year":2020,"finding":"Recruitment of MgATP following glutathione-complexed [2Fe-2S] cluster binding to Atm1p/ABCB7 promotes a structural transition from closed to open conformations mediated by coupling helices; MgATP hydrolysis facilitates return to the closed state, defining the transport cycle mechanism.","method":"Biochemical assays of yeast Atm1p with cluster substrate, conformational analysis, ATPase assays with mechanistic dissection","journal":"Metallomics : integrated biometal science","confidence":"High","confidence_rationale":"Tier 1 — mechanistic dissection of transport cycle with substrate and conformational transitions","pmids":["32337520"],"is_preprint":false},{"year":2020,"finding":"Residue E433 of human ABCB7 plays a key role in promoting Fe/S cluster transport; the E433K disease-causing mutation impairs cluster export, demonstrated by functional comparison of wild-type vs. mutant ABCB7 in transport assays. ABCB7 evolved from bacterial heavy metal transporters that utilize metal-glutathione adducts.","method":"Functional transport assay comparing native vs. E433K mutant ABCB7, BLAST evolutionary analysis","journal":"Archives of biochemistry and biophysics","confidence":"Medium","confidence_rationale":"Tier 1–2 — direct functional comparison of mutant vs. wild-type in transport assay, single lab","pmids":["33157103"],"is_preprint":false},{"year":2021,"finding":"ABCB7 is required for bone marrow B cell development (conditional deletion causes block at pro-B cell stage), proliferation, and class switch recombination; loss of ABCB7 causes replication-induced DNA damage and slowed DNA replication in pro-B cells, independent of VDJ recombination, without triggering ferroptosis or apoptosis.","method":"Conditional deletion using Mb1-cre and CD23-cre, B cell development analysis by flow cytometry, intracellular iron measurement, ROS measurement, DNA damage markers, proliferation assays","journal":"eLife","confidence":"High","confidence_rationale":"Tier 2 — conditional KO with multiple orthogonal mechanistic readouts across two Cre lines","pmids":["34762046"],"is_preprint":false},{"year":2022,"finding":"Mutant SF3B1 induces coordinated missplicing of both TMEM14C and ABCB7 (reducing protein expression via 5' UTR alteration), and functional rescue of both TMEM14C and ABCB7 together markedly decreases ring sideroblast formation; rescue of either alone is insufficient, demonstrating that both mitochondrial transporters jointly prevent mitochondrial iron sequestration.","method":"iPSC model of SF3B1-mutant MDS, in vitro erythroid differentiation recapitulating ring sideroblasts, rescue overexpression of TMEM14C and/or ABCB7, ring sideroblast quantification, translation efficiency assay","journal":"Blood","confidence":"High","confidence_rationale":"Tier 2 — physiological iPSC model with genetic rescue dissecting individual contributions","pmids":["34861039"],"is_preprint":false}],"current_model":"ABCB7 is a mitochondrial inner membrane ABC half-transporter that exports glutathione-coordinated [2Fe-2S] cluster precursors from the mitochondrial matrix to the cytosol (driven by ATP hydrolysis via a closed→open→closed conformational cycle), thereby enabling cytosolic Fe/S cluster protein maturation; it also physically complexes with ferrochelatase and ABCB10 to support heme biosynthesis, and its loss causes mitochondrial iron overload, activation of IRP1/2, impaired heme synthesis, and downstream defects in erythropoiesis, B cell development, and other high-energy tissues."},"narrative":{"teleology":[{"year":1997,"claim":"Establishing that the ABCB7 ortholog Atm1p resides on the mitochondrial inner membrane and is required for mitochondrial iron homeostasis answered the foundational question of where and why this transporter functions — its deletion caused massive mitochondrial iron accumulation and oxidative stress.","evidence":"ATM1 gene disruption in yeast with cytochrome analysis, iron quantification, and oxidative stress assays","pmids":["9428742"],"confidence":"High","gaps":["Transported substrate unknown","Mechanism linking transporter loss to iron accumulation unresolved","Human ortholog not yet studied"]},{"year":1999,"claim":"Epistasis analysis in yeast revealed that Atm1p specifically exports Fe/S cluster precursors from the mitochondrial matrix to the cytosol, distinguishing its role from general iron transport and placing it upstream of cytosolic Fe/S protein assembly.","evidence":"Yeast Δatm1 and Δnfs1 mutants with compartment-specific Fe/S protein activity assays and genetic complementation","pmids":["10406803"],"confidence":"High","gaps":["Chemical identity of the exported Fe/S precursor unknown","Transport mechanism (direct vs. indirect) unresolved"]},{"year":1998,"claim":"Demonstrating that human ABCB7 localizes to mitochondria and functionally complements yeast Δatm1 established cross-species conservation and validated ABCB7 as the human ortholog mediating the same Fe/S export function.","evidence":"Immunostaining and yeast complementation with cytochrome, iron, and glutathione measurements","pmids":["9883897"],"confidence":"High","gaps":["Endogenous human loss-of-function phenotype not yet defined","Substrate specificity not tested"]},{"year":1999,"claim":"Identification of the I400M and subsequently E433K mutations as causes of X-linked sideroblastic anemia with ataxia (XLSA/A), validated by loss-of-function in yeast complementation, linked ABCB7 to human disease and pinpointed functionally critical transmembrane and cytoplasmic residues.","evidence":"Patient mutation screening with yeast complementation of Δatm1 using wild-type and mutant ABCB7, Fe/S protein activity assays","pmids":["10196363","11050011"],"confidence":"High","gaps":["Structural basis for how these mutations impair transport unknown","Full allelic spectrum of XLSA/A mutations not characterized"]},{"year":2002,"claim":"Discovery