ALAS2

Existing Annotations Review

GO Term	Evidence	Action	Reason
GO:0005739 mitochondrion	IBA GO_REF:0000033	ACCEPT	Summary: Phylogenetic (IBA) assertion that ALAS2 is active in the mitochondrion. This is well supported: ALAS2 has an N-terminal mitochondrial transit peptide and localizes to the matrix side of the mitochondrial inner membrane, consistent with all ALAS orthologs. Reason: Correct compartment and consistent with experimental localization data for human ALAS2. A more specific term (mitochondrial matrix) is also annotated separately. Supporting Evidence: PMID:10727444 The first and the rate-limiting enzyme of heme biosynthesis is delta-aminolevulinate synthase (ALAS), which is localized in mitochondria file:human/ALAS2/ALAS2-uniprot.txt Localizes to the matrix side of the mitochondrion
GO:0006783 heme biosynthetic process	IBA GO_REF:0000033	ACCEPT	Summary: Phylogenetic (IBA) assertion that ALAS2 participates in heme biosynthesis. ALAS2 catalyzes the first and rate-limiting step of the heme biosynthetic pathway, so this is a core biological process. Reason: Directly supported by the enzyme's catalytic role at the committed entry point of the heme pathway; conserved across ALAS orthologs. Supporting Evidence: PMID:32499479 The first and rate-limiting step is carried out by 5′-aminolevulinate synthase (ALAS; EC 2.3.1.37) in the mitochondria PMID:2050125 5-Aminolevulinate synthase (ALAS) catalyzes the first step of the heme biosynthetic pathway
GO:0003870 5-aminolevulinate synthase activity	IBA GO_REF:0000033	ACCEPT	Summary: Phylogenetic (IBA) assertion of the defining molecular function of ALAS2: 5-aminolevulinate synthase activity (EC 2.3.1.37). This is the core, experimentally established function of the protein. Reason: This is the primary catalytic activity of ALAS2, backed by multiple experimental annotations and structural/kinetic characterization; conserved across the family. Supporting Evidence: PMID:32499479 ALAS catalyses the pyridoxal 5′-phosphate (PLP)-dependent condensation of succinyl-CoA and glycine to form aminolevulinic acid (ALA), with CoA and CO2 as by-products
GO:0042541 hemoglobin biosynthetic process	IBA GO_REF:0000033	KEEP AS NON CORE	Summary: Phylogenetic (IBA) assertion linking ALAS2 to hemoglobin biosynthesis. ALAS2 supplies the heme moiety of hemoglobin, so this is a downstream physiological role rather than the enzyme's direct molecular activity. Reason: Biologically valid: erythroid heme produced by ALAS2 is incorporated into hemoglobin. However, ALAS2 does not itself synthesize globin or assemble hemoglobin; this is a downstream consequence of its heme-synthesis role, best retained as a non-core process. Supporting Evidence: PMID:14643893 the major splice isoform of ALAS2 is functional in vivo and could significantly contribute to erythroid heme biosynthesis and hemoglobin formation
GO:0003870 5-aminolevulinate synthase activity	IEA GO_REF:0000120	ACCEPT	Summary: Electronic (IEA) assignment of 5-aminolevulinate synthase activity via combined automated methods (ARBA, InterPro, RHEA:12921, EC:2.3.1.37). Correctly captures the core molecular function. Reason: IEA mapping is consistent with the experimentally validated catalytic activity and the RHEA/EC assignment for ALAS2. Supporting Evidence: file:human/ALAS2/ALAS2-uniprot.txt succinyl-CoA + glycine + H(+) = 5-aminolevulinate + CO2 + CoA
GO:0005743 mitochondrial inner membrane	IEA GO_REF:0000044	ACCEPT	Summary: Electronic (IEA) location term from UniProt subcellular-location mapping. ALAS2 is a peripheral membrane protein on the matrix side of the mitochondrial inner membrane, so this term is accurate. Reason: Matches the curated UniProt subcellular location and experimental data; the enzyme is associated with the inner membrane on its matrix face. Supporting Evidence: file:human/ALAS2/ALAS2-uniprot.txt Mitochondrion inner membrane PMID:14643893 the first 49 amino acids of the ALAS2 pre-protein are necessary and sufficient for translocation across the mitochondrial inner membrane
GO:0005759 mitochondrial matrix	IEA GO_REF:0000002	ACCEPT	Summary: Electronic (InterPro-based) location term. ALAS2 functions on the matrix side of the mitochondrial inner membrane; the mitochondrial matrix is the most informative compartment for its catalytic activity. Reason: Consistent with UniProt ("Localizes to the matrix side of the mitochondrion inner membrane") and with the Reactome TAS annotation to the same term. Supporting Evidence: file:human/ALAS2/ALAS2-uniprot.txt Localizes to the matrix side of the mitochondrion
GO:0006778 porphyrin-containing compound metabolic process	IEA GO_REF:0000002	ACCEPT	Summary: Electronic (InterPro-based) assignment to a broad parent process. Heme is a porphyrin-containing compound and ALAS2 initiates its biosynthesis, so the term is correct although general. Reason: Accurate but non-specific parent of heme biosynthesis; acceptable as an IEA annotation. The more specific heme biosynthetic process term is also annotated. Supporting Evidence: file:human/ALAS2/ALAS2-uniprot.txt Porphyrin-containing compound metabolism
GO:0016740 transferase activity	IEA GO_REF:0000002	MODIFY	Summary: Electronic (InterPro-based) assignment of the very general parent term transferase activity. ALAS2 is specifically an acyltransferase (5-aminolevulinate synthase, EC 2.3.1.37); the general term is uninformative given the specific function is known. Reason: Too general. ALAS2's specific transferase activity is 5-aminolevulinate synthase activity, which is already annotated experimentally; replace the generic parent with the specific child term. Proposed replacements: 5-aminolevulinate synthase activity Supporting Evidence: file:human/ALAS2/ALAS2-uniprot.txt succinyl-CoA + glycine + H(+) = 5-aminolevulinate + CO2 + CoA
GO:0030170 pyridoxal phosphate binding	IEA GO_REF:0000002	ACCEPT	Summary: Electronic (InterPro-based) assignment of PLP binding. ALAS2 is a PLP-dependent enzyme; PLP is covalently bound to active-site Lys391 as an internal aldimine. This is a correct secondary molecular function. Reason: Supported by the crystal structure and UniProt cofactor/binding-site annotations; PLP binding is intrinsic to catalysis. Supporting Evidence: PMID:32499479 PLP is covalently attached to the active site lysine (Lys391 in human ALAS2 (hsALAS2)) as an internal aldimine adduct
GO:0033014 tetrapyrrole biosynthetic process	IEA GO_REF:0000002	ACCEPT	Summary: Electronic (InterPro-based) assignment to the broad tetrapyrrole biosynthesis parent. Heme is a tetrapyrrole and ALAS2 initiates its biosynthesis, so the term is correct though general. Reason: Accurate but non-specific parent of heme biosynthesis; acceptable for an IEA annotation alongside the more specific heme biosynthetic process term. Supporting Evidence: PMID:32499479 The first and rate-limiting step is carried out by 5′-aminolevulinate synthase (ALAS; EC 2.3.1.37) in the mitochondria
GO:0005515 protein binding	IPI PMID:25416956 A proteome-scale map of the human interactome network.	MARK AS OVER ANNOTATED	Summary: IPI annotation to the uninformative generic term protein binding, from a large-scale binary interactome (Y2H) screen reporting an ALAS2-BANP (Q8N9N5) interaction. The bare term conveys no specific molecular function and the interaction is not functionally characterized. Reason: Per curation guidelines, bare protein binding is uninformative and should not be treated as a core function. The BANP interaction derives from a high-throughput proteome-scale map and has no established biological significance for ALAS2. Supporting Evidence: PMID:25416956 a systematic map of ?14,000 high-quality human binary protein-protein interactions
GO:0005739 mitochondrion	IEA GO_REF:0000107	ACCEPT	Summary: Electronic (Ensembl Compara) location transfer from the mouse ortholog placing ALAS2 in the mitochondrion. Correct compartment, corroborated by experimental data. Reason: Consistent with the mitochondrial localization of ALAS2 established experimentally and by the transit peptide. Supporting Evidence: PMID:10727444 The first and the rate-limiting enzyme of heme biosynthesis is delta-aminolevulinate synthase (ALAS), which is localized in mitochondria
GO:0006783 heme biosynthetic process	IEA GO_REF:0000107	ACCEPT	Summary: Electronic (Ensembl Compara) transfer from the mouse ortholog for heme biosynthetic process. This is a core process for ALAS2, which catalyzes the committed first step. Reason: Correct and consistent with the experimental and IBA annotations to the same term. Supporting Evidence: PMID:32499479 The first and rate-limiting step is carried out by 5′-aminolevulinate synthase (ALAS; EC 2.3.1.37) in the mitochondria
