BE-40644, a new human thioredoxin system inhibitor isolated from Actinoplanes sp. A40644

Bacterial terpenome

Covering: up to mid-2020 Terpenoids, also called isoprenoids, are the largest and most structurally diverse family of natural products. Found in all domains of life, there are over 80 000 known compounds. The majority of characterized terpenoids, which include some of the most well known, pharmaceutically relevant, and commercially valuable natural products, are produced by plants and fungi. Comparatively, terpenoids of bacterial origin are rare. This is counter-intuitive to the fact that recent microbial genomics revealed that almost all bacteria have the biosynthetic potential to create the C5 building blocks necessary for terpenoid biosynthesis. In this review, we catalogue terpenoids produced by bacteria. We collected 1062 natural products, consisting of both primary and secondary metabolites, and classified them into two major families and 55 distinct subfamilies. To highlight the structural and chemical space of bacterial terpenoids, we discuss their structures, biosynthesis, and biological activities. Although the bacterial terpenome is relatively small, it presents a fascinating dichotomy for future research. Similarities between bacterial and non-bacterial terpenoids and their biosynthetic pathways provides alternative model systems for detailed characterization while the abundance of novel skeletons, biosynthetic pathways, and bioactivies presents new opportunities for drug discovery, genome mining, and enzymology.

Engineering Isoprenoid Quinone Production in Yeast

Isoprenoid quinones are bioactive molecules that include an isoprenoid chain and a quinone head. They are traditionally found to be involved in primary metabolism, where they act as electron transporters, but specialized isoprenoid quinones are also produced by all domains of life. Here, we report the engineering of a baker's yeast strain, Saccharomyces cerevisiae EPYFA3, for the production of isoprenoid quinones. Our yeast strain was developed through overexpression of the shikimate pathway in a well-established recipient strain (S. cerevisiae EPY300) where the mevalonate pathway is overexpressed. As a proof of concept, our new host strain was used to overproduce the endogenous isoprenoid quinone coenzyme Q₆, resulting in a nearly 3-fold production increase. EPYFA3 represents a valuable platform for the heterologous production of high value isoprenoid quinones. EPYFA3 will also facilitate the elucidation of isoprenoid quinone biosynthetic pathways.

The plastid genome of some eustigmatophyte algae harbours a bacteria-derived six-gene cluster for biosynthesis of a novel secondary metabolite

Acquisition of genes by plastid genomes (plastomes) via horizontal gene transfer (HGT) seems to be a rare phenomenon. Here, we report an interesting case of HGT revealed by sequencing the plastomes of the eustigmatophyte algae Monodopsis sp. MarTras21 and Vischeria sp. CAUP Q 202. These plastomes proved to harbour a unique cluster of six genes, most probably acquired from a bacterium of the phylum Bacteroidetes, with homologues in various bacteria, typically organized in a conserved uncharacterized putative operon. Sequence analyses of the six proteins encoded by the operon yielded the following annotation for them: (i) a novel family without discernible homologues; (ii) a new family within the superfamily of metallo-dependent hydrolases; (iii) a novel subgroup of the UbiA superfamily of prenyl transferases; (iv) a new clade within the sugar phosphate cyclase superfamily; (v) a new family within the xylose isomerase-like superfamily; and (vi) a hydrolase for a phosphate moiety-containing substrate. We suggest that the operon encodes enzymes of a pathway synthesizing an isoprenoid–cyclitol-derived compound, possibly an antimicrobial or other protective substance. To the best of our knowledge, this is the first report of an expansion of the metabolic capacity of a plastid mediated by HGT into the plastid genome.

Synthesis of the Racemate of the Stereoisomer at C-6a of BE-40644, a Bioactive Metabolite of Actinoplanes sp. with a Sesquiterpene-substituted p-Benzoquinone Structure

BE-40644 is a tetracyclic metabolite of Actinoplanes sp. A 40644 possessing a sesquiterpene-substituted p-benzoquinone structure with cis-fused B/C ring stereochemistry that inhibits the human thioredoxin system as the well as the growth of several cancer cell lines. Its B/C trans-fused stereoisomer at C-6a was synthesized as a racemate starting from geranylacetone and 3,5-dihydroxybenzoic acid.

A new cytotoxic sesquiterpene quinone produced by Penicillium sp. F00120 isolated from a deep sea sediment sample

A new fungal strain, displaying strong toxic activity against brine shrimp larvae, was isolated from a deep sea sediment sample collected at a depth of 1300 m. The strain, designated as F00120, was identified as a member of the genus Penicillium on the basis of morphology and ITS sequence analysis. One new sesquiterpene quinone, named penicilliumin A (1), along with two known compounds ergosterol (2) and ergosterol peroxide (3), were isolated and purified from the cultures of F00120 by silica gel column, Sephadex LH-20 column, and preparative thin layer chromatography. Their structures were elucidated by detailed nuclear magnetic resonance (NMR) and mass spectroscopic (MS) analysis as well as comparison with literature data. The new compound penicilliumin A inhibited in vitro proliferation of mouse melanoma (B16), human melanoma (A375), and human cervical carcinoma (Hela) cell lines moderately.

