Electron self-exchange in high-potential iron-sulfur proteins. Characterization of protein I from Ectothiorhodospira vacuolata

Bertini, Ivano; Gaudemer, A.; Luchinat, Claudio; Piccioli, Mario

doi:10.1021/bi00210a042

Cited by 44 publications

(32 citation statements)

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“…6 we show the experimental points obtained using the T,' values for oxidized RJ ferrnentuns and E. halophila iso-11 HiPIPs measured in this work, and previously reported values for C. vinosum [63], R. gelutinosus 1661, R. globiformis [28], and E. vucuolatu iso-I [67] and iso-I1 [29] HiPIPs. We have assumed for E. halophila iso-I1 HiPIP the same geometry as found for E. halophila iso-I HiPIP [41], for R. gelutinosus and for RJ: ferrnentans HiPIPs the geometry of C. vinosum HiPIP [65], and for E. vucuoluta iso-I HiPIP the geometry of E. vucuolatu iso-I1 HiPIP 1431.…”

Section: Analysis Of T;' Values For Cysteine Protons Of Oxidizedsupporting

confidence: 64%

¹H NMR of High‐Potential Iron‐Sulfur Protein from the Purple Non‐Sulfur Bacterium Rhodoferax fermentans

Ciurli

Cremonini

Kofod³

et al. 1996

European Journal of Biochemistry

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Oxidized and reduced forms of high-potential iron-sulfur protein (HiPIP) from the purple non-sulfur photosynthetic bacterium Rhodoferux fermentam have been characterized using 'H-NMR spectroscopy. Pairwise and sequence-specific assignments of hyperfine-shifted 'H-NMR signals to protons of cysteine residues bound to the [4Fe-4SI3+'*+ cluster have been performed using one-dimensional NOE and exchange spectroscopy experiments. 'H-NMR hyperfine shifts and relaxation rates of cluster-bound Cys P-CH, protons indicate that in the [4Fe-4SJi+ cluster one iron ion can be formally described as Fe(III), while electron density corresponding to one electron is unevenly delocalized onto the remaining three iron ions. This delocalization is effected by means of two different electronic distributions interconverting rapidly on the NMR time scale. The mechanism of paramagnetic proton relaxation, studied by analyzing longitudinal relaxation rates of Cys P-CH, protons in HiPlPs from six different sources as a function of the Fe-S-CP-Ca dihedral angle, indicate that the major contribution is due to a dipolar metal-centered mechanism, with a non-negligeable contribution from a ligand-centered dipolar mechanism which involves the 3p orbital of the Cys sulfur atom. A semi-quantitative tool for extracting structural information from relaxation time measurements is proposed.Keywords: bacterial photosynthesis ; high-potential iron-sulfur protein ; Rhodoferux ferrnentuns ; NMR.High-potential iron-sulfur proteins (HiPIPs) are a class of biomolecules that have been extensively investigated as electron-transfer models [I -81. They feature a [4Fe-4S]i+'2' cluster in the oxidized and reduced form, respectively [9-111, and reduction potentials in the range +90 to +450 mV [6, 121. Their structural and spectroscopic properties are well characterized [13], whereas their biological function is still a matter of discussion (14-171. Recent results have shown that HiPIP from the purple non-sulfur bacterium Rhodoferux ferrnentuns is able to re-reduce the homologous photo-oxidized photosynthetic reaction center with half times of the order of microseconds, thus shedding light on the possible physiological role of HiPIP in phototropic bacteria [I 8, 191.'H-NMR spectroscopy has been particularly valuable for the characterization of geometric and electronic structures of HiPIPs [ 131 (and references therein). HiPIPs from Ectothiorhodospiru hulophilu [20, 211 and Chrornutium vinosum 122, 231 represent the first cases of structure determination of paramagnetic proteins in solution using 'H NMR, and the same type of spectroscopy has been crucial to elucidate the electronic distribution within the [4Fe-4SIi+ cluster of oxidized HiPIPs [24-311.In a continuing effort to establish structure/function relationships for this class of proteins, we present here a 'H-NMR spectroscopic characterization of R$ ferrnentuns HiPIP, together with a critical comparison of 'H-NMR data with those of HiPIPs from other sources. The goal of this study is to elucidate the electronic...

