Gene Ontology annotation through association of InterPro records with GO terms
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IPR015317 is a family-specific InterPro signature ("Alpha-haemoglobin stabilising protein") whose four GO mappings - GO:0030492, GO:0006457, GO:0030218, GO:0050821 - were verified against the live interpro2go file and match the four GO_REF:0000002 rows on this gene exactly.
Annotation inferences using phylogenetic trees
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All four IBA rows cite MGI:MGI:2158492 (Q9CY02, AHSP_MOUSE, reviewed, 102 aa) plus PANTHER:PTN000408386. QuickGO shows the donor carries its own IDA or IMP from PMID:12066189 at each of the four propagated terms - GO:0005737, GO:0006457, GO:0030218 and GO:0050821 - so every propagation lands at exactly the term its donor holds experimentally.
Combined Automated Annotation using Multiple IEA Methods
An abundant erythroid protein that stabilizes free alpha-haemoglobin.
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Discovery of AHSP in a screen for GATA-1-induced genes. AHSP is abundant and erythroid-specific, binds free alpha-haemoglobin, and does not bind beta-haemoglobin or the alpha2beta2 tetramer.
"Stabilizing Protein (AHSP) is an abundant, erythroid-specific protein that forms a stable complex with free alpha-haemoglobin but not with beta-haemoglobin or haemoglobin A (alpha(2)beta(2))."
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AHSP prevents precipitation of free alpha-haemoglobin both in solution and in cells.
"Moreover, AHSP specifically protects free alpha-haemoglobin from precipitation in solution and in live cells."
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Ahsp-null mice have reticulocytosis and abnormal erythrocytes containing inclusion bodies of denatured haemoglobin - the basis of the mouse IMP that propagates to human by IBA.
"AHSP-gene-ablated mice exhibit reticulocytosis and abnormal erythrocyte morphology with intracellular inclusion bodies that stain positively for denatured haemoglobins"
Biophysical characterization of the alpha-globin binding protein alpha-hemoglobin stabilizing protein.
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AHSP and alpha-globin are each monomeric and associate 1:1 with an association constant of about 1e7 M-1, a stoichiometry and affinity that make the interaction physiologically meaningful at erythroblast concentrations.
"AHSP and alpha-globin are both monomeric in solution as determined by analytical ultracentrifugation and bind each other to form a complex with 1:1 subunit stoichiometry"
NMR structure of the alpha-hemoglobin stabilizing protein: insights into conformational heterogeneity and binding.
Molecular mechanism of AHSP-mediated stabilization of alpha-hemoglobin.
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Crystal structure of AHSP bound to Fe(II) alpha-haemoglobin at 2.8 A (PDB 1Y01). The interface engages the G and H helices of the globin and reproduces the alpha1-beta1 contact of HbA.
"The crystal structure of AHSP bound to Fe(II)-alphaHb reveals that AHSP specifically recognizes the G and H helices of alphaHb through a hydrophobic interface that largely recapitulates the alpha1-beta1 interface of hemoglobin."
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The interface is deliberately suboptimal, which is the structural basis for handing alpha-globin on to beta-globin rather than sequestering it.
"The AHSP-alphaHb interactions are extensive but suboptimal, explaining why beta-hemoglobin can competitively displace AHSP to form HbA."
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Binding drives conversion of oxy-alpha-haemoglobin to a deoxygenated, oxidized, fully coordinated and non-reactive form.
"Importantly, binding to AHSP facilitates the conversion of oxy-alphaHb to a deoxygenated, oxidized [Fe(III)], nonreactive form in which all six coordinate positions are occupied."
Structure of oxidized alpha-haemoglobin bound to AHSP reveals a protective mechanism for haem.
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AHSP inhibits the ability of alpha-haemoglobin to generate reactive oxygen species and prevents its precipitation under oxidant stress - the primary statement behind the proposed GO:1903427 row.
"The alpha-haemoglobin-stabilizing protein (AHSP) binds alpha-haemoglobin (alphaHb), inhibits the ability of alphaHb to generate reactive oxygen species and prevents its precipitation on exposure to oxidant stress."
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Crystal structure of the ferric complex at 2.4 A (PDB 1Z8U) shows a bis-histidyl configuration in which both proximal and distal histidines coordinate the haem iron, reached by repositioning several alpha-helices of the globin.
"Our findings reveal a striking bis-histidyl configuration in which both the proximal and the distal histidines coordinate the haem iron atom."
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The ferric bis-histidine state specifically blocks redox catalysis and haem loss.
"Moreover, conversion to the ferric bis-histidine configuration strongly and specifically inhibits redox chemistry catalysis and haem loss from alphaHb."
Towards a proteome-scale map of the human protein-protein interaction network.
Biochemical fates of alpha hemoglobin bound to alpha hemoglobin-stabilizing protein AHSP.
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Beta-haemoglobin displaces AHSP from either the ferrous or the ferric complex to give tetrameric HbA - the hand-off step of the mechanism.
"The addition of betaHb to either Fe(II) or Fe(III) alphaHb.AHSP displaces AHSP to generate tetrameric (alpha(2)beta(2)) HbA species."
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Unlike free ferric alpha-haemoglobin hemichromes, the AHSP-bound form does not precipitate and can be recycled into functional HbA after enzymatic reduction.
"In contrast to free Fe(III) alphaHb hemichromes, AHSP-bound Fe(III) alphaHb does not precipitate and can be recycled into functional HbA."
Reduction of AHSP synthesis in hemin-induced K562 cells and EPO-induced CD34(+) cells leads to alpha-globin precipitation, impairment of normal hemoglobin production, and increased cell death.
