{"gene":"ALAS2","run_date":"2026-04-28T17:12:37","timeline":{"discoveries":[{"year":2008,"finding":"C-terminal frameshift deletions in ALAS2 (p.E569GfsX24 and p.M567EfsX2) markedly increase enzymatic activity (gain-of-function), causing X-linked dominant protoporphyria rather than sideroblastic anemia, demonstrating that the 19-20 C-terminal residues normally constrain ALAS2 activity.","method":"Prokaryotic expression of mutant enzymes with enzymatic activity assays","journal":"American journal of human genetics","confidence":"High","confidence_rationale":"Tier 1 — in vitro enzymatic reconstitution of expressed mutant proteins with functional validation; replicated across eight families","pmids":["18760763"],"is_preprint":false},{"year":2000,"finding":"ALAS2 (ALAS-E) physically interacts in mitochondria with the beta subunit of ATP-specific succinyl-CoA synthetase (SCS-betaA); the D190V XLSA mutant fails to associate with SCS-betaA, suggesting this interaction promotes efficient succinyl-CoA utilization or mitochondrial import of ALAS2.","method":"Yeast two-hybrid screen of human bone marrow cDNA library, followed by transient expression and co-immunoprecipitation in mammalian cells","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 2 — reciprocal co-IP plus yeast two-hybrid, with disease-linked mutant showing loss of interaction","pmids":["10727444"],"is_preprint":false},{"year":2012,"finding":"ALAS2 C-terminal residues (around Met567/Ser568) are required for binding to the beta subunit of succinyl-CoA synthetase (SUCLA2); mutations abolishing SUCLA2 binding cause XLSA even with normal in vitro enzymatic activity and stability, indicating that the ALAS2-SUCLA2 complex is required for full in vivo heme synthetic activity. Additionally, XLSA mutations R452C and R452H retain SUCLA2 binding but show loss of positive cooperativity for succinyl-CoA, increased Km for succinyl-CoA, and reduced vitamin B6 affinity.","method":"SUCLA2 affinity column binding assays, enzyme kinetics of expressed mutant proteins, in vitro substrate cooperativity analysis","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — reconstituted binding and kinetic assays with multiple mutants and orthogonal methods","pmids":["22740690"],"is_preprint":false},{"year":1994,"finding":"The F165L missense mutation in the first conserved catalytic domain of ALAS2 reduces specific enzymatic activity to ~26% of normal; pyridoxal 5'-phosphate (PLP) activates and stabilizes the mutant enzyme in vitro, mechanistically explaining pyridoxine responsiveness in affected patients.","method":"Prokaryotic expression and affinity purification of mutant and wild-type ALAS2 fusion proteins; enzymatic activity assays with and without PLP","journal":"Blood","confidence":"High","confidence_rationale":"Tier 1 — in vitro reconstitution with purified recombinant enzyme and cofactor stabilization experiments","pmids":["7949148"],"is_preprint":false},{"year":1995,"finding":"ALAS2 missense mutations K299Q and A172T cause marked thermolability of the recombinant enzyme; addition of pyridoxal 5'-phosphate in vitro stabilizes both mutant enzymes, demonstrating that PLP acts as a cofactor stabilizer and explaining pyridoxine responsiveness.","method":"In vitro expression of recombinant mutant ALAS2 enzymes; thermostability assays with and without PLP","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 1 — purified recombinant enzyme thermostability assay with PLP rescue, replicated in two independent mutations","pmids":["7560104"],"is_preprint":false},{"year":2013,"finding":"A 130-bp enhancer in intron 1 of ALAS2 contains a GATA1-binding cis-element essential for erythroid-specific ALAS2 expression; GATA1 binds this element in vivo and in vitro, and mutations disrupting the GATA site abolish enhancer activity and cause congenital sideroblastic anemia.","method":"Chromatin immunoprecipitation (ChIP), electrophoretic mobility shift assay (EMSA), luciferase reporter assays in K562 cells, patient mutation analysis","journal":"Haematologica","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods (ChIP, EMSA, reporter assay) confirming GATA1-dependent enhancer function","pmids":["23935018"],"is_preprint":false},{"year":2016,"finding":"The intron 1 GATA site (int-1-GATA) of ALAS2 is indispensable for ALAS2 expression in vivo; deletion of this 13-bp fragment in mice causes embryonic lethality from severe anemia due to absent ALAS2 expression. The int-1-GATA site forms a long-range chromatin loop with the intron 8 GATA site and the proximal promoter, anchoring an enhancer complex containing GATA1, TAL1, LMO2, LDB1, and Pol II.","method":"CRISPR/Cas9-mediated in vivo deletion in mice; chromatin conformation/loop analysis; ChIP for transcription factor occupancy","journal":"Nucleic acids research","confidence":"High","confidence_rationale":"Tier 2 — in vivo genetic deletion with lethal phenotype, complemented by ChIP and chromatin loop data","pmids":["28123038"],"is_preprint":false},{"year":2003,"finding":"A C-to-G transversion at nucleotide -206 in the ALAS2 proximal promoter causes a 94% loss of luciferase reporter activity in K562 erythroid cells and reduces ALAS2 mRNA by 87% in patient erythroblasts, identifying this region as a critical erythroid regulatory element.","method":"Luciferase reporter assay in K562 cells; primer extension; mRNA quantification in patient erythroid precursors","journal":"Blood","confidence":"High","confidence_rationale":"Tier 2 — reporter assay with patient-derived mRNA confirmation, two orthogonal methods","pmids":["12663458"],"is_preprint":false},{"year":2011,"finding":"Ten ALAS2 missense mutations associated with XLSA were expressed in E. coli; five caused decreased enzymatic activity under standard conditions, and two showed decreased activity only without exogenous PLP and increased thermosensitivity, establishing that PLP-dependent stabilization is the primary mechanism for pyridoxine-responsive variants.","method":"Prokaryotic expression of mutant ALAS2 proteins; in vitro enzymatic activity assays with and without exogenous PLP; thermosensitivity assays","journal":"Human mutation","confidence":"High","confidence_rationale":"Tier 1 — systematic in vitro enzyme characterization of 10 independent mutants","pmids":["21309041"],"is_preprint":false},{"year":2019,"finding":"XLP gain-of-function truncation mutations in the ALAS2 C-terminal region increase Vmax for both succinyl-CoA and glycine substrates (1.4- to 5.6-fold), with an inverse correlation between thermostability and activity increase, indicating that increased molecular flexibility/active-site openness in the C-terminal region is the mechanism of enhanced enzymatic function.","method":"Site-directed mutagenesis; prokaryotic expression and purification; enzyme kinetic assays for Vmax, Km; thermostability assays","journal":"Molecular medicine","confidence":"High","confidence_rationale":"Tier 1 — reconstituted in vitro with multiple truncation variants and kinetic characterization","pmids":["30678654"],"is_preprint":false},{"year":2011,"finding":"A gain-of-function ALAS2 mutation (Y586F, c.1757 A>T) significantly increases the rate of 5-aminolevulinate