α-Hemoglobin Stabilizing Protein (AHSP) Markedly Decreases the Redox Potential and Reactivity of α-Subunits of Human HbA with Hydrogen Peroxide
Year: 2012
Type: article
Abstract: α-Hemoglobin stabilizing protein (AHSP) is a molecular chaperone that binds monomeric α-subunits of human hemoglobin A (HbA) and modulates heme iron oxidation and subunit folding states. Although AHSP·αHb complexes autoxidize more rapidly than HbA, the redox mechanisms appear to be similar. Both metHbA and isolated met-β-subunits undergo further oxidation in the presence of hydrogen peroxide (H 2 O 2 ) to form ferryl heme species. Surprisingly, much lower levels of H 2 O 2 -induced ferryl heme are produced by free met-α-subunits as compared with met-β-subunits, and no ferryl heme is detected in H 2 O 2 -treated AHSP·met-α-complex at pH values from 5.0 to 9.0 at 23 °C. Ferryl heme species were similarly not detected in AHSP·met-α Pro-30 mutants known to exhibit different rates of autoxidation and hemin loss. EPR data suggest that protein-based radicals associated with the ferryl oxidation state exist within HbA α- and β-subunits. In contrast, treatment of free α-subunits with H 2 O 2 yields much smaller radical signals, and no radicals are detected when H 2 O 2 is added to AHSP·α-complexes. 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. Hexacoordination in the AHSP·met-α complex markedly decreases the rate of the initial H 2 O 2 reaction with iron and thus provides α-subunits protection against damaging oxidative reactions. Background: α-Hemoglobin stabilizing protein (AHSP) modifies the redox properties of bound α-subunits. Results: Isolated hemoglobin subunits exhibit significantly different redox properties compared with HbA. A significant decrease in the reduction potential of α-subunits bound to AHSP results in preferential binding of ferric α. Conclusion: AHSP·α-subunit complexes do not participate in ferric-ferryl heme redox cycling. Significance: AHSP binding to α-subunits inhibits subunit pseudoperoxidase activity.
Source: Journal of Biological Chemistry
Language: English
Subfield: Cell Biology
Domain: Life Sciences
Open Access status: hybrid
Estimated APC paid: $3,430
Awards: G2154546777, G2764334610, Biotechnology Research Training Grant, G3591803973, MECHANISMS AND MODULATION OF ACCELLULAR HbA TOXICITY, Functional Properties of Hemoglobins and Myoglobins, The Role of Alpha Hemoglobin Stabilizing Protein in Human Beta Thalassemia, Trim58 and the Ubiquitin Proteasome System in Erythro-megakaryopoiesis, The function and regulation of alpha hemoglobin stabilizing protein (AHSP) in hem, G6861968899, Design of Heme Protein-Based Blood Substitutes, G8795219913, Abramson Cancer Center Support Grant
OpenAlex ID: W2073967491