Prenylated indole derivatives are hybrid natural products containing both aromatic and isoprenoid moieties and are widely spread in plants, fungi and bacteria. Some of these complex natural products, e.g. the ergot alkaloids ergotamine and fumigaclavine C as well as the diketopiperazine derivative fumitremorgin C and its biosynthetic precursors tryprostatin A and B, show a wide range of biological and pharmacological activities. Prenyl transfer reactions catalysed by prenyltransferases represent key steps in the biosynthesis of these compounds and often result in formation of products which possess biological activities distinct from their non-prenylated precursors. Recently, a series of putative indole prenyltransferase genes could be identified in the genome sequences of different fungal strains including Aspergillus fumigatus. The gene products show significant sequence similarities to dimethylallyltryptophan synthases from fungi. We have cloned and overexpressed six of these genes, fgaPT1, fgaPT2, ftmPT1, ftmPT2, 7- dmats and cdpNPT from A. fumigatus in E. coli and S. cerevisiae. The overproduced enzymes were characterised biochemically. Three additional prenyltransferases, DmaW-Cs, TdiB and MaPT were identified and characterised in a Clavicipitalean fungus, Aspergillus nidulans and Malbranchea aurantiaca, respectively. Sequence analysis and alignments with known aromatic prenyltransferases as well as phylogenetic analysis revealed that these enzymes belong to a new group of “aromatic prenyltransferases”. They differ clearly from membrane-bound aromatic prenyltransferases from different sources and soluble prenyltransferases from bacteria. The characterised enzymes are soluble proteins, catalyse different prenyl transfer reactions on indole moieties of various substrates and do not require divalent metal ions for their enzymatic reactions. All of the enzymes accepted only dimethylallyl diphosphate as prenyl donor. On the other hand, they showed broad substrate specificity towards their aromatic substrates. Diverse tryptophan derivatives and tryptophancontaining cyclic dipeptides were accepted by these enzymes, providing a new strategy for convenient production of biologically active substances, e.g. by chemoenzymatic synthesis.
Keywords: Aspergillus, biochemical characterisation, chemoenzymatic synthesis, cyclic dipeptide, diketopiperazine, heterologous overexpression, indole alkaloid, prenyltransferase
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