release compared to wild-type ALAS2, demonstrating that the penultimate C-terminal residue modulates catalytic turnover and that ALAS2 gain-of-function can act as a modifier gene in congenital erythropoietic porphyria.","method":"Prokaryotic expression of Y586F mutant ALAS2; enzymatic activity assay measuring ALA release rate","journal":"Blood","confidence":"High","confidence_rationale":"Tier 1 — in vitro enzymatic assay of expressed mutant protein","pmids":["21653323"],"is_preprint":false},{"year":2002,"finding":"ALAS2-null definitive erythroblasts (derived from Alas2-null ES cells differentiated in culture) accumulate 15-fold more non-heme iron in the cytoplasm (not mitochondria) and exhibit increased lipid peroxidation compared to wild-type, demonstrating that ALAS2 deficiency per se causes cytoplasmic iron accumulation and oxidative stress without blocking erythroid differentiation.","method":"ES cell differentiation to definitive erythroblast stage; quantitative non-heme iron measurement; electron microscopy for iron localization; lipid peroxidation assays","journal":"Blood","confidence":"High","confidence_rationale":"Tier 2 — defined KO cellular model with multiple readouts and direct iron localization by EM","pmids":["12393610"],"is_preprint":false},{"year":1998,"finding":"The R411C ALAS2 mutation reduces enzymatic activity to 12-25% of wild-type (depending on PLP concentration), demonstrating a direct mechanistic link between this catalytic-core mutation and pyridoxine-responsive XLSA.","method":"E. coli expression and purification of mutant ALAS2; ALAS activity assays with and without PLP","journal":"British journal of haematology","confidence":"High","confidence_rationale":"Tier 1 — in vitro purified recombinant enzyme assay","pmids":["9858242"],"is_preprint":false},{"year":1995,"finding":"A G-to-A mutation at nucleotide 871 (exon 7) causing a Gly-to-Ser substitution in ALAS2 markedly decreases enzymatic activity of the expressed mutant protein, establishing the catalytic importance of this glycine residue.","method":"Prokaryotic expression of mutant ALAS2; enzymatic activity measurement","journal":"Human genetics","confidence":"Medium","confidence_rationale":"Tier 1 — in vitro enzymatic assay, single lab/single paper","pmids":["7705839"],"is_preprint":false},{"year":2015,"finding":"The ALAS2 Y365C mutation impairs binding of the essential cofactor pyridoxal 5'-phosphate (PLP) to the enzyme, resulting in protein destabilization and loss of function; X inactivation in reticulocytes showed complete skewing toward the WT allele, indicating strong selective pressure against ALAS2-deficient erythroid precursors.","method":"Whole-exome sequencing; biochemical characterization of expressed mutant enzyme (PLP binding assay); X-inactivation analysis in blood fractions and primary erythroid cultures","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 2 — biochemical PLP binding assay plus in vivo cell-selective pressure demonstrated by X-inactivation skewing","pmids":["25705881"],"is_preprint":false},{"year":2015,"finding":"miR-218 directly targets the 3'-UTR of ALAS2 mRNA to repress its expression; overexpression of miR-218 in K562 cells inhibits erythroid differentiation and alters iron metabolism in a manner phenocopying ALAS2 knockdown.","method":"3'-UTR luciferase reporter assay; miR-218 overexpression; ALAS2 shRNA knockdown as functional control; flow cytometry for erythroid differentiation markers","journal":"International journal of molecular sciences","confidence":"Medium","confidence_rationale":"Tier 2 — reporter assay plus phenocopy experiment; single lab","pmids":["26703568"],"is_preprint":false},{"year":2022,"finding":"ALAS2 knockdown in human erythroblasts (XLSA model) increases susceptibility to ferroptosis, associated with elevated lipid peroxides, enhanced BACH1 expression, and BACH1-mediated repression of iron metabolism and glutathione synthesis genes.","method":"CRISPR/base-editing introduction of ALAS2 missense mutations in cord blood-derived erythroblasts; ferroptosis inducer (erastin) treatment; lipid peroxide measurement; gene expression profiling; BACH1 functional analysis","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2 — defined cellular model with functional ferroptosis assay and mechanistic pathway placement; single lab","pmids":["35637209"],"is_preprint":false},{"year":2024,"finding":"Two C-terminal ALAS2 loss-of-function variants (V562A and M567I) do not cause gross structural perturbations but show decreased enzyme stability (V562A) and altered cooperativity of substrate binding (M567I); PLP addition moderately increases stability of both variants, indicating that the C-terminal extension modulates active-site geometry and substrate cooperativity.","method":"Site-directed mutagenesis; prokaryotic expression and purification; enzyme kinetic assays; thermal stability assays; PLP binding assays","journal":"Biochemistry","confidence":"High","confidence_rationale":"Tier 1 — reconstituted in vitro kinetic and stability characterization of purified mutant proteins","pmids":["38888931"],"is_preprint":false},{"year":2025,"finding":"Mature human ALAS2 in the mitochondrial matrix is inhibited by heme through a reversible mixed-inhibition mechanism; structure-based modeling identifies two flexible regions of ALAS2 that interact with heme, locking the enzyme in an inactive conformation and occluding the active site, constituting a negative feedback loop for erythroid heme biosynthesis.","method":"Enzymatic inhibition assays with heme; structure-based computational modeling of heme-ALAS2 interaction; affinity measurements","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 1 enzymatic assay plus structural modeling, but preprint and not yet peer-reviewed","pmids":["bio_10.1101_2025.06.09.658730"],"is_preprint":true},{"year":2016,"finding":"Two ALAS2 missense mutations (p.Leu406Phe and p.Tyr500Cys) reduce ALAS2 specific enzymatic activity to 14% and 7% of control respectively when expressed in E. coli, confirming their pathogenic mechanism in XLSA.","method":"Prokaryotic expression; in vitro ALAS2 enzymatic activity assays","journal":"Molecular genetics & genomic medicine","confidence":"Medium","confidence_rationale":"Tier 1 — in vitro enzymatic assay, single lab/single paper","pmids":["27247955"],"is_preprint":false},{"year":2017,"finding":"A novel 11-bp deletion in exon 10 of ALAS2 produces a monomeric rather than homodimeric protein structure (as predicted by SWISS model), resulting in marked loss of function and protein instability in a female infant with XLSA.","method":"Protein structural modeling (SWISS-MODEL); genetic mutation characterization","journal":"Journal of pediatric hematology/oncology","confidence":"Low","confidence_rationale":"Tier 4 — computational structural prediction only, no direct biochemical validation","pmids":["28731922"],"is_preprint":false}],"current_model":"ALAS2 is the mitochondrial, erythroid-specific, rate-limiting enzyme of heme biosynthesis that catalyzes condensation of glycine and succinyl-CoA (derived from ALAS2-bound succinyl-CoA synthetase SUCLA2) to produce 5-aminolevulinic acid; its activity requires pyridoxal 5'-phosphate as a stabilizing cofactor, is negatively regulated by heme product feedback via direct heme binding causing reversible mixed inhibition, is positively regulated in erythroid cells through a GATA1/TAL1/LMO2/LDB1 enhancer complex at its intron 1 GATA site, and is modulated by C-terminal residues that normally restrain enzymatic turnover and mediate SUCLA2 interaction, with loss-of-function mutations causing X-linked sideroblastic anemia and gain-of-function C-terminal truncations causing X-linked protoporphyria."