Nonribosomal peptides (NRPs) are a class of microbial secondary metabolites that have a wide variety of medicinally important biological activities, such as antibiotic (vancomycin), immunosuppressive (cyclosporin A), antiviral (luzopeptin A) and antitumor (echinomycin and triostin A) activities. However, many microbes are not amenable to cultivation and require time-consuming empirical optimization of incubation conditions for mass production of desired secondary metabolites for clinical and commercial use. Therefore, a fast, simple system for heterologous production of natural products is much desired. Here we show the first example of the de novo total biosynthesis of biologically active forms of heterologous NRPs in Escherichia coli. Our system can serve not only as an effective and flexible platform for large-scale preparation of natural products from simple carbon and nitrogen sources, but also as a general tool for detailed characterizations and rapid engineering of biosynthetic pathways for microbial syntheses of novel compounds and their analogs.

Polyether metabolites are an important class of natural products. Although their biosynthesis, especially construction of polyether skeletons, attracted organic chemists for many years, no experimental data on the enzymatic polyether formation has been obtained. In this study, a putative epoxide hydrolase gene lsd19 found on the biosynthetic gene cluster of an ionophore polyether lasalocid was cloned and successfully overexpressed in Escherichia coli. Using the purified Lsd19, a proposed substrate, bisepoxyprelasalocid, and its synthesized analogue were successfully converted into lasalocid A and its derivative via a 6-endo-tet cyclization mode. On the other hand, treatment of the bisepoxide with trichloroacetic acid gave isolasalocid A via a 5-exo-tet cyclization mode. Therefore, the enzymatic conversion observed in this study unambiguously showed that the bisepoxyprelasalocid is an intermediate of the lasalocid biosynthesis and that Lsd19 catalyzes the sequential cyclic ether formations involving an energetically disfavored 6-endo-tet cyclization. This is the first example of the enzymatic epoxide-opening reactions leading to a polyether natural product.

No abstract

Enantioselective epoxidation followed by regioselective epoxide opening reaction are the key processes in construction of the polyether skeleton. Recent genetic analysis of ionophore polyether biosynthetic gene clusters suggested that flavin-containing monooxygenases (FMOs) could be involved in the oxidation steps. In vivo and in vitro analyses of Lsd18, an FMO involved in the biosynthesis of polyether lasalocid, using simple olefin or truncated diene of a putative substrate as substrate mimics demonstrated that enantioselective epoxidation affords natural type mono- or bis-epoxide in a stepwise manner. These findings allow us to figure out enzymatic polyether construction in lasalocid biosynthesis.

Our recent findings of the first epoxide hydrolase Lsd19, involved in lasalocid A biosynthesis, led us to investigate a long-standing controversial issue on the mechanism of enzymatic epoxide-opening cascades. The site-directed mutagenesis and domain dissection analysis to reveal the mechanism of the reaction catalyzed by Lsd19 is examined, especially in the role of acidic amino acid pair and catalytic domains.

No abstract

Recently, we reported that the epoxide hydrolase Lsd19, the first enzyme shown to catalyze epoxide-opening cascades, can catalyze the conversion of a putative bisepoxide intermediate to polyether antibiotic lasalocid, which involves energetically disfavored 6-endo-tet cyclization of the epoxy alcohol. Here, we examined the substrate tolerance of Lsd19. Lsd19 accepts various substrate analogues differing in the left segment of lasalocid and epoxide stereochemistry to afford either THF-THP or THF-THF products with excellent regioselectivity.

No abstract