GO:0030218 erythrocyte differentiation	IEA GO_REF:0000107	KEEP AS NON CORE	Summary: Electronic (Ensembl Compara) transfer for erythrocyte differentiation. ALAS2 is the erythroid-specific isozyme, and heme flux governs erythroid maturation; this is a downstream physiological role rather than the direct molecular function. Reason: Biologically valid because ALAS2-driven heme synthesis is required for terminal erythroid differentiation, but ALAS2's core function is catalytic; this developmental process is best retained as non-core. Supporting Evidence: PMID:32499479 ALAS2 (gene location Xp11.21) is predominantly expressed in erythroid progenitor cells, and synthesizes 85–90% of total body heme specifically for hemoglobin production during erythropoiesis
GO:0042541 hemoglobin biosynthetic process	IEA GO_REF:0000107	KEEP AS NON CORE	Summary: Electronic (Ensembl Compara) transfer for hemoglobin biosynthesis. ALAS2 supplies heme for hemoglobin; a downstream physiological role, not the direct catalytic function. Reason: Valid downstream role (erythroid heme feeds hemoglobin), consistent with the IBA/ISS annotations to the same term, but non-core relative to the enzyme's catalytic activity. Supporting Evidence: PMID:14643893 the major splice isoform of ALAS2 is functional in vivo and could significantly contribute to erythroid heme biosynthesis and hemoglobin formation
GO:0006785 heme B biosynthetic process	IDA PMID:2050125 Human erythroid 5-aminolevulinate synthase: promoter analysi...	ACCEPT	Summary: IDA annotation to heme B biosynthetic process. Heme b (protoheme IX) is the end-product of the pathway that ALAS2 initiates, and ALAS2 is the erythroid isozyme providing heme for hemoglobin (which uses heme b). This is a more specific, correct child of heme biosynthesis. Reason: Consistent with ALAS2's role as the committed first enzyme of the pathway that produces heme b for hemoglobin. Curated by UniProt (IDA) from the original erythroid ALAS characterization; deferring to the curator's reading of the full text. Supporting Evidence: PMID:2050125 5-Aminolevulinate synthase (ALAS) catalyzes the first step of the heme biosynthetic pathway
GO:0003870 5-aminolevulinate synthase activity	EXP PMID:34492704 The immunometabolite itaconate inhibits heme synthesis and r...	ACCEPT	Summary: Experimental (EXP) annotation of 5-aminolevulinate synthase activity. Recombinant human ALAS2 was assayed enzymatically (Km ~10 uM for succinyl-CoA) and shown to be competitively inhibited by itaconyl-CoA, directly demonstrating the catalytic activity. Reason: Direct experimental evidence for the core catalytic function of ALAS2 using purified enzyme. Supporting Evidence: PMID:34492704 itaconyl-CoA is a competitive inhibitor of the erythroid-specific 5-aminolevulinate synthase (ALAS2), the first and rate-limiting step in heme synthesis PMID:34492704 itaconyl-CoA to be a competitive inhibitor of recombinant ALAS2 with an inhibitory constant of 100 ± 20 μM
GO:0005739 mitochondrion	HTP PMID:34800366 Quantitative high-confidence human mitochondrial proteome an...	ACCEPT	Summary: High-throughput (HTP) mitochondrial-proteome study identifying ALAS2 among the high-confidence human mitochondrial proteome (MitoCoP). Corroborates the mitochondrial localization. Reason: Consistent with the established mitochondrial localization; a large-scale proteomic confirmation of compartment. Supporting Evidence: PMID:34800366 defined a mitochondrial high-confidence proteome of >1,100 proteins (MitoCoP)
GO:0003870 5-aminolevulinate synthase activity	IMP PMID:21252495 New mutation in erythroid-specific delta-aminolevulinate syn...	ACCEPT	Summary: IMP annotation of 5-aminolevulinate synthase activity. A novel XLSA K156E ALAS2 variant was shown by a spectrophotometric enzyme assay to severely decrease ALAS2 activity, functionally demonstrating the enzyme's catalytic activity via mutation. Reason: Mutant characterization directly ties ALAS2 to 5-aminolevulinate synthase activity; supports the core function. Supporting Evidence: PMID:21252495 X-linked SA, which results from mutations in erythroid-specific δ-aminolevulinate synthase (ALAS2), the first enzyme in heme biosynthesis PMID:21252495 A novel K156E substitution in ALAS2 was discovered in 1 pyridoxine-responsive patient. The functional study showed that this substitution severely decreases ALAS2 enzyme activity
GO:0003870 5-aminolevulinate synthase activity	IMP PMID:21309041 Sideroblastic anemia: molecular analysis of the ALAS2 gene i...	ACCEPT	Summary: IMP annotation of 5-aminolevulinate synthase activity. Ten XLSA missense mutations were expressed in E. coli and assayed; several showed decreased enzymatic activity, functionally confirming the catalytic function through mutation. Reason: Multiple mutant enzyme assays directly link ALAS2 to 5-aminolevulinate synthase activity; supports the core function. Supporting Evidence: PMID:21309041 XLSA is due to mutations in the erythroid-specific 5-aminolevulinate synthase (ALAS2) gene PMID:21309041 Five missense mutations resulted in decreased enzymatic activity under standard conditions
GO:0003870 5-aminolevulinate synthase activity	IMP PMID:21653323 ALAS2 acts as a modifier gene in patients with congenital er...	ACCEPT	Summary: IMP annotation of 5-aminolevulinate synthase activity. A C-terminal gain-of-function variant (Y586F) showed significantly increased 5-aminolevulinate release relative to wild-type, functionally demonstrating the catalytic activity and the C-terminal regulatory role. Reason: Mutant enzyme characterization directly ties ALAS2 to 5-aminolevulinate synthase activity; supports the core function. Supporting Evidence: PMID:21653323 The rate of 5-aminolevulinate release from Y586F was significantly increased over that of wild-type ALAS2
GO:0003870 5-aminolevulinate synthase activity	IDA PMID:32499479 Human aminolevulinate synthase structure reveals a eukaryoti...	ACCEPT	Summary: IDA annotation of 5-aminolevulinate synthase activity. Recombinant human ALAS2 was structurally and kinetically characterized (Km 31 uM succinyl-CoA, 11.8 uM glycine), directly demonstrating the PLP-dependent condensation of succinyl-CoA and glycine to form ALA. Reason: Direct in vitro demonstration of the core catalytic activity with a crystal structure of the human enzyme. Supporting Evidence: PMID:32499479 ALAS catalyses the pyridoxal 5′-phosphate (PLP)-dependent condensation of succinyl-CoA and glycine to form aminolevulinic acid (ALA), with CoA and CO2 as by-products
GO:0003870 5-aminolevulinate synthase activity	IDA PMID:14643893 The major splice variant of human 5-aminolevulinate synthase...	ACCEPT	Summary: IDA annotation of 5-aminolevulinate synthase activity. In vitro studies showed the major ALAS2 splice variant and isoforms produce a functional enzyme, directly demonstrating the catalytic activity of the human protein. Reason: Direct experimental evidence for the core catalytic function; the curator read the full text of this isoform characterization. Supporting Evidence: PMID:14643893 The initial step of the heme biosynthetic pathway in erythroid cells is catalyzed by an erythroid-specific isoform of 5-aminolevulinate synthase-2 (ALAS2)
GO:0003870 5-aminolevulinate synthase activity	IDA PMID:14643893 The major splice variant of human 5-aminolevulinate synthase...	ACCEPT	Summary: IDA annotation of 5-aminolevulinate synthase activity (a second GOA record for the same reference, assigned by UniProt). As above, in vitro studies of the human ALAS2 splice variant and isoforms demonstrated a functional enzyme, directly supporting the catalytic activity. Reason: Duplicate of the MGI-assigned IDA annotation to the same term/reference; direct experimental evidence for the core catalytic function. Supporting Evidence: PMID:14643893 The initial step of the heme biosynthetic pathway in erythroid cells is catalyzed by an erythroid-specific isoform of 5-aminolevulinate synthase-2 (ALAS2)
GO:0005739 mitochondrion	IDA PMID:14643893 The major splice variant of human 5-aminolevulinate synthase...	ACCEPT	Summary: IDA localization to the mitochondrion. The ALAS2 pre-protein's N-terminal 49 residues were shown to be necessary and sufficient for translocation into mitochondria, directly establishing the mitochondrial localization. Reason: Direct experimental evidence for mitochondrial localization via transit-peptide translocation assays. Supporting Evidence: PMID:14643893 the first 49 amino acids of the ALAS2 pre-protein are necessary and sufficient for translocation across the mitochondrial inner membrane
GO:0005759 mitochondrial matrix	TAS Reactome:R-HSA-189442	ACCEPT	Summary: TAS annotation (Reactome) placing the ALAS2-catalyzed condensation of succinyl-CoA and glycine in the mitochondrial matrix. Matches the enzyme's location on the matrix side of the inner membrane. Reason: Consistent with the UniProt subcellular location and the IEA matrix annotation; the matrix is the most informative compartment for the catalytic reaction. Supporting Evidence: file:human/ALAS2/ALAS2-uniprot.txt Localizes to the matrix side of the mitochondrion