},"narrative":{"teleology":[{"year":1994,"claim":"Establishing how catalytic-domain mutations reduce ALAS2 function and why patients respond to pyridoxine: the F165L mutation reduces activity to ~26% of normal, and exogenous PLP rescues the mutant enzyme by stabilizing its structure, providing the first biochemical mechanism for pyridoxine-responsive X-linked sideroblastic anemia.","evidence":"Prokaryotic expression and purification of recombinant wild-type and F165L ALAS2; enzymatic activity assays ± PLP","pmids":["7949148"],"confidence":"High","gaps":["Crystal structure of PLP-bound ALAS2 not determined","Mechanism of PLP stabilization at atomic level unknown"]},{"year":1995,"claim":"Generalization of the PLP-stabilization mechanism: two additional XLSA mutations (K299Q, A172T) showed marked thermolability rescued by PLP, confirming that cofactor-dependent stabilization—not catalytic rescue per se—is the primary basis for pyridoxine responsiveness across multiple ALAS2 variants.","evidence":"Recombinant mutant enzyme thermostability assays ± PLP","pmids":["7560104","7705839"],"confidence":"High","gaps":["Number of PLP-binding sites and their structural basis unresolved","In vivo PLP pharmacokinetics in erythroblasts not addressed"]},{"year":2000,"claim":"Discovery that ALAS2 does not function in isolation: it physically interacts with the ATP-specific succinyl-CoA synthetase beta subunit (SCS-βA/SUCLA2) in mitochondria, and the XLSA mutant D190V disrupts this interaction, suggesting substrate channeling as a requirement for efficient heme synthesis.","evidence":"Yeast two-hybrid screen of human bone marrow cDNA library; reciprocal co-immunoprecipitation in mammalian cells","pmids":["10727444"],"confidence":"High","gaps":["Stoichiometry and structural basis of the ALAS2–SUCLA2 complex unknown","Whether SUCLA2 interaction affects ALAS2 mitochondrial import unresolved"]},{"year":2002,"claim":"Demonstrating downstream cellular consequences of ALAS2 loss: ALAS2-null erythroblasts accumulate 15-fold excess cytoplasmic (not mitochondrial) non-heme iron and exhibit lipid peroxidation, establishing that ALAS2 deficiency per se—not just reduced heme—drives iron-mediated oxidative damage in sideroblastic anemia.","evidence":"ES cell-derived definitive erythroblasts from Alas2-null cells; non-heme iron quantification; electron microscopy; lipid peroxidation assays","pmids":["12393610"],"confidence":"High","gaps":["Mechanism of cytoplasmic rather than mitochondrial iron accumulation not explained","Whether iron accumulation is cause or consequence of differentiation block unclear"]},{"year":2003,"claim":"Identification of the proximal promoter as a critical erythroid regulatory element: a point mutation at nucleotide −206 reduced reporter activity by 94% and patient erythroblast ALAS2 mRNA by 87%, showing that transcriptional regulation is an independent disease mechanism for congenital sideroblastic anemia.","evidence":"Luciferase reporter assay in K562 cells; mRNA quantification in patient erythroid precursors","pmids":["12663458"],"confidence":"High","gaps":["Transcription factor(s) binding the −206 element not identified","Relationship between promoter and intron 1 enhancer elements not established"]},{"year":2008,"claim":"Reversal of the disease paradigm: C-terminal frameshift deletions (removing 19–20 residues) markedly increase ALAS2 activity rather than reducing it, causing X-linked protoporphyria—demonstrating that the C-terminal extension is an autoinhibitory domain and that gain-of-function and loss-of-function mutations in the same gene cause distinct porphyrias.","evidence":"Prokaryotic expression of frameshift mutant enzymes; enzymatic activity assays across eight families","pmids":["18760763"],"confidence":"High","gaps":["Structural basis of C-terminal autoinhibition not resolved at atomic level","Whether C-terminal truncations alter subcellular localization in vivo unknown"]},{"year":2011,"claim":"Systematic kinetic profiling of ten XLSA mutations consolidated the PLP-stabilization model and revealed that the penultimate C-terminal residue (Y586) modulates ALA product release rate, extending the functional map of the C-terminal region beyond simple autoinhibition.","evidence":"Prokaryotic expression of ten XLSA and one gain-of-function (Y586F) mutant; kinetic and thermostability assays ± PLP","pmids":["21309041","21653323"],"confidence":"High","gaps":["No crystal structure of C-terminal region","Product release kinetics not measured for all known gain-of-function variants"]},{"year":2012,"claim":"Defining the dual role of the C-terminus: C-terminal residues around Met567/Ser568 are required for SUCLA2 binding, and XLSA mutations that abolish this interaction lose in vivo function despite normal in vitro activity, establishing SUCLA2 coupling as essential for physiological heme synthesis; separately, R452 mutations disrupt succinyl-CoA cooperativity and PLP affinity.","evidence":"SUCLA2 affinity column binding assays; enzyme kinetics with multiple mutants","pmids":["22740690"],"confidence":"High","gaps":["Whether SUCLA2 binding and autoinhibition are separable C-terminal functions not fully dissected","In vivo validation of SUCLA2-binding requirement lacking"]},{"year":2013,"claim":"Identification of the intron 1 GATA element as the master erythroid enhancer of ALAS2: GATA1 binds this 130-bp element in vivo and in vitro, and patient mutations disrupting the GATA site abolish enhancer activity and cause congenital sideroblastic anemia, linking cis-regulatory disruption to disease.","evidence":"ChIP, EMSA, luciferase reporter assays in K562 cells; patient mutation analysis","pmids":["23935018"],"confidence":"High","gaps":["Full composition of the enhancer-bound complex not determined","Whether intron 1 GATA site functions autonomously or requires cooperation with other regulatory elements unclear"]},{"year":2016,"claim":"In vivo confirmation and mechanistic elaboration: CRISPR deletion of the 13-bp intron 1 GATA site in mice caused embryonic lethality from severe anemia, and chromatin conformation analysis revealed long-range loops connecting intron 1, intron 8, and the promoter, anchored by a GATA1/TAL1/LMO2/LDB1/Pol II complex.","evidence":"CRISPR/Cas9 mouse knockout; ChIP; chromatin loop analysis","pmids":["28123038"],"confidence":"High","gaps":["Order of assembly of the enhancer complex unknown","Whether the intron 8 GATA site is independently required not tested"]},{"year":2019,"claim":"Mechanistic basis of C-terminal gain-of-function refined: XLP truncation mutations increase Vmax up to 5.6-fold with an inverse correlation between thermostability