Dataset Information

Changing Fates of the Substrate Radicals Generated in the Active Sites of the B₁₂-Dependent Radical SAM Enzymes OxsB and AlsB.

ABSTRACT: OxsB is a B₁₂-dependent radical SAM enzyme that catalyzes the oxidative ring contraction of 2'-deoxyadenosine 5'-phosphate to the dehydrogenated, oxetane containing precursor of oxetanocin A phosphate. AlsB is a homologue of OxsB that participates in a similar reaction during the biosynthesis of albucidin. Herein, OxsB and AlsB are shown to also catalyze radical mediated, stereoselective C2'-methylation of 2'-deoxyadenosine monophosphate. This reaction proceeds with inversion of configuration such that the resulting product also possesses a C2' hydrogen atom available for abstraction. However, in contrast to methylation, subsequent rounds of catalysis result in C-C dehydrogenation of the newly added methyl group to yield a 2'-methylidene followed by radical addition of a 5'-deoxyadenosyl moiety to produce a heterodimer. These observations expand the scope of reactions catalyzed by B₁₂-dependent radical SAM enzymes and emphasize the susceptibility of radical intermediates to bifurcation along different reaction pathways even within the highly organized active site of an enzyme.

SUBMITTER: Lee YH

PROVIDER: S-EPMC9940012 | biostudies-literature | 2023 Feb

REPOSITORIES: biostudies-literature

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Changing Fates of the Substrate Radicals Generated in the Active Sites of the B<sub>12</sub>-Dependent Radical SAM Enzymes OxsB and AlsB.

Lee Yu-Hsuan YH Yeh Yu-Cheng YC Fan Po-Hsun PH Zhong Aoshu A Ruszczycky Mark W MW Liu Hung-Wen HW

Journal of the American Chemical Society 20230131 6

OxsB is a B<sub>12</sub>-dependent radical SAM enzyme that catalyzes the oxidative ring contraction of 2'-deoxyadenosine 5'-phosphate to the dehydrogenated, oxetane containing precursor of oxetanocin A phosphate. AlsB is a homologue of OxsB that participates in a similar reaction during the biosynthesis of albucidin. Herein, OxsB and AlsB are shown to also catalyze radical mediated, stereoselective C2'-methylation of 2'-deoxyadenosine monophosphate. This reaction proceeds with inversion of confi ...[more]

PMID: 36719327

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Project description:A [4Fe-4S](+) cluster reduces a bound S-adenosylmethionine (SAM) molecule, cleaving it into methionine and a 5'-deoxyadenosyl radical (5'-dA(•)). This step initiates the varied chemistry catalyzed by each of the so-called radical SAM enzymes. The strongly oxidizing 5'-dA(•) is quenched by abstracting a H-atom from a target species. In some cases, this species is an exogenous molecule of substrate, for example, L-tyrosine in the [FeFe] hydrogenase maturase, HydG. In other cases, the target is a proteinaceous residue as in all the glycyl radical forming enzymes. The generation of this initial radical species and the subsequent chemistry involving downstream radical intermediates is meticulously controlled by the enzyme so as to prevent unwanted reactions. But the manner in which this control is exerted is unknown. Electron paramagnetic resonance (EPR) spectroscopy has proven to be a valuable tool used to gain insight into these mechanisms. In this Account, we summarize efforts to trap such radical intermediates in radical SAM enzymes and highlight four examples in which EPR spectroscopic results have shed significant light on the corresponding mechanism. For lysine 2,3-aminomutase, nearly each possible intermediate, from an analogue of the initial 5'-dA(•) to the product radical L-β-lysine, has been explored. A paramagnetic intermediate observed in biotin synthase is shown to involve an auxiliary [FeS] cluster whose bridging sulfide is a co-substrate for the final step in the biosynthesis of vitamin B7. In HydG, the L-tyrosine substrate is converted in unprecedented fashion to a 4-oxidobenzyl radical on the way to generating CO and CN(-) ligands for the [FeFe] cluster of hydrogenase. And finally, EPR has confirmed a mechanistic proposal for the antibiotic resistance protein Cfr, which methylates the unactivated sp(2)-hybridized C8-carbon of an adenosine base of 23S ribosomal RNA. These four systems provide just a brief survey of the ever-growing set of radical SAM enzymes. The diverse chemistries catalyzed by these enzymes make them an intriguing target for continuing study, and EPR spectroscopy, in particular, seems ideally placed to contribute to our understanding.

Dataset Information

Changing Fates of the Substrate Radicals Generated in the Active Sites of the B₁₂-Dependent Radical SAM Enzymes OxsB and AlsB.

Publications

Changing Fates of the Substrate Radicals Generated in the Active Sites of the B<sub>12</sub>-Dependent Radical SAM Enzymes OxsB and AlsB.

Similar Datasets

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Dataset Information

Changing Fates of the Substrate Radicals Generated in the Active Sites of the B12-Dependent Radical SAM Enzymes OxsB and AlsB.

Publications

Changing Fates of the Substrate Radicals Generated in the Active Sites of the B<sub>12</sub>-Dependent Radical SAM Enzymes OxsB and AlsB.

Similar Datasets

OmicsDI is part of the ELIXIR infrastructure

Tweets

Changing Fates of the Substrate Radicals Generated in the Active Sites of the B₁₂-Dependent Radical SAM Enzymes OxsB and AlsB.