GO:0006879 intracellular iron ion homeostasis	ISS GO_REF:0000024	KEEP AS NON CORE	Summary: ISS annotation (from the ALAS1 ortholog) for intracellular iron ion homeostasis. ALAS2 translation is coupled to iron availability via an iron-responsive element in its 5' UTR, and heme synthesis is a major consumer of the erythroid iron flux; this is a peripheral, indirect role rather than a core function. Reason: ALAS2 participates in erythroid iron utilization indirectly (its output consumes iron via downstream ferrochelatase and its expression is iron-regulated), but it is not an iron-homeostasis effector per se; retain as non-core. Supporting Evidence: PMID:2050125 An iron-responsive element (IRE) motif has been identified in the 5'-untranslated region of the human erythroid ALAS mRNA
GO:0032364 intracellular oxygen homeostasis	NAS PMID:16234850 Erythroid-specific 5-aminolevulinate synthase protein is sta...	KEEP AS NON CORE	Summary: NAS annotation for intracellular oxygen homeostasis. This derives from the observation that ALAS2 protein stability is oxygen-dependent (hypoxia and proteasome inhibition stabilize it via an LXXLAP prolyl-hydroxylation / vHL pathway). This reflects ALAS2 being regulated by oxygen rather than ALAS2 controlling cellular oxygen levels. Reason: The evidence shows ALAS2 is a target of oxygen-dependent regulation, not an effector of oxygen homeostasis. Kept as non-core because the underlying observation (O2-dependent stability) is real but the process term overstates ALAS2's role. Supporting Evidence: PMID:16234850 Hypoxia (1% O2) and inhibition of the proteasome increased both the stability and the specific activity of ALAS2
GO:0001666 response to hypoxia	IDA PMID:16234850 Erythroid-specific 5-aminolevulinate synthase protein is sta...	KEEP AS NON CORE	Summary: IDA annotation for response to hypoxia. ALAS2 protein is stabilized under low oxygen (1% O2) and by proteasome inhibition, and interacts with the vHL protein under normoxia, consistent with an oxygen/hypoxia-responsive regulatory behavior of the protein. Reason: Experimentally observed oxygen-dependent stabilization is a genuine regulatory response, but it is peripheral to ALAS2's core catalytic role in heme synthesis; retain as non-core. Supporting Evidence: PMID:16234850 Hypoxia (1% O2) and inhibition of the proteasome increased both the stability and the specific activity of ALAS2
GO:0005515 protein binding	IPI PMID:16234850 Erythroid-specific 5-aminolevulinate synthase protein is sta...	MARK AS OVER ANNOTATED	Summary: IPI annotation to the generic term protein binding, capturing an ALAS2 interaction with the von Hippel-Lindau (vHL) protein (UniProtKB:P40337) detected by co-immunoprecipitation under normoxia. The interaction is real and mechanistically meaningful (targeting ALAS2 for degradation), but the bare protein binding term is uninformative. Reason: Per curation guidelines, bare protein binding does not convey a specific molecular function. The underlying vHL interaction is captured biologically under the hypoxia/oxygen-regulation annotations. Supporting Evidence: PMID:16234850 The von Hippel-Lindau (vHL) protein was immunoprecipitated with FLAG epitope-tagged ALAS2 produced in normoxic cells
GO:0005515 protein binding	IPI PMID:10727444 Interaction between succinyl CoA synthetase and the heme-bio...	MARK AS OVER ANNOTATED	Summary: IPI annotation to the generic term protein binding, capturing the ALAS2 (ALAS-E) interaction with SUCLA2 (SCS-betaA, UniProtKB:Q9P2R7), the beta subunit of ATP-specific succinyl-CoA synthetase. This is a functionally meaningful interaction (supplying/channeling the succinyl-CoA substrate), but the bare term is uninformative. Reason: The SUCLA2 interaction is biologically important and well documented, but per curation guidelines the generic protein binding term should not stand as a core molecular function. A specific substrate-supply role would be better captured by a dedicated term or GO-CAM relation. Supporting Evidence: PMID:10727444 mitochodrially expressed SCS-betaA associates specifically with ALAS-E and not with ALAS-N
GO:0005739 mitochondrion	IDA PMID:10727444 Interaction between succinyl CoA synthetase and the heme-bio...	ACCEPT	Summary: IDA localization to the mitochondrion. The study used the mitochondrial form of human ALAS-E and confirmed mitochondrial association of the enzyme and its SUCLA2 partner. Reason: Direct evidence consistent with the established mitochondrial localization of ALAS2. Supporting Evidence: PMID:10727444 The first and the rate-limiting enzyme of heme biosynthesis is delta-aminolevulinate synthase (ALAS), which is localized in mitochondria
GO:0006783 heme biosynthetic process	ISS GO_REF:0000024	ACCEPT	Summary: ISS annotation (from the ALAS1 ortholog) for heme biosynthetic process, the core process of ALAS2 as the first, rate-limiting enzyme of the pathway. Reason: Correct and consistent with the experimental, IBA and IEA annotations to the same term. Supporting Evidence: PMID:32499479 The first and rate-limiting step is carried out by 5′-aminolevulinate synthase (ALAS; EC 2.3.1.37) in the mitochondria
GO:0006783 heme biosynthetic process	NAS PMID:14643893 The major splice variant of human 5-aminolevulinate synthase...	ACCEPT	Summary: NAS annotation for heme biosynthetic process, based on the authors' statement that ALAS2 catalyzes the initial step of the erythroid heme biosynthetic pathway. Reason: Correct core process; corroborated by experimental/IBA/IEA/ISS annotations to the same term. Supporting Evidence: PMID:14643893 The initial step of the heme biosynthetic pathway in erythroid cells is catalyzed by an erythroid-specific isoform of 5-aminolevulinate synthase-2 (ALAS2)
GO:0030218 erythrocyte differentiation	ISS GO_REF:0000024	KEEP AS NON CORE	Summary: ISS annotation (from the ALAS1 ortholog) for erythrocyte differentiation. As the erythroid-specific isozyme supplying heme for maturation, this is a downstream physiological role rather than the core catalytic function. Reason: Biologically valid downstream role in erythroid maturation; retained as non-core relative to the enzyme's molecular function, consistent with the IEA annotation to the same term. Supporting Evidence: PMID:32499479 ALAS2 (gene location Xp11.21) is predominantly expressed in erythroid progenitor cells, and synthesizes 85–90% of total body heme specifically for hemoglobin production during erythropoiesis
GO:0042541 hemoglobin biosynthetic process	ISS GO_REF:0000024	KEEP AS NON CORE	Summary: ISS annotation (from the ALAS1 ortholog) for hemoglobin biosynthesis. ALAS2 supplies the heme required for hemoglobin; a downstream physiological role. Reason: Valid downstream role consistent with the IBA/IEA annotations to the same term; non-core relative to the catalytic activity. Supporting Evidence: PMID:14643893 the major splice isoform of ALAS2 is functional in vivo and could significantly contribute to erythroid heme biosynthesis and hemoglobin formation
GO:0005515 protein binding	IPI PMID:14643893 The major splice variant of human 5-aminolevulinate synthase...	MARK AS OVER ANNOTATED	Summary: IPI annotation to the generic term protein binding, capturing the ALAS2-SUCLA2 (Q9P2R7) interaction demonstrated during the isoform characterization. The interaction is meaningful (succinyl-CoA supply) but the bare term is uninformative. Reason: Per curation guidelines, bare protein binding should not stand as a core molecular function; the SUCLA2 interaction is captured biologically and is redundant with the same interaction reported in PMID:10727444. Supporting Evidence: PMID:32499479 capable of forming an interaction with the previously reported partner, beta subunit (SUCLA2) of the succinyl-CoA synthetase complex
GO:0005743 mitochondrial inner membrane	IDA PMID:14643893 The major splice variant of human 5-aminolevulinate synthase...	ACCEPT	Summary: IDA localization to the mitochondrial inner membrane. The ALAS2 pre-protein was shown to translocate across the mitochondrial inner membrane, and UniProt annotates it as a peripheral inner-membrane protein on the matrix side. Reason: Direct experimental evidence; consistent with UniProt subcellular location. Supporting Evidence: PMID:14643893 the first 49 amino acids of the ALAS2 pre-protein are necessary and sufficient for translocation across the mitochondrial inner membrane file:human/ALAS2/ALAS2-uniprot.txt Mitochondrion inner membrane
GO:0030218 erythrocyte differentiation	NAS PMID:2050125 Human erythroid 5-aminolevulinate synthase: promoter analysi...	KEEP AS NON CORE	Summary: NAS annotation for erythrocyte differentiation, based on ALAS2 being the erythroid-specific isozyme with erythroid-specific promoter elements (GATA-1, NF-E2) supplying heme during erythropoiesis. Reason: Valid downstream/developmental role reflecting the erythroid-restricted expression and function of ALAS2; retained as non-core relative to its catalytic activity, consistent with the ISS/IEA annotations to the same term. Supporting Evidence: PMID:2050125 putative erythroid-specific cis-acting elements including both a GATA-1 and an NF-E2 binding site