and activity, indicating that loss of C-terminal residues increases active-site flexibility and accelerates catalytic turnover.","evidence":"Site-directed mutagenesis; purified recombinant enzyme kinetics; thermostability assays","pmids":["30678654"],"confidence":"High","gaps":["No direct structural evidence for active-site opening","Effect of gain-of-function on SUCLA2 interaction not systematically tested"]},{"year":2022,"claim":"Linking ALAS2 deficiency to ferroptosis: ALAS2 knockdown in human erythroblasts increases lipid peroxidation and ferroptosis susceptibility via BACH1-mediated repression of iron metabolism and glutathione synthesis genes, providing a pathway-level mechanism for the oxidative damage seen in sideroblastic anemia.","evidence":"CRISPR/base-editing of ALAS2 in cord blood-derived erythroblasts; erastin-induced ferroptosis; lipid peroxide quantification; gene expression profiling","pmids":["35637209"],"confidence":"Medium","gaps":["BACH1 involvement not validated by genetic rescue","Whether ferroptosis contributes to ringed sideroblast formation in vivo unknown","Single-lab finding"]},{"year":2024,"claim":"Fine-mapping of C-terminal residue function: V562A decreases enzyme stability while M567I alters substrate cooperativity without gross structural change, demonstrating that individual C-terminal residues independently tune stability versus active-site geometry.","evidence":"Purified recombinant V562A and M567I mutant enzymes; kinetic and thermal stability assays; PLP binding","pmids":["38888931"],"confidence":"High","gaps":["High-resolution crystal or cryo-EM structure of C-terminal extension still lacking","Whether these residues affect SUCLA2 binding differentially not tested"]},{"year":null,"claim":"Major open questions include: the atomic-resolution structure of full-length ALAS2 (including the C-terminal extension), the structural basis and physiological relevance of heme feedback inhibition in erythroid cells, and how the ALAS2–SUCLA2 complex is organized to channel succinyl-CoA within the mitochondrial matrix.","evidence":"","pmids":[],"confidence":"High","gaps":["No experimentally determined structure of full-length human ALAS2","Heme feedback mechanism demonstrated only in vitro (preprint) and not validated in vivo","In vivo stoichiometry and dynamics of ALAS2–SUCLA2 interaction unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0016740","term_label":"transferase activity","supporting_discovery_ids":[0,3,4,8,9,10,12,17]},{"term_id":"GO:0016874","term_label":"ligase activity","supporting_discovery_ids":[3,8,9]}],"localization":[{"term_id":"GO:0005739","term_label":"mitochondrion","supporting_discovery_ids":[1,2,11]}],"pathway":[{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[0,3,8,9,11]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[5,6,14]}],"complexes":["ALAS2-SUCLA2"],"partners":["SUCLA2","GATA1","TAL1","LMO2","LDB1","BACH1"],"other_free_text":[]},"mechanistic_narrative":"ALAS2 is the erythroid-specific, mitochondrial 5-aminolevulinate synthase that catalyzes the rate-limiting condensation of glycine and succinyl-CoA to form 5-aminolevulinic acid, the first committed step in heme biosynthesis. The enzyme requires pyridoxal 5'-phosphate (PLP) as an essential cofactor that stabilizes protein folding and active-site integrity, and it physically associates with the beta subunit of succinyl-CoA synthetase (SUCLA2) in mitochondria to ensure efficient substrate channeling; its C-terminal extension normally constrains catalytic turnover, with gain-of-function truncations increasing Vmax and causing X-linked protoporphyria, while loss-of-function missense mutations reduce activity and cause X-linked sideroblastic anemia [PMID:18760763, PMID:10727444, PMID:22740690, PMID:7560104, PMID:30678654]. Erythroid-specific transcription is governed by a GATA1/TAL1/LMO2/LDB1 enhancer complex at the intron 1 GATA site, which forms long-range chromatin loops with the intron 8 GATA site and proximal promoter; deletion of this element causes embryonic lethality from absent ALAS2 expression [PMID:28123038, PMID:23935018]. ALAS2 deficiency leads to cytoplasmic iron overload and increased susceptibility to ferroptosis in erythroid precursors [PMID:12393610, PMID:35637209]."},"prefetch_data":{"uniprot":{"accession":"P22557","full_name":"5-aminolevulinate synthase, erythroid-specific, mitochondrial","aliases":["5-aminolevulinic acid synthase 2","Delta-ALA synthase 2","Delta-aminolevulinate synthase 2"],"length_aa":587,"mass_kda":64.6,"function":"Catalyzes the pyridoxal 5'-phosphate (PLP)-dependent condensation of succinyl-CoA and glycine to form aminolevulinic acid (ALA), with CoA and CO2 as by-products (PubMed:14643893, PubMed:21252495, PubMed:21309041, PubMed:21653323, PubMed:32499479, PubMed:34492704). Contributes significantly to heme formation during erythropoiesis (PubMed:2050125) Catalyzes the pyridoxal 5'-phosphate (PLP)-dependent condensation of succinyl-CoA and glycine to form aminolevulinic acid (ALA), with CoA and CO2 as by-products (PubMed:14643893). Catalytic activity is 75-85% of isoform 1 activity (PubMed:14643893) Catalyzes the pyridoxal 5'-phosphate (PLP)-dependent condensation of succinyl-CoA and glycine to form aminolevulinic acid (ALA), with CoA and CO2 as by-products (PubMed:14643893). Catalytic activity is 65-75% of isoform 1 activity (PubMed:14643893)","subcellular_location":"Mitochondrion inner membrane","url":"https://www.uniprot.org/uniprotkb/P22557/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/ALAS2","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1208,"dependency_fraction":0.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/ALAS2","total_profiled":1310},"omim":[{"mim_id":"619523","title":"ANEMIA, SIDEROBLASTIC, 5; SIDBA5","url":"https://www.omim.org/entry/619523"},{"mim_id":"618015","title":"PROTOPORPHYRIA, ERYTHROPOIETIC, 2; EPP2","url":"https://www.omim.org/entry/618015"},{"mim_id":"616860","title":"ANEMIA, SIDEROBLASTIC, 3, PYRIDOXINE-REFRACTORY; SIDBA3","url":"https://www.omim.org/entry/616860"},{"mim_id":"615611","title":"CASEINOLYTIC MITOCHONDRIAL MATRIX PEPTIDASE CHAPERONE SUBUNIT; CLPX","url":"https://www.omim.org/entry/615611"},{"mim_id":"612386","title":"FERROCHELATASE; FECH","url":"https://www.omim.org/entry/612386"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Tissue enriched","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"bone marrow","ntpm":571.0}],"url":"https://www.proteinatlas.org/search/ALAS2"},"hgnc":{"alias_symbol":["ALAS-E"],"prev_symbol":["ASB"]},"alphafold":{"accession":"P22557","domains":[{"cath_id":"-","chopping":"2-83","consensus_level":"high","plddt":53.9226,"start":2,"end":83},{"cath_id":"3.40.640.10","chopping":"207-441","consensus_level":"high","plddt":97.5066,"start":207,"end":441},{"cath_id":"-","chopping":"550-587","consensus_level":"medium","plddt":65.355,"start":550,"end":587}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P22557","model_url":"https://alphafold.ebi.ac.uk/files/AF-P22557-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P22557-F1-predicted_aligned_error_v6.png","plddt_mean":82.19},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=ALAS2","jax_strain_url":"https://www.jax.org/strain/search?query=ALAS2"},"sequence":{"accession":"P22557","fasta_url":"https://rest.uniprot.org/uniprotkb/P22557.