that ABCB7 physically interacts with ferrochelatase and promotes heme production linked Fe/S cluster export to the terminal step of heme biosynthesis, suggesting functional coupling between these two mitochondrial pathways.","evidence":"In vitro and in vivo pull-down assays, colocalization, antisense knockdown, and overexpression in MEL cells","pmids":["12480705"],"confidence":"High","gaps":["Stoichiometry and architecture of the complex unknown","Whether ABCB7 directly supplies Fe/S to ferrochelatase or acts indirectly unresolved"]},{"year":2004,"claim":"Demonstrating that Atm1p functions as a homodimer dependent on Walker A/B-mediated ATP binding and hydrolysis established the basic enzymology — the transporter operates via a canonical ABC mechanism requiring nucleotide-driven dimerization.","evidence":"In vivo yeast mutagenesis of Walker A/B motifs with dimerization and functional analysis","pmids":["15225610"],"confidence":"Medium","gaps":["No purified protein ATPase kinetics yet","Conformational cycle during transport not defined","Single lab without independent replication"]},{"year":2006,"claim":"Purified Atm1p reconstituted into proteoliposomes revealed that its ATPase activity is specifically stimulated by thiol-containing compounds, narrowing the transported substrate to a sulfhydryl-rich species — while conditional knockout in mice and knockdown in human cells confirmed that ABCB7 loss causes mitochondrial iron overload, impaired cytosolic Fe/S maturation, and hematopoietic failure.","evidence":"In vitro ATPase assay with substrate panel in proteoliposomes; Cre/loxP conditional deletion in mouse liver and hematopoietic cells; siRNA in HeLa with iron quantification and enzyme activity assays","pmids":["16754360","16467350","17192393","17192398"],"confidence":"High","gaps":["Exact chemical identity of the physiological substrate still unresolved","Transport directionality not directly demonstrated in reconstituted system"]},{"year":2014,"claim":"Identification of the glutathione-coordinated [2Fe-2S] cluster as the substrate that stimulates Atm1p ATPase activity (KD ~68 μM) and direct demonstration of its translocation across proteoliposome membranes resolved the long-standing question of substrate identity.","evidence":"ATPase stimulation assay, KD determination, flow cytometry and colorimetric metal translocation in proteoliposomes","pmids":["24584132","25556595"],"confidence":"High","gaps":["Whether additional substrates are transported in vivo unknown","Structural basis for substrate recognition not determined"]},{"year":2016,"claim":"Discovery that mutant SF3B1 causes aberrant splicing and NMD-mediated degradation of ABCB7 mRNA explained how ABCB7 downregulation contributes to ring sideroblast formation in MDS, extending the gene's disease relevance beyond Mendelian XLSA/A.","evidence":"RNA-seq, CRISPR/Cas9 SF3B1-mutant cell line, NMD inhibitor treatment, RT-PCR splice variant analysis","pmids":["27211273"],"confidence":"High","gaps":["Whether ABCB7 downregulation alone is sufficient for ring sideroblasts not tested","Contribution of other misspliced genes not excluded"]},{"year":2019,"claim":"Crosslinking mass spectrometry defined a tripartite complex of ABCB7–ferrochelatase–ABCB10 bridged by ferrochelatase, and showed that ABCB7 knockdown first depletes mitochondrial Fe/S proteins before affecting cytosolic ones, activates IRP1/2, and impairs heme synthesis through ALAS2 translational repression and ferrochelatase destabilization.","evidence":"Chemical crosslinking tandem mass spectrometry, inducible ABCB7-knockdown cell lines, mutational analysis, IRP activity and hemoglobinization assays","pmids":["30765471"],"confidence":"High","gaps":["High-resolution structure of the tripartite complex lacking","Whether ABCB7 exports substrate directly to ferrochelatase within the complex unknown"]},{"year":2020,"claim":"Mechanistic dissection of the transport cycle showed that glutathione-[2Fe-2S] binding recruits MgATP, promoting a closed-to-open conformational transition via coupling helices, with ATP hydrolysis driving return to the closed state — defining the complete conformational cycle.","evidence":"Biochemical assays of Atm1p with cluster substrate, conformational and ATPase mechanistic analysis","pmids":["32337520"],"confidence":"High","gaps":["No cryo-EM or crystal structure of human ABCB7 in substrate-bound state","Role of coupling helices not confirmed by structural data"]},{"year":2021,"claim":"Conditional deletion in B cells revealed that ABCB7 is required for B lymphocyte development at the pro-B stage, proliferation, and class switch recombination — loss causes replication-induced DNA damage and slowed replication, broadening ABCB7's physiological role beyond erythropoiesis.","evidence":"Conditional deletion using Mb1-cre and CD23-cre in mice, flow cytometry, DNA damage markers, proliferation assays","pmids":["34762046"],"confidence":"High","gaps":["Which cytosolic Fe/S enzyme deficiency causes replication stress not identified","Whether other rapidly dividing cell types are similarly affected unknown"]},{"year":2022,"claim":"Genetic rescue in an iPSC model of SF3B1-mutant MDS demonstrated that co-restoration of both ABCB7 and TMEM14C is required to prevent ring sideroblast formation, establishing that coordinated missplicing of two mitochondrial transporters jointly drives the MDS phenotype.","evidence":"iPSC-derived erythroid differentiation with individual and combined rescue of ABCB7 and TMEM14C, ring sideroblast quantification","pmids":["34861039"],"confidence":"High","gaps":["Whether additional SF3B1 missplicing targets contribute to disease not excluded","Mechanism by which TMEM14C cooperates with ABCB7 at the substrate level undefined"]},{"year":null,"claim":"A high-resolution structure of human ABCB7 in substrate-bound and nucleotide-bound states is needed to define the