📄 View Raw YAML

id: P22557
gene_symbol: ALAS2
product_type: PROTEIN
status: INITIALIZED
taxon:
  id: NCBITaxon:9606
  label: Homo sapiens
description: >-
  ALAS2 is the erythroid-specific 5-aminolevulinate synthase (ALAS-E; EC 2.3.1.37),
  the first and rate-limiting enzyme of the heme biosynthetic pathway in developing
  erythroid cells. It is a pyridoxal 5'-phosphate (PLP)-dependent enzyme that catalyzes
  the condensation of glycine with succinyl-CoA to form 5-aminolevulinate (ALA), with
  CoA and CO2 released as by-products. ALAS2 acts as an obligate homodimer in which the
  active site is shared between subunits, with PLP covalently bound to an active-site
  lysine (Lys391) as an internal aldimine. The enzyme carries an N-terminal transit
  peptide that targets it to mitochondria, where it localizes to the matrix side of the
  mitochondrial inner membrane. ALAS2 is one of two ALAS isozymes: the ubiquitous
  housekeeping ALAS1 supplies basal heme for cytochromes and other hemoproteins, whereas
  ALAS2 is expressed in erythroid progenitors and provides the high heme flux required
  for hemoglobin production during erythropoiesis. Its output governs downstream porphyrin
  and heme synthesis and, ultimately, erythrocyte maturation. ALAS2 activity is regulated
  at multiple levels, including an iron-responsive element in the 5' UTR that couples
  translation to cellular iron, oxygen-dependent protein stability, and a eukaryote-specific
  C-terminal autoinhibitory loop that gates substrate access. Loss-of-function mutations
  cause X-linked sideroblastic anemia, whereas C-terminal gain-of-function mutations cause
  X-linked (dominant) protoporphyria.
alternative_products:
- name: '1'
  id: P22557-1
- name: 2 (Delta4)
  id: P22557-2
  sequence_note: VSP_042852
- name: 3 (F143M)
  id: P22557-3
  sequence_note: VSP_042851, VSP_042853
- name: '4'
  id: P22557-4
  sequence_note: VSP_047330, VSP_042852
existing_annotations:
- term:
    id: GO:0005739
    label: mitochondrion
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: is_active_in
  review:
    summary: >-
      Phylogenetic (IBA) assertion that ALAS2 is active in the mitochondrion. This is
      well supported: ALAS2 has an N-terminal mitochondrial transit peptide and localizes
      to the matrix side of the mitochondrial inner membrane, consistent with all ALAS
      orthologs.
    action: ACCEPT
    reason: >-
      Correct compartment and consistent with experimental localization data for human
      ALAS2. A more specific term (mitochondrial matrix) is also annotated separately.
    supported_by:
    - reference_id: PMID:10727444
      supporting_text: >-
        The first and the rate-limiting enzyme of heme biosynthesis is
        delta-aminolevulinate synthase (ALAS), which is localized in mitochondria
    - reference_id: file:human/ALAS2/ALAS2-uniprot.txt
      supporting_text: Localizes to the matrix side of the mitochondrion
- term:
    id: GO:0006783
    label: heme biosynthetic process
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: involved_in
  review:
    summary: >-
      Phylogenetic (IBA) assertion that ALAS2 participates in heme biosynthesis. ALAS2
      catalyzes the first and rate-limiting step of the heme biosynthetic pathway, so
      this is a core biological process.
    action: ACCEPT
    reason: >-
      Directly supported by the enzyme's catalytic role at the committed entry point of
      the heme pathway; conserved across ALAS orthologs.
    supported_by:
    - reference_id: PMID:32499479
      supporting_text: >-
        The first and rate-limiting step is carried out by 5′-aminolevulinate synthase
        (ALAS; EC 2.3.1.37) in the mitochondria
    - reference_id: PMID:2050125
      supporting_text: >-
        5-Aminolevulinate synthase (ALAS) catalyzes the first step of the heme
        biosynthetic pathway
- term:
    id: GO:0003870
    label: 5-aminolevulinate synthase activity
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: enables
  review:
    summary: >-
      Phylogenetic (IBA) assertion of the defining molecular function of ALAS2:
      5-aminolevulinate synthase activity (EC 2.3.1.37). This is the core, experimentally
      established function of the protein.
    action: ACCEPT
    reason: >-
      This is the primary catalytic activity of ALAS2, backed by multiple experimental
      annotations and structural/kinetic characterization; conserved across the family.
    supported_by:
    - reference_id: PMID:32499479
      supporting_text: >-
        ALAS catalyses the pyridoxal 5′-phosphate (PLP)-dependent condensation of
        succinyl-CoA and glycine to form aminolevulinic acid (ALA), with CoA and CO2 as
        by-products
- term:
    id: GO:0042541
    label: hemoglobin biosynthetic process
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: involved_in
  review:
    summary: >-
      Phylogenetic (IBA) assertion linking ALAS2 to hemoglobin biosynthesis. ALAS2 supplies
      the heme moiety of hemoglobin, so this is a downstream physiological role rather than
      the enzyme's direct molecular activity.
    action: KEEP_AS_NON_CORE
    reason: >-
      Biologically valid: erythroid heme produced by ALAS2 is incorporated into hemoglobin.
      However, ALAS2 does not itself synthesize globin or assemble hemoglobin; this is a
      downstream consequence of its heme-synthesis role, best retained as a non-core process.
    supported_by:
    - reference_id: PMID:14643893
      supporting_text: >-
        the major splice isoform of ALAS2 is functional in vivo and could significantly
        contribute to erythroid heme biosynthesis and hemoglobin formation
- term:
    id: GO:0003870
    label: 5-aminolevulinate synthase activity
  evidence_type: IEA
  original_reference_id: GO_REF:0000120
  qualifier: enables
  review:
    summary: >-
      Electronic (IEA) assignment of 5-aminolevulinate synthase activity via combined
      automated methods (ARBA, InterPro, RHEA:12921, EC:2.3.1.37). Correctly captures the
      core molecular function.
    action: ACCEPT
    reason: >-
      IEA mapping is consistent with the experimentally validated catalytic activity and
      the RHEA/EC assignment for ALAS2.
    supported_by:
    - reference_id: file:human/ALAS2/ALAS2-uniprot.txt
      supporting_text: succinyl-CoA + glycine + H(+) = 5-aminolevulinate + CO2 + CoA
- term:
    id: GO:0005743
    label: mitochondrial inner membrane
  evidence_type: IEA
  original_reference_id: GO_REF:0000044
  qualifier: located_in
  review:
    summary: >-
      Electronic (IEA) location term from UniProt subcellular-location mapping. ALAS2 is a
      peripheral membrane protein on the matrix side of the mitochondrial inner membrane,
      so this term is accurate.
    action: ACCEPT
    reason: >-
      Matches the curated UniProt subcellular location and experimental data; the enzyme is
      associated with the inner membrane on its matrix face.
    supported_by:
    - reference_id: file:human/ALAS2/ALAS2-uniprot.txt
      supporting_text: Mitochondrion inner membrane
    - reference_id: PMID:14643893
      supporting_text: >-
        the first 49 amino acids of the ALAS2 pre-protein are necessary and sufficient for
        translocation across the mitochondrial inner membrane
- term:
    id: GO:0005759
    label: mitochondrial matrix
  evidence_type: IEA
  original_reference_id: GO_REF:0000002
  qualifier: located_in
  review:
    summary: >-
      Electronic (InterPro-based) location term. ALAS2 functions on the matrix side of the
      mitochondrial inner membrane; the mitochondrial matrix is the most informative
      compartment for its catalytic activity.
    action: ACCEPT
    reason: >-
      Consistent with UniProt ("Localizes to the matrix side of the mitochondrion inner
      membrane") and with the Reactome TAS annotation to the same term.
    supported_by:
    - reference_id: file:human/ALAS2/ALAS2-uniprot.txt
      supporting_text: Localizes to the matrix side of the mitochondrion
- term:
    id: GO:0006778
    label: porphyrin-containing compound metabolic process
  evidence_type: IEA
  original_reference_id: GO_REF:0000002
  qualifier: involved_in
  review:
    summary: >-
      Electronic (InterPro-based) assignment to a broad parent process. Heme is a
      porphyrin-containing compound and ALAS2 initiates its biosynthesis, so the term is
      correct although general.
    action: ACCEPT
    reason: >-
      Accurate but non-specific parent of heme biosynthesis; acceptable as an IEA
      annotation. The more specific heme biosynthetic process term is also annotated.
    supported_by:
    - reference_id: file:human/ALAS2/ALAS2-uniprot.txt
      supporting_text: Porphyrin-containing compound metabolism
- term:
    id: GO:0016740
    label: transferase activity
  evidence_type: IEA
  original_reference_id: GO_REF:0000002
  qualifier: enables