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P22557/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P22557"}},"corpus_meta":[{"pmid":"18760763","id":"PMC_18760763","title":"C-terminal deletions in the ALAS2 gene lead to gain of function and cause X-linked dominant protoporphyria without anemia or iron overload.","date":"2008","source":"American journal of human genetics","url":"https://pubmed.ncbi.nlm.nih.gov/18760763","citation_count":215,"is_preprint":false},{"pmid":"16325183","id":"PMC_16325183","title":"ASB proteins interact with Cullin5 and Rbx2 to form E3 ubiquitin ligase complexes.","date":"2005","source":"FEBS letters","url":"https://pubmed.ncbi.nlm.nih.gov/16325183","citation_count":98,"is_preprint":false},{"pmid":"7560104","id":"PMC_7560104","title":"Late-onset X-linked sideroblastic anemia. Missense mutations in the erythroid delta-aminolevulinate synthase (ALAS2) gene in two pyridoxine-responsive patients initially diagnosed with acquired refractory anemia and ringed sideroblasts.","date":"1995","source":"The Journal of clinical investigation","url":"https://pubmed.ncbi.nlm.nih.gov/7560104","citation_count":86,"is_preprint":false},{"pmid":"7949148","id":"PMC_7949148","title":"X-linked sideroblastic anemia: identification of the mutation in the erythroid-specific delta-aminolevulinate synthase gene (ALAS2) in the original family described by Cooley.","date":"1994","source":"Blood","url":"https://pubmed.ncbi.nlm.nih.gov/7949148","citation_count":81,"is_preprint":false},{"pmid":"11682484","id":"PMC_11682484","title":"ASB-2 inhibits growth and promotes commitment in myeloid leukemia cells.","date":"2001","source":"The Journal of biological 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replicated across eight families\",\n      \"pmids\": [\"18760763\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"ALAS2 (ALAS-E) physically interacts in mitochondria with the beta subunit of ATP-specific succinyl-CoA synthetase (SCS-betaA); the D190V XLSA mutant fails to associate with SCS-betaA, suggesting this interaction promotes efficient succinyl-CoA utilization or mitochondrial import of ALAS2.\",\n      \"method\": \"Yeast two-hybrid screen of human bone marrow cDNA library, followed by transient expression and co-immunoprecipitation in mammalian cells\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal co-IP plus yeast two-hybrid, with disease-linked mutant showing loss of interaction\",\n      \"pmids\": [\"10727444\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"ALAS2 C-terminal residues (around Met567/Ser568) are required for binding to the beta subunit of succinyl-CoA synthetase (SUCLA2); mutations abolishing SUCLA2 binding cause XLSA even with normal in vitro enzymatic activity and stability, indicating that the ALAS2-SUCLA2 complex is required for full in vivo heme synthetic activity. Additionally, XLSA mutations R452C and R452H retain SUCLA2 binding but show loss of positive cooperativity for succinyl-CoA, increased Km for succinyl-CoA, and reduced vitamin B6 affinity.\",\n      \"method\": \"SUCLA2 affinity column binding assays, enzyme kinetics of expressed mutant proteins, in vitro substrate cooperativity analysis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstituted binding and kinetic assays with multiple mutants and orthogonal methods\",\n      \"pmids\": [\"22740690\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"The F165L missense mutation in the first conserved catalytic domain of ALAS2 reduces specific enzymatic activity to ~26% of normal; pyridoxal 5'-phosphate (PLP) activates and stabilizes the mutant enzyme in vitro, mechanistically explaining pyridoxine responsiveness in affected patients.\",\n      \"method\": \"Prokaryotic expression and affinity purification of mutant and wild-type ALAS2 fusion proteins; enzymatic activity assays with and without PLP\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution with purified recombinant enzyme and cofactor stabilization experiments\",\n      \"pmids\": [\"7949148\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"ALAS2 missense mutations K299Q and A172T cause marked thermolability of the recombinant enzyme; addition of pyridoxal 5'-phosphate in vitro stabilizes both mutant enzymes, demonstrating that PLP acts as a cofactor stabilizer and explaining pyridoxine responsiveness.\",\n      \"method\": \"In vitro expression of recombinant mutant ALAS2 enzymes; thermostability assays with and without PLP\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — purified recombinant enzyme thermostability assay with PLP rescue, replicated in two independent mutations\",\n      \"pmids\": [\"7560104\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"A 130-bp enhancer in intron 1 of ALAS2 contains a GATA1-binding cis-element essential for erythroid-specific ALAS2 expression; GATA1 binds this element in vivo and in vitro, and mutations disrupting the GATA site abolish enhancer activity and cause congenital sideroblastic anemia.\",\n      \"method\": \"Chromatin immunoprecipitation (ChIP), electrophoretic mobility shift assay (EMSA), luciferase reporter assays in K562 cells, patient mutation analysis\",\n      \"journal\": \"Haematologica\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (ChIP, EMSA, reporter assay) confirming GATA1-dependent enhancer function\",\n      \"pmids\": [\"23935018\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"The intron 1 GATA site (int-1-GATA) of ALAS2 is indispensable for ALAS2 expression in vivo; deletion of this 13-bp fragment in mice causes embryonic lethality from severe anemia due to absent ALAS2 expression. The int-1-GATA site forms a long-range chromatin loop with the intron 8 GATA site and the proximal promoter, anchoring an enhancer complex containing GATA1, TAL1, LMO2, LDB1, and Pol II.\",\n      \"method\": \"CRISPR/Cas9-mediated in vivo deletion in mice; chromatin conformation/loop analysis; ChIP for transcription factor occupancy\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — in vivo genetic deletion with lethal phenotype, complemented by ChIP and chromatin loop data\",\n      \"pmids\": [\"28123038\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"A C-to-G transversion at nucleotide -206 in the ALAS2 proximal promoter causes a 94% loss of luciferase reporter activity in K562 erythroid cells and reduces ALAS2 mRNA by 87% in patient erythroblasts, identifying this region as a critical erythroid regulatory element.\",\n      \"method\": \"Luciferase reporter assay in K562 cells; primer extension; mRNA quantification in patient erythroid precursors\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reporter assay with patient-derived mRNA confirmation, two orthogonal methods\",\n      \"pmids\": [\"12663458\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Ten ALAS2 missense mutations associated with XLSA were expressed in E. coli; five caused decreased enzymatic activity under standard conditions, and two showed decreased activity only without exogenous PLP and increased thermosensitivity, establishing that PLP-dependent stabilization is the primary mechanism for pyridoxine-responsive variants.