Optimizing dimodular nonribosomal peptide synthetases and natural dipeptides in an Escherichia coli heterologous host

Nonribosomal peptides are an important class of natural products that have a broad range of biological activities. Their structural complexity often prevents simple chemical synthesis, and production from the natural producer is often low, which deters pharmaceutical development. Expression of biosynthetic machinery in heterologous host organisms like Escherichia coli is one way to access these structures, and subsequent optimization of these systems is critical for future development. We utilized the aureusimine biosynthetic gene cluster as a model system to identify the optimal conditions to produce nonribosomal peptides in the isopropyl beta-D-1-thiogalactopyranoside (IPTG)-inducible T7 promoter system of pET28. Single reaction monitoring of nonribosomal products was used to find the optimal concentration of IPTG, postinduction temperature, and the effect of amino acid precursor supplementation. In addition, principle component analysis of these extracts identified 3 previously undiscovered pyrazine products of the aureusimine biosynthetic locus, highlighting the utility of heterologously expressing nonribosomal peptide synthetases to find new products.