Purification and characterization of Streptomyces griseus catechol O-methyltransferase

Identification of a polyphenol O-methyltransferase with broad substrate flexibility in Streptomyces albidoflavus J1074

Flavonoids are a large and important group of phytochemicals with a great variety of bioactivities. The addition of methyl groups during biosynthesis of flavonoids and other polyphenols enhances their bioactivities and increases their stability. In a previous study of our research group, we detected a novel flavonoid O-methyltransferase activity in Streptomyces albidoflavus J1074, which led to the heterologous biosynthesis of homohesperetin from hesperetin in feeding cultures. In this study, we identify the O-methyltransferase responsible for the generation of this methylated flavonoid through the construction of a knockout mutant of the gene XNR_0417, which was selected after a blast analysis using the sequence of a caffeic acid 3'-O-methyltransferase from Zea mays against the genome of S. albidoflavus J1074. This mutant strain, S. albidoflavus ∆XNR_0417, was no longer able to produce homohesperetin after hesperetin feeding. Subsequently, we carried out a genetic complementation of the mutant strain in order to confirm that the enzyme encoded by XNR_0417 is responsible for the observed O-methyltransferase activity. This new strain, S. albidoflavus SP43-XNR_0417, was able to produce not only homohesperetin from hesperetin, but also different mono-, di-, tri- and tetra-methylated derivatives on other flavanones, flavones and stilbenes, revealing a broad substrate flexibility. Additionally, in vitro experiments were conducted using the purified enzyme on the substrates previously tested in vivo, demonstrating doubtless the capability of XNR_0417 to generate various methylated derivatives.

Enhanced Prodigiosin Production in Serratia marcescens JNB5-1 by Introduction of a Polynucleotide Fragment into the pigN 3' Untranslated Region and Disulfide Bonds into O-Methyl Transferase (PigF)

In Serratia marcescens JNB5-1, prodigiosin was highly produced at 30°C, but it was noticeably repressed at ≥37°C. Our initial results demonstrated that both the production and the stability of the O-methyl transferase (PigF) and oxidoreductase (PigN) involved in the prodigiosin pathway in S. marcescens JNB5-1 sharply decreased at ≥37°C. Therefore, in this study, we improved mRNA stability and protein production using de novo polynucleotide fragments (PNFs) and the introduction of disulfide bonds, respectively, and observed their effects on prodigiosin production. Our results demonstrate that adding PNFs at the 3' untranslated regions of pigF and pigN significantly improved the mRNA half-lives of these genes, leading to an increase in the transcript and expression levels. Subsequently, the introduction of disulfide bonds in pigF improved the thermal stability, pH stability, and copper ion resistance of PigF. Finally, shake flask fermentation showed that the prodigiosin titer with the engineered S. marcescens was increased by 61.38% from 5.36 to 8.65 g/liter compared to the JNB5-1 strain at 30°C and, significantly, the prodigiosin yield increased 2.05-fold from 0.38 to 0.78 g/liter at 37°C. In this study, we revealed that the introduction of PNFs and disulfide bonds greatly improved the expression and stability of pigF and pigN, hence efficiently enhancing prodigiosin production with S. marcescens at 30 and 37°C. IMPORTANCE This study highlights a promising strategy to improve mRNA/enzyme stability and to increase production using de novo PNF libraries and the introduction of disulfide bonds into the protein. PNFs could increase the half-life of target gene mRNA and effectively prevent its degradation. Moreover, PNFs could increