A structural model for heme in high-spin ferric hemoproteins. Iron atom centering, porphinato core expansion, and molecular stereochemistry of high-spin diaquo(meso-tetraphenylporphinato)iron(III) perchlorate

Wr, Scheidt; Ia, Cohen; Me, Kastner

doi:10.1021/bi00583a017

Cited by 81 publications

(55 citation statements)

References 37 publications

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“…A similar effect has been noted for the related species [Fem(tpp)(EtOH)2] ÷ (Scheidt, Geiger, Lee, Gans & Marchon, 1992). The Fe--N bond lengths lie between those in pure high-spin complexes [S = 5/2, 2.045/~, (Scheidt, Cohen & Kastner, 1979;Mashiko, Kastner, Spartalian, Scheidt & Reed, 1978)] and, for example, those found in [Fem(oep)(thf)2] ÷ [1.999 (2)/~, (Masuda et al, 1982;Cheng et al, 1994)], with admixed intermediate spin (Scheidt & Reed, 1981;Scheidt & Lee, 1987 The macrocycle conformation is essentially planar. The average deviation from planarity of the 24 atoms of the macrocycle is 0.026/~, while the largest deviations from the N4 plane are of the order of 0.15/~, and are for some Cb atoms.…”

supporting

confidence: 71%

“…Due to the crystallographically imposed symmetry, the N atoms are coplanar with the Fe atom located in the N4 plane ( (Scheidt, Cohen & Kastner, 1979;Mashiko, Kastner, Spartalian, Scheidt & Reed, 1978). Compounds with similar Fe---O distances are the admixed intermediate spin complex [Fem(oep) suda et al, 1982;Cheng et al, 1994) (Scheidt, Geiger, Lee, Gans & Marchon, 1992)].…”

mentioning

confidence: 99%

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Bis(methanol-O)(2,3,7,8,12,13,17,18-octaethylporphyrinato-N,N',N'',N''')iron(III) Perchlorate Bis(methanol) Solvate, [FeIII(oep)(HOCH3)2](ClO4).2CH3OH

Senge¹

1996

Acta Crystallogr C

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confidence: 71%

mentioning

confidence: 99%

Bis(methanol-O)(2,3,7,8,12,13,17,18-octaethylporphyrinato-N,N',N'',N''')iron(III) Perchlorate Bis(methanol) Solvate, [FeIII(oep)(HOCH3)2](ClO4).2CH3OH

Senge¹

1996

Acta Crystallogr C

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“…In the optical spectra of Fig. 2, the bisaquo H175G exhibits a broad Soret band with a maximum at 395 nm, similar to the [Fe(TPP)(OH2)2]+ model complex (14,15) and to the low-pH forms of myoglobin (16,17) and cyt c (18) proposed. Titration of the bisaquo H175G protein with Im at pH 7 results in a two-state conversion to a form with an optical spectrum that is essentially that of the high-spin ferric wild-type enzyme, with a Soret maximum at 408 nm (Fig.…”

Section: Methodsmentioning

confidence: 74%

Construction of a bisaquo heme enzyme and binding by exogenous ligands.

McRee

Jensen

Fitzgerald

et al. 1994

Proc. Natl. Acad. Sci. U.S.A.

