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Radical-mediated enzymatic carbon chain fragmentation-recombination

Abstract

The radical S-adenosylmethionine (S-AdoMet) superfamily contains thousands of proteins that catalyze highly diverse conversions, most of which are poorly understood, owing to a lack of information regarding chemical products and radical-dependent transformations. We here report that NosL, involved in forming the indole side ring of the thiopeptide nosiheptide (NOS), is a radical S-AdoMet 3-methyl-2-indolic acid (MIA) synthase. NosL catalyzed an unprecedented carbon chain reconstitution of L-tryptophan to give MIA, showing removal of the Cα-N unit and shift of the carboxylate to the indole ring. Dissection of the enzymatic process upon the identification of products and a putative glycyl intermediate uncovered a radical-mediated, unusual fragmentation-recombination reaction. This finding unveiled a key step in radical S-AdoMet enzyme–catalyzed structural rearrangements during complex biotransformations. Additionally, NosL tolerated fluorinated L-tryptophan as the substrate, allowing for production of a regiospecifically halogenated thiopeptide that has not been found among the more than 80 members of the naturally occurring thiopeptide family.

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Figure 1: Structures of polycyclic thiopeptides and their side ring formations.
Figure 2: Characterization of NosL-catalyzed reaction.
Figure 3: Different patterns for cleaving the Cα-Cβ bond of L-tryptophan neutral radical 11.
Figure 4: Production of NOS and fluorinated thiopeptide.

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Acknowledgements

We thank H.G. Floss (University of Washington) for providing S. actuosus ATCC25421 and for his pioneering work on NOS biosynthesis and Y. Zhang and W. Tong, (High Magnetic Field Laboratory, Chinese Academy of Sciences) for assistance with EPR analysis. This work was supported in part by grants from US National Institutes of Health (CA094426 to B.S.), Chinese National Natural Science Foundation (20832009, 30525001, 90713012 and 20921091), Chinese Ministry of Science and Technology (2009ZX09501-008), Chinese National Basic Research Program (“973 program,” 2010CB833200), Chinese Academy of Sciences (KJCX2-YW-H08 and KSCX2-YW-G-06) and Science and Technology Commission of Shanghai Municipality (09QH1402700) of China (all to W.L).

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Contributions

Q.Z., D.C., Y.Y. and L.D. carried out the experiments; Y.L. performed the theoretical calculations; Q.Z., B.S. and W.L. analyzed the data and wrote the paper; and W.L. designed the research. All authors discussed results and approved the final manuscript.

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Correspondence to Wen Liu.

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The authors declare no competing financial interests.

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Supplementary Methods, Supplementary Figures 1–19 and Supplementary Tables 1–5 (PDF 2161 kb)

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Zhang, Q., Li, Y., Chen, D. et al. Radical-mediated enzymatic carbon chain fragmentation-recombination. Nat Chem Biol 7, 154–160 (2011). https://doi.org/10.1038/nchembio.512

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