Structural changes upon oxygenation of an iron(II)(porphyrinato)(imidazole) complex

Jameson, Geoffrey B.; Molinaro, Frank S.; Ibers, James A.; Collman, James P.; Brauman, John I.; Rose, Éric; Suslick, Kenneth S.

doi:10.1021/ja00489a046

Cited by 114 publications

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“…As the size of the E7 amino acid is increased from Gly to Phe, decreases in k O2 , In 1970, Perutz (1) proposed that the distal histidines located at the E7 helical positions, 3 ␣His-58 and ␤His-63, play crucial structural roles for regulating both the affinities and rates of O 2 binding to adult human hemoglobin (HbA). 4 These ideas were based on the suggestion by Pauling (2) that His(E7) could stabilize bound O 2 by donating a hydrogen bond to the partial negative charge on the superoxide-Fe(III)-like FeO 2 complex and on the idea by Perutz and Mathews (3) that the distal histidine could also be acting as gate for ligand entry and exit. Studies of model heme compounds and naturally occurring globins with His(E7) replacements suggested strongly that the distal histidine also plays a key role in discrimination between O 2 and CO binding (4 -9).…”

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“…For example, His(E7) refers to the histidine at the seventh position along the E-helix, which in the ␣ and ␤ subunits are His-58 and His-63, respectively. 4 The abbreviations used are: HbA, adult human hemoglobin; WT, wild type; FTIR, Fourier-transform infrared spectroscopy. …”

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confidence: 99%

“…4 These ideas were based on the suggestion by Pauling (2) that His(E7) could stabilize bound O 2 by donating a hydrogen bond to the partial negative charge on the superoxide-Fe(III)-like FeO 2 complex and on the idea by Perutz and Mathews (3) that the distal histidine could also be acting as gate for ligand entry and exit. Studies of model heme compounds and naturally occurring globins with His(E7) replacements suggested strongly that the distal histidine also plays a key role in discrimination between O 2 and CO binding (4 -9).…”

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confidence: 99%

“…The slow phases represent ligand binding to the equilibrium conformational state of the ␣-deoxyHb mutant, in which the indole side chain fills the E7 channel and blocks ligand entry. Rotation of the indole side chain into the entry channel occurs at a rate that competes with bimolecular CO binding to the open conformation (ϳ10 4 …”

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Distal Histidine Stabilizes Bound O2 and Acts as a Gate for Ligand Entry in Both Subunits of Adult Human Hemoglobin

Birukou

Schweers²,

Olson

2010

Journal of Biological Chemistry

100

174

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The role of the distal histidine in regulating ligand binding to adult human hemoglobin (HbA) was re-examined systematically by preparing His(E7) to Gly, Ala, Leu, Gln, Phe, and Trp mutants of both Hb subunits. Rate constants for O 2 , CO, and NO binding were measured using rapid mixing and laser photolysis experiments designed to minimize autoxidation of the unstable apolar E7 mutants. Replacing His(E7) with Gly, Ala, Leu, or Phe causes 20 -500-fold increases in the rates of O 2 dissociation from either Hb subunit, demonstrating unambiguously that the native His(E7) imidazole side chain forms a strong hydrogen bond with bound O 2 in both the ␣ and ␤ chains (⌬G His(E7)H-bond ≈ ؊8 kJ/mol). As the size of the E7 amino acid is increased from Gly to Phe, decreases in k O2 , In 1970, Perutz (1) proposed that the distal histidines located at the E7 helical positions, 3 ␣His-58 and ␤His-63, play crucial structural roles for regulating both the affinities and rates of O 2 binding to adult human hemoglobin (HbA). 4 These ideas were based on the suggestion by Pauling (2) that His(E7) could stabilize bound O 2 by donating a hydrogen bond to the partial negative charge on the superoxide-Fe(III)-like FeO 2 complex and on the idea by Perutz and Mathews (3) that the distal histidine could also be acting as gate for ligand entry and exit. Studies of model heme compounds and naturally occurring globins with His(E7) replacements suggested strongly that the distal histidine also plays a key role in discrimination between O 2 and CO binding (4 -9).The first mutagenesis studies on sperm whale Mb and human HbA reported that His(E7) to Gly mutations in ␣ subunits and Mb cause marked increases in the rates of O 2 dissociation and significant decreases in affinity, both of which indicate strong stabilization of the FeO 2 complex by proton donation from the wild-type His(E7) side chain (7, 10, 11). In addition, the association rate constants for O 2 and CO binding increased 5-10-fold. The latter results were interpreted in terms of the distal histidine gate mechanism, with the His(E7) to Gly mutation resulting in an open E7 channel. In contrast, neither the dissociation nor association rate constants for O 2 binding to the R state ␤Gly(E7) mutant of HbA appeared to increase significantly, implying no electrostatic stabilization of bound ligands by the native His(E7) in ␤ subunits and an already open gate or alternative pathway. These surprising kinetic results were explained by the first high resolution structure of human oxyhemoglobin published by Shaanan (12), in which the N⑀H atoms of distal histidine in ␤ subunits seemed to be further away from the bound O 2 atoms and pointing toward the heme plane.Between 1989 and 1999, our group and others constructed large libraries of mammalian Mb mutants as a model system for understanding the structural mechanisms of ligand binding to vertebrate globins involved in O 2 transport and storage. A detailed molecular mechanism for O 2 binding has emerged. Ligand entry into myoglobin occurs through t...