molecular basis of substrate recognition, the structural effects of XLSA/A mutations, and the architecture of the ABCB7–ferrochelatase–ABCB10 complex.","evidence":"","pmids":[],"confidence":"Low","gaps":["No cryo-EM or crystal structure of human ABCB7 available","Identity of all physiological substrates beyond GS-[2Fe-2S] not established","Mechanism linking Fe/S cluster deficiency to DNA replication stress unresolved"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140657","term_label":"ATP-dependent activity","supporting_discovery_ids":[6,10,13,19]},{"term_id":"GO:0005215","term_label":"transporter activity","supporting_discovery_ids":[1,13,14,19,20]}],"localization":[{"term_id":"GO:0005739","term_label":"mitochondrion","supporting_discovery_ids":[0,2,5,7,8,16]}],"pathway":[{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[0,1,5,8,9,16]},{"term_id":"R-HSA-382551","term_label":"Transport of small molecules","supporting_discovery_ids":[1,10,13,14,19]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[21]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[3,4,15,22]}],"complexes":["ABCB7 homodimer","ABCB7–ferrochelatase–ABCB10 complex"],"partners":["FECH","ABCB10","TMEM14C","IRP1","IRP2"],"other_free_text":[]},"mechanistic_narrative":"ABCB7 is a mitochondrial inner membrane ABC half-transporter that exports glutathione-coordinated [2Fe-2S] cluster precursors from the matrix to the cytosol, thereby enabling the maturation of cytosolic iron-sulfur proteins and maintaining cellular iron homeostasis [PMID:10406803, PMID:25556595, PMID:32337520]. It functions as a homodimer whose ATPase activity is specifically stimulated by thiol-containing substrates, particularly glutathione-coordinated [2Fe-2S] clusters, driving a closed→open→closed conformational transport cycle [PMID:16754360, PMID:24584132, PMID:32337520]. ABCB7 physically complexes with ferrochelatase and ABCB10 to coordinate heme biosynthesis with Fe/S cluster export; its loss causes mitochondrial iron overload, activation of IRP1/2, impaired heme synthesis, and downstream defects in erythropoiesis, B cell development, and DNA replication [PMID:30765471, PMID:34762046, PMID:17192398]. Mutations in ABCB7 cause X-linked sideroblastic anemia with cerebellar ataxia (XLSA/A), and SF3B1 mutations in myelodysplastic syndrome downregulate ABCB7 through aberrant splicing and nonsense-mediated decay, jointly contributing to ring sideroblast formation [PMID:10196363, PMID:27211273, PMID:34861039]."},"prefetch_data":{"uniprot":{"accession":"O75027","full_name":"Iron-sulfur clusters transporter ABCB7, mitochondrial","aliases":["ATP-binding cassette sub-family B member 7, mitochondrial","ATP-binding cassette transporter 7","ABC transporter 7 protein"],"length_aa":752,"mass_kda":82.6,"function":"Exports glutathione-coordinated iron-sulfur clusters such as [2Fe-2S]-(GS)4 cluster from the mitochondria to the cytosol in an ATP-dependent manner allowing the assembly of the cytosolic iron-sulfur (Fe/S) cluster-containing proteins and participates in iron homeostasis (PubMed:10196363, PubMed:17192393, PubMed:33157103). Moreover, through a functional complex formed of ABCB7, FECH and ABCB10, also plays a role in the cellular iron homeostasis, mitochondrial function and heme biosynthesis (PubMed:30765471). In cardiomyocytes, regulates cellular iron homeostasis and cellular reactive oxygen species (ROS) levels through its interaction with COX4I1 (By similarity). May also play a role in hematopoiesis (By similarity)","subcellular_location":"Mitochondrion inner membrane","url":"https://www.uniprot.org/uniprotkb/O75027/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":true,"resolved_as":"","url":"https://depmap.org/portal/gene/ABCB7","classification":"Common Essential","n_dependent_lines":1135,"n_total_lines":1208,"dependency_fraction":0.9395695364238411},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/ABCB7","total_profiled":1310},"omim":[{"mim_id":"614506","title":"BRCA1-ASSOCIATED ATM ACTIVATOR 1; BRAT1","url":"https://www.omim.org/entry/614506"},{"mim_id":"605452","title":"ATP-BINDING CASSETTE, SUBFAMILY B, MEMBER 6; ABCB6","url":"https://www.omim.org/entry/605452"},{"mim_id":"302500","title":"SPINOCEREBELLAR ATAXIA, X-LINKED 1; SCAX1","url":"https://www.omim.org/entry/302500"},{"mim_id":"301310","title":"SPINOCEREBELLAR ATAXIA, X-LINKED 6, WITH OR WITHOUT SIDEROBLASTIC ANEMIA; SCAX6","url":"https://www.omim.org/entry/301310"},{"mim_id":"300135","title":"ATP-BINDING CASSETTE, SUBFAMILY B, MEMBER 7; ABCB7","url":"https://www.omim.org/entry/300135"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Mitochondria","reliability":"Approved"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/ABCB7"},"hgnc":{"alias_symbol":["EST140535","Atm1p","ASAT"],"prev_symbol":["ABC7"]},"alphafold":{"accession":"O75027","domains":[{"cath_id":"1.20.1560.10","chopping":"107-450","consensus_level":"medium","plddt":88.3093,"start":107,"end":450},{"cath_id":"3.40.50.300","chopping":"473-717","consensus_level":"high","plddt":89.0718,"start":473,"end":717},{"cath_id":"1.20.5","chopping":"722-752","consensus_level":"medium","plddt":49.189,"start":722,"end":752}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/O75027","model_url":"https://alphafold.ebi.ac.uk/files/AF-O75027-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-O75027-F1-predicted_aligned_error_v6.png","plddt_mean":78.12},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=ABCB7","jax_strain_url":"https://www.jax.org/strain/search?query=ABCB7"},"sequence":{"accession":"O75027","fasta_url":"https://rest.uniprot.org/uniprotkb/O75027.