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The crystal structure of the His-175 -) Gly (H175G) mutant of cytochrome-c peroxidase (EC 1.11.1.5), missing its only heme ligand, reveals that the histidine is replaced by solvent to give a bisaquo heme protein. This protein retains some residual activity, which can be stimulated or inhibited by addition of exogenous ligands. Structural analysis confirms the binding of imidazole to the heme at the position of the wild-type histidine ligand. This imidazole complex reacts readily with hydrogen peroxide to produce a radical species with novel properties. However, reactivation in this complex is incomplete (""5%), which, in view ofthe very similar structures of the wild-type and the H175G/imidazole forms, implies a critical role for tethering of the axial ligand in catalysis. This study demonstrates the feasibility of constructing heme enzymes with no covalent link to the protein and with unnatural ligand replacements. Such enzymes may prove useful in studies of electron transfer mechanisms and in the engineering of novel heme-based catalysts.The parameters required of the axial ligands for defining the diverse chemistry of heme enzymes are elusive. Peroxidases often contain a histidine ligand to the iron, whereas cysteine is found in monooxygenases and tyrosine in catalases (1, 2). Cytochrome-c peroxidase (CCP; EC 1.11.1.5) catalyzes the oxidation of cytochrome c (cyt c) by H202 through an intermediate state (ES) that consists of a ferryl (Fe4+=O) heme and a free radical localized on Trp-191 (3). The buried carboxylate of Asp-235 stabilizes this free radical and also accepts a hydrogen bond from the histidine heme ligand, His-175. The resulting Asp/His/metal triad is a common motif in metalloproteins and is reminiscent of the Asp/His/ Ser triad of serine proteases (4,5). In this study, we report the deletion of the histidine iron ligand of CCP to produce a heme enzyme which contains no covalent link to the protein. The facile occupation ofthis cavity by exogenous small molecules demonstrates the potential for producing heme catalysts containing a wide range of unnatural ligands. MATERIALS AND METHODSProtein Expression and Purification. Wild-type and mutant CCP proteins were overexpressed in Escherichia coli BL21(DE3) using the plasmid pT7CCP (6). Wild-type CCP in our laboratory is that with Met-Lys-Thr at the N terminus and containing Ile-53 and Gly-152 (7). The His-175 --Gly (H175G) mutant was created by site-directed mutagenesis, expressed, purified to homogeneity, and reconstituted with heme as described (6). This purified reconstituted protein was crystallized twice against distilled water and stored as a crystal suspension at 77 K. Protein concentrations were determined from the extinction coefficients determined by pyridine hemochromogens (8, 9). In the case of H175G the extinction coefficient was determined for the 280-nm band because of the variability (with pH and temperature) in the intensity and energy of the Soret band (see below).X-Ray Crystallography.t Attempts to obtain crystals of H175G by ...

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“…Samples for Mössbauer spectroscopy were prepared by immobilization of the crystalline material in Apiezon M grease. [31] (50 mg, 0.05 mmol) was stirred with KCN (50 mg, 0.77 mmol) in methanol (8 mL) for 3 h. After the evaporation of solvent, 0.6 mL of 1-methylimidazole in 3 mL of CHCl 3 was added and the solution was stirred overnight. The resulting solution was filtered and hexanes were slowly diffused into the solution.…”

Section: Experimental Section General Informationmentioning

confidence: 99%

New Insights on the Electronic and Molecular Structure of Cyanide-Ligated Iron(III) Porphyrinates

Noll

Schulz

et al. 2007

Inorg. Chem.

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The preparation and characterization of several new cyanoligated six-coordinate low-spin iron(III) porphyrinates are reported. The synthesis and structure of the new bis(cyanide) derivative K(222)] [Fe(TMP)(CN) 2 ] (TMP= tetramesitylporphyrinate) is described. Three mixed-ligand species of the general form [Fe(Porph)(CN)(L)], where L = 1-methylimidazole or pyridine, have also been prepared and structurally characterized. All complexes have been studied with EPR spectroscopy in frozen solution and in microcrystalline form. In some cases, especially those of the bis(cyanide) derivative above and the previously reported [Fe(TPP)(CN) 2 ] − , there are significant differences in the EPR spectra as a result of the state change. These spectral differences can be correlated with changes in the electron configuration that are the likely result of a differing environment of the coordinated cyanide ligands; core conformation and electronic structure of the porphyrin ligand are unlikely to play a role. All four new complexes and [Fe(TPP)(CN) 2 ] − have been studied by Mössbauer spectroscopy with variable temperature and applied magnetic field measurements. The sign of the quadrupole splitting value has been established as negative. These measurements have allowed us to give estimates of the energy difference between the two close-lying d π (d xz and d yz ) orbitals. These splitting values range from ∼267 cm −1 for [Fe(TPP)(CN) 2 ] − to ∼614 cm −1 for [Fe(TPP)(CN)(Py)].

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A structural model for heme in high-spin ferric hemoproteins. Iron atom centering, porphinato core expansion, and molecular stereochemistry of high-spin diaquo(meso-tetraphenylporphinato)iron(III) perchlorate

Cited by 81 publications

References 37 publications

Bis(methanol-O)(2,3,7,8,12,13,17,18-octaethylporphyrinato-N,N',N'',N''')iron(III) Perchlorate Bis(methanol) Solvate, [FeIII(oep)(HOCH3)2](ClO4).2CH3OH

Bis(methanol-O)(2,3,7,8,12,13,17,18-octaethylporphyrinato-N,N',N'',N''')iron(III) Perchlorate Bis(methanol) Solvate, [FeIII(oep)(HOCH3)2](ClO4).2CH3OH

Construction of a bisaquo heme enzyme and binding by exogenous ligands.

New Insights on the Electronic and Molecular Structure of Cyanide-Ligated Iron(III) Porphyrinates

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