Methylcorrinoids Methylate Radicals—Their Second Biological Mode of Action?

Mosimann, Hervé; Kräutler, Bernhard

doi:10.1002/(sici)1521-3773(20000117)39:2<393::aid-anie393>3.0.co;2-m

Cited by 47 publications

(23 citation statements)

References 8 publications

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“…We and others hypothesize that Fom3 uses radical SAM characteristic chemistry to generate Ado-CH 2 •, which could subsequently abstract a hydrogen atom from the C-2 position of 2-HEP to generate a substrate radical and 5'- deoxyadenosine (Ado-CH3)(Scheme 3) [40, 41]. Under biologically relevant conditions, CH 3 -Cbl(III) has been shown to methylate organic radicals [42]. Therefore, the 2-HEP substrate radical could react with CH 3 -Cbl(III) to yield 2-HPP and Cbl(II) (Scheme 3) [40, 41].…”

Section: Resultsmentioning

confidence: 99%

Initial characterization of Fom3 from Streptomyces wedmorensis: The methyltransferase in fosfomycin biosynthesis

Allen

Wang

2014

Archives of Biochemistry and Biophysics

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Fosfomycin is a broad-spectrum antibiotic that is useful against multi-drug resistant bacteria. Although its biosynthesis was first studied over 40 years ago, characterization of the penultimate methyl transfer reaction has eluded investigators. The enzyme believed to catalyze this reaction, Fom3, has been identified as a radical S-adenosyl-L-methionine (SAM) superfamily member. Radical SAM enzymes use SAM and a four-iron, four-sulfur ([4Fe-4S]) cluster to catalyze complex chemical transformations. Fom3 also belongs to a family of radical SAM enzymes that contain a putative cobalamin-binding motif, suggesting that it uses cobalamin for methylation. Here we describe the first biochemical characterization of Fom3 from Streptomyces wedmorensis. Since recombinant Fom3 is insoluble, we developed a successful refolding and iron-sulfur cluster reconstitution procedure. Spectroscopic analyses demonstrate that Fom3 binds a [4Fe-4S] cluster which undergoes a transition between a +2 “resting” state and a +1 active state characteristic of radical SAM enzymes. Site-directed mutagenesis of the cysteine residues in the radical SAM CxxxCxxC motif indicates that each residue is essential for functional cluster formation. We also provide preliminary evidence that Fom3 adds a methyl group to 2-hydroxyethylphosphonate (2- HEP) to form 2-hydroxypropylphosphonate (2-HPP) in an apparently SAM-, sodium dithionite-, and methylcobalamin-dependent manner.

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Section: Resultsmentioning

confidence: 99%

Initial characterization of Fom3 from Streptomyces wedmorensis: The methyltransferase in fosfomycin biosynthesis

Allen

Wang

2014

Archives of Biochemistry and Biophysics

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“…This challenging methylation as well as other methylation reactions catalyzed by members of this enzyme class have been hypothesized to require both Cbl and AdoMet as shown in Figure 4a [36,37,39–41,48,49,51,52]. Unlike the traditional Cbl-dependent methyltransferase reactions, these enzymes are hypothesized to catalyze methylation of a substrate following homolytic Co-C bond cleavage of MeCbl; precedent for transfer of a methyl radical species comes from Cbl model chemistry [53]. …”

Section: An Emerging Superfamily Of Cbl-dependent S-adenosylmethioninmentioning

confidence: 99%

Vitamin B 12 in the spotlight again

Bridwell‐Rabb

Drennan

2017

Current Opinion in Chemical Biology

101

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The ability of cobalamin to coordinate different upper axial ligands gives rise to a diversity of reactivity. Traditionally, adenosylcobalamin is associated with radical-based rearrangements, and methylcobalamin with methyl cation transfers. Recently, however, a new role for adenosylcobalamin has been discovered as a light sensor, and a methylcobalamin-dependent enzyme has been identified that is suggested to transfer a methyl anion. Additionally, recent studies have provided a wealth of new information about a third class of cobalamin-dependent enzymes that do not appear to use an upper ligand. They function in reductive dehalogenations and epoxide reduction reactions. Finally, mechanistic details are beginning to emerge about the cobalamin-dependent S-adenosylmethionine radical enzyme superfamily for which the role of cobalamin has been largely enigmatic.

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“…An analogous methyl transfer, by a radical substitution mechanism, has precedence in cobalamin model chemistry. 23 Regeneration of MeCbl from Cbl(II) can be achieved by reduction to Cbl(I) by the [4Fe–4S] +1 cluster followed by SAM-mediated methylation. Repetition of this sequence results in the successive formation of the isopropyl, t -butyl, and sec -butyl ethers of 21 .…”

mentioning

confidence: 99%

Biosynthesis of Branched Alkoxy Groups: Iterative Methyl Group Alkylation by a Cobalamin-Dependent Radical SAM Enzyme

et al. 2017

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The biosynthesis of branched alkoxy groups, such as the unique t-butyl group found in a variety of natural products, is still poorly understood. Recently, cystobactamids were isolated and identified from Cystobacter sp as novel antibacterials. These metabolites contain an isopropyl group proposed to be formed using CysS, a cobalamin-dependent radical S-adenosylmethionine (SAM) methyltransferase. Here, we reconstitute the CysS-catalyzed reaction, on p-aminobenzoate thioester substrates, and demonstrate that it not only catalyzes sequential methylations of a methyl group to form ethyl and isopropyl groups but remarkably also sec-butyl and t-butyl groups. To our knowledge, this is the first in vitro reconstitution of a cobalamin-dependent radical SAM enzyme catalyzing the conversion of a methyl group to a t-butyl group.

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Methylcorrinoids Methylate Radicals—Their Second Biological Mode of Action?

Abstract: An unprecedented methylation of alkyl radicals is possible with the diamagnetic vitamin B(12) derivative methylcobalamin (see schematic representation). Methylcorrinoids can thus also be considered as methylating cofactors in radical C-methylations.

Cited by 47 publications

References 8 publications

Initial characterization of Fom3 from Streptomyces wedmorensis: The methyltransferase in fosfomycin biosynthesis

Initial characterization of Fom3 from Streptomyces wedmorensis: The methyltransferase in fosfomycin biosynthesis

Vitamin B 12 in the spotlight again

Biosynthesis of Branched Alkoxy Groups: Iterative Methyl Group Alkylation by a Cobalamin-Dependent Radical SAM Enzyme

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