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/O75027/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/O75027"}},"corpus_meta":[{"pmid":"10406803","id":"PMC_10406803","title":"The mitochondrial proteins Atm1p and Nfs1p are essential for biogenesis of cytosolic Fe/S proteins.","date":"1999","source":"The EMBO journal","url":"https://pubmed.ncbi.nlm.nih.gov/10406803","citation_count":561,"is_preprint":false},{"pmid":"10196363","id":"PMC_10196363","title":"Mutation of a putative mitochondrial iron transporter gene (ABC7) in X-linked sideroblastic anemia and ataxia (XLSA/A).","date":"1999","source":"Human molecular genetics","url":"https://pubmed.ncbi.nlm.nih.gov/10196363","citation_count":324,"is_preprint":false},{"pmid":"9428742","id":"PMC_9428742","title":"The ABC transporter Atm1p is required for mitochondrial iron homeostasis.","date":"1997","source":"FEBS letters","url":"https://pubmed.ncbi.nlm.nih.gov/9428742","citation_count":230,"is_preprint":false},{"pmid":"11050011","id":"PMC_11050011","title":"Human ABC7 transporter: gene structure and mutation causing X-linked sideroblastic anemia with ataxia with disruption of cytosolic iron-sulfur protein 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deletion causes 30-fold accumulation of mitochondrial free iron, loss of heme-containing protein holoforms, and hypersensitivity to oxidative stress despite normal heme synthesis and transport.\",\n      \"method\": \"ATM1 gene disruption in yeast, cytochrome analysis, iron quantification, glutathione measurement, oxidative stress assays\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean KO with multiple orthogonal phenotypic readouts, foundational paper >200 citations\",\n      \"pmids\": [\"9428742\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"Mitochondrial Atm1p (ABCB7 ortholog) performs an essential function specifically in the export of Fe/S cluster precursors from the mitochondrial matrix to the cytosol, enabling biogenesis of cytosolic Fe/S proteins; the matrix-localized cysteine desulfurase Nfs1p initiates this pathway by producing elemental sulfur.\",\n      \"method\": \"Yeast deletion mutants (Δatm1, Δnfs1), genetic complementation, Fe/S protein activity assays in mitochondrial and cytosolic fractions\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — epistasis and compartment-specific Fe/S protein assays, replicated foundational paper >500 citations\",\n      \"pmids\": [\"10406803\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"Human ABC7 (ABCB7) protein localizes to mitochondria and functionally complements yeast Δatm1 cells, restoring normal cytochrome levels, mitochondrial iron content, and glutathione levels, establishing it as the functional ortholog of yeast Atm1p.\",\n      \"method\": \"Immunostaining with specific antibody, yeast complementation assay, cytochrome analysis, iron and glutathione measurements\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — direct localization experiment with functional complementation, multiple orthogonal readouts\",\n      \"pmids\": [\"9883897\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"A missense mutation I400M in the ABC7 gene (ABCB7), located in a predicted transmembrane segment, causes X-linked sideroblastic anemia with ataxia (XLSA/A); the corresponding mutation introduced into yeast ATM1 causes partial loss of function, and human wild-type ABC7 complements ATM1 deletion.\",\n      \"method\": \"Patient mutation screening, yeast complementation with wild-type and mutant protein, disease segregation analysis\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — disease mutation functionally validated by yeast complementation and loss-of-function assay\",\n      \"pmids\": [\"10196363\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"A glutamate-to-lysine charge inversion mutation at residue E433 (E433K) of ABCB7 causes XLSA/A by impairing cytosolic Fe/S protein maturation; wild-type ABCB7 almost fully complements Δatm1 yeast, whereas E433K mutant protein has markedly reduced ability to support cytosolic Fe/S assembly.\",\n      \"method\": \"Patient mutation identification (G→A at nt 1305), yeast complementation of Δatm1 cells with wild-type vs. mutant ABCB7, Fe/S protein activity assays\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — active-site/disease mutation with functional assay in orthologous system, multiple orthogonal methods\",\n      \"pmids\": [\"11050011\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"ABCB7 physically interacts with the C-terminal iron-sulfur cluster-containing region of ferrochelatase (the last enzyme in heme biosynthesis); ABCB7 colocalizes with ferrochelatase in mitochondria, and its overexpression increases ferrochelatase activity and promotes heme production during erythroid differentiation.\",\n      \"method\": \"In vitro and in vivo pull-down assays, immunostaining colocalization, antisense oligonucleotide knockdown of heme measurement, stable overexpression in MEL cells\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — reciprocal pull-down (in vitro and in vivo) plus functional rescue, replicated across multiple cell systems\",\n      \"pmids\": [\"12480705\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Atm1p (ABCB7 ortholog) functions as a homodimer; conserved Walker A and B motif residues required for ATP binding and hydrolysis are essential for Atm1p function, and ATP binding is important for homodimerization.\",\n      \"method\": \"In vivo yeast mutagenesis of Walker A/B motifs, dimerization analysis\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — mutagenesis with functional and dimerization readouts, single lab\",\n      \"pmids\": [\"15225610\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Mouse Abcb7 is essential in extra-embryonic tissues and in numerous cell types; conditional hepatic deletion impairs cytosolic Fe/S cluster assembly, causing loss of IRP1 regulation, dysregulation of iron regulatory protein 1 activity, and hepatocyte iron metabolic disturbance without lethality.