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Du J, Sono M, Dawson JH. Ferric His93Gly myoglobin cavity mutant and its complexes with thioether and selenolate as heme protein models. J PORPHYR PHTHALOCYA 2012. [DOI: 10.1142/s1088424610002872] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
The composition of ferric exogenous ligand-free His93Gly sperm whale myoglobin (H93G Mb) at neutral pH has been determined by examination of the spectral properties of the protein over the pH range from 3.0 to 10.5. An apparent pKa value of ~6.6 has been observed for the conversion of a postulated six-coordinate bis-water-bound coordination structure at pH 5.0 to a five-coordinate hydroxide-bound form at pH 10.5. Starting from the exogenous ligand-free ferric H93G protein, ferric mono- and bis-thioether (tetrahydrothiophene, THT)-ligated adducts have been prepared and characterized by UV-visible (UV-vis) absorption and magnetic circular dichroism (MCD) spectroscopy. The mon-THT ferric H93G Mb species has hydroxide as the sixth ligand. The bis-THT derivative is a model for the low-spin ferric heme binding site of native bis-Met-ligated bacterioferritin or streptococcal heme-associated protein (Shp). A novel THT-bound ferryl H93G Mb moiety has been partially formed. The high-spin five-coordinate ferric H93G(selenolate) Mb complex has been prepared using benzeneselenol and characterized by UV-vis and MCD spectroscopy as a model for Se-Cys-ligated ferric cytochrome P450. The results described herein further demonstrate the versatility of the H93G cavity mutant for modeling the coordination structures of novel heme iron protein active sites.
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Affiliation(s)
- Jing Du
- Department of Chemistry and Biochemistry, University of South Carolina, 631 Sumter St., Columbia, SC 29208, USA
| | - Masanori Sono
- Department of Chemistry and Biochemistry, University of South Carolina, 631 Sumter St., Columbia, SC 29208, USA
| | - John H. Dawson
- Department of Chemistry and Biochemistry, University of South Carolina, 631 Sumter St., Columbia, SC 29208, USA
- School of Medicine, University of South Carolina, 631 Sumter St., Columbia, SC 29208, USA
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Molecular basis for the inability of an oxygen atom donor ligand to replace the natural sulfur donor heme axial ligand in cytochrome P450 catalysis. Spectroscopic characterization of the Cys436Ser CYP2B4 mutant. Arch Biochem Biophys 2010; 507:119-25. [PMID: 21147058 DOI: 10.1016/j.abb.2010.12.010] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2010] [Revised: 12/06/2010] [Accepted: 12/07/2010] [Indexed: 11/21/2022]
Abstract
All cytochrome P450s (CYPs) contain a cysteinate heme iron proximal ligand that plays a crucial role in their mechanism of action. Conversion of the proximal Cys436 to Ser in NH(2)-truncated microsomal CYP2B4 (ΔCYP2B4) transforms the enzyme into a two-electron NADPH oxidase producing H(2)O(2) without monooxygenase activity [K.P. Vatsis, H.M. Peng, M.J. Coon, J. Inorg. Biochem. 91 (2002) 542-553]. To examine the effects of this ligation change on the heme iron spin-state and coordination structure of ΔC436S CYP2B4, the magnetic circular dichroism and electronic absorption spectra of several oxidation/ligation states of the variant have been measured and compared with those of structurally defined heme complexes. The spectra of the substrate-free ferric mutant are indicative of a high-spin five-coordinate structure ligated by anionic serinate. The spectroscopic properties of the dithionite-reduced (deoxyferrous) protein are those of a five-coordinate (high-spin) state, and it is concluded that the proximal ligand has been protonated to yield neutral serine (ROH-donor). Low-spin six-coordinate ferrous complexes of the mutant with neutral sixth ligands (NO, CO, and O(2)) examined are also likely ligated by neutral serine, as would be expected for ferric complexes with anionic sixth ligands such as the hydroperoxo-ferric catalytic intermediate. Ligation of the heme iron by neutral serine vs. deprotonated cysteine is likely the result of the large difference in their acidity. Thus, without the necessary proximal ligand push of the cysteinate, although the ΔC436S mutant can accept two electrons and two protons, it is unable to heterolytically cleave the O-O bond of the hydroperoxo-ferric species to generate Compound I and hydroxylate the substrate.
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Jiang Y, Ortiz de Montellano PR. Selenolate complexes of CYP101 and the heme-bound hHO-1/H25A proximal cavity mutant. Inorg Chem 2008; 47:3480-2. [PMID: 18376820 DOI: 10.1021/ic800148a] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Thiolate and selenolate complexes of CYP101 (P450cam) and the H25A proximal cavity mutant of heme-bound human heme oxygenase-1 (hHO-1) have been examined by UV-vis spectroscopy. Both thiolate and selenolate ligands bound to the heme distal side in CYP101 and gave rise to characteristic hyperporphyrin spectra. Thiolate ligands also bound to the proximal side of the heme in the cavity created by the H25A mutation in hHO-1, giving a Soret absorption similar to that of the H25C hHO-1 mutant. Selenolate ligands also bound to this cavity mutant under anaerobic conditions but reduced the heme iron to the ferrous state, as shown by the formation of a ferrous CO complex. Under aerobic conditions, the selenolate ligand but not the thiolate ligand was rapidly oxidized. These results indicate that selenocysteine-coordinated heme proteins will not be stable species in the absence of a redox potential stabilizing effect.
