Biological Radical Sulfur Insertion Reactions

Fontecave, Marc; Choudens, Sandrine Ollagnier de; Mulliez, Etienne

doi:10.1021/cr020427j

Cited by 183 publications

(110 citation statements)

References 125 publications

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“…The second implication of the mechanism is that the aromatic hydrogen atom at position 2 of adenine would be directly abstracted by the 5Ј-deoxyadenosyl radical (Scheme 2, reaction 2). As a matter of fact, in Radical-AdoMet enzymes, the substrate is directly activated by H-atom abstraction by 5Ј-deoxyadenosyl radical (14,30). This difficult reaction in the case of MiaB protein is not demonstrated at the present stage and will require further experiments.…”

Section: Discussionmentioning

confidence: 78%

“…In contrast, during the last years, this question has been extensively addressed in the case of biotin synthase and lipoic acid synthase, two Radical-AdoMet enzymes catalyzing sulfur insertion reactions leading to biotin and lipoic acid synthesis respectively. However, despite much effort, the chemistry involved in these systems is still not understood and is a matter of controversy (14,15). In starting an investigation of MiaB, a third sulfur insertion system of the same class, we hoped to find solutions to those questions.…”

Section: Discussionmentioning

confidence: 99%

“…However, the presence of a strictly conserved canonical cysteine triad Cys-Xaa-Xaa-Xaa-Cys-XaaXaa-Cys (Xaa, any amino acid) in the sequence has led to the identification of MiaB as a member of the recently characterized "Radical-AdoMet" family (10) such as the anaerobic ribonucleotide reductase-activating enzyme (ARR-AE), pyruvate formate lyase-AE (PFL-AE), lysine aminomutase (LAM), biotin synthase (BioB), and lipoate synthase (LipA) (11)(12)(13)(14)(15). In the case of BioB enzyme, which also catalyzes C-H to C-S bond conversion reactions, this motif was shown to provide cysteine ligands for a catalytically essential [4Fe-4S] 2ϩ/1ϩ cluster (16).…”

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confidence: 99%

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MiaB Protein Is a Bifunctional Radical-S-Adenosylmethionine Enzyme Involved in Thiolation and Methylation of tRNA

Pierrel

Douki

Fontecave

et al. 2004

Journal of Biological Chemistry

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157

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The last biosynthetic step for 2-methylthio-N 6 -isopentenyl-adenosine (ms 2 i 6 A), present at position 37 in some tRNAs, consists of the methylthiolation of the isopentenyl-adenosine (i 6 A) precursor. In this work we have reconstituted in vitro the conversion of i 6 A to ms 2 i 6 A within a tRNA substrate using the iron-sulfur MiaB protein, S-adenosylmethionine (AdoMet), and a reducing agent. We show that a synthetic i 6 A-containing RNA corresponding to the anticodon stem loop of tRNA Phe is also a substrate. This study demonstrates that MiaB protein is a bifunctional system, involved in both thiolation and methylation of i 6 A. In this process, one molecule of AdoMet is converted to 5 -deoxyadenosine, probably through reductive cleavage and intermediate formation of a 5 -deoxyadenosyl radical as observed in other "Radical-AdoMet" enzymes, and a second molecule of AdoMet is used as a methyl donor as shown by labeling experiments. The origin of the sulfur atom is discussed.In all organisms, the nucleosides of transfer RNA (tRNA) undergo different post-transcriptional modifications that are important for their biological activity (1). These modifications are part of the complex process of tRNA maturation and are introduced through the action of many different enzymes on the polynucleotide transcripts (2). Although modified bases are found at different positions in tRNA, the anticodon loop is the most heavily modified region of the molecule and contains the greatest variety of modified nucleosides. To date, a total of 86 structurally distinguishable modified nucleosides in tRNA from many diverse organisms of the three major phylogenetic domains of life have been identified (medstat.med.utah.edu/ RNAmods/). Among these modified nucleosides, the so-called thionucleosides containing a sulfur atom have been the subject of particular attention in the recent years.In Escherichia coli four different thiolated nucleosides have been characterized; these are 4-thiouridine (s 4 U), 1 2-thiocytidine (s 2 C), 5-methylaminomethyl-2-thiouridine (mnm 5 s 2 U), and 2-methylthio-N 6 -isopentenyl-adenosine (ms 2 i 6 A). If the synthesis of thiopyrimidines involves a non-redox substitution reaction of an oxygen atom by sulfur, the reaction leading to the synthesis of 2-methylthio-N 6 -isopentenyl-adenosine (ms 2 i 6 A) consists of a chemically highly challenging aromatic C-H to C-S bond conversion. This is an oxidation reaction whose mechanism has yet to be investigated. The modified nucleoside ms 2 i 6 A is found at position 37, next to the anticodon on the 3Ј-position in almost all eukaryotic and bacterial tRNAs that read codons beginning with U except tRNA I,V Ser (3).Initial studies on ms 2 i 6 A biosynthesis in E. coli and Salmonella typhimurium established a requirement for at least two enzymes (4). The first step consists in the addition of the isopentenyl group to the N 6 nitrogen of adenosine. This reaction is catalyzed by the well characterized tRNA-isopentenylpyrophosphate transferase enzyme, encoded by the miaA gene (5...