\",\n      \"method\": \"Inducible Cre/loxP deletion of Abcb7 exons 9–10, X-chromosome inactivation assays, tissue-specific deletions, IRP1 activity assay, iron metabolism studies\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — conditional KO with multiple defined cellular and molecular phenotypes, replicated across tissues\",\n      \"pmids\": [\"16467350\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"siRNA silencing of ABCB7 in HeLa cells causes ~6-fold mitochondrial iron accumulation, reduced cytosolic aconitase (IRP1) activity, increased protoporphyrin IX, and reduced mitochondrial superoxide dismutase 2 activity, supporting a role for ABCB7 in transferring iron from mitochondria to cytosol and maturing cytosolic Fe/S enzymes.\",\n      \"method\": \"Sequential siRNA transfection, iron quantification (mitochondrial fractionation), aconitase activity assay, SOD2 activity assay, H2O2 sensitivity assay\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — knockdown with multiple orthogonal biochemical readouts\",\n      \"pmids\": [\"17192393\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Abcb7 is essential for hematopoiesis; partial loss-of-function mutations directly or indirectly inhibit heme biosynthesis, causing the sideroblastic anemia phenotype of XLSA/A.\",\n      \"method\": \"Conditional Abcb7 deletion in hematopoietic cells (mouse model), heme biosynthesis assays\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — tissue-specific KO with defined hematopoietic phenotype\",\n      \"pmids\": [\"17192398\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Purified Atm1p (ABCB7 ortholog) reconstituted into proteoliposomes exhibits stable ATPase activity (Km ~0.1 mM, turnover ~127 min⁻¹) that is inhibited by vanadate; this ATPase activity is specifically stimulated 3–5-fold by thiol-containing compounds, particularly cysteine thiols in peptides, suggesting the physiological substrate contains multiple sulfhydryl groups.\",\n      \"method\": \"E. coli expression and purification of Atm1p, reconstitution into proteoliposomes, in vitro ATPase activity assay with substrate panel, vanadate inhibition\",\n      \"journal\": \"Molecular membrane biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution with biochemical characterization and substrate screening\",\n      \"pmids\": [\"16754360\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"abcb7 mutation in medaka fish causes abnormal iron metabolism in erythrocytes and lipid accumulation in the liver, with dysregulation of iron and lipid metabolism gene expression, revealing a role for Abcb7 in liver development and function.\",\n      \"method\": \"Positional cloning, mutagenesis screen, microarray gene expression, in situ hybridization in medaka\",\n      \"journal\": \"Development, growth & differentiation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — vertebrate KO model with defined phenotype, single lab\",\n      \"pmids\": [\"19046159\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Loss of C. elegans abtm-1 (ABCB7 ortholog) causes accumulation of ferric iron, increased oxidative stress, and embryonic morphogenetic defects with premature cell death; DAF-16/FOXO nuclear accumulation and SOD-3 upregulation extend lifespan in abtm-1 mutants.\",\n      \"method\": \"C. elegans mutant and RNAi, ferric iron staining, oxidative stress assays, DAF-16::GFP localization, SOD-3 expression, lifespan assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — ortholog KO with multiple readouts, single lab\",\n      \"pmids\": [\"21464130\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Glutathione-complexed [2Fe-2S] cluster significantly stimulates the ATPase activity of an ABCB7-type transporter (KD ~68 μM in proteoliposome-bound form), identifying the glutathione-coordinated Fe/S cluster as a likely natural substrate; a substrate-binding site was identified on a structural model of the active transporter.\",\n      \"method\": \"ATPase stimulation assay in solution and proteoliposome-bound forms, structural modeling, KD determination\",\n      \"journal\": \"Chemical communications (Cambridge, England)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution with substrate-stimulated ATPase assay and structural model\",\n      \"pmids\": [\"24584132\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"The glutathione-coordinated [2Fe-2S] cluster is a viable physiological substrate for mitochondrial ABCB7/Atm1p transport, demonstrated by quantitative flow cytometry and colorimetric assays of metal translocation in proteoliposomes.\",\n      \"method\": \"Flow cytometry, colorimetric metal translocation assay, proteoliposome reconstitution\",\n      \"journal\": \"Chemical communications (Cambridge, England)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct transport assay in reconstituted proteoliposomes with two orthogonal detection methods\",\n      \"pmids\": [\"25556595\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Mutant SF3B1 causes aberrant splicing of ABCB7 via usage of an alternative 3' splice site, generating a premature termination codon; the aberrantly spliced ABCB7 mRNA is degraded by nonsense-mediated decay (NMD), leading to ABCB7 downregulation and mitochondrial iron accumulation in MDS with ring sideroblasts.\",\n      \"method\": \"RNA sequencing, CRISPR/Cas9-generated SF3B1 mutant cell line, NMD inhibitor (cycloheximide) treatment, RT-PCR splice variant analysis\",\n      \"journal\": \"Leukemia\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — mechanism defined by multiple orthogonal methods including CRISPR model and NMD inhibition\",\n      \"pmids\": [\"27211273\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"ABCB7 forms a defined multiprotein complex with dimeric ferrochelatase and ABCB10 homodimers; ferrochelatase physically bridges ABCB7 and ABCB10 by binding near the nucleotide-binding domains of each transporter. Knockdown of ABCB7 preferentially depletes mitochondrial Fe/S proteins before causing cytosolic Fe/S defects, activates IRP1/2, upregulates mitoferrin-1, and causes defective heme biosynthesis via translational repression of ALAS2 and decreased ferrochelatase stability.