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Abstract
This chapter reviews how allosteric (heterotrophic) effectors and natural mutations impact hemoglobin (Hb) primary physiological function of oxygen binding and transport. First, an introduction about the structure of Hb is provided, including the ensemble of tense and relaxed Hb states and the dynamic equilibrium of Hb multistate. This is followed by a brief review of Hb variants with altered Hb structure and oxygen binding properties. Finally, a review of different endogenous and exogenous allosteric effectors of Hb is presented with particular emphasis on the atomic interactions of synthetic ligands with altered allosteric function of Hb that could potentially be harnessed for the treatment of diseases.
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Affiliation(s)
- Mostafa H Ahmed
- Department of Medicinal Chemistry, School of Pharmacy, Virginia Commonwealth University, Richmond, VA, 23219, USA
| | - Mohini S Ghatge
- Department of Medicinal Chemistry, School of Pharmacy, Virginia Commonwealth University, Richmond, VA, 23219, USA.,Institute for Structural Biology, Drug Discovery and Development, Virginia Commonwealth University, Richmond, VA, 23219, USA
| | - Martin K Safo
- Department of Medicinal Chemistry, School of Pharmacy, Virginia Commonwealth University, Richmond, VA, 23219, USA. .,Institute for Structural Biology, Drug Discovery and Development, Virginia Commonwealth University, Richmond, VA, 23219, USA.
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2
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Safo MK, Ko TP, Schreiter ER, Russell JE. Structural basis for the antipolymer activity of Hb ζ 2β s2 trapped in a tense conformation. J Mol Struct 2015. [PMID: 26207073 DOI: 10.1016/j.molstruc.2015.06.047] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
The phenotypical severity of sickle-cell disease (SCD) can be mitigated by modifying mutant hemoglobin S (Hb S, Hb α2βs2) to contain embryonic ζ-globin in place of adult α-globin subunits (Hb ζ2βs2). Crystallographical analyses of liganded Hb ζζ2βs2, though, demonstrate a tense (T-state) quaternary structure that paradoxically predicts its participation in--rather than its exclusion from--pathological deoxyHb S polymers. We resolved this structure-function conundrum by examining the effects of α→ζ exchange on the characteristics of specific amino acids that mediate sickle polymer assembly. Superposition analyses of the βs subunits of T-state deoxyHb α2βs2 and T-state CO-liganded Hb ζ2βs2 reveal significant displacements of both mutant βsVal6 and conserved β-chain contact residues, predicting weakening of corresponding polymer-stabilizing interactions. Similar comparisons of the α- and ζ-globin subunits implicate four amino acids that are either repositioned or undergo non-conservative substitution, abrogating critical polymer contacts. CO-Hb ζ2βs2 additionally exhibits a unique trimer-of-heterotetramers crystal packing that is sustained by novel intermolecular interactions involving the pathological βsVal6, contrasting sharply with the classical double-stranded packing of deoxyHb S. Finally, the unusually large buried solvent-accessible surface area for CO-Hb ζ2βs2 suggests that it does not co-assemble with deoxyHb S in vivo. In sum, the antipolymer activities of Hb ζ2βs2 appear to arise from both repositioning and replacement of specific α- and βs-chain residues, favoring an alternate T-state solution structure that is excluded from pathological deoxyHb S polymers. These data account for the antipolymer activity of Hb ζ2βs2, and recommend the utility of SCD therapeutics that capitalize on α-globin exchange strategies.
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Affiliation(s)
- Martin K Safo
- Institute for Structural Biology and Drug Discovery, and the Department of Medicinal Chemistry, School of Pharmacy, Virginia Commonwealth University, Richmond, VA 23298;
| | - Tzu-Ping Ko
- Institute of Biological Chemistry, Academia Sinica, Taipei 11529, Taiwan;
| | - Eric R Schreiter
- Howard Hughes Medical Institute, Janelia Farm Research Campus, Ashburn, VA 20147;
| | - J Eric Russell
- Division of Hematology-Oncology, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA 19104;
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Kassa T, Jana S, Strader MB, Meng F, Jia Y, Wilson MT, Alayash AI. Sickle Cell Hemoglobin in the Ferryl State Promotes βCys-93 Oxidation and Mitochondrial Dysfunction in Epithelial Lung Cells (E10). J Biol Chem 2015; 290:27939-58. [PMID: 26396189 DOI: 10.1074/jbc.m115.651257] [Citation(s) in RCA: 37] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2015] [Indexed: 01/02/2023] Open
Abstract
Polymerization of intraerythrocytic deoxyhemoglobin S (HbS) is the primary molecular event that leads to hemolytic anemia in sickle cell disease (SCD). We reasoned that HbS may contribute to the complex pathophysiology of SCD in part due to its pseudoperoxidase activity. We compared oxidation reactions and the turnover of oxidation intermediates of purified human HbS and HbA. Hydrogen peroxide (H2O2) drives a catalytic cycle that includes the following three distinct steps: 1) initial oxidation of ferrous (oxy) to ferryl Hb; 2) autoreduction of the ferryl intermediate to ferric (metHb); and 3) reaction of metHb with an additional H2O2 molecule to regenerate the ferryl intermediate. Ferrous and ferric forms of both proteins underwent initial oxidation to the ferryl heme in the presence of H2O2 at equal rates. However, the rate of autoreduction of ferryl to the ferric form was slower in the HbS solutions. Using quantitative mass spectrometry and the spin trap, 5,5-dimethyl-1-pyrroline-N-oxide, we found more irreversibly oxidized βCys-93in HbS than in HbA. Incubation of the ferric or ferryl HbS with cultured lung epithelial cells (E10) induced a drop in mitochondrial oxygen consumption rate and impairment of cellular bioenergetics that was related to the redox state of the iron. Ferryl HbS induced a substantial drop in the mitochondrial transmembrane potential and increases in cytosolic heme oxygenase (HO-1) expression and mitochondrial colocalization in E10 cells. Thus, highly oxidizing ferryl Hb and heme, the product of oxidation, may be central to the evolution of vasculopathy in SCD and may suggest therapeutic modalities that interrupt heme-mediated inflammation.