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Affiliation(s)
- Yongying Jiang
- Department of Pharmaceutical Chemistry, University of California, San Francisco, CA 94158-2517, USA
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Sook BR, Block DR, Sumithran S, Montañez GE, Rodgers KR, Dawson JH, Eichenbaum Z, Dixon DW. Characterization of SiaA, a Streptococcal Heme-Binding Protein Associated with a Heme ABC Transport System. Biochemistry 2008; 47:2678-88. [DOI: 10.1021/bi701604y] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Brian R. Sook
- Department of Chemistry, Georgia State University, Atlanta, Georgia 30302-4098, Department of Chemistry, Biochemistry, and Molecular Biology, North Dakota State University, Fargo, North Dakota 58105-5516, Department of Chemistry and Biochemistry, University of South Carolina, Columbia, South Carolina 29208, and Department of Biology, Georgia State University, Atlanta, Georgia 30303
| | - Darci R. Block
- Department of Chemistry, Georgia State University, Atlanta, Georgia 30302-4098, Department of Chemistry, Biochemistry, and Molecular Biology, North Dakota State University, Fargo, North Dakota 58105-5516, Department of Chemistry and Biochemistry, University of South Carolina, Columbia, South Carolina 29208, and Department of Biology, Georgia State University, Atlanta, Georgia 30303
| | - Suganya Sumithran
- Department of Chemistry, Georgia State University, Atlanta, Georgia 30302-4098, Department of Chemistry, Biochemistry, and Molecular Biology, North Dakota State University, Fargo, North Dakota 58105-5516, Department of Chemistry and Biochemistry, University of South Carolina, Columbia, South Carolina 29208, and Department of Biology, Georgia State University, Atlanta, Georgia 30303
| | - Griselle E. Montañez
- Department of Chemistry, Georgia State University, Atlanta, Georgia 30302-4098, Department of Chemistry, Biochemistry, and Molecular Biology, North Dakota State University, Fargo, North Dakota 58105-5516, Department of Chemistry and Biochemistry, University of South Carolina, Columbia, South Carolina 29208, and Department of Biology, Georgia State University, Atlanta, Georgia 30303
| | - Kenton R. Rodgers
- Department of Chemistry, Georgia State University, Atlanta, Georgia 30302-4098, Department of Chemistry, Biochemistry, and Molecular Biology, North Dakota State University, Fargo, North Dakota 58105-5516, Department of Chemistry and Biochemistry, University of South Carolina, Columbia, South Carolina 29208, and Department of Biology, Georgia State University, Atlanta, Georgia 30303
| | - John H. Dawson
- Department of Chemistry, Georgia State University, Atlanta, Georgia 30302-4098, Department of Chemistry, Biochemistry, and Molecular Biology, North Dakota State University, Fargo, North Dakota 58105-5516, Department of Chemistry and Biochemistry, University of South Carolina, Columbia, South Carolina 29208, and Department of Biology, Georgia State University, Atlanta, Georgia 30303
| | - Zehava Eichenbaum
- Department of Chemistry, Georgia State University, Atlanta, Georgia 30302-4098, Department of Chemistry, Biochemistry, and Molecular Biology, North Dakota State University, Fargo, North Dakota 58105-5516, Department of Chemistry and Biochemistry, University of South Carolina, Columbia, South Carolina 29208, and Department of Biology, Georgia State University, Atlanta, Georgia 30303
| | - Dabney W. Dixon
- Department of Chemistry, Georgia State University, Atlanta, Georgia 30302-4098, Department of Chemistry, Biochemistry, and Molecular Biology, North Dakota State University, Fargo, North Dakota 58105-5516, Department of Chemistry and Biochemistry, University of South Carolina, Columbia, South Carolina 29208, and Department of Biology, Georgia State University, Atlanta, Georgia 30303
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Eakanunkul S, Lukat-Rodgers GS, Sumithran S, Ghosh A, Rodgers KR, Dawson JH, Wilks A. Characterization of the Periplasmic Heme-Binding Protein ShuT from the Heme Uptake System of Shigella dysenteriae. Biochemistry 2005; 44:13179-91. [PMID: 16185086 DOI: 10.1021/bi050422r] [Citation(s) in RCA: 86] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The heme uptake systems by which bacterial pathogens acquire and utilize heme have recently been described. Such systems may utilize heme directly from the host's hemeproteins or via a hemophore that sequesters and transports heme to an outer membrane receptor and subsequently to the translocating proteins by which heme is further transported into the cell. However, little is known of the heme binding and release mechanisms that facilitate the uptake of heme into the pathogenic organism. As a first step toward elucidating the molecular level events that drive heme binding and release, we have undertaken a spectroscopic and mutational study of the first purified periplasmic heme-binding protein (PBP), ShuT from Shigella dysenteriae. On the basis of sequence identity, the ShuT protein is most closely related to the class of PBPs typified by the vitamin B(12) (BtuF) and iron-hydroxamate (FhuD) PBPs and is a monomeric protein having a molecular mass of 28.5 kDa following proteolytic processing of the periplasmic signaling peptide. ShuT binds one b-type heme per monomer with high affinity and bears no significant homology with other known heme proteins. The resonance Raman, MCD, and UV-visible spectra of WT heme-ShuT are consistent with a five-coordinate high spin heme having an anionic O-bound proximal ligand. Site-directed ShuT mutants of the absolutely conserved Tyr residues, Tyr-94 (Y94A) and Tyr-228 (Y228F), which are found in all putative periplasmic heme-binding proteins, were subjected to UV-visible, resonance Raman, and MCD spectroscopic investigations of heme coordination environment and rates of heme release. The results of these experiments confirmed Tyr-94 as the only axial heme ligand and Tyr-228 as making a significant contribution to the stability of heme-loaded ShuT, albeit without directly interacting with the heme iron.
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Affiliation(s)
- Suntara Eakanunkul
- Department of Pharmaceutical Sciences, School of Pharmacy, 20 Penn Street, University of Maryland, Baltimore, Maryland 21201, USA
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