\",\n      \"method\": \"Inducible ABCB7-knockdown cell lines, chemical crosslinking, tandem mass spectrometry, mutational analysis, iron distribution assays, IRP activity, hemoglobinization measurement\",\n      \"journal\": \"Haematologica\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — crosslinking MS with mutational mapping of complex interfaces plus multiple functional readouts\",\n      \"pmids\": [\"30765471\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"ABCB7 knockdown in cardiomyocytes (H9C2 cells) increases ROS, ferritin and transferrin receptor expression, and iron overload in both mitochondria and cytoplasm; ABCB7 was found to interact with mitochondrial complexes IV and V. ABCB7 overexpression rescues these changes in pressure-overload cardiac hypertrophy.\",\n      \"method\": \"ABCB7 siRNA knockdown in H9C2 cells, ABCB7 overexpression rescue, angiotensin II stimulation, ROS measurement, iron quantification, co-immunoprecipitation with mitochondrial complexes IV and V\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — KD/OE with rescue and Co-IP, single lab\",\n      \"pmids\": [\"31511561\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"ABCB7 reduces mitochondrial reactive oxygen species to suppress non-apoptotic cell death, and promotes HIF1α accumulation (independent of hypoxia) by controlling intracellular iron homeostasis, which suppresses apoptosis via inhibition of leucine zipper downregulated in cancer 1 (LDOC1) and maintenance of NF-κB signaling.\",\n      \"method\": \"ABCB7 knockdown and overexpression in cancer cells, mitochondrial ROS measurement, HIF1α and LDOC1 protein quantification, NF-κB signaling assays, flow cytometry for cell death\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — mechanistic pathway placement with multiple readouts, single lab\",\n      \"pmids\": [\"31772327\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Recruitment of MgATP following glutathione-complexed [2Fe-2S] cluster binding to Atm1p/ABCB7 promotes a structural transition from closed to open conformations mediated by coupling helices; MgATP hydrolysis facilitates return to the closed state, defining the transport cycle mechanism.\",\n      \"method\": \"Biochemical assays of yeast Atm1p with cluster substrate, conformational analysis, ATPase assays with mechanistic dissection\",\n      \"journal\": \"Metallomics : integrated biometal science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — mechanistic dissection of transport cycle with substrate and conformational transitions\",\n      \"pmids\": [\"32337520\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Residue E433 of human ABCB7 plays a key role in promoting Fe/S cluster transport; the E433K disease-causing mutation impairs cluster export, demonstrated by functional comparison of wild-type vs. mutant ABCB7 in transport assays. ABCB7 evolved from bacterial heavy metal transporters that utilize metal-glutathione adducts.\",\n      \"method\": \"Functional transport assay comparing native vs. E433K mutant ABCB7, BLAST evolutionary analysis\",\n      \"journal\": \"Archives of biochemistry and biophysics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1–2 — direct functional comparison of mutant vs. wild-type in transport assay, single lab\",\n      \"pmids\": [\"33157103\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"ABCB7 is required for bone marrow B cell development (conditional deletion causes block at pro-B cell stage), proliferation, and class switch recombination; loss of ABCB7 causes replication-induced DNA damage and slowed DNA replication in pro-B cells, independent of VDJ recombination, without triggering ferroptosis or apoptosis.\",\n      \"method\": \"Conditional deletion using Mb1-cre and CD23-cre, B cell development analysis by flow cytometry, intracellular iron measurement, ROS measurement, DNA damage markers, proliferation assays\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — conditional KO with multiple orthogonal mechanistic readouts across two Cre lines\",\n      \"pmids\": [\"34762046\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Mutant SF3B1 induces coordinated missplicing of both TMEM14C and ABCB7 (reducing protein expression via 5' UTR alteration), and functional rescue of both TMEM14C and ABCB7 together markedly decreases ring sideroblast formation; rescue of either alone is insufficient, demonstrating that both mitochondrial transporters jointly prevent mitochondrial iron sequestration.\",\n      \"method\": \"iPSC model of SF3B1-mutant MDS, in vitro erythroid differentiation recapitulating ring sideroblasts, rescue overexpression of TMEM14C and/or ABCB7, ring sideroblast quantification, translation efficiency assay\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — physiological iPSC model with genetic rescue dissecting individual contributions\",\n      \"pmids\": [\"34861039\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"ABCB7 is a mitochondrial inner membrane ABC half-transporter that exports glutathione-coordinated [2Fe-2S] cluster precursors from the mitochondrial matrix to the cytosol (driven by ATP hydrolysis via a closed→open→closed conformational cycle), thereby enabling cytosolic Fe/S cluster protein maturation; it also physically complexes with ferrochelatase and ABCB10 to support heme biosynthesis, and its loss causes mitochondrial iron overload, activation of IRP1/2, impaired heme synthesis, and downstream defects in erythropoiesis, B cell development, and other high-energy tissues.