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Tsutsui Y, Kobayashi K, Takeuchi F, Tsubaki M, Kozawa T. Reaction Intermediates of Nitric Oxide Synthase from Deinococcus radiodurans as Revealed by Pulse Radiolysis: Evidence for Intramolecular Electron Transfer from Biopterin to Fe II-O 2 Complex. Biochemistry 2018; 57:1611-1619. [PMID: 29320163 DOI: 10.1021/acs.biochem.7b00887] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Nitric oxide synthase (NOS) is a cytochrome P450-type mono-oxygenase that catalyzes the oxidation of l-arginine (Arg) to nitric oxide (NO) through a reaction intermediate N-hydroxy-l-arginine (NHA). The mechanism underlying the reaction catalyzed by NOS from Deinococcus radiodurans was investigated using pulse radiolysis. Radiolytically generated hydrated electrons reduced the heme iron of NOS within 2 μs. Subsequently, ferrous heme reacted with O2 to form a ferrous-dioxygen intermediate with a second-order rate constant of 2.8 × 108 M-1 s-1. In the tetrahydrofolate (H4F)-bound enzyme, the ferrous-dioxygen intermediate was found to decay an another intermediate with a first-order rate constant of 2.2 × 103 s-1. The spectrum of the intermediate featured an absorption maximum at 440 nm and an absorption minimum at 390 nm. In the absence of H4F, this step did not proceed, suggesting that H4F was reduced with the ferrous-dioxygen intermediate to form a second intermediate. The intermediate further converted to the original ferric form with a first-order rate constant of 4 s-1. A similar intermediate could be detected after pulse radiolysis in the presence of NHA, although the intermediate decayed more slowly (0.5 s-1). These data suggested that a common catalytically active intermediate involved in the substrate oxidation of both Arg and NHA may be formed during catalysis. In addition, we investigated the solvent isotope effects on the kinetics of the intermediate after pulse radiolysis. Our experiments revealed dramatic kinetic solvent isotope effects on the conversion of the intermediate to the ferric form, of 10.5 and 2.5 for Arg and NHA, respectively, whereas the faster phases were not affected. These data suggest that the proton transfer in DrNOS is the rate-limiting reaction of the intermediate with the substrates.
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Affiliation(s)
- Yuko Tsutsui
- The Institute of Scientific and Industrial Research , Osaka University , Mihogaoka 8-1 , Ibaraki , Osaka 567-0047 , Japan
| | - Kazuo Kobayashi
- The Institute of Scientific and Industrial Research , Osaka University , Mihogaoka 8-1 , Ibaraki , Osaka 567-0047 , Japan
| | - Fusako Takeuchi
- Institute for Promotion of Higher Education , Kobe University , 1-2-1 Tsurukabuto , Nada-ku, Kobe , Hyogo 657-8501 , Japan
| | - Motonari Tsubaki
- Graduate School of Science, Department of Chemistry , Kobe University , 1-1 Rokkodai-cho , Nada-ku, Kobe , Hyogo 657-8501 , Japan
| | - Takahiro Kozawa
- The Institute of Scientific and Industrial Research , Osaka University , Mihogaoka 8-1 , Ibaraki , Osaka 567-0047 , Japan
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Recuenco MC, Rahman MM, Takeuchi F, Kobayashi K, Tsubaki M. Electron transfer reactions of candidate tumor suppressor 101F6 protein, a cytochrome b561 homologue, with ascorbate and monodehydroascorbate radical. Biochemistry 2013; 52:3660-8. [PMID: 23641721 DOI: 10.1021/bi301607s] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The candidate tumor suppressor 101F6 protein is a homologue of adrenal chromaffin granule cytochrome b561, which is involved in the electron transfer from cytosolic ascorbate to intravesicular monodehydroascorbate radical. Since the tumor suppressor activity of 101F6 was enhanced in the presence of ascorbate, it was suggested that 101F6 might utilize a similar transmembrane electron transfer reaction. Detailed kinetic analyses were conducted on the detergent-solubilized recombinant human 101F6 for its electron transfer reactions with ascorbate and monodehydroascorbate radical by stopped-flow and pulse radiolysis techniques. The reduction of oxidized 101F6 with ascorbate was found to be independent of pH in contrast to those observed for chromaffin granule and Zea mays cytochromes b561 in which both cytochromes exhibited very slow rates at pH 5.0 but faster at pH 6.0 and 7.0. The absence of the inhibition for the electron acceptance from ascorbate upon the treatment with diethyl pyrocarbonate suggested that 101F6 might not utilize a "concerted proton/electron transfer mechanism". The second-order rate constant for the electron donation from the ascorbate-reduced 101F6 to the pulse-generated monodehydroascorbate radical was found to be 5.0 × 10(7) M(-1 )s(-1), about 2-fold faster than that of bovine chromaffin granule cytochrome b561 and about five times faster than that of Zea mays cytochrome b561, suggesting that human 101F6 is very effective for regenerating ascorbate from monodehydroascorbate radical in cells. Present observations suggest that 101F6 employs distinct electron transfer mechanisms on both sides of the membranes from those of other members of cytochrome b561 protein family.