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confidence: 99%

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confidence: 99%

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confidence: 99%

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confidence: 99%

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Distal Histidine Stabilizes Bound O2 and Acts as a Gate for Ligand Entry in Both Subunits of Adult Human Hemoglobin

Birukou

Schweers²,

Olson

2010

Journal of Biological Chemistry

100

174

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“…4 A structural basis for discrimination against CO was suggested based on the crystal structures of MbCO which seemed to indicate that the protein forces CO to bind in a bent Fe-C-O geometry. 5 It was found that CO binds to model hemes with a linear Fe-C-O geometry 6 but binds to Mb in a bent geometry, 5 and that O 2 binds to model hemes [7][8][9] and Mb with a similar bent Fe-O-O geometry. 10 Considering that the O 2 prefers to bind to the heme in a bent geometry, which is unaffected by the Mb, it was presumed that the protein forces CO to bind in a bent geometry, thereby reducing the affinity of the heme in Mb for CO relative to O 2 .…”

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The Orientation of CO in Heme Proteins Determined by Time-Resolved Mid-IR Spectroscopy: Anisotropy Correction for Finite Photolysis of an Optically Thick Sample

2002

Bulletin of the Korean Chemical Society

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A systematic way of determining the equilibrium orientation of carbon monoxide (CO) in heme proteins using time-resolved polarized mid-IR spectroscopy is presented. The polarization anisotropy at pump-probe delay time of zero in the limit of zero photolysis and the angular distribution function of CO are required to obtain the equilibrium orientation of CO. An approach is developed for determining the polarization anisotropy in the zero-photolysis limit from the anisotropy measured under finite photolysis conditions in an optically thick sample where the fraction of molecules photolyzed decreases as the pump pulse passes through and is absorbed by the sample. This approach is verified by measuring the polarization anisotropy of CO of carbonmonoxy myoglobin at various levels of photolysis. This method can be readily applied to other photoselection experiments determining precise angle between transition dipoles.

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Iron Porphyrin Chemistry

Walker¹,

Simonis²

2005

Encyclopedia of Inorganic Chemistry

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This article reviews most aspects of the chemistry of iron porphyrins, from Fe(0) to Fe(V), including occurrence and roles of natural iron porphyrins (hemes) and their synthetic analogs, structures and electron configurations of iron porphyrins of all oxidation and spin states, π electron configuration of the porphyrin ring, synthesis of metal‐free porphyrins and other related macrocycles, insertion of iron into free‐base porphyrins and related macrocycles, the properties, reactions, uses and biological relevance of iron(0), ‐(I), ‐(II) porphyrins (the latter with S = 0, 1, and 2 spin state possibilities), of iron(II) porphyrin π‐cation radicals, of iron(III) porphyrins (with S = 1/2, 3/2, and 5/2 spin state possibilities), of iron(III) porphyrin and corrole π‐cation radicals, of iron(IV) porphyrins (including five‐ and six‐coordinate ferryl (FeO) 2+ , iron(IV) phenyl, carbene and hydrazine complexes, and the bis‐methoxide complex) and a comparison of iron(IV) porphyrins to iron(III) porphyrin π‐cation radicals, of iron(IV) porphyrin π‐cation radicals, and of the possible existence of iron(V) porphyrins. Included in the Fe(II) part are sections on addition of ligands to four‐coordinate iron(II) porphyrins, including equilibrium binding constants, photodissociation of ligands from PFeL 2 complexes, binding of small molecules (O 2 , CO, NO, HNO) to 5‐coordinate iron(II) porphyrins and design of porphyrin ligands that will mimic the active sites of heme proteins such as myoglobin and hemoglobin, the cytochromes P450 and nitric oxide synthases, and the nitrophorins and guanylyl cyclases. Included in the iron(III) part are sections on both 5‐ and 6‐coordinate high‐spin complexes and their similarities and differences, bridged or through‐space magnetically coupled complexes of high‐spin iron(III) porphyrins with other metal complexes as possible models for cytochrome oxidase and the assimilatory sulfite reductases, coupled oxidation of hemes by hydrogen peroxide or its equivalent, and the relationship of this reactivity to the reactions of heme oxygenase, iron(III) porphyrins as reduction catalysts, and photochemistry of iron(III) porphyrins, possible electron configurations of low‐spin iron(III) porphyrins, the phenomenon and possible electronic consequences of ruffling of the porphinato core in iron(III) porphyrins, the preferred orientation of planar axial ligands bound to low‐spin iron(III) porphyrins, NO complexes of iron(III) porphyrins, reduction potentials, equilibrium constants and rates of axial‐ligand addition and exchange, kinetics of axial‐ligand rotation and porphyrin ring inversion, kinetics of reduction and autoreduction of iron(III) porphyrins, electron self‐exchange between low‐spin iron(III) and iron(II) porphyrins, synthetic ferriheme proteins, and synthesis of five‐coordinate low‐spin iron(III) porphyrins having σ‐alkyl or σ‐aryl groups as axial ligands. The iron(IV) and iron(IV) cation radical sections discuss the high‐valent states of cytochromes P450 and related enzymes.

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Structural changes upon oxygenation of an iron(II)(porphyrinato)(imidazole) complex

Cited by 114 publications

References 1 publication

Distal Histidine Stabilizes Bound O2 and Acts as a Gate for Ligand Entry in Both Subunits of Adult Human Hemoglobin

Distal Histidine Stabilizes Bound O2 and Acts as a Gate for Ligand Entry in Both Subunits of Adult Human Hemoglobin

The Orientation of CO in Heme Proteins Determined by Time-Resolved Mid-IR Spectroscopy: Anisotropy Correction for Finite Photolysis of an Optically Thick Sample

Iron Porphyrin Chemistry

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