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"ABCB7 is a mitochondrial inner membrane ABC half-transporter that exports glutathione-coordinated [2Fe-2S] cluster precursors from the matrix to the cytosol, thereby enabling the maturation of cytosolic iron-sulfur proteins and maintaining cellular iron homeostasis [PMID:10406803, PMID:25556595, PMID:32337520]. It functions as a homodimer whose ATPase activity is specifically stimulated by thiol-containing substrates, particularly glutathione-coordinated [2Fe-2S] clusters, driving a closed→open→closed conformational transport cycle [PMID:16754360, PMID:24584132, PMID:32337520]. ABCB7 physically complexes with ferrochelatase and ABCB10 to coordinate heme biosynthesis with Fe/S cluster export; its loss causes mitochondrial iron overload, activation of IRP1/2, impaired heme synthesis, and downstream defects in erythropoiesis, B cell development, and DNA replication [PMID:30765471, PMID:34762046, PMID:17192398]. Mutations in ABCB7 cause X-linked sideroblastic anemia with cerebellar ataxia (XLSA/A), and SF3B1 mutations in myelodysplastic syndrome downregulate ABCB7 through aberrant splicing and nonsense-mediated decay, jointly contributing to ring sideroblast formation [PMID:10196363, PMID:27211273, PMID:34861039].\",\n  \"teleology\": [\n    {\n      \"year\": 1997,\n      \"claim\": \"Establishing that the ABCB7 ortholog Atm1p resides on the mitochondrial inner membrane and is required for mitochondrial iron homeostasis answered the foundational question of where and why this transporter functions — its deletion caused massive mitochondrial iron accumulation and oxidative stress.\",\n      \"evidence\": \"ATM1 gene disruption in yeast with cytochrome analysis, iron quantification, and oxidative stress assays\",\n      \"pmids\": [\"9428742\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Transported substrate unknown\", \"Mechanism linking transporter loss to iron accumulation unresolved\", \"Human ortholog not yet studied\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Epistasis analysis in yeast revealed that Atm1p specifically exports Fe/S cluster precursors from the mitochondrial matrix to the cytosol, distinguishing its role from general iron transport and placing it upstream of cytosolic Fe/S protein assembly.\",\n      \"evidence\": \"Yeast Δatm1 and Δnfs1 mutants with compartment-specific Fe/S protein activity assays and genetic complementation\",\n      \"pmids\": [\"10406803\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Chemical identity of the exported Fe/S precursor unknown\", \"Transport mechanism (direct vs. indirect) unresolved\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"Demonstrating that human ABCB7 localizes to mitochondria and functionally complements yeast Δatm1 established cross-species conservation and validated ABCB7 as the human ortholog mediating the same Fe/S export function.\",\n      \"evidence\": \"Immunostaining and yeast complementation with cytochrome, iron, and glutathione measurements\",\n      \"pmids\": [\"9883897\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Endogenous human loss-of-function phenotype not yet defined\", \"Substrate specificity not tested\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Identification of the I400M and subsequently E433K mutations as causes of X-linked sideroblastic anemia with ataxia (XLSA/A), validated by loss-of-function in yeast complementation, linked ABCB7 to human disease and pinpointed functionally critical transmembrane and cytoplasmic residues.\",\n      \"evidence\": \"Patient mutation screening with yeast complementation of Δatm1 using wild-type and mutant ABCB7, Fe/S protein activity assays\",\n      \"pmids\": [\"10196363\", \"11050011\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis for how these mutations impair transport unknown\", \"Full allelic spectrum of XLSA/A mutations not characterized\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Discovery that ABCB7 physically interacts with ferrochelatase and promotes heme production linked Fe/S cluster export to the terminal step of heme biosynthesis, suggesting functional coupling between these two mitochondrial pathways.\",\n      \"evidence\": \"In vitro and in vivo pull-down assays, colocalization, antisense knockdown, and overexpression in MEL cells\",\n      \"pmids\": [\"12480705\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Stoichiometry and architecture of the complex unknown\", \"Whether ABCB7 directly supplies Fe/S to ferrochelatase or acts indirectly unresolved\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Demonstrating that Atm1p functions as a homodimer dependent on Walker A/B-mediated ATP binding and hydrolysis established the basic enzymology — the transporter operates via a canonical ABC mechanism requiring nucleotide-driven dimerization.\",\n      \"evidence\": \"In vivo yeast mutagenesis of Walker A/B motifs with dimerization and functional analysis\",\n      \"pmids\": [\"15225610\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No purified protein ATPase kinetics yet\", \"Conformational cycle during transport not defined\", \"Single lab without independent replication\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Purified Atm1p reconstituted into proteoliposomes revealed that its ATPase activity is specifically stimulated by thiol-containing compounds, narrowing the transported substrate to a sulfhydryl-rich species — while conditional knockout in mice and knockdown in human cells confirmed that ABCB7 loss causes mitochondrial iron overload, impaired cytosolic Fe/S maturation, and hematopoietic failure.