\",\n      \"method\": \"Prokaryotic expression of mutant ALAS2 proteins; in vitro enzymatic activity assays with and without exogenous PLP; thermosensitivity assays\",\n      \"journal\": \"Human mutation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — systematic in vitro enzyme characterization of 10 independent mutants\",\n      \"pmids\": [\"21309041\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"XLP gain-of-function truncation mutations in the ALAS2 C-terminal region increase Vmax for both succinyl-CoA and glycine substrates (1.4- to 5.6-fold), with an inverse correlation between thermostability and activity increase, indicating that increased molecular flexibility/active-site openness in the C-terminal region is the mechanism of enhanced enzymatic function.\",\n      \"method\": \"Site-directed mutagenesis; prokaryotic expression and purification; enzyme kinetic assays for Vmax, Km; thermostability assays\",\n      \"journal\": \"Molecular medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstituted in vitro with multiple truncation variants and kinetic characterization\",\n      \"pmids\": [\"30678654\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"A gain-of-function ALAS2 mutation (Y586F, c.1757 A>T) significantly increases the rate of 5-aminolevulinate release compared to wild-type ALAS2, demonstrating that the penultimate C-terminal residue modulates catalytic turnover and that ALAS2 gain-of-function can act as a modifier gene in congenital erythropoietic porphyria.\",\n      \"method\": \"Prokaryotic expression of Y586F mutant ALAS2; enzymatic activity assay measuring ALA release rate\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro enzymatic assay of expressed mutant protein\",\n      \"pmids\": [\"21653323\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"ALAS2-null definitive erythroblasts (derived from Alas2-null ES cells differentiated in culture) accumulate 15-fold more non-heme iron in the cytoplasm (not mitochondria) and exhibit increased lipid peroxidation compared to wild-type, demonstrating that ALAS2 deficiency per se causes cytoplasmic iron accumulation and oxidative stress without blocking erythroid differentiation.\",\n      \"method\": \"ES cell differentiation to definitive erythroblast stage; quantitative non-heme iron measurement; electron microscopy for iron localization; lipid peroxidation assays\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — defined KO cellular model with multiple readouts and direct iron localization by EM\",\n      \"pmids\": [\"12393610\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"The R411C ALAS2 mutation reduces enzymatic activity to 12-25% of wild-type (depending on PLP concentration), demonstrating a direct mechanistic link between this catalytic-core mutation and pyridoxine-responsive XLSA.\",\n      \"method\": \"E. coli expression and purification of mutant ALAS2; ALAS activity assays with and without PLP\",\n      \"journal\": \"British journal of haematology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro purified recombinant enzyme assay\",\n      \"pmids\": [\"9858242\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"A G-to-A mutation at nucleotide 871 (exon 7) causing a Gly-to-Ser substitution in ALAS2 markedly decreases enzymatic activity of the expressed mutant protein, establishing the catalytic importance of this glycine residue.\",\n      \"method\": \"Prokaryotic expression of mutant ALAS2; enzymatic activity measurement\",\n      \"journal\": \"Human genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 — in vitro enzymatic assay, single lab/single paper\",\n      \"pmids\": [\"7705839\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"The ALAS2 Y365C mutation impairs binding of the essential cofactor pyridoxal 5'-phosphate (PLP) to the enzyme, resulting in protein destabilization and loss of function; X inactivation in reticulocytes showed complete skewing toward the WT allele, indicating strong selective pressure against ALAS2-deficient erythroid precursors.\",\n      \"method\": \"Whole-exome sequencing; biochemical characterization of expressed mutant enzyme (PLP binding assay); X-inactivation analysis in blood fractions and primary erythroid cultures\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — biochemical PLP binding assay plus in vivo cell-selective pressure demonstrated by X-inactivation skewing\",\n      \"pmids\": [\"25705881\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"miR-218 directly targets the 3'-UTR of ALAS2 mRNA to repress its expression; overexpression of miR-218 in K562 cells inhibits erythroid differentiation and alters iron metabolism in a manner phenocopying ALAS2 knockdown.\",\n      \"method\": \"3'-UTR luciferase reporter assay; miR-218 overexpression; ALAS2 shRNA knockdown as functional control; flow cytometry for erythroid differentiation markers\",\n      \"journal\": \"International journal of molecular sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — reporter assay plus phenocopy experiment; single lab\",\n      \"pmids\": [\"26703568\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"ALAS2 knockdown in human erythroblasts (XLSA model) increases susceptibility to ferroptosis, associated with elevated lipid peroxides, enhanced BACH1 expression, and BACH1-mediated repression of iron metabolism and glutathione synthesis genes.\",\n      \"method\": \"CRISPR/base-editing introduction of ALAS2 missense mutations in cord blood-derived erythroblasts; ferroptosis inducer (erastin) treatment; lipid peroxide measurement; gene expression profiling; BACH1 functional analysis\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — defined cellular model with functional ferroptosis assay and mechanistic pathway placement; single lab\",\n      \"pmids\": [\"35637209\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Two C-terminal ALAS2 loss-of-function variants (V562A and M567I) do not cause gross structural perturbations but show decreased enzyme stability (V562A) and altered cooperativity of substrate binding (M567I); PLP addition moderately increases stability of both variants, indicating that the C-terminal extension modulates active-site geometry and substrate cooperativity.\",\n      \"method\": \"Site-directed mutagenesis; prokaryotic expression and purification; enzyme kinetic assays; thermal stability assays; PLP binding assays\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstituted in vitro kinetic and stability characterization of purified mutant proteins\",\n      \"pmids\": [\"38888931\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Mature human ALAS2 in the mitochondrial matrix is inhibited by heme through a reversible mixed-inhibition mechanism; structure-based modeling identifies two flexible regions of ALAS2 that interact with heme, locking the enzyme in an inactive conformation and occluding the active site, constituting a negative feedback loop for erythroid heme biosynthesis.