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Section: Discussionmentioning

confidence: 78%

Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 99%

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MiaB Protein Is a Bifunctional Radical-S-Adenosylmethionine Enzyme Involved in Thiolation and Methylation of tRNA

Pierrel

Douki

Fontecave

et al. 2004

Journal of Biological Chemistry

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157

180

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“…Finally, this study provides an additional illustration of the richness of the redox chemistry used for tRNA modification. The first reported metalloenzyme involved in tRNA modification was MiaB, an iron-sulfur protein (50,51). MiaE, which uses a nonheme diiron center, is the second one.…”

Section: Discussionmentioning

confidence: 99%

tRNA-modifying MiaE protein fromSalmonella typhimuriumis a nonheme diiron monooxygenase

Mathevon

Pierrel

Oddou

et al. 2007

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

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MiaE catalyzes the posttranscriptional allylic hydroxylation of 2-methylthio-N-6-isopentenyl adenosine in tRNAs. The Salmonella typhimurium enzyme was heterologously expressed in Escherichia coli. The purified enzyme is a monomer with two iron atoms and displays activity in in vitro assays. The type and properties of the iron center were investigated by using a combination of UV-visible absorption, EPR, HYSCORE, and Mö ssbauer spectroscopies which demonstrated that the MiaE enzyme contains a nonheme dinuclear iron cluster, similar to that found in the hydroxylase component of methane monooxygenase. This is the first example of an enzyme from this important class of diiron monooxygenases to be involved in the hydroxylation of a biological macromolecule and the second example of a redox metalloenzyme participating in tRNA modification.EPR spectroscopy ͉ Mö ssbauer spectroscopy ͉ nonheme dinuclear iron cluster ͉ tRNA modification enzyme

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“…HydE and HydG proteins belong to the recently characterized ''Radical-S-adenosyl-Lmethionine (SAM or AdoMet)" family [22,23] whereas HydF is a GTPase [24]. Radical-SAM enzymes generally catalyze chemically difficult reactions such as C-H to C-S bond formation, for example during biotin or lipoic acid synthesis [25], and glycyl radical formation during the activation of ribonucleotide reductase (RNR) or pyruvate-formate lyase (PFL) [26]. The one-electron transfer from a conserved [Fe 4 S 4 ] cluster to AdoMet generates methionine and the highly oxidizing 5 0 -deoxyadenosyl radical, Ado°.…”

Section: Introductionmentioning

confidence: 99%

The role of the maturase HydG in [FeFe]‐hydrogenase active site synthesis and assembly

et al. 2009

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a b s t r a c t[FeFe]-hydrogenases catalyze the protons/hydrogen interconversion through a unique di-iron active site consisting of three CO and two CN ligands, and a non-protein SCH 2 XCH 2 S (X = N or O) dithiolate bridge. Site assembly requires two ''Radical-S-adenosylmethionine (SAM or AdoMet)" iron-sulfur enzymes, HydE and HydG, and one GTPase, HydF. The sequence homology between HydG and ThiH, a Radical-SAM enzyme which cleaves tyrosine into p-cresol and dehydroglycine, and the finding of a similar cleavage reaction catalyzed by HydG suggests a mechanism for hydrogenase maturation. Here we propose that HydG is specifically involved in the synthesis of the dithiolate ligand, with two tyrosine-derived dehydroglycines as precursors along with an [FeS] cluster of HydG functioning both as electron shuttle and source of the sulfur atoms.

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Biological Radical Sulfur Insertion Reactions

Cited by 183 publications

References 125 publications

MiaB Protein Is a Bifunctional Radical-S-Adenosylmethionine Enzyme Involved in Thiolation and Methylation of tRNA

MiaB Protein Is a Bifunctional Radical-S-Adenosylmethionine Enzyme Involved in Thiolation and Methylation of tRNA

tRNA-modifying MiaE protein fromSalmonella typhimuriumis a nonheme diiron monooxygenase

The role of the maturase HydG in [FeFe]‐hydrogenase active site synthesis and assembly

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