Publications

• Oxidative cyclization of N-methyl-dopa by a fungal flavoenzyme of the amine oxidase family.

  Lahham M., Pavkov-Keller T., Fuchs M., Niederhauser J., Chalhoub G., Daniel B., Kroutil W., Gruber K., Macheroux P.

  Flavin-dependent enzymes catalyze many oxidations, including formation of ring structures in natural products. The gene cluster for biosynthesis of fumisoquins, secondary metabolites structurally related to isoquinolines, in the filamentous fungus <i>Aspergillus fumigatus</i> harbors a gene that e ... >> More

  Flavin-dependent enzymes catalyze many oxidations, including formation of ring structures in natural products. The gene cluster for biosynthesis of fumisoquins, secondary metabolites structurally related to isoquinolines, in the filamentous fungus <i>Aspergillus fumigatus</i> harbors a gene that encodes a flavoprotein of the amine oxidase family, termed <i>fsqB</i> (fumisoquin biosynthesis gene B). This enzyme catalyzes an oxidative ring closure reaction that leads to the formation of isoquinoline products. This reaction is reminiscent of the oxidative cyclization reported for berberine bridge enzyme and tetrahydrocannabinol synthase. Despite these similarities, amine oxidases and berberine bridge enzyme-like enzymes possess distinct structural properties, prompting us to investigate the structure-function relationships of FsqB. Here, we report the recombinant production and purification of FsqB, elucidation of its crystal structure, and kinetic analysis employing five putative substrates. The crystal structure at 2.6 Å resolution revealed that FsqB is a member of the amine oxidase family with a covalently bound FAD cofactor. <i>N</i>-methyl-dopa was the best substrate for FsqB and was completely converted to the cyclic isoquinoline product. The absence of the <i>meta</i>-hydroxyl group, as <i>e.g.</i> in l-<i>N</i>-methyl-tyrosine, resulted in a 25-fold lower rate of reduction and the formation of the demethylated product l-tyrosine, instead of a cyclic product. Surprisingly, FsqB did not accept the d-stereoisomer of <i>N</i>-methyltyrosine, in contrast to <i>N</i>-methyl-dopa, for which both stereoisomers were oxidized with similar rates. On the basis of the crystal structure and docking calculations, we postulate a substrate-dependent population of distinct binding modes that rationalizes stereospecific oxidation in the FsqB active site. << Less

  J. Biol. Chem. 293:17021-17032(2018) [PubMed] [EuropePMC]

  This publication is cited by 2 other entries.

• Plant-like biosynthesis of isoquinoline alkaloids in Aspergillus fumigatus.

  Baccile J.A., Spraker J.E., Le H.H., Brandenburger E., Gomez C., Bok J.W., Macheleidt J., Brakhage A.A., Hoffmeister D., Keller N.P., Schroeder F.C.

  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 gen ... >> More

  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. << Less

  Nat. Chem. Biol. 12:419-424(2016) [PubMed] [EuropePMC]

  This publication is cited by 2 other entries.