\",\n      \"method\": \"Enzymatic inhibition assays with heme; structure-based computational modeling of heme-ALAS2 interaction; affinity measurements\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 enzymatic assay plus structural modeling, but preprint and not yet peer-reviewed\",\n      \"pmids\": [\"bio_10.1101_2025.06.09.658730\"],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Two ALAS2 missense mutations (p.Leu406Phe and p.Tyr500Cys) reduce ALAS2 specific enzymatic activity to 14% and 7% of control respectively when expressed in E. coli, confirming their pathogenic mechanism in XLSA.\",\n      \"method\": \"Prokaryotic expression; in vitro ALAS2 enzymatic activity assays\",\n      \"journal\": \"Molecular genetics & genomic medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 — in vitro enzymatic assay, single lab/single paper\",\n      \"pmids\": [\"27247955\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"A novel 11-bp deletion in exon 10 of ALAS2 produces a monomeric rather than homodimeric protein structure (as predicted by SWISS model), resulting in marked loss of function and protein instability in a female infant with XLSA.\",\n      \"method\": \"Protein structural modeling (SWISS-MODEL); genetic mutation characterization\",\n      \"journal\": \"Journal of pediatric hematology/oncology\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 4 — computational structural prediction only, no direct biochemical validation\",\n      \"pmids\": [\"28731922\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"ALAS2 is the mitochondrial, erythroid-specific, rate-limiting enzyme of heme biosynthesis that catalyzes condensation of glycine and succinyl-CoA (derived from ALAS2-bound succinyl-CoA synthetase SUCLA2) to produce 5-aminolevulinic acid; its activity requires pyridoxal 5'-phosphate as a stabilizing cofactor, is negatively regulated by heme product feedback via direct heme binding causing reversible mixed inhibition, is positively regulated in erythroid cells through a GATA1/TAL1/LMO2/LDB1 enhancer complex at its intron 1 GATA site, and is modulated by C-terminal residues that normally restrain enzymatic turnover and mediate SUCLA2 interaction, with loss-of-function mutations causing X-linked sideroblastic anemia and gain-of-function C-terminal truncations causing X-linked protoporphyria.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"ALAS2 is the erythroid-specific, mitochondrial 5-aminolevulinate synthase that catalyzes the rate-limiting condensation of glycine and succinyl-CoA to form 5-aminolevulinic acid, the first committed step in heme biosynthesis. The enzyme requires pyridoxal 5'-phosphate (PLP) as an essential cofactor that stabilizes protein folding and active-site integrity, and it physically associates with the beta subunit of succinyl-CoA synthetase (SUCLA2) in mitochondria to ensure efficient substrate channeling; its C-terminal extension normally constrains catalytic turnover, with gain-of-function truncations increasing Vmax and causing X-linked protoporphyria, while loss-of-function missense mutations reduce activity and cause X-linked sideroblastic anemia [PMID:18760763, PMID:10727444, PMID:22740690, PMID:7560104, PMID:30678654]. Erythroid-specific transcription is governed by a GATA1/TAL1/LMO2/LDB1 enhancer complex at the intron 1 GATA site, which forms long-range chromatin loops with the intron 8 GATA site and proximal promoter; deletion of this element causes embryonic lethality from absent ALAS2 expression [PMID:28123038, PMID:23935018]. ALAS2 deficiency leads to cytoplasmic iron overload and increased susceptibility to ferroptosis in erythroid precursors [PMID:12393610, PMID:35637209].\",\n  \"teleology\": [\n    {\n      \"year\": 1994,\n      \"claim\": \"Establishing how catalytic-domain mutations reduce ALAS2 function and why patients respond to pyridoxine: the F165L mutation reduces activity to ~26% of normal, and exogenous PLP rescues the mutant enzyme by stabilizing its structure, providing the first biochemical mechanism for pyridoxine-responsive X-linked sideroblastic anemia.\",\n      \"evidence\": \"Prokaryotic expression and purification of recombinant wild-type and F165L ALAS2; enzymatic activity assays ± PLP\",\n      \"pmids\": [\"7949148\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Crystal structure of PLP-bound ALAS2 not determined\", \"Mechanism of PLP stabilization at atomic level unknown\"]\n    },\n    {\n      \"year\": 1995,\n      \"claim\": \"Generalization of the PLP-stabilization mechanism: two additional XLSA mutations (K299Q, A172T) showed marked thermolability rescued by PLP, confirming that cofactor-dependent stabilization—not catalytic rescue per se—is the primary basis for pyridoxine responsiveness across multiple ALAS2 variants.\",\n      \"evidence\": \"Recombinant mutant enzyme thermostability assays ± PLP\",\n      \"pmids\": [\"7560104\", \"7705839\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Number of PLP-binding sites and their structural basis unresolved\", \"In vivo PLP pharmacokinetics in erythroblasts not addressed\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Discovery that ALAS2 does not function in isolation: it physically interacts with the ATP-specific succinyl-CoA synthetase beta subunit (SCS-βA/SUCLA2) in mitochondria, and the XLSA mutant D190V disrupts this interaction, suggesting substrate channeling as a requirement for efficient heme synthesis.\",\n      \"evidence\": \"Yeast two-hybrid screen of human bone marrow cDNA library; reciprocal co-immunoprecipitation in mammalian cells\",\n      \"pmids\": [\"10727444\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Stoichiometry and structural basis of the ALAS2–SUCLA2 complex unknown\", \"Whether SUCLA2 interaction affects ALAS2 mitochondrial import unresolved\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Demonstrating downstream cellular consequences of ALAS2 loss: ALAS2-null erythroblasts accumulate 15-fold excess cytoplasmic (not mitochondrial) non-heme iron and exhibit lipid peroxidation, establishing that ALAS2 deficiency per se—not just reduced heme—drives iron-mediated oxidative damage in sideroblastic anemia.\",\n      \"evidence\": \"ES cell-derived definitive erythroblasts from Alas2-null cells; non-heme iron quantification; electron microscopy; lipid peroxidation assays\",\n      \"pmids\": [\"12393610\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism of cytoplasmic rather than mitochondrial iron accumulation not explained\", \"Whether iron accumulation is cause or consequence of differentiation block unclear\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Identification of the proximal promoter as a critical erythroid regulatory element: a point mutation at nucleotide −206 reduced reporter activity by 94% and patient erythroblast ALAS2 mRNA by 87%, showing that transcriptional regulation is an independent disease mechanism for congenital sideroblastic anemia.