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Plant-like biosynthesis of isoquinoline alkaloids in Aspergillus fumigatus

Abstract

Natural product discovery efforts have focused primarily on microbial biosynthetic gene clusters (BGCs) containing large multimodular polyketide synthases and nonribosomal peptide synthetases; however, sequencing of fungal genomes has revealed a vast number of BGCs containing smaller NRPS-like genes of unknown biosynthetic function. Using comparative metabolomics, we show that a BGC in the human pathogen Aspergillus fumigatus named fsq, which contains an NRPS-like gene lacking a condensation domain, produces several new isoquinoline alkaloids known as the fumisoquins. These compounds derive from carbon-carbon bond formation between two amino acid–derived moieties followed by a sequence that is directly analogous to isoquinoline alkaloid biosynthesis in plants. Fumisoquin biosynthesis requires the N-methyltransferase FsqC and the FAD-dependent oxidase FsqB, which represent functional analogs of coclaurine N-methyltransferase and berberine bridge enzyme in plants. Our results show that BGCs containing incomplete NRPS modules may reveal new biosynthetic paradigms and suggest that plant-like isoquinoline biosynthesis occurs in diverse fungi.

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Figure 1: Analysis of the fsq gene cluster and metabolite production.
Figure 2: Comparative metabolomics of fsq gene cluster mutants by HPLC/MS.
Figure 3: Model for fumisoquin biosynthesis.
Figure 4: The fumisoquins incorporate L-serine, L-tyrosine and an L-methionine–derived methyl group.
Figure 5: Enzymatic activity of recombinant FsqB.

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Acknowledgements

This research was funded in part by NIH R01GM112739-01 (to N.P.K. and F.C.S.), NIH CBI training grant T32GM008500 (J.A.B.) and an NSF Graduate Research Fellowship under grant DGE-1256259 (to J.E.S.). A.A.B. and D.H. were supported by the Deutsche Forschungsgemeinschaft (CRC ChemBioSys 1127). The authors would like to thank D. Kiemle for his kind assistance in operating the Bruker Avance III HD 800 MHz NMR spectrometer.

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Authors

Contributions

J.A.B. and F.C.S. characterized and identified metabolites and biosynthetic pathways. J.E.S. and J.W.B. created all of the A. fumigatus mutants used. J.A.B. and C.G. performed stable-isotope labeling experiments. H.H.L., E.B. and D.H. contributed biochemical assays. J.M. and A.A.B. contributed to the identification of new metabolites. J.A.B., J.E.S., D.H., N.P.K. and F.C.S. wrote the manuscript.

Corresponding authors

Correspondence to Nancy P Keller or Frank C Schroeder.

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The authors declare no competing financial interests.

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Supplementary Results, Supplementary Tables 1–5, Supplementary Figures 1–17 and Supplementary Note. (PDF 22940 kb)

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Baccile, J., Spraker, J., Le, H. et al. Plant-like biosynthesis of isoquinoline alkaloids in Aspergillus fumigatus. Nat Chem Biol 12, 419–424 (2016). https://doi.org/10.1038/nchembio.2061

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