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shRNA knockdown of AHSP in human K562 cells and human CD34+ erythroblasts causes alpha-globin precipitation and a significant fall in haemoglobin formation.
"RNA interference-mediated knockdown of AHSP expression resulted in considerable alphaHb precipitation, as well as in a significant decrease in HbF formation."
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The same knockdown raises reactive oxygen species and apoptosis - the human loss-of-function support for the proposed GO:1903427 row.
"AHSP-knockdown cells demonstrated an increased ROS production and increased rate of apoptosis."
A cis-proline in alpha-hemoglobin stabilizing protein directs the structural reorganization of alpha-hemoglobin.
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States the mechanism in one sentence: AHSP suppresses haem-catalysed generation of reactive oxygen species by converting alpha-globin to the bis-histidyl coordinated conformation. Direct support for the proposed GO:1903427 row.
"AHSP forms a specific complex with alphaHb and suppresses the heme-catalyzed evolution of reactive oxygen species by converting alphaHb to a conformation in which the heme is coordinated at both axial positions by histidine side chains (bis-histidyl coordination)."
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A third X-ray co-crystal structure of the complex (PDB 3IA3) together with the mutagenesis that identifies Pro30 of AHSP loop 1, in a cis-peptidyl conformation contacting the N terminus of alpha-globin helix G, as the element that transmits the conformational change to the haem pocket.
"In complex with alphaHb, AHSP Pro(30) adopts a cis-peptidyl conformation and makes contact with the N terminus of helix G in alphaHb."
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Substituting Pro30 reduces the conversion activity, and mutations that stabilise the cis-peptidyl conformation of free AHSP enhance it - a two-directional structure-function test rather than a single loss-of-function observation.
"Mutation of Pro(30) to a variety of residue types results in reduced ability to convert alphaHb."
AHSP (α-haemoglobin-stabilizing protein) stabilizes apo-α-haemoglobin in a partially folded state.
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AHSP forms a heterodimer with haem-free alpha-globin, inhibits its aggregation and promotes its folding - the basis of the proposed GO:0044183 molecular function.
"AHSP forms a heterodimeric complex with αo that inhibits αo aggregation and promotes αo folding in the absence of haem."
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The folding it produces is partial, not native: AHSP shifts apo-alpha-globin from unfolded to partially folded and holds it there with substantial conformational flexibility retained.
"Addition of AHSP leads to dissociation of soluble αo aggregates, formation of a stable αo:AHSP dimer, and a dramatic shift from unfolded to partially folded forms of αo."
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Human material throughout, which is what makes IDA rather than ISS the correct code on the proposed row.
"Hb A, αh and βh were obtained from human blood."
Kinetics of α-globin binding to α-hemoglobin stabilizing protein (AHSP) indicate preferential stabilization of hemichrome folding intermediate.
α-Hemoglobin stabilizing protein (AHSP) markedly decreases the redox potential and reactivity of α-subunits of human HbA with hydrogen peroxide.
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AHSP lowers the alpha-subunit redox potential from +40 to -78 mV, demonstrating much higher affinity for the ferric than the ferrous subunit.
"AHSP binding also dramatically reduces the redox potential of α-subunits, from +40 to -78 mV in 1 m glycine buffer, pH 6.0, at 8 °C, demonstrating independently that AHSP has a much higher affinity for Fe(III) versus Fe(II) α-subunits."
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Protein-based radicals form in HbA alpha- and beta-subunits on peroxide treatment, and are undetectable when AHSP is bound - evidence that more than one reactive species is suppressed, which is why the generic ROS term rather than a species-specific child was proposed.
"EPR data suggest that protein-based radicals associated with the ferryl oxidation state exist within HbA α- and β-subunits."
HSP70 sequestration by free α-globin promotes ineffective erythropoiesis in β-thalassaemia.
A proteome-scale map of the human interactome network.
Oxidative instability of hemoglobin E (β26 Glu→Lys) is increased in the presence of free α subunits and reversed by α-hemoglobin stabilizing protein (AHSP): Relevance to HbE/β-thalassemia.
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AHSP holds the alpha-subunit in a redox-inactive hexacoordinate conformation that cannot undergo the ferric/ferryl transition, and this protection extends to the partner beta subunit, reducing betaCys93 oxidation in both HbA and HbE.
"In the presence of Alpha-hemoglobin stabilizing protein (AHSP), which stabilizes the α-subunit in a redox inactive hexacoordinate conformation (thus unable to undergo the redox ferric/ferryl transition), Cys93 oxidation was substantially reduced in both proteins."
A reference map of the human binary protein interactome.
Stage Specific Expression Pattern of Alpha-Hemoglobin-Stabilizing-Protein (AHSP) Portrayed in Erythroblast Chronology.
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In human primary erythroblasts AHSP protein is negligible at the CFU-E stage, peaks at day 12 of culture, and its subcellular distribution shifts from cytoplasmic-and-nuclear to predominantly nuclear, with the protein expelled alongside the nucleus at enucleation.
"Notably, sub-cellular location of AHSP is both in the cytoplasm and nucleus in the early erythroblasts while in the late stages of maturation AHSP is found predominantly in the nucleus, being expelled with it during enucleation."
Multimodal cell maps as a foundation for structural and functional genomics.
Publisher Correction: Multimodal cell maps as a foundation for structural and functional genomics.
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The correction to PMID:40205054 replaces a duplicated equation in the Methods "Loss functions" section and does not affect the interaction data.
"In the version of the article initially published, the fourth equation in the “Loss functions” section of the Methods was a duplicate of the fifth equation."