Alkaloid Biosynthetic Enzyme Generates Diastereomeric Pair via Two Distinct Mechanisms

Non-enzymatic reactions in biogenesis of fungal natural products

Fungi have long been regarded as abundant sources of natural products (NPs) exhibiting significant biological activities. Decades of studies on the biosynthesis of fungal NPs revealed that most of the biosynthetic steps are catalyzed by sophisticated enzymes encoded in biosynthetic gene clusters, whereas some reactions proceed without enzymes. These non-enzymatic reactions complicate biosynthetic analysis of NPs and play important roles in diversifying the structure of the products. Therefore, knowledge on the non-enzymatic reactions is important for elucidating the biosynthetic mechanism. This review focuses on non-enzymatic reactions we recently encountered during biosynthetic studies of four types of NPs (viridicatins, Sch210972, lentopeptins, and lentofuranine).

Reactive Azlactone Intermediate Drives Fungal Secondary Metabolite Cross-Pathway Generation

Pathogenic fungi of Aspergillus section Fumigati are known to produce various secondary metabolites. A reported isolation of a compound with an atypical carbon skeleton called fumimycin from A. fumisynnematus prompted us to examine a related fungus, A. lentulus, for production of similar products. Here we report the isolation of fumimycin and a related new racemic compound we named lentofuranine. Detailed analyses revealed that both compounds were assembled by a nonenzymatic condensation of a polyketide intermediate from the terrein biosynthetic pathway and a highly reactive azlactone intermediate produced by an unrelated nonribosomal peptide synthetase carrying a terminal condensation-like domain. While highly reactive azlactone is commonly used in chemical synthesis, its production by a conventional non-metalloenzyme and employment as a biosynthetic pathway intermediate is unprecedented. The observed unusual carbon skeleton formation is likely due to the reactivity of azlactone. Our finding provides another example of a chemical principle being aptly exploited by a biological system.

Talaropeptins A and B, Tripeptides with an N-trans-Cinnamoyl Moiety from the Marine-Derived Fungus Talaromyces purpureogenus CX11

We report the discovery of talaropeptins A (1) and B (2), tripeptides with an unusual 5/6/5 heterocyclic scaffold and an N-trans-cinnamoyl moiety, which were identified from the marine-derived fungus Talaromyces purpureogenus CX11. A bioinformatic analysis of the genome of T. purpureogenus CX11 and gene inactivation revealed that the biosynthesis of talaropeptins involves a nonribosomal peptide synthase gene cluster. Their chemical structures were elucidated using a combination of 1D and 2D NMR spectroscopy and mass spectrometry. The absolute configurations of 1 and 2 were established by electronic circular dichroism calculations and Marfey's method. The plausible biosynthesis of 1 and 2 is also proposed on the basis of gene deletion, substrate feeding, and heterologous expression. Compounds 1 and 2 showed moderate antifungal activity against phytopathogenic fungus Fusarium oxysporum with MIC values of 12.5 and 25 μg/mL, respectively.

Hot off the Press

A personal selection of 32 recent papers is presented covering various aspects of current developments in bioorganic chemistry and novel natural products such as chevalinulin A from Aspergillus chevalieri.

Improving Ergometrine Production by easO and easP Knockout in Claviceps paspali

Ergometrine is widely used for the treatment of excessive postpartum uterine bleeding. Claviceps paspali is a common species for industrial production of ergometrine, which is often accompanied by lysergic acid α-hydroxyethylamide (LAH) and lysergic acid amide (LAA). Currently, direct evidence on the biosynthetic mechanism of LAH and LAA from lysergic acid in C. paspali is absent, except that LAH and LAA share the common precursor with ergometrine and LAA is spontaneously transformed from LAH. A comparison of the gene clusters between C. purpurea and C. paspali showed that the latter harbored the additional easO and easP genes. Thus, the knockout of easO and easP in the species should not only improve the ergometrine production but also elucidate the function. In this study, gene knockout of C. paspali by homologous recombination yielded two mutants ∆easOhetero-1 and ∆easPhetero-34 with ergometrine titers of 1559.36 mg∙L−1 and 837.57 mg∙L−1, which were four and two times higher than that of the wild-type control, respectively. While the total titer of LAH and LAA of ∆easOhetero-1 was lower than that of the wild-type control. The Aspergillus nidulans expression system was adopted to verify the function of easO and easP. Heterologous expression in A. nidulans further demonstrated that easO, but not easP, determines the formation of LAA.

Discovery of a Cyclic Depsipeptide from Chaetomium mollipilium by the Genome Mining Approach

Genome mining and bioinformatics analyses allowed us to rationally find a candidate biosynthetic gene cluster for a new cyclic depsipeptide of Chaetomium mollipilium. A heterologous reconstitution of the identified biosynthetic pathway predictably afforded a new cyclic depsipeptide composed of l-leucine, l-tryptophan, and a polyketide moiety. Interestingly, the 10-membered macrocycle structure generated equilibrium to an unprecedented cyclol structure. This study demonstrates the advantage of a synthetic biology method in achieving rational access to new natural products.