\",\n      \"evidence\": \"In vitro ATPase assay with substrate panel in proteoliposomes; Cre/loxP conditional deletion in mouse liver and hematopoietic cells; siRNA in HeLa with iron quantification and enzyme activity assays\",\n      \"pmids\": [\"16754360\", \"16467350\", \"17192393\", \"17192398\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Exact chemical identity of the physiological substrate still unresolved\", \"Transport directionality not directly demonstrated in reconstituted system\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Identification of the glutathione-coordinated [2Fe-2S] cluster as the substrate that stimulates Atm1p ATPase activity (KD ~68 μM) and direct demonstration of its translocation across proteoliposome membranes resolved the long-standing question of substrate identity.\",\n      \"evidence\": \"ATPase stimulation assay, KD determination, flow cytometry and colorimetric metal translocation in proteoliposomes\",\n      \"pmids\": [\"24584132\", \"25556595\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether additional substrates are transported in vivo unknown\", \"Structural basis for substrate recognition not determined\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Discovery that mutant SF3B1 causes aberrant splicing and NMD-mediated degradation of ABCB7 mRNA explained how ABCB7 downregulation contributes to ring sideroblast formation in MDS, extending the gene's disease relevance beyond Mendelian XLSA/A.\",\n      \"evidence\": \"RNA-seq, CRISPR/Cas9 SF3B1-mutant cell line, NMD inhibitor treatment, RT-PCR splice variant analysis\",\n      \"pmids\": [\"27211273\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether ABCB7 downregulation alone is sufficient for ring sideroblasts not tested\", \"Contribution of other misspliced genes not excluded\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Crosslinking mass spectrometry defined a tripartite complex of ABCB7–ferrochelatase–ABCB10 bridged by ferrochelatase, and showed that ABCB7 knockdown first depletes mitochondrial Fe/S proteins before affecting cytosolic ones, activates IRP1/2, and impairs heme synthesis through ALAS2 translational repression and ferrochelatase destabilization.\",\n      \"evidence\": \"Chemical crosslinking tandem mass spectrometry, inducible ABCB7-knockdown cell lines, mutational analysis, IRP activity and hemoglobinization assays\",\n      \"pmids\": [\"30765471\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"High-resolution structure of the tripartite complex lacking\", \"Whether ABCB7 exports substrate directly to ferrochelatase within the complex unknown\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Mechanistic dissection of the transport cycle showed that glutathione-[2Fe-2S] binding recruits MgATP, promoting a closed-to-open conformational transition via coupling helices, with ATP hydrolysis driving return to the closed state — defining the complete conformational cycle.\",\n      \"evidence\": \"Biochemical assays of Atm1p with cluster substrate, conformational and ATPase mechanistic analysis\",\n      \"pmids\": [\"32337520\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No cryo-EM or crystal structure of human ABCB7 in substrate-bound state\", \"Role of coupling helices not confirmed by structural data\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Conditional deletion in B cells revealed that ABCB7 is required for B lymphocyte development at the pro-B stage, proliferation, and class switch recombination — loss causes replication-induced DNA damage and slowed replication, broadening ABCB7's physiological role beyond erythropoiesis.\",\n      \"evidence\": \"Conditional deletion using Mb1-cre and CD23-cre in mice, flow cytometry, DNA damage markers, proliferation assays\",\n      \"pmids\": [\"34762046\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Which cytosolic Fe/S enzyme deficiency causes replication stress not identified\", \"Whether other rapidly dividing cell types are similarly affected unknown\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Genetic rescue in an iPSC model of SF3B1-mutant MDS demonstrated that co-restoration of both ABCB7 and TMEM14C is required to prevent ring sideroblast formation, establishing that coordinated missplicing of two mitochondrial transporters jointly drives the MDS phenotype.\",\n      \"evidence\": \"iPSC-derived erythroid differentiation with individual and combined rescue of ABCB7 and TMEM14C, ring sideroblast quantification\",\n      \"pmids\": [\"34861039\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether additional SF3B1 missplicing targets contribute to disease not excluded\", \"Mechanism by which TMEM14C cooperates with ABCB7 at the substrate level undefined\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"A high-resolution structure of human ABCB7 in substrate-bound and nucleotide-bound states is needed to define the molecular basis of substrate recognition, the structural effects of XLSA/A mutations, and the architecture of the ABCB7–ferrochelatase–ABCB10 complex.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No cryo-EM or crystal structure of human ABCB7 available\", \"Identity of all physiological substrates beyond GS-[2Fe-2S] not established\", \"Mechanism linking Fe/S cluster deficiency to DNA replication stress unresolved\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140657\", \"supporting_discovery_ids\": [6, 10, 13, 19]},\n      {\"term_id\": \"GO:0005215\", \"supporting_discovery_ids\": [1, 13, 14, 19, 20]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005739\", \"supporting_discovery_ids\": [0, 2, 5, 7, 8, 16]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": []},\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [0, 1, 5, 8, 9, 16]},\n      {\"term_id\": \"R-HSA-382551\", \"supporting_discovery_ids\": [1, 10, 13, 14, 19]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [21]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [3, 4, 15, 22]}\n    ],\n    \"complexes\": [\n      \"ABCB7 homodimer\",\n      \"ABCB7–ferrochelatase–ABCB10 complex\"\n    ],\n    \"partners\": [\n      \"FECH\",\n      \"ABCB10\",\n      \"TMEM14C\",\n      \"IRP1\",\n      \"IRP2\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}