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Section: Analysis Of T;' Values For Cysteine Protons Of Oxidizedsupporting

confidence: 64%

¹H NMR of High‐Potential Iron‐Sulfur Protein from the Purple Non‐Sulfur Bacterium Rhodoferax fermentans

Ciurli

Cremonini

Kofod³

et al. 1996

European Journal of Biochemistry

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“…This hydrophobic patch is conserved among the three-dimensional structures of HiPIPs of other species. Spectroscopic study has shown that HiPIPs are capable of forming temporary dimers in solution by using the hydrophobic surface and that the electron transfer can occur between the two monomers in the dimeric structure (53,54), suggesting that the HiPIP monomer in solution interacts temporally with the other protein via its hydrophobic patch to transfer electrons.…”

Section: Resultsmentioning

confidence: 99%

Crystal structures of photosynthetic reaction center and high-potential iron-sulfur protein from Thermochromatium tepidum : Thermostability and electron transfer

Nogi

Fathir²,

Kobayashi³

et al. 2000

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

167

133

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The reaction center (RC) of photosynthetic bacteria is a membrane protein complex that promotes a light-induced charge separation during the primary process of photosynthesis. In the photosynthetic electron transfer chain, the soluble electron carrier proteins transport electrons to the RC and reduce the photo-oxidized special-pair of bacteriochlorophyll. The high-potential iron-sulfur protein (HiPIP) is known to serve as an electron donor to the RC in some species, where the c-type cytochrome subunit, the peripheral subunit of the RC, directly accepts electrons from the HiPIP. Here we report the crystal structures of the RC and the HiPIP from Thermochromatium (Tch.) tepidum, at 2.2-Å and 1.5-Å resolution, respectively. Tch. tepidum can grow at the highest temperature of all known purple bacteria, and the Tch. tepidum RC shows some degree of stability to high temperature. Comparison with the RCs of mesophiles, such as Blastochloris viridis, has shown that the Tch. tepidum RC possesses more Arg residues at the membrane surface, which might contribute to the stability of this membrane protein. The RC and the HiPIP both possess hydrophobic patches on their respective surfaces, and the HiPIP is expected to interact with the cytochrome subunit by hydrophobic interactions near the heme-1, the most distal heme to the special-pair. In photosynthetic purple bacteria, the electron transfer reactions of photosynthesis are performed by the following three components: the photosynthetic reaction center (RC), the cytochrome (Cyt) bc 1 complex, and the soluble electron carrier protein. First, the RC promotes the light-induced charge separation across the plasma membrane, which results in the oxidation of the special-pair and the reduction of the quinone to the quinol. The quinol then leaves the RC and moves to the Cyt bc 1 complex through the quinone pool of the plasma membrane. Second, the Cyt bc 1 complex reoxidizes the quinol to the quinone, and the released electrons are transferred to the soluble electron carriers. Third, the soluble electron carriers transport the electrons to the RC through the periplasmic space. Finally, the photo-oxidized special-pair is reduced by the soluble electron carriers, and the RC comes back to the initial state. In the course of the oxidation and the reduction of the quinones, the transmembrane electrochemical gradient of the protons is formed, and its energy is used to produce ATP by ATP synthase.Thermochromatium (Tch.; formerly Chromatium) tepidum is a purple sulfur bacterium originally isolated from the hot springs in Yellowstone National Park (1, 2) and belongs to the ␥-subclass. Tch. tepidum is a thermophilic bacterium and can grow at the highest temperature of all known purple bacteria. The optimum growth temperature is 48-50°C, the maximum temperature 58°C. The RC from Tch. tepidum is stable up to 70°C in chromatophore and to 48°C in detergent-micelle (3). The RC is the first membrane protein whose three-dimensional structure has been determined at an atomic resolution (4, 5), and the...

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“…Ferricyanide oxidation of a number of [4Fe-4S] proteins leads to EPR signals with either an average gЈ value (g av ) of ϳ2.01 and narrow ⌬g range, as exemplified by A. vinlandii FdI (26), endonuclease III (27), and aconitase (13), or to a broader signal covering the gЈ value range from ϳ2.12 to 2.02, found for HiPiPs (24,42). The EPR spectra of oxidized RumA (Fig.…”

Section: Discussionmentioning

confidence: 99%

Redox Reactions of the Iron-Sulfur Cluster in a Ribosomal RNA Methyltransferase, RumA