\",\n      \"evidence\": \"Luciferase reporter assay in K562 cells; mRNA quantification in patient erythroid precursors\",\n      \"pmids\": [\"12663458\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Transcription factor(s) binding the −206 element not identified\", \"Relationship between promoter and intron 1 enhancer elements not established\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Reversal of the disease paradigm: C-terminal frameshift deletions (removing 19–20 residues) markedly increase ALAS2 activity rather than reducing it, causing X-linked protoporphyria—demonstrating that the C-terminal extension is an autoinhibitory domain and that gain-of-function and loss-of-function mutations in the same gene cause distinct porphyrias.\",\n      \"evidence\": \"Prokaryotic expression of frameshift mutant enzymes; enzymatic activity assays across eight families\",\n      \"pmids\": [\"18760763\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of C-terminal autoinhibition not resolved at atomic level\", \"Whether C-terminal truncations alter subcellular localization in vivo unknown\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Systematic kinetic profiling of ten XLSA mutations consolidated the PLP-stabilization model and revealed that the penultimate C-terminal residue (Y586) modulates ALA product release rate, extending the functional map of the C-terminal region beyond simple autoinhibition.\",\n      \"evidence\": \"Prokaryotic expression of ten XLSA and one gain-of-function (Y586F) mutant; kinetic and thermostability assays ± PLP\",\n      \"pmids\": [\"21309041\", \"21653323\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No crystal structure of C-terminal region\", \"Product release kinetics not measured for all known gain-of-function variants\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Defining the dual role of the C-terminus: C-terminal residues around Met567/Ser568 are required for SUCLA2 binding, and XLSA mutations that abolish this interaction lose in vivo function despite normal in vitro activity, establishing SUCLA2 coupling as essential for physiological heme synthesis; separately, R452 mutations disrupt succinyl-CoA cooperativity and PLP affinity.\",\n      \"evidence\": \"SUCLA2 affinity column binding assays; enzyme kinetics with multiple mutants\",\n      \"pmids\": [\"22740690\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether SUCLA2 binding and autoinhibition are separable C-terminal functions not fully dissected\", \"In vivo validation of SUCLA2-binding requirement lacking\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Identification of the intron 1 GATA element as the master erythroid enhancer of ALAS2: GATA1 binds this 130-bp element in vivo and in vitro, and patient mutations disrupting the GATA site abolish enhancer activity and cause congenital sideroblastic anemia, linking cis-regulatory disruption to disease.\",\n      \"evidence\": \"ChIP, EMSA, luciferase reporter assays in K562 cells; patient mutation analysis\",\n      \"pmids\": [\"23935018\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full composition of the enhancer-bound complex not determined\", \"Whether intron 1 GATA site functions autonomously or requires cooperation with other regulatory elements unclear\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"In vivo confirmation and mechanistic elaboration: CRISPR deletion of the 13-bp intron 1 GATA site in mice caused embryonic lethality from severe anemia, and chromatin conformation analysis revealed long-range loops connecting intron 1, intron 8, and the promoter, anchored by a GATA1/TAL1/LMO2/LDB1/Pol II complex.\",\n      \"evidence\": \"CRISPR/Cas9 mouse knockout; ChIP; chromatin loop analysis\",\n      \"pmids\": [\"28123038\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Order of assembly of the enhancer complex unknown\", \"Whether the intron 8 GATA site is independently required not tested\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Mechanistic basis of C-terminal gain-of-function refined: XLP truncation mutations increase Vmax up to 5.6-fold with an inverse correlation between thermostability and activity, indicating that loss of C-terminal residues increases active-site flexibility and accelerates catalytic turnover.\",\n      \"evidence\": \"Site-directed mutagenesis; purified recombinant enzyme kinetics; thermostability assays\",\n      \"pmids\": [\"30678654\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No direct structural evidence for active-site opening\", \"Effect of gain-of-function on SUCLA2 interaction not systematically tested\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Linking ALAS2 deficiency to ferroptosis: ALAS2 knockdown in human erythroblasts increases lipid peroxidation and ferroptosis susceptibility via BACH1-mediated repression of iron metabolism and glutathione synthesis genes, providing a pathway-level mechanism for the oxidative damage seen in sideroblastic anemia.\",\n      \"evidence\": \"CRISPR/base-editing of ALAS2 in cord blood-derived erythroblasts; erastin-induced ferroptosis; lipid peroxide quantification; gene expression profiling\",\n      \"pmids\": [\"35637209\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"BACH1 involvement not validated by genetic rescue\", \"Whether ferroptosis contributes to ringed sideroblast formation in vivo unknown\", \"Single-lab finding\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Fine-mapping of C-terminal residue function: V562A decreases enzyme stability while M567I alters substrate cooperativity without gross structural change, demonstrating that individual C-terminal residues independently tune stability versus active-site geometry.\",\n      \"evidence\": \"Purified recombinant V562A and M567I mutant enzymes; kinetic and thermal stability assays; PLP binding\",\n      \"pmids\": [\"38888931\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"High-resolution crystal or cryo-EM structure of C-terminal extension still lacking\", \"Whether these residues affect SUCLA2 binding differentially not tested\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Major open questions include: the atomic-resolution structure of full-length ALAS2 (including the C-terminal extension), the structural basis and physiological relevance of heme feedback inhibition in erythroid cells, and how the ALAS2–SUCLA2 complex is organized to channel succinyl-CoA within the mitochondrial matrix.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No experimentally determined structure of full-length human ALAS2\", \"Heme feedback mechanism demonstrated only in vitro (preprint) and not validated in vivo\", \"In vivo stoichiometry and dynamics of ALAS2–SUCLA2 interaction unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0016740\", \"supporting_discovery_ids\": [0, 3, 4, 8, 9, 10, 12, 17]},\n      {\"term_id\": \"GO:0016874\", \"supporting_discovery_ids\": [3, 8, 9]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005739\", \"supporting_discovery_ids\": [1, 2, 11]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [0, 3, 8, 9, 11]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [5, 6, 14]}\n    ],\n    \"complexes\": [\n      \"ALAS2-SUCLA2\"\n    ],\n    \"partners\": [\n      \"SUCLA2\",\n      \"GATA1\",\n      \"TAL1\",\n      \"LMO2\",\n      \"LDB1\",\n      \"BACH1\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}