Expression of a strain-specific non-ribosomal peptide synthetase from Aspergillus lentulus lead to the discovery of a new fungal alkaloid lentoquinazoline.

Fungi have a potential to produce a variety of natural products for their survival by utilizing dozens of biosynthetic gene clusters (BGCs). Fungal BGCs are typically conserved in species but recent studies showed that many BGCs are maintained in limited number of strains. However, little is reported for the products of strain specific BGCs. In this study, we analyzed publicly available genomic data of human pathogenic fungus Aspergillus lentulus and identified seven strain-specific BGCs in addition to (-)- and (+)-auranthine BGCs. One of these BGCs, leq cluster, was found in nine of thirteen A. lentulus strains and a new compound named lentoquinazoline (1) appeared in the metabolites when non-ribosomal peptide synthetase (NRPS) gene leqA was heterologously expressed in Aspergillus nidulans. The structure of 1 was determined by the combination of 2D NMR analysis and advanced Marfey's method to be composed of anthranilic acid, L-leucine and L-asparagine. Whereas 6-6-6 tricyclic quinazoline-synthesizing NRPSs typically contain an epimerase domain and incorporate one molecule of D-amino acid to the product, LeqA was found to introduce only L-amino acids due to the mutations in the active site of the epimerase domain.