Genetic organization of the putative salbostatin biosynthetic gene cluster including the 2-epi-5-epi-valiolone synthase gene in Streptomyces albus ATCC 21838

The cyclization of sedoheptulose 7-phosphate to 2-epi-5-epi-valiolone, catalyzed by the 2-epi-5-epi-valiolone synthases, is the first committed step in the biosynthesis of C( 7 )N-aminocyclitol-containing natural products, such as validamycin and acarbose. These natural products contain in their structures a valienamine unit, which is important for their biological activity. The same core unit is also found in salbostatin, a related pseudodisaccharide that has strong trehalase inhibitory activity. In silico analysis of the putative biosynthetic gene cluster of salbostatin from Streptomyces albus ATCC 21838 revealed 20 open reading frames, including an acbC homolog gene (salQ), which is believed to be involved in the biosynthesis of salbostatin. The salQ gene was overexpressed in Escherichia coli and the catalytic function of the recombinant protein was confirmed to be a 2-epi-5-epi-valiolone synthase. In addition, SalF, SalL, SalM, SalN, SalO, and SalR were found to be homologous to AcbR, AcbM, AcbL, AcbN, AcbO, and AcbP from the acarbose pathway, respectively, which suggests that the biosynthesis of C(7)N-aminocyclitol moiety of salbostatin may be very similar to that of acarbose.

Biosynthesis of unusual aminocyclitol-containing natural products

The aminocyclitol family of natural products is a class of sugar-derived microbial secondary metabolites that demonstrate significant biological activities. Within this class of natural products are the C7N-aminocyclitol-containing compounds, which were originally associated with potent sugar-hydrolase inhibition. However, recent discoveries indicate a broader array of chemical structures and biological activities of this class of compounds. Using both conventional feeding experiments and contemporary molecular genetic approaches, some progress has been made in understanding the biosynthesis of this class of natural products. Results of in silico investigation also suggest a wide distribution of this class of natural products or closely related compounds across different classes of microorganisms, including cyanobacteria and fungi. This review describes our recent progress in the biosynthetic studies of a number of C7N-aminocyclitol-containing compounds and the potential use of bioinformatic approaches to search for novel aminocyclitol-containing natural products.

Studies on Biosynthetic Genes and Enzymes of Isoprenoids Produced by Actinomycetes

Most Streptomyces strains are equipped with only the 2-C-methyl-D-erythritol 4-phosphate (MEP) pathway for the formation of isopentenyl diphosphate, a common precursor of isoprenoids. In addition to this pathway, some Streptomyces strains possess the mevalonate (MV) pathway via which isoprenoid antibiotics are produced. We have recently cloned and analyzed the MV pathway gene clusters and their flanking regions from terpentecin, BE-40644, and furaquinocin A producers. All these clusters contained genes coding for mevalonate kinase, mevalonate diphosphate decarboxylase, phosphomevalonate kinase, type 2 IPP isomerase, HMG-CoA reductase, and HMG-CoA synthase. The order of each of the open reading frames (ORFs) is also the same, and the respective homologous ORFs show more than 70% amino acid identity with each other. In contrast to these conservative gene organizations, the biosynthetic genes of terpentecin, BE-40644, and furaquinocin A were located just upstream and/or downstream of the MV pathway gene cluster. These facts suggested that all the actinomycete strains possessing both the MV and MEP pathways produce isoprenoid compounds and the biosynthetic genes of one of these isoprenoids usually exist adjacent to the MV pathway gene cluster. Therefore, when the presence of the MV cluster is detected by molecular genetic techniques, isoprenoids may be produced by the cultivation of these actinomycete strains. During the course of these studies, we identified diterpene cyclases possessing unique primary structures that differ from those of eukaryotes and catalyze unique reactions.

Thioredoxin reductase

The mammalian thioredoxin reductases (TrxRs) are a family of selenium-containing pyridine nucleotide-disulphide oxidoreductases with mechanistic and sequence identity, including a conserved -Cys-Val-Asn-Val-Gly-Cys- redox catalytic site, to glutathione reductases. TrxRs catalyse the NADPH-dependent reduction of the redox protein thioredoxin (Trx), as well as of other endogenous and exogenous compounds. The broad substrate specificity of mammalian TrxRs is due to a second redox-active site, a C-terminal -Cys-SeCys- (where SeCys is selenocysteine), that is not found in glutathione reductase or Escherichia coli TrxR. There are currently two confirmed forms of mammalian TrxRs, TrxR1 and TrxR2, and it is possible that other forms will be identified. The availability of Se is a key factor determining TrxR activity both in cell culture and in vivo, and the mechanism(s) for the incorporation of Se into TrxRs, as well as the regulation of TrxR activity, have only recently begun to be investigated. The importance of Trx to many aspects of cell function make it likely that TrxRs also play a role in protection against oxidant injury, cell growth and transformation, and the recycling of ascorbate from its oxidized form. Since TrxRs are able to reduce a number of substrates other than Trx, it is likely that additional biological effects will be discovered for TrxR. Furthermore, inhibiting TrxR with drugs may lead to new treatments for human diseases such as cancer, AIDS and autoimmune diseases.