  review:
    summary: >-
      Electronic (InterPro-based) assignment of the very general parent term transferase
      activity. ALAS2 is specifically an acyltransferase (5-aminolevulinate synthase,
      EC 2.3.1.37); the general term is uninformative given the specific function is known.
    action: MODIFY
    reason: >-
      Too general. ALAS2's specific transferase activity is 5-aminolevulinate synthase
      activity, which is already annotated experimentally; replace the generic parent with
      the specific child term.
    proposed_replacement_terms:
    - id: GO:0003870
      label: 5-aminolevulinate synthase activity
    supported_by:
    - reference_id: file:human/ALAS2/ALAS2-uniprot.txt
      supporting_text: succinyl-CoA + glycine + H(+) = 5-aminolevulinate + CO2 + CoA
- term:
    id: GO:0030170
    label: pyridoxal phosphate binding
  evidence_type: IEA
  original_reference_id: GO_REF:0000002
  qualifier: enables
  review:
    summary: >-
      Electronic (InterPro-based) assignment of PLP binding. ALAS2 is a PLP-dependent enzyme;
      PLP is covalently bound to active-site Lys391 as an internal aldimine. This is a
      correct secondary molecular function.
    action: ACCEPT
    reason: >-
      Supported by the crystal structure and UniProt cofactor/binding-site annotations; PLP
      binding is intrinsic to catalysis.
    supported_by:
    - reference_id: PMID:32499479
      supporting_text: >-
        PLP is covalently attached to the active site lysine (Lys391 in human ALAS2
        (hsALAS2)) as an internal aldimine adduct
- term:
    id: GO:0033014
    label: tetrapyrrole biosynthetic process
  evidence_type: IEA
  original_reference_id: GO_REF:0000002
  qualifier: involved_in
  review:
    summary: >-
      Electronic (InterPro-based) assignment to the broad tetrapyrrole biosynthesis parent.
      Heme is a tetrapyrrole and ALAS2 initiates its biosynthesis, so the term is correct
      though general.
    action: ACCEPT
    reason: >-
      Accurate but non-specific parent of heme biosynthesis; acceptable for an IEA
      annotation alongside the more specific heme biosynthetic process term.
    supported_by:
    - reference_id: PMID:32499479
      supporting_text: >-
        The first and rate-limiting step is carried out by 5′-aminolevulinate synthase
        (ALAS; EC 2.3.1.37) in the mitochondria
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:25416956
  qualifier: enables
  review:
    summary: >-
      IPI annotation to the uninformative generic term protein binding, from a large-scale
      binary interactome (Y2H) screen reporting an ALAS2-BANP (Q8N9N5) interaction. The bare
      term conveys no specific molecular function and the interaction is not functionally
      characterized.
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      Per curation guidelines, bare protein binding is uninformative and should not be treated
      as a core function. The BANP interaction derives from a high-throughput proteome-scale
      map and has no established biological significance for ALAS2.
    supported_by:
    - reference_id: PMID:25416956
      supporting_text: >-
        a systematic map of ?14,000 high-quality human binary protein-protein interactions
- term:
    id: GO:0005739
    label: mitochondrion
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  qualifier: located_in
  review:
    summary: >-
      Electronic (Ensembl Compara) location transfer from the mouse ortholog placing ALAS2 in
      the mitochondrion. Correct compartment, corroborated by experimental data.
    action: ACCEPT
    reason: >-
      Consistent with the mitochondrial localization of ALAS2 established experimentally and by
      the transit peptide.
    supported_by:
    - reference_id: PMID:10727444
      supporting_text: >-
        The first and the rate-limiting enzyme of heme biosynthesis is
        delta-aminolevulinate synthase (ALAS), which is localized in mitochondria
- term:
    id: GO:0006783
    label: heme biosynthetic process
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  qualifier: involved_in
  review:
    summary: >-
      Electronic (Ensembl Compara) transfer from the mouse ortholog for heme biosynthetic
      process. This is a core process for ALAS2, which catalyzes the committed first step.
    action: ACCEPT
    reason: >-
      Correct and consistent with the experimental and IBA annotations to the same term.
    supported_by:
    - reference_id: PMID:32499479
      supporting_text: >-
        The first and rate-limiting step is carried out by 5′-aminolevulinate synthase
        (ALAS; EC 2.3.1.37) in the mitochondria
- term:
    id: GO:0030218
    label: erythrocyte differentiation
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  qualifier: involved_in
  review:
    summary: >-
      Electronic (Ensembl Compara) transfer for erythrocyte differentiation. ALAS2 is the
      erythroid-specific isozyme, and heme flux governs erythroid maturation; this is a
      downstream physiological role rather than the direct molecular function.
    action: KEEP_AS_NON_CORE
    reason: >-
      Biologically valid because ALAS2-driven heme synthesis is required for terminal erythroid
      differentiation, but ALAS2's core function is catalytic; this developmental process is
      best retained as non-core.
    supported_by:
    - reference_id: PMID:32499479
      supporting_text: >-
        ALAS2 (gene location Xp11.21) is predominantly expressed in erythroid progenitor cells,
        and synthesizes 85–90% of total body heme specifically for hemoglobin production during
        erythropoiesis
- term:
    id: GO:0042541
    label: hemoglobin biosynthetic process
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  qualifier: involved_in
  review:
    summary: >-
      Electronic (Ensembl Compara) transfer for hemoglobin biosynthesis. ALAS2 supplies heme for
      hemoglobin; a downstream physiological role, not the direct catalytic function.
    action: KEEP_AS_NON_CORE
    reason: >-
      Valid downstream role (erythroid heme feeds hemoglobin), consistent with the IBA/ISS
      annotations to the same term, but non-core relative to the enzyme's catalytic activity.
    supported_by:
    - reference_id: PMID:14643893
      supporting_text: >-
        the major splice isoform of ALAS2 is functional in vivo and could significantly
        contribute to erythroid heme biosynthesis and hemoglobin formation
- term:
    id: GO:0006785
    label: heme B biosynthetic process
  evidence_type: IDA
  original_reference_id: PMID:2050125
  qualifier: involved_in
  review:
    summary: >-
      IDA annotation to heme B biosynthetic process. Heme b (protoheme IX) is the end-product of
      the pathway that ALAS2 initiates, and ALAS2 is the erythroid isozyme providing heme for
      hemoglobin (which uses heme b). This is a more specific, correct child of heme biosynthesis.
    action: ACCEPT
    reason: >-
      Consistent with ALAS2's role as the committed first enzyme of the pathway that produces
      heme b for hemoglobin. Curated by UniProt (IDA) from the original erythroid ALAS
      characterization; deferring to the curator's reading of the full text.
    supported_by:
    - reference_id: PMID:2050125
      supporting_text: >-
        5-Aminolevulinate synthase (ALAS) catalyzes the first step of the heme biosynthetic
        pathway
- term:
    id: GO:0003870
    label: 5-aminolevulinate synthase activity
  evidence_type: EXP
  original_reference_id: PMID:34492704
  qualifier: enables
  review:
    summary: >-
      Experimental (EXP) annotation of 5-aminolevulinate synthase activity. Recombinant human
      ALAS2 was assayed enzymatically (Km ~10 uM for succinyl-CoA) and shown to be competitively
      inhibited by itaconyl-CoA, directly demonstrating the catalytic activity.
    action: ACCEPT
    reason: >-
      Direct experimental evidence for the core catalytic function of ALAS2 using purified enzyme.
    supported_by:
    - reference_id: PMID:34492704
      supporting_text: >-
        itaconyl-CoA is a competitive inhibitor of the erythroid-specific 5-aminolevulinate
        synthase (ALAS2), the first and rate-limiting step in heme synthesis
    - reference_id: PMID:34492704
      supporting_text: >-
        itaconyl-CoA to be a competitive inhibitor of recombinant ALAS2 with an inhibitory
        constant of 100 ± 20 μM
- term:
    id: GO:0005739
    label: mitochondrion
  evidence_type: HTP
  original_reference_id: PMID:34800366
  qualifier: located_in
  review:
    summary: >-
      High-throughput (HTP) mitochondrial-proteome study identifying ALAS2 among the
      high-confidence human mitochondrial proteome (MitoCoP). Corroborates the mitochondrial
      localization.
    action: ACCEPT
    reason: >-
      Consistent with the established mitochondrial localization; a large-scale proteomic
      confirmation of compartment.