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Affiliation(s)
- Tigist Kassa
- From the Laboratory of Biochemistry and Vascular Biology, Center for Biologics Evaluation and Research, Food and Drug Administration, Silver Spring, Maryland 20993 and
| | - Sirsendu Jana
- From the Laboratory of Biochemistry and Vascular Biology, Center for Biologics Evaluation and Research, Food and Drug Administration, Silver Spring, Maryland 20993 and
| | - Michael Brad Strader
- From the Laboratory of Biochemistry and Vascular Biology, Center for Biologics Evaluation and Research, Food and Drug Administration, Silver Spring, Maryland 20993 and
| | - Fantao Meng
- From the Laboratory of Biochemistry and Vascular Biology, Center for Biologics Evaluation and Research, Food and Drug Administration, Silver Spring, Maryland 20993 and
| | - Yiping Jia
- From the Laboratory of Biochemistry and Vascular Biology, Center for Biologics Evaluation and Research, Food and Drug Administration, Silver Spring, Maryland 20993 and
| | - Michael T Wilson
- the Department of Biological Sciences, University of Essex, Wivenhoe Park, Colchester CO4 3SQ, United Kingdom
| | - Abdu I Alayash
- From the Laboratory of Biochemistry and Vascular Biology, Center for Biologics Evaluation and Research, Food and Drug Administration, Silver Spring, Maryland 20993 and
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Dickson CF, Jacques DA, Clubb RT, Guss JM, Gell DA. The structure of haemoglobin bound to the haemoglobin receptor IsdH from Staphylococcus aureus shows disruption of the native α-globin haem pocket. ACTA CRYSTALLOGRAPHICA. SECTION D, BIOLOGICAL CRYSTALLOGRAPHY 2015; 71:1295-306. [PMID: 26057669 PMCID: PMC8518021 DOI: 10.1107/s1399004715005817] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/02/2015] [Accepted: 03/23/2015] [Indexed: 12/13/2022]
Abstract
Staphylococcus aureus is a common and serious cause of infection in humans. The bacterium expresses a cell-surface receptor that binds to, and strips haem from, human haemoglobin (Hb). The binding interface has previously been identified; however, the structural changes that promote haem release from haemoglobin were unknown. Here, the structure of the receptor-Hb complex is reported at 2.6 Å resolution, which reveals a conformational change in the α-globin F helix that disrupts the haem-pocket structure and alters the Hb quaternary interactions. These features suggest potential mechanisms by which the S. aureus Hb receptor induces haem release from Hb.
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Balasubramanian M, Sathya Moorthy P, Neelagandan K, Ramadoss R, Kolatkar PR, Ponnuswamy MN. Structure of liganded T-state haemoglobin from cat (Felis silvestris catus), a low oxygen-affinity species, in two different crystal forms. ACTA ACUST UNITED AC 2014; 70:1898-906. [DOI: 10.1107/s139900471400916x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2013] [Accepted: 04/23/2014] [Indexed: 11/10/2022]
Abstract
Haemoglobin (Hb) is an iron-containing metalloprotein which plays a major role in the transportation of oxygen from the lungs to tissues and of carbon dioxide back to the lungs. Hb is in equilibrium between low-affinity tense (T) and high-affinity relaxed (R) states associated with its unliganded and liganded forms, respectively. Mammalian species can be classified into two groups on the basis of whether they express `high' or `low' oxygen-affinity Hbs. Although Hbs from the former group have been studied extensively, a more limited number of structural studies have been performed for low oxygen-affinity Hbs. Here, the crystal structure of low oxygen-affinity cat methaemoglobin (metHb) has been solved at 2.0 and 2.4 Å resolution in two different crystal forms. Even though both structures are fully liganded, they unusually adopt a T-state-like quaternary conformation but with several localized R-like tertiary-structural and quaternary-structural features. The study provides atomic-level insights into the ligand-binding properties of this Hb, including its low cooperativity, blunt response to allosteric effectors and low affinity for oxygen, as well as further contributing to the mechanism underlying Hb allostery.
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