Biosynthesis of nitrogen-containing natural products, C7N aminocyclitols and bis-indoles, from actinomycetes

Miglitol, an Oral Antidiabetic Drug, Downregulates Melanogenesis in B16F10 Melanoma Cells through the PKA, MAPK, and GSK3β/β-Catenin Signaling Pathways

Hyperpigmentation is a common condition that causes darker spots or patches on the skin, which often look brown, black, gray, red, or pink. This results in unresolved psychological impact due to high anxiety, depression, and somatoform disorder. We aimed to repurpose an antidiabetic drug, miglitol, as an effective compound against hyperpigmentation when applied as a cosmeceutical agent. The present study investigated the antimelanogenic effects of miglitol and the trehalase inhibitor validamycin A. Miglitol in isolation exhibited no cytotoxicity and significantly reduced the melanin production and intracellular tyrosinase activity in B16F10 melanoma cells. The Western blotting results showed that miglitol reduces the expression of melanogenic regulatory factors, including tyrosinase, tyrosinase-related protein (TRP)-1, TRP-2, and microphthalmia-associated transcription factor (MITF). Mechanistically, miglitol appears to suppress melanin synthesis through cAMP-dependent protein kinase (PKA)-dependent downregulation of MITF, a master transcription factor in melanogenesis. The antimelanogenic effects of miglitol was mediated by downregulation of the p38 signaling pathway and upregulation of extracellular signal-regulated kinase (ERK). Moreover, miglitol decreases P-GSK3β and β-catenin levels compared to those in the untreated group. However, miglitol activated P-β-catenin expression compared to that in the untreated group. Finally, we tested the potential of miglitol in topical application through primary human skin irritation tests on the normal skin (upper back) of 33 volunteers. In these assays, miglitol (125 and 250 μM) did not induce any adverse reactions. Taken together, these findings suggest that the regulation of melanogenesis by miglitol may be mediated by the PKA, MAPK, and GSK3β/β-Catenin signaling pathways and that miglitol might provide new insights into drug repurposing for the treatment of hyperpigmentation symptoms.

Effects of carbon ion beam-induced mutagenesis for the screening of RED production-deficient mutants of Streptomyces coelicolor JCM4020

Streptomyces lividans TK23 interacts with mycolic acid-containing bacteria (MACB), such as Tsukamurella pulmonis TP-B0596, and this direct cell contact activates its secondary metabolism (e.g., the production of undecylprodigiosin: RED). Here, we employed carbon (12C5+) ion beam-induced mutagenesis to investigate the signature of induced point mutations and further identify the gene(s) responsible for the production of secondary metabolites induced by T. pulmonis. We irradiated spores of the Streptomyces coelicolor strain JCM4020 with carbon ions to generate a mutant library. We screened the RED production-deficient mutants of S. coelicolor by mixing them with T. pulmonis TP-B0596 on agar plates, identifying the red/white phenotype of the growing colonies. Through this process, we selected 59 RED-deficient mutants from around 152,000 tested spores. We resequenced the genomes of 16 mutants and identified 44 point mutations, which revealed the signatures induced by 12C5+-irradiation. Via gene complementation experiments, we also revealed that two genes-glutamate synthase (gltB) and elongation factor G (fusA)-are responsible for the reduced production of RED.

Biosynthesis of cyclitols

Review covering up to 2021Cyclitols derived from carbohydrates are naturally stable hydrophilic substances under ordinary physiological conditions, increasing the water solubility of whole molecules in cells. The stability of cyclitols is derived from their carbocyclic structures bearing no acetal groups, in contrast to sugar molecules. Therefore, carbocycle-forming reactions are critical for the biosynthesis of cyclitols. Herein, we review naturally occurring cyclitols that have been identified to date and categorize them according to the type of carbocycle-forming enzymatic reaction. Furthermore, the cyclitol-forming enzymatic reaction mechanisms and modification pathways of the initially generated cyclitols are reviewed.