Agarwalla

Stroud

Gaffney

2004

Journal of Biological Chemistry

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RumA, an S-adenosyl-L-methionine-dependent methyltransferase specifically catalyzes the methylation of U1939 of 23 S ribosomal RNA to yield 5-methyluridine (m 5 U) 1 or ribothymidine (1). This enzyme was found to contain a [4Fe-4S] cluster, a prosthetic group usually not associated with methyltransferase enzymes. The x-ray structure of RumA revealed that the cluster is located in the RNA binding domain of the threedomain protein (2). It is held by four Cys-iron bonds provided by Cys 81 , Cys 87 , Cys 90 , and Cys 162 and is buried in a largely hydrophobic region, but one of its sulfur atoms is quite exposed to solvent. The closest distance between the cluster and the sulfur of the catalytic nucleophile, Cys 389 , is ϳ19 Å. RumA is a member of a growing list of nucleic acid modifying enzymes where the function of the iron-sulfur (FeS) cluster remains enigmatic.The reaction mechanism of m 5 U methyltransferases is similar to that of thymidylate synthase, and has been studied mainly employing the tRNA m 5 U54 methyltransferase, TrmA (3-5). It involves Michael addition of the catalytic Cys to carbon 6 (C-6) of pyrimidine, which activates C-5 for a nucleophilic attack on the methyl group of S-adenosyl-L-methionine. Following the methyl transfer, the enzyme is resolved by abstraction of a proton from C-5 and ␤-elimination. TrmA, as well as DNA and RNA 5-methylcytidine methyltransferases, which employ a similar catalytic mechanism (6), do not posses an FeS cluster or any other prosthetic group. Lack of a redox step in the catalytic mechanism, and absence of the cluster in enzymes that employ a similar mechanism preclude a direct role for [4Fe-4S] cluster in the RumA-catalyzed reaction.Two features distinguish the FeS cluster in RumA from the clusters in a different class of S-adenosyl-L-methionine-dependent enzymes that proceed by free radical mechanisms. The RumA cluster is ligated by 4 cysteines and the iron-binding sequence motif is CX 5 CX 2 CX n C. In contrast, the radical Sadenosyl-L-methionine enzymes, of which MiaB (7) and biotin synthase (8) are examples, have a [4Fe-4S] cluster built of a CX 3 CX 2 C sequence that leaves one iron of the cluster free to participate in catalysis. MiaB is a member of a family of enzymes catalyzing addition of sulfur to tRNA bases (9). The FeS sequence motifs in the DNA repair enzymes, endonuclease III (10) and MutY (11), are CX 6 CX 2 CX 5 C, somewhat similar to the RumA sequence. Although the FeS clusters in these enzymes are usually regarded as structural, recently it was shown that the redox potential of MutY is altered by DNA binding and that a change in charge of the [4Fe-4S] 3ϩ/2ϩ cluster might alter its affinity for DNA (12).The redox potentials of [4Fe-4S] clusters vary widely (13-16). Of particular interest in many contemporary studies of FeS proteins is understanding the factors that influence the potentials, and thus functions, of these clusters (17,18). Proteins with four Cys-iron bonds to the [4Fe-4S] cluster fall into two general redox groups, ones with an accessib...

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Electron self-exchange in high-potential iron-sulfur proteins. Characterization of protein I from Ectothiorhodospira vacuolata

Cited by 44 publications

References 53 publications

¹H NMR of High‐Potential Iron‐Sulfur Protein from the Purple Non‐Sulfur Bacterium Rhodoferax fermentans

¹H NMR of High‐Potential Iron‐Sulfur Protein from the Purple Non‐Sulfur Bacterium Rhodoferax fermentans

Crystal structures of photosynthetic reaction center and high-potential iron-sulfur protein from Thermochromatium tepidum : Thermostability and electron transfer

Redox Reactions of the Iron-Sulfur Cluster in a Ribosomal RNA Methyltransferase, RumA

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Electron self-exchange in high-potential iron-sulfur proteins. Characterization of protein I from Ectothiorhodospira vacuolata

Cited by 44 publications

References 53 publications

1H NMR of High‐Potential Iron‐Sulfur Protein from the Purple Non‐Sulfur Bacterium Rhodoferax fermentans

1H NMR of High‐Potential Iron‐Sulfur Protein from the Purple Non‐Sulfur Bacterium Rhodoferax fermentans

Crystal structures of photosynthetic reaction center and high-potential iron-sulfur protein from Thermochromatium tepidum : Thermostability and electron transfer

Redox Reactions of the Iron-Sulfur Cluster in a Ribosomal RNA Methyltransferase, RumA

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¹H NMR of High‐Potential Iron‐Sulfur Protein from the Purple Non‐Sulfur Bacterium Rhodoferax fermentans

¹H NMR of High‐Potential Iron‐Sulfur Protein from the Purple Non‐Sulfur Bacterium Rhodoferax fermentans