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Affiliation(s)
- Mariam C Recuenco
- Department of Chemistry, Graduate School of Science, Kobe University , Rokkodai-cho 1-1, Nada-ku, Kobe, Hyogo 657-8501, Japan
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Recuenco MC, Rahman MM, Sakamoto Y, Takeuchi F, Hori H, Tsubaki M. Functional characterization of the recombinant human tumour suppressor 101F6 protein, a cytochrome b(561) homologue. J Biochem 2012; 153:233-42. [PMID: 23235316 DOI: 10.1093/jb/mvs139] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
Candidate human tumour suppressor gene product, 101F6 protein, is a highly hydrophobic transmembrane protein and a member of cytochrome b(561) family. Purified 101F6 protein expressed in Pichia pastoris cells showed visible absorption spectra similar but distinct from those of cytochrome b(561). Haem content analysis indicated presence of two haems B per molecule. Midpoint potentials of the purified protein were found as +109 and +26 mV for two haems, slightly lower than those for bovine chromaffin granule or plant Zea mays cytochromes b(561). Electron paramagnetic resonance (EPR) spectra in oxidized state at 5 K showed only a highly anisotropic low-spin (HALS) signal at g(z) = 3.75. However, at 15 and 20 K, another HALS-type signal appeared at g(z) = 3.65 being overlapped with that of g(z) = 3.75. The rhombic EPR signal at g(z) = 3.16 previously seen in other cytochromes b(561) was not observed, suggesting distinct haem environments. Absence of the inhibition in the electron transfer from ascorbate by a treatment of 101F6 protein with diethylpyrocarbonate showed a remarkable contrast from those of other cytochromes b(561) where the 'concerted H(+)/e(-) transfer mechanism' at the cytosolic haem centre was blocked by specific Nε-carbethoxylation of haem-coordinating imidazole, suggesting that 101F6 protein might accept electrons via a mechanism distinct from other cytochromes b(561).
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Affiliation(s)
- Mariam C Recuenco
- Department of Chemistry, Graduate School of Science, Kobe University, Kobe, Hyogo, Japan
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Liu W, da Silva GFZ, Wu G, Palmer G, Tsai AL, Kulmacz RJ. Functional and structural roles of residues in the third extramembrane segment of adrenal cytochrome b561. Biochemistry 2011; 50:3149-60. [PMID: 21401125 DOI: 10.1021/bi101796m] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Several residues in the third extramembrane segment (EM3) of adrenal cytochrome b(561) have been proposed to be involved in this cytochrome's interaction with ascorbate, but there has been no systematic evaluation of residues in the segment. We used alanine scanning mutagenesis to assess the functional and structural roles of the EM3 residues and several adjacent residues (residues 70-85) in the bovine cytochrome. Each alanine mutant was expressed in a bacterial system, solubilized with detergent, and affinity-purified. The recombinant proteins contained approximately two hemes per monomer and, except for R74A, retained basic functionality (≥ 94% reduced by 20 mM ascorbate). Equilibrium spectrophotometric titrations with ascorbate were used to analyze the α-band line shape and amplitude during reduction of the high- and low-potential heme centers (b(H) and b(L), respectively) and the midpoint ascorbate concentrations for the b(H) and b(L) transitions (C(H) and C(L), respectively). Y73A and K85A markedly narrowed the b(H) α-band peak; other mutants had weaker effects or no effect on b(H) or b(L) spectra. Relative changes in C(H) for the mutants were larger than changes in C(L), with 1.5-2.9-fold increases in C(H) for L70A, L71A, Y73A, R74A, N78A, and K85A. The amounts of functional b(H) and b(L) centers in additional Arg74 mutants, assessed by ascorbate titration and EPR spectroscopy, declined in concert in the following order: wild type > R74K > R74Q > R74T and R74Y > R74E. The results of this first comprehensive experimental test of the proposed roles of EM3 residues have identified residues with a direct or indirect impact on ascorbate interactions, on the environment of the b(H) heme center, and on formation of the native b(H)-b(L) unit. Surprisingly, no individual EM3 residue was by itself indispensable for the interaction with ascorbate, and the role of the segment appears to be more subtle than previously thought. These results also support our topological model of the adrenal cytochrome, which positions b(H) near the cytoplasmic side of the membrane.