A simple and efficient copper-catalyzed three-component reaction to synthesize (Z)-1,2-dihydro-2-iminoquinolines

A operationally simple synthesis of (Z)-1,2-dihydro-2-iminoquinolines that proceeds under mild conditions is achieved by copper-catalyzed reaction of 1-(2-aminophenyl)ethan-1-ones, sulfonyl azides and terminal ynones. In particular, the reaction goes through a base-free CuAAC/ring-opening process to obtain the Z-configured products due to hydrogen bonding.

Recent advances in the biosynthesis strategies of nitrogen heterocyclic natural products

Covering: 2015 to 2020Nitrogen heterocyclic natural products (NHNPs) are primary or secondary metabolites containing nitrogen heterocyclic (N-heterocyclic) skeletons. Due to the existence of the N-heterocyclic structure, NHNPs exhibit various bioactivities such as anticancer and antibacterial, which makes them widely used in medicines, pesticides, and food additives. However, the low content of these NHNPs in native organisms severely restricts their commercial application. Although a variety of NHNPs have been produced through extraction or chemical synthesis strategies, these methods suffer from several problems. The development of biotechnology provides new options for the production of NHNPs. This review introduces the recent progress of two strategies for the biosynthesis of NHNPs: enzymatic biosynthesis and microbial cell factory. In the enzymatic biosynthesis part, the recent progress in the mining of enzymes that synthesize N-heterocyclic skeletons (e.g., pyrrole, piperidine, diketopiperazine, and isoquinoline), the engineering of tailoring enzymes, and enzyme cascades constructed to synthesize NHNPs are discussed. In the microbial cell factory part, with tropane alkaloids (TAs) and tetrahydroisoquinoline (THIQ) alkaloids as the representative compounds, the strategies of unraveling unknown natural biosynthesis pathways of NHNPs in plants are summarized, and various metabolic engineering strategies to enhance their production in microbes are introduced. Ultimately, future perspectives for accelerating the biosynthesis of NHNPs are discussed.

A Validamycin Shunt Pathway for Valienamine Synthesis in Engineered Streptomyces hygroscopicus 5008

Valienamine is the key functional component of many natural glycosidase inhibitors, including the crop protectant validamycin A and the clinical antidiabetic agent acarbose. Due to its important biomedical activity, it is also the prominent lead compound for the exploration of therapeutic agents, such as the stronger α-glucosidase inhibitor voglibose. Currently, the main route for obtaining valienamine is a multistep biosynthetic process involving the synthesis and degradation of validamycin A. Here, we established an alternative, vastly simplified shunt pathway for the direct synthesis of valienamine based on an envisioned non-natural transamination in the validamycin A producer Streptomyces hygroscopicus 5008. We first identified candidate aminotransferases for the non-natural ketone substrate valienone and conducted molecular evolution in vitro. The WecE enzyme from Escherichia coli was verified to complete the envisioned step with >99.9% enantiomeric excess and was further engineered to produce a 32.6-fold more active mutant, VarB, through protein evolution. Subsequently, two copies of VarB were introduced into the host, and the new shunt pathway produced 0.52 mg/L valienamine after a 96-h fermentation. Our study thus illustrates a dramatically simplified alternative shunt pathway for valienamine production and introduces a promising foundational platform for increasing the production of valienamine and its valuable N-modified derivatives for use in pharmaceutical applications.

Synthesis and Biological Evaluation of the Novel Growth Inhibitor Streptol Glucoside, Isolated from an Obligate Plant Symbiont

The plant Psychotria kirkii hosts an obligatory bacterial symbiont, Candidatus Burkholderia kirkii, in nodules on their leaves. Recently, a glucosylated derivative of (+)-streptol, (+)-streptol glucoside, was isolated from the nodulated leaves and was found to possess a plant growth inhibitory activity. To establish a structure-activity relationship study, a convergent strategy was developed to obtain several pseudosugars from a single synthetic precursor. Furthermore, the glucosylation of streptol was investigated in detail and conditions affording specifically the α or β glucosidic anomer were identified. Although (+)-streptol was the most active compound, its concentration in P. kirkii plant leaves extract was approximately ten-fold lower than that of (+)-streptol glucoside. These results provide compelling evidence that the glucosylation of (+)-streptol protects the plant host against the growth inhibitory effect of the compound, which might constitute a molecular cornerstone for this successful plant-bacteria symbiosis.