    supported_by:
    - reference_id: PMID:34800366
      supporting_text: >-
        defined a mitochondrial high-confidence proteome of >1,100 proteins (MitoCoP)
- term:
    id: GO:0003870
    label: 5-aminolevulinate synthase activity
  evidence_type: IMP
  original_reference_id: PMID:21252495
  qualifier: enables
  review:
    summary: >-
      IMP annotation of 5-aminolevulinate synthase activity. A novel XLSA K156E ALAS2 variant was
      shown by a spectrophotometric enzyme assay to severely decrease ALAS2 activity, functionally
      demonstrating the enzyme's catalytic activity via mutation.
    action: ACCEPT
    reason: >-
      Mutant characterization directly ties ALAS2 to 5-aminolevulinate synthase activity; supports
      the core function.
    supported_by:
    - reference_id: PMID:21252495
      supporting_text: >-
        X-linked SA, which results from mutations in erythroid-specific δ-aminolevulinate synthase
        (ALAS2), the first enzyme in heme biosynthesis
    - reference_id: PMID:21252495
      supporting_text: >-
        A novel K156E substitution in ALAS2 was discovered in 1 pyridoxine-responsive patient. The
        functional study showed that this substitution severely decreases ALAS2 enzyme activity
- term:
    id: GO:0003870
    label: 5-aminolevulinate synthase activity
  evidence_type: IMP
  original_reference_id: PMID:21309041
  qualifier: enables
  review:
    summary: >-
      IMP annotation of 5-aminolevulinate synthase activity. Ten XLSA missense mutations were
      expressed in E. coli and assayed; several showed decreased enzymatic activity, functionally
      confirming the catalytic function through mutation.
    action: ACCEPT
    reason: >-
      Multiple mutant enzyme assays directly link ALAS2 to 5-aminolevulinate synthase activity;
      supports the core function.
    supported_by:
    - reference_id: PMID:21309041
      supporting_text: >-
        XLSA is due to mutations in the erythroid-specific 5-aminolevulinate synthase (ALAS2) gene
    - reference_id: PMID:21309041
      supporting_text: >-
        Five missense mutations resulted in decreased enzymatic activity under standard conditions
- term:
    id: GO:0003870
    label: 5-aminolevulinate synthase activity
  evidence_type: IMP
  original_reference_id: PMID:21653323
  qualifier: enables
  review:
    summary: >-
      IMP annotation of 5-aminolevulinate synthase activity. A C-terminal gain-of-function variant
      (Y586F) showed significantly increased 5-aminolevulinate release relative to wild-type,
      functionally demonstrating the catalytic activity and the C-terminal regulatory role.
    action: ACCEPT
    reason: >-
      Mutant enzyme characterization directly ties ALAS2 to 5-aminolevulinate synthase activity;
      supports the core function.
    supported_by:
    - reference_id: PMID:21653323
      supporting_text: >-
        The rate of 5-aminolevulinate release from Y586F was significantly increased over that of
        wild-type ALAS2
- term:
    id: GO:0003870
    label: 5-aminolevulinate synthase activity
  evidence_type: IDA
  original_reference_id: PMID:32499479
  qualifier: enables
  review:
    summary: >-
      IDA annotation of 5-aminolevulinate synthase activity. Recombinant human ALAS2 was
      structurally and kinetically characterized (Km 31 uM succinyl-CoA, 11.8 uM glycine), directly
      demonstrating the PLP-dependent condensation of succinyl-CoA and glycine to form ALA.
    action: ACCEPT
    reason: >-
      Direct in vitro demonstration of the core catalytic activity with a crystal structure of the
      human enzyme.
    supported_by:
    - reference_id: PMID:32499479
      supporting_text: >-
        ALAS catalyses the pyridoxal 5′-phosphate (PLP)-dependent condensation of succinyl-CoA and
        glycine to form aminolevulinic acid (ALA), with CoA and CO2 as by-products
- term:
    id: GO:0003870
    label: 5-aminolevulinate synthase activity
  evidence_type: IDA
  original_reference_id: PMID:14643893
  qualifier: enables
  review:
    summary: >-
      IDA annotation of 5-aminolevulinate synthase activity. In vitro studies showed the major ALAS2
      splice variant and isoforms produce a functional enzyme, directly demonstrating the catalytic
      activity of the human protein.
    action: ACCEPT
    reason: >-
      Direct experimental evidence for the core catalytic function; the curator read the full text of
      this isoform characterization.
    supported_by:
    - reference_id: PMID:14643893
      supporting_text: >-
        The initial step of the heme biosynthetic pathway in erythroid cells is catalyzed by an
        erythroid-specific isoform of 5-aminolevulinate synthase-2 (ALAS2)
- term:
    id: GO:0003870
    label: 5-aminolevulinate synthase activity
  evidence_type: IDA
  original_reference_id: PMID:14643893
  qualifier: enables
  review:
    summary: >-
      IDA annotation of 5-aminolevulinate synthase activity (a second GOA record for the same
      reference, assigned by UniProt). As above, in vitro studies of the human ALAS2 splice
      variant and isoforms demonstrated a functional enzyme, directly supporting the catalytic
      activity.
    action: ACCEPT
    reason: >-
      Duplicate of the MGI-assigned IDA annotation to the same term/reference; direct experimental
      evidence for the core catalytic function.
    supported_by:
    - reference_id: PMID:14643893
      supporting_text: >-
        The initial step of the heme biosynthetic pathway in erythroid cells is catalyzed by an
        erythroid-specific isoform of 5-aminolevulinate synthase-2 (ALAS2)
- term:
    id: GO:0005739
    label: mitochondrion
  evidence_type: IDA
  original_reference_id: PMID:14643893
  qualifier: located_in
  review:
    summary: >-
      IDA localization to the mitochondrion. The ALAS2 pre-protein's N-terminal 49 residues were shown
      to be necessary and sufficient for translocation into mitochondria, directly establishing the
      mitochondrial localization.
    action: ACCEPT
    reason: >-
      Direct experimental evidence for mitochondrial localization via transit-peptide translocation
      assays.
    supported_by:
    - reference_id: PMID:14643893
      supporting_text: >-
        the first 49 amino acids of the ALAS2 pre-protein are necessary and sufficient for
        translocation across the mitochondrial inner membrane
- term:
    id: GO:0005759
    label: mitochondrial matrix
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-189442
  qualifier: located_in
  review:
    summary: >-
      TAS annotation (Reactome) placing the ALAS2-catalyzed condensation of succinyl-CoA and glycine in
      the mitochondrial matrix. Matches the enzyme's location on the matrix side of the inner membrane.
    action: ACCEPT
    reason: >-
      Consistent with the UniProt subcellular location and the IEA matrix annotation; the matrix is the
      most informative compartment for the catalytic reaction.
    supported_by:
    - reference_id: file:human/ALAS2/ALAS2-uniprot.txt
      supporting_text: Localizes to the matrix side of the mitochondrion
- term:
    id: GO:0006879
    label: intracellular iron ion homeostasis
  evidence_type: ISS
  original_reference_id: GO_REF:0000024
  qualifier: involved_in
  review:
    summary: >-
      ISS annotation (from the ALAS1 ortholog) for intracellular iron ion homeostasis. ALAS2 translation
      is coupled to iron availability via an iron-responsive element in its 5' UTR, and heme synthesis is
      a major consumer of the erythroid iron flux; this is a peripheral, indirect role rather than a core
      function.
    action: KEEP_AS_NON_CORE
    reason: >-
      ALAS2 participates in erythroid iron utilization indirectly (its output consumes iron via downstream
      ferrochelatase and its expression is iron-regulated), but it is not an iron-homeostasis effector per
      se; retain as non-core.
    supported_by:
    - reference_id: PMID:2050125
      supporting_text: >-
        An iron-responsive element (IRE) motif has been identified in the 5'-untranslated region of the
        human erythroid ALAS mRNA
- term:
    id: GO:0032364
    label: intracellular oxygen homeostasis
  evidence_type: NAS
  original_reference_id: PMID:16234850
  qualifier: involved_in
  review:
    summary: >-
      NAS annotation for intracellular oxygen homeostasis. This derives from the observation that ALAS2
      protein stability is oxygen-dependent (hypoxia and proteasome inhibition stabilize it via an LXXLAP
      prolyl-hydroxylation / vHL pathway). This reflects ALAS2 being regulated by oxygen rather than ALAS2
      controlling cellular oxygen levels.
    action: KEEP_AS_NON_CORE
    reason: >-
      The evidence shows ALAS2 is a target of oxygen-dependent regulation, not an effector of oxygen
      homeostasis. Kept as non-core because the underlying observation (O2-dependent stability) is real but