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Affiliation(s)
- Wen Liu
- Department of Internal Medicine, University of Texas Health Science Center, Houston, Texas 77030, United States
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Axial ligation of the high-potential heme center in an Arabidopsis
cytochrome b
561. FEBS Lett 2011; 585:545-8. [DOI: 10.1016/j.febslet.2011.01.006] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2010] [Revised: 12/21/2010] [Accepted: 01/04/2011] [Indexed: 11/19/2022]
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Nakanishi N, Rahman MM, Sakamoto Y, Takigami T, Kobayashi K, Hori H, Hase T, Park SY, Tsubaki M. Importance of the conserved lysine 83 residue of Zea mays cytochrome b(561) for ascorbate-specific transmembrane electron transfer as revealed by site-directed mutagenesis studies. Biochemistry 2009; 48:10665-78. [PMID: 19803484 DOI: 10.1021/bi9010682] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Cytochromes b(561), a novel class of transmembrane electron transport proteins residing in a large variety of eukaryotic cells, have a number of common structural features including six hydrophobic transmembrane alpha-helices and two heme ligation sites. We found that recombinant Zea mays cytochrome b(561) obtained by a heterologous expression system using yeast Pichia pastoris cells could utilize the ascorbate/mondehydroascorbate radical as a physiological electron donor/acceptor. We found further that a concerted proton/electron transfer mechanism might be operative in Z. mays cytochrome b(561) as well upon the electron acceptance from ascorbate to the cytosolic heme center. The well-conserved Lys(83) residue in a cytosolic loop was found to have a very important role(s) for the binding of ascorbate and the succeeding electron transfer via electrostatic interactions based on the analyses of three site-specific mutants, K83A, K83E, and K83D. Further, unusual behavior of the K83A mutant in pulse radiolysis experiments indicated that Lys(83) might also be responsible for the intramolecular electron transfer to the intravesicular heme. On the other hand, pulse radiolysis experiments on two site-specific mutants, S118A and W122A, for the well-conserved residues in the putative monodehydroascorbate radical binding site showed that their electron transfer activities to the monodehydroascorbate radical were very similar to those of the wild-type protein, indicating that Ser(118) and Trp(122) do not have major roles for the redox events on the intravesicular side.
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Affiliation(s)
- Nobuyuki Nakanishi
- Department of Molecular Science and Material Engineering, Graduate School of Science and Technology, Graduate School of Science, Kobe University, 1-1 Rokkodai-cho, Nada-ku, Kobe, Hyogo 657-8501, Japan
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Nakanishi N, Rahman MM, Sakamoto Y, Miura M, Takeuchi F, Park SY, Tsubaki M. Inhibition of electron acceptance from ascorbate by the specific N-carbethoxylations of maize cytochrome b561: a common mechanism for the transmembrane electron transfer in cytochrome b561 protein family. J Biochem 2009; 146:857-66. [PMID: 19762344 DOI: 10.1093/jb/mvp146] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Cytochromes b(561) constitute a novel class of proteins in eukaryotic cells with a number of highly relevant common features including six transmembrane alpha-helices and two haem groups. Of particular interest is the presence of a large number of plant homologues having putative ascorbate- and monodehydroascorbate radical-binding sites. We conducted a diethylpyrocarbonate-modification study employing Zea mays cytochrome b(561) heterologously expressed in Pichia pastoris cells. Pre-treatment of cytochrome b(561) with diethylpyrocarbonate in oxidized form caused N-carbethoxylation of His(86), His(159) and Lys(83), leading to a drastic inhibition of the electron transfer from ascorbate. The activity was protected by the inclusion of ascorbate during the treatment. However, midpoint potentials of two haem centres did show only slight decreases upon the treatment, suggesting that changes in the midpoint potentials were not the major cause of the inhibition. Present results indicated that Zea mays cytochrome b(561) conducted an ascorbate-specific transmembrane electron transfer by utilizing a concerted H(+)/e(-) transfer mechanism and that the specific N-carbethoxylation of haem axial His(86) that would inhibit the removal of a proton from the bound ascorbate was a major cause of the inhibition. On the other hand, Lys(83) might be important for an initial step(s) of the fast electron acceptance from ascorbate.
