Organometallic Complex Formed by an Unconventional Radical <i>S</i>-Adenosylmethionine Enzyme

Dong, Min; Horitani, Masaki; Dzikovski, Boris; Pandelia, Maria-Eirini; Krebs, Carsten; Freed, Jack H.; Hoffman, Brian M.; Lin, Hening

doi:10.1021/jacs.6b04155

Cited by 21 publications

(16 citation statements)

References 20 publications

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“…These two components were designated conformer 1 and conformer 2, respectively. Similar spectra reported in previous studies of the Fe-S cluster concluded that the spectra are derived from a mixture of two different structures of the [4Fe-4S] cluster 30 , or from an identical form of the [4Fe-4S] cluster but in two different reduction states 31 . Accordingly, the Supplementary Fig.…”

Section: Resultssupporting

confidence: 84%

The [4Fe-4S] cluster of sulfurtransferase TtuA desulfurizes TtuB during tRNA modification in Thermus thermophilus

et al. 2020

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TtuA and TtuB are the sulfurtransferase and sulfur donor proteins, respectively, for biosynthesis of 2-thioribothymidine (s 2 T) at position 54 of transfer RNA (tRNA), which is responsible for adaptation to high temperature environments in Thermus thermophilus. The enzymatic activity of TtuA requires an iron-sulfur (Fe-S) cluster, by which a sulfur atom supplied by TtuB is transferred to the tRNA substrate. Here, we demonstrate that the Fe-S cluster directly receives sulfur from TtuB through its inherent coordination ability. TtuB forms a [4Fe-4S]-TtuB intermediate, but that sulfur is not immediately released from TtuB. Further desulfurization assays and mutation studies demonstrated that the release of sulfur from the thiocarboxylated C-terminus of TtuB is dependent on adenylation of the substrate tRNA, and the essential residue for TtuB desulfurization was identified. Based on these findings, the molecular mechanism of sulfur transfer from TtuB to Fe-S cluster is proposed.

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Section: Resultssupporting

confidence: 84%

The [4Fe-4S] cluster of sulfurtransferase TtuA desulfurizes TtuB during tRNA modification in Thermus thermophilus

et al. 2020

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“…Our studies here thus have revealed that the [4Fe-4S] cluster in a radical SAM enzyme can be tuned to cleave any one of the three bonds to the sulfonium sulfur of SAM or analogues. Together with recent studies on PFL-AE and Ph Dph2, 17,29 our study provides compelling evidence for the versatility of these [4Fe-4S] clusters.…”

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confidence: 82%

Substrate-Dependent Cleavage Site Selection by Unconventional Radical S-Adenosylmethionine Enzymes in Diphthamide Biosynthesis

et al. 2017

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S -adenosylmethionine (SAM) has a sulfonium ion with three distinct C-S bonds. Conventional radical SAM enzymes use a [4Fe–4S] cluster to homolytically cleave the C5′,adenosine-S bond of SAM to generate a 5′-deoxyadenosyl radical, which catalyzes various downstream chemical reactions. Radical SAM enzymes involved in diphthamide biosynthesis, such as Pyrococcus horikoshii Dph2 (PhDph2) and yeast Dph1-Dph2 instead cleave the Cγ,Met–S bond of methionine to generate the 3-amino-3-carboxylpropyl radical. We here show that radical SAM enzymes can be tuned to cleave the third C-S bond to the sulfonium sulfur by changing the structure of SAM. With a decarboxyl SAM analogue (dc-SAM), PhDph2 cleaves the Cmethyl–S bond, forming 5′-deoxy-5′-(3-aminopropylthio) adenosine (dAPTA, 1). The methyl cleavage activity, like the cleavage of the other two C-S bonds, is dependent on the presence of a [4Fe-4S]+ cluster. Electron-nuclear double resonance (ENDOR) and mass spectroscopy data suggests that mechanistically, one of the S atoms in the [4Fe-4S] cluster captures the methyl group from dc-SAM, forming a distinct EPR-active intermediate, which can transfer the methyl group to nucleophiles such as dithiothreitol. This reveals that the [4Fe-4S] cluster in a radical SAM enzyme can be tuned to cleave any one of the three bonds to the sulfonium sulfur of SAM or analogues, and is the first demonstration that a radical SAM enzyme could switch from an Fe-based one electron transfer reaction to a S-based two electron transfer reaction in a substrate-dependent manner. This study thus provides a remarkable illustration of the versatile reactivity of Fe-S clusters.

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“…33b). 154 Originally, SAM CA was used as a potential means of trapping the ACP radical as a stable allylic radical. However, the expected radical was not observed, and instead, the reaction of PhDph2 with SAM CA produced sulfinic acids 83 and 84 as a result of quenching of the expected allylic radical by sodium dithionite.…”

Section: Noncanonical Radical Sam Enzymesmentioning

confidence: 99%

C–C bond forming radical SAM enzymes involved in the construction of carbon skeletons of cofactors and natural products

Yokoyama

Lilla

2018

Nat. Prod. Rep.

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C–C bond formations are frequently the key steps in cofactor and natural product biosynthesis. Historically, C–C bond formations were thought to proceed by two electron mechanisms, represented by Claisen condensation in fatty acids and polyketide biosynthesis. These types of mechanisms require activated substrates to create a nucleophile and an electrophile. More recently, increasing number of C–C bond formations catalyzed by radical SAM enzymes are being identified. These free radical mediated reactions can proceed between almost any sp3 and sp2 carbon centers, allowing introduction of C–C bonds at unconventional positions in metabolites. Therefore, free radical mediated C–C bond formations are frequently found in the construction of structurally unique and complex metabolites. This review discusses our current understanding of the functions and mechanisms of C–C bond forming radical SAM enzymes and highlights their important roles in the biosynthesis of structurally complex, naturally occurring organic molecules. Mechanistic consideration of C–C bond formation by radical SAM enzymes identifies the significance of three key mechanistic factors: radical initiation, acceptor substrate activation and radical quenching. Understanding the functions and mechanisms of these characteristic enzymes will be important not only in promoting our understanding of radical SAM enzymes, but also for understanding natural product and cofactor biosynthesis.

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Organometallic Complex Formed by an Unconventional Radical S-Adenosylmethionine Enzyme

Cited by 21 publications

References 20 publications

The [4Fe-4S] cluster of sulfurtransferase TtuA desulfurizes TtuB during tRNA modification in Thermus thermophilus

The [4Fe-4S] cluster of sulfurtransferase TtuA desulfurizes TtuB during tRNA modification in Thermus thermophilus

Substrate-Dependent Cleavage Site Selection by Unconventional Radical S-Adenosylmethionine Enzymes in Diphthamide Biosynthesis

C–C bond forming radical SAM enzymes involved in the construction of carbon skeletons of cofactors and natural products

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