      the process term overstates ALAS2's role.
    supported_by:
    - reference_id: PMID:16234850
      supporting_text: >-
        Hypoxia (1% O2) and inhibition of the proteasome increased both the stability and the specific
        activity of ALAS2
- term:
    id: GO:0001666
    label: response to hypoxia
  evidence_type: IDA
  original_reference_id: PMID:16234850
  qualifier: involved_in
  review:
    summary: >-
      IDA annotation for response to hypoxia. ALAS2 protein is stabilized under low oxygen (1% O2) and by
      proteasome inhibition, and interacts with the vHL protein under normoxia, consistent with an
      oxygen/hypoxia-responsive regulatory behavior of the protein.
    action: KEEP_AS_NON_CORE
    reason: >-
      Experimentally observed oxygen-dependent stabilization is a genuine regulatory response, but it is
      peripheral to ALAS2's core catalytic role in heme synthesis; retain as non-core.
    supported_by:
    - reference_id: PMID:16234850
      supporting_text: >-
        Hypoxia (1% O2) and inhibition of the proteasome increased both the stability and the specific
        activity of ALAS2
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:16234850
  qualifier: enables
  review:
    summary: >-
      IPI annotation to the generic term protein binding, capturing an ALAS2 interaction with the von
      Hippel-Lindau (vHL) protein (UniProtKB:P40337) detected by co-immunoprecipitation under normoxia.
      The interaction is real and mechanistically meaningful (targeting ALAS2 for degradation), but the
      bare protein binding term is uninformative.
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      Per curation guidelines, bare protein binding does not convey a specific molecular function. The
      underlying vHL interaction is captured biologically under the hypoxia/oxygen-regulation annotations.
    supported_by:
    - reference_id: PMID:16234850
      supporting_text: >-
        The von Hippel-Lindau (vHL) protein was immunoprecipitated with FLAG epitope-tagged ALAS2 produced
        in normoxic cells
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:10727444
  qualifier: enables
  review:
    summary: >-
      IPI annotation to the generic term protein binding, capturing the ALAS2 (ALAS-E) interaction with
      SUCLA2 (SCS-betaA, UniProtKB:Q9P2R7), the beta subunit of ATP-specific succinyl-CoA synthetase. This
      is a functionally meaningful interaction (supplying/channeling the succinyl-CoA substrate), but the
      bare term is uninformative.
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      The SUCLA2 interaction is biologically important and well documented, but per curation guidelines the
      generic protein binding term should not stand as a core molecular function. A specific substrate-supply
      role would be better captured by a dedicated term or GO-CAM relation.
    supported_by:
    - reference_id: PMID:10727444
      supporting_text: >-
        mitochodrially expressed SCS-betaA associates specifically with ALAS-E and not with ALAS-N
- term:
    id: GO:0005739
    label: mitochondrion
  evidence_type: IDA
  original_reference_id: PMID:10727444
  qualifier: located_in
  review:
    summary: >-
      IDA localization to the mitochondrion. The study used the mitochondrial form of human ALAS-E and
      confirmed mitochondrial association of the enzyme and its SUCLA2 partner.
    action: ACCEPT
    reason: >-
      Direct evidence consistent with the established mitochondrial localization of ALAS2.
    supported_by:
    - reference_id: PMID:10727444
      supporting_text: >-
        The first and the rate-limiting enzyme of heme biosynthesis is delta-aminolevulinate synthase
        (ALAS), which is localized in mitochondria
- term:
    id: GO:0006783
    label: heme biosynthetic process
  evidence_type: ISS
  original_reference_id: GO_REF:0000024
  qualifier: involved_in
  review:
    summary: >-
      ISS annotation (from the ALAS1 ortholog) for heme biosynthetic process, the core process of ALAS2 as
      the first, rate-limiting enzyme of the pathway.
    action: ACCEPT
    reason: >-
      Correct and consistent with the experimental, IBA and IEA annotations to the same term.
    supported_by:
    - reference_id: PMID:32499479
      supporting_text: >-
        The first and rate-limiting step is carried out by 5′-aminolevulinate synthase (ALAS; EC 2.3.1.37)
        in the mitochondria
- term:
    id: GO:0006783
    label: heme biosynthetic process
  evidence_type: NAS
  original_reference_id: PMID:14643893
  qualifier: involved_in
  review:
    summary: >-
      NAS annotation for heme biosynthetic process, based on the authors' statement that ALAS2 catalyzes the
      initial step of the erythroid heme biosynthetic pathway.
    action: ACCEPT
    reason: >-
      Correct core process; corroborated by experimental/IBA/IEA/ISS annotations to the same term.
    supported_by:
    - reference_id: PMID:14643893
      supporting_text: >-
        The initial step of the heme biosynthetic pathway in erythroid cells is catalyzed by an
        erythroid-specific isoform of 5-aminolevulinate synthase-2 (ALAS2)
- term:
    id: GO:0030218
    label: erythrocyte differentiation
  evidence_type: ISS
  original_reference_id: GO_REF:0000024
  qualifier: involved_in
  review:
    summary: >-
      ISS annotation (from the ALAS1 ortholog) for erythrocyte differentiation. As the erythroid-specific
      isozyme supplying heme for maturation, this is a downstream physiological role rather than the core
      catalytic function.
    action: KEEP_AS_NON_CORE
    reason: >-
      Biologically valid downstream role in erythroid maturation; retained as non-core relative to the
      enzyme's molecular function, consistent with the IEA annotation to the same term.
    supported_by:
    - reference_id: PMID:32499479
      supporting_text: >-
        ALAS2 (gene location Xp11.21) is predominantly expressed in erythroid progenitor cells, and
        synthesizes 85–90% of total body heme specifically for hemoglobin production during erythropoiesis
- term:
    id: GO:0042541
    label: hemoglobin biosynthetic process
  evidence_type: ISS
  original_reference_id: GO_REF:0000024
  qualifier: involved_in
  review:
    summary: >-
      ISS annotation (from the ALAS1 ortholog) for hemoglobin biosynthesis. ALAS2 supplies the heme required
      for hemoglobin; a downstream physiological role.
    action: KEEP_AS_NON_CORE
    reason: >-
      Valid downstream role consistent with the IBA/IEA annotations to the same term; non-core relative to
      the catalytic activity.
    supported_by:
    - reference_id: PMID:14643893
      supporting_text: >-
        the major splice isoform of ALAS2 is functional in vivo and could significantly contribute to
        erythroid heme biosynthesis and hemoglobin formation
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:14643893
  qualifier: enables
  review:
    summary: >-
      IPI annotation to the generic term protein binding, capturing the ALAS2-SUCLA2 (Q9P2R7) interaction
      demonstrated during the isoform characterization. The interaction is meaningful (succinyl-CoA supply)
      but the bare term is uninformative.
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      Per curation guidelines, bare protein binding should not stand as a core molecular function; the
      SUCLA2 interaction is captured biologically and is redundant with the same interaction reported in
      PMID:10727444.
    supported_by:
    - reference_id: PMID:32499479
      supporting_text: >-
        capable of forming an interaction with the previously reported partner, beta subunit (SUCLA2) of
        the succinyl-CoA synthetase complex
- term:
    id: GO:0005743
    label: mitochondrial inner membrane
  evidence_type: IDA
  original_reference_id: PMID:14643893
  qualifier: located_in
  review:
    summary: >-
      IDA localization to the mitochondrial inner membrane. The ALAS2 pre-protein was shown to translocate
      across the mitochondrial inner membrane, and UniProt annotates it as a peripheral inner-membrane
      protein on the matrix side.
    action: ACCEPT
    reason: >-
      Direct experimental evidence; consistent with UniProt subcellular location.
    supported_by:
    - reference_id: PMID:14643893
      supporting_text: >-
        the first 49 amino acids of the ALAS2 pre-protein are necessary and sufficient for translocation
        across the mitochondrial inner membrane
    - reference_id: file:human/ALAS2/ALAS2-uniprot.txt
      supporting_text: Mitochondrion inner membrane
- term:
    id: GO:0030218
    label: erythrocyte differentiation
  evidence_type: NAS
  original_reference_id: PMID:2050125
  qualifier: involved_in
  review:
    summary: >-
      NAS annotation for erythrocyte differentiation, based on ALAS2 being the erythroid-specific isozyme