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Affiliation(s)
- Nobuyuki Nakanishi
- Department of Molecular Science and Material Engineering, Graduate School of Science and Technology, Kobe University, 1-1 Rokkodai-cho, Nada-ku, Kobe, Japan
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Liu W, Rogge CE, da Silva GFZ, Shinkarev VP, Tsai AL, Kamensky Y, Palmer G, Kulmacz RJ. His92 and His110 selectively affect different heme centers of adrenal cytochrome b(561). BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2008; 1777:1218-28. [PMID: 18501187 DOI: 10.1016/j.bbabio.2008.04.039] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/26/2008] [Revised: 04/14/2008] [Accepted: 04/16/2008] [Indexed: 11/26/2022]
Abstract
Adrenal cytochrome b(561) (cyt b(561)), a transmembrane protein that shuttles reducing equivalents derived from ascorbate, has two heme centers with distinct spectroscopic signals and reactivity towards ascorbate. The His54/His122 and His88/His161 pairs furnish axial ligands for the hemes, but additional amino acid residues contributing to the heme centers have not been identified. A computational model of human cyt b(561) (Bashtovyy, D., Berczi, A., Asard, H., and Pali, T. (2003) Protoplasma 221, 31-40) predicts that His92 is near the His88/His161 heme and that His110 abuts the His54/His122 heme. We tested these predictions by analyzing the effects of mutations at His92 or His110 on the spectroscopic and functional properties. Wild type cytochrome and mutants with substitutions in other histidine residues or in Asn78 were used for comparison. The largest lineshape changes in the optical absorbance spectrum of the high-potential (b(H)) peak were seen with mutation of His92; the largest changes in the low-potential (b(L)) peak lineshape were observed with mutation of His110. In the EPR spectra, mutation of His92 shifted the position of the g=3.1 signal (b(H)) but not the g=3.7 signal (b(L)). In reductive titrations with ascorbate, mutations in His92 produced the largest increase in the midpoint for the b(H) transition; mutations in His110 produced the largest decreases in DeltaA(561) for the b(L) transition. These results indicate that His92 can be considered part of the b(H) heme center, and His110 part of the b(L) heme center, in adrenal cyt b(561).
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Affiliation(s)
- Wen Liu
- Department of Internal Medicine, University of Texas Health Science Center at Houston, Houston, Texas, USA
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Oakhill JS, Marritt SJ, Gareta EG, Cammack R, McKie AT. Functional characterization of human duodenal cytochrome b (Cybrd1): Redox properties in relation to iron and ascorbate metabolism. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2008; 1777:260-8. [DOI: 10.1016/j.bbabio.2007.12.001] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/18/2007] [Revised: 12/11/2007] [Accepted: 12/12/2007] [Indexed: 10/22/2022]
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Kamensky Y, Liu W, Tsai AL, Kulmacz RJ, Palmer G. Axial ligation and stoichiometry of heme centers in adrenal cytochrome b561. Biochemistry 2007; 46:8647-58. [PMID: 17602662 PMCID: PMC2551744 DOI: 10.1021/bi700054g] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
Cytochrome (cyt) b561 transports electrons across the membrane of chromaffin granules (CG) present in the adrenal medulla, supporting the biosynthesis of norepinephrine in the CG matrix. We have conducted a detailed characterization of cyt b561 using electron paramagnetic resonance (EPR) and optical spectroscopy on the wild-type and mutant forms of the cytochrome expressed in insect cells. The gz = 3.7 (low-potential heme) and gz = 3.1 (high-potential heme) signals were found to represent the only two authentic hemes of cyt b561; models that propose smaller or greater amounts of heme can be ruled out. We identified the axial ligands to hemes in cyt b561 by mutating four conserved histidines (His54 and His122 at the matrix-side heme center and His88 and His161 at the cytoplasmic-side heme center), thus confirming earlier structural models. Single mutations of any of these histidines produced a constellation of spectroscopic changes that involve not one but both heme centers. We hypothesize that the two hemes and their axial ligands in cyt b561 are integral parts of a structural unit that we term the "kernel". Histidine to glutamine substitutions in the cytoplasmic-side heme center but not in the matrix-side heme center led to the retention of a small fraction of the low-potential heme with gz = 3.7. We provisionally assign the low-potential heme to the matrix side of the membrane; this arrangement suggests that the membrane potential modulates electron transport across the CG membrane.
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Affiliation(s)
- Yury Kamensky
- Department of Biochemistry and Cell Biology, Rice University, Houston, Texas 77251, USA.
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