Production of α-keto carboxylic acid dimers in yeast by overexpression of NRPS-like genes from Aspergillus terreus

Non-ribosomal peptide synthetases (NRPSs) are key enzymes in microorganisms for the assembly of peptide backbones of biologically and pharmacologically active natural products. The monomodular NRPS-like enzymes comprise often an adenylation (A), a thiolation (T), and a thioesterase (TE) domain. In contrast to the NRPSs, they do not contain any condensation domain and usually catalyze a dimerization of alpha-keto carboxylic acids and thereby provide diverse scaffolds for further modifications. In this study, we established an expression system for NRPS-like genes in Saccharomyces cerevisiae. By expression of four known genes from Aspergillus terreus, their predicted function was confirmed and product yields of up to 35 mg per liter culture were achieved. Furthermore, expression of ATEG_03090 from the same fungus, encoding for the last uncharacterized NRPS-like enzyme with an A-T-TE domain structure, led to the formation of the benzoquinone derivative atromentin. All the accumulated products were isolated and their structures were elucidated by NMR and MS analyses. This study provides a convenient system for proof of gene function as well as a basis for synthetic biology, since additional genes encoding modification enzymes can be introduced.