      with erythroid-specific promoter elements (GATA-1, NF-E2) supplying heme during erythropoiesis.
    action: KEEP_AS_NON_CORE
    reason: >-
      Valid downstream/developmental role reflecting the erythroid-restricted expression and function of
      ALAS2; retained as non-core relative to its catalytic activity, consistent with the ISS/IEA
      annotations to the same term.
    supported_by:
    - reference_id: PMID:2050125
      supporting_text: >-
        putative erythroid-specific cis-acting elements including both a GATA-1 and an NF-E2 binding site
core_functions:
- description: >-
    5-aminolevulinate synthase activity: ALAS2 catalyzes the PLP-dependent condensation of glycine and
    succinyl-CoA to form 5-aminolevulinate, CoA and CO2 in the mitochondrion, performing the first and
    rate-limiting step of heme biosynthesis in erythroid cells.
  molecular_function:
    id: GO:0003870
    label: 5-aminolevulinate synthase activity
  directly_involved_in:
  - id: GO:0006783
    label: heme biosynthetic process
  locations:
  - id: GO:0005759
    label: mitochondrial matrix
  - id: GO:0005739
    label: mitochondrion
  supported_by:
  - reference_id: PMID:32499479
    supporting_text: >-
      ALAS catalyses the pyridoxal 5′-phosphate (PLP)-dependent condensation of succinyl-CoA and glycine
      to form aminolevulinic acid (ALA), with CoA and CO2 as by-products
  - reference_id: PMID:34492704
    supporting_text: >-
      itaconyl-CoA is a competitive inhibitor of the erythroid-specific 5-aminolevulinate synthase
      (ALAS2), the first and rate-limiting step in heme synthesis
- description: >-
    Pyridoxal phosphate binding: as a class-II PLP-dependent enzyme, ALAS2 binds pyridoxal 5'-phosphate,
    which is covalently attached to active-site Lys391 as an internal aldimine and is essential for
    catalysis. This is a secondary molecular function supporting the primary synthase activity.
  molecular_function:
    id: GO:0030170
    label: pyridoxal phosphate binding
  directly_involved_in:
  - id: GO:0006783
    label: heme biosynthetic process
  locations:
  - id: GO:0005759
    label: mitochondrial matrix
  supported_by:
  - reference_id: PMID:32499479
    supporting_text: >-
      PLP is covalently attached to the active site lysine (Lys391 in human ALAS2 (hsALAS2)) as an internal
      aldimine adduct
references:
- id: GO_REF:0000002
  title: Gene Ontology annotation through association of InterPro records with GO
    terms
  findings: []
- id: GO_REF:0000024
  title: Manual transfer of experimentally-verified manual GO annotation data to orthologs
    by curator judgment of sequence similarity
  findings: []
- id: GO_REF:0000033
  title: Annotation inferences using phylogenetic trees
  findings: []
- id: GO_REF:0000044
  title: Gene Ontology annotation based on UniProtKB/Swiss-Prot Subcellular Location
    vocabulary mapping, accompanied by conservative changes to GO terms applied by
    UniProt
  findings: []
- id: GO_REF:0000107
  title: Automatic transfer of experimentally verified manual GO annotation data to
    orthologs using Ensembl Compara
  findings: []
- id: GO_REF:0000120
  title: Combined Automated Annotation using Multiple IEA Methods
  findings: []
- id: PMID:10727444
  title: Interaction between succinyl CoA synthetase and the heme-biosynthetic enzyme
    ALAS-E is disrupted in sideroblastic anemia.
  findings: []
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: >-
      Identifies the ALAS2 (ALAS-E) interaction with SUCLA2 (SCS-betaA) and its
      mitochondrial localization; supports substrate-supply and localization claims.
- id: PMID:14643893
  title: The major splice variant of human 5-aminolevulinate synthase-2 contributes
    significantly to erythroid heme biosynthesis.
  findings: []
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: >-
      Isoform characterization; establishes functional enzyme, transit-peptide-driven
      mitochondrial import, and SUCLA2 interaction for human ALAS2.
- id: PMID:16234850
  title: Erythroid-specific 5-aminolevulinate synthase protein is stabilized by low
    oxygen and proteasomal inhibition.
  findings: []
  reference_review:
    relevance: MEDIUM
    correctness: VERIFIED
    review_notes: >-
      Establishes oxygen-dependent ALAS2 protein stability and vHL interaction; basis
      for the hypoxia/oxygen-homeostasis annotations (regulatory, not core).
- id: PMID:2050125
  title: 'Human erythroid 5-aminolevulinate synthase: promoter analysis and identification
    of an iron-responsive element in the mRNA.'
  findings: []
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: >-
      Original human erythroid ALAS characterization; IRE, erythroid promoter elements,
      and the first-step-of-heme-synthesis claim.
- id: PMID:21252495
  title: New mutation in erythroid-specific delta-aminolevulinate synthase as the
    cause of X-linked sideroblastic anemia responsive to pyridoxine.
  findings: []
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: >-
      Functional assay of the K156E XLSA variant showing decreased ALAS2 activity;
      supports the IMP synthase-activity annotation.
- id: PMID:21309041
  title: 'Sideroblastic anemia: molecular analysis of the ALAS2 gene in a series of
    29 probands and functional studies of 10 missense mutations.'
  findings: []
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: >-
      Expression and enzyme assays of 10 XLSA missense mutants; supports the IMP
      synthase-activity annotation.
- id: PMID:21653323
  title: ALAS2 acts as a modifier gene in patients with congenital erythropoietic
    porphyria.
  findings: []
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: >-
      Characterizes the Y586F C-terminal gain-of-function variant with increased ALA
      release; supports the IMP synthase-activity annotation and C-terminal regulation.
- id: PMID:25416956
  title: A proteome-scale map of the human interactome network.
  findings: []
  reference_review:
    relevance: LOW
    correctness: VERIFIED
    review_notes: >-
      Large-scale binary interactome (Y2H) reporting an ALAS2-BANP interaction; basis
      for a generic protein binding IPI with no established functional significance.
- id: PMID:32499479
  title: Human aminolevulinate synthase structure reveals a eukaryotic-specific autoinhibitory
    loop regulating substrate binding and product release.
  findings: []
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: >-
      Human ALAS2 crystal structure, PLP/active-site details, homodimer, kinetics, and
      C-terminal autoinhibitory loop; strongest structural/mechanistic reference.
- id: PMID:34492704
  title: The immunometabolite itaconate inhibits heme synthesis and remodels cellular
    metabolism in erythroid precursors.
  findings: []
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: >-
      Enzymatic assay of recombinant ALAS2 with itaconyl-CoA competitive inhibition;
      supports the EXP synthase-activity annotation and rate-limiting-step framing.
- id: PMID:34800366
  title: Quantitative high-confidence human mitochondrial proteome and its dynamics
    in cellular context.
  findings: []
  reference_review:
    relevance: MEDIUM
    correctness: VERIFIED
    review_notes: >-
      High-throughput mitochondrial proteome (MitoCoP) including ALAS2; corroborates
      mitochondrial localization.
- id: Reactome:R-HSA-189442
  title: ALAS condenses SUCC-CoA and Gly to form dALA
  findings: []
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: >-
      Reactome reaction for the ALAS2-catalyzed condensation in the mitochondrial
      matrix; supports the TAS matrix-location annotation.
- id: file:human/ALAS2/ALAS2-uniprot.txt
  title: UniProtKB P22557 (HEM0_HUMAN) 5-aminolevulinate synthase, erythroid-specific, mitochondrial
  findings: []
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: >-
      Curated UniProt record; source for catalytic reaction, cofactor, subcellular
      location, family, and isoform annotations.

Gene Description

Existing Annotations Review

Core Functions

5-aminolevulinate synthase activity: ALAS2 catalyzes the PLP-dependent condensation of glycine and succinyl-CoA to form 5-aminolevulinate, CoA and CO2 in the mitochondrion, performing the first and rate-limiting step of heme biosynthesis in erythroid cells.

Pyridoxal phosphate binding: as a class-II PLP-dependent enzyme, ALAS2 binds pyridoxal 5'-phosphate, which is covalently attached to active-site Lys391 as an internal aldimine and is essential for catalysis. This is a secondary molecular function supporting the primary synthase activity.

References

📚 Additional Documentation

Notes

ALAS2 (human) — review notes

Core biology (grounded in ALAS2-uniprot.txt + cached publications)

Disease

GOA MF term

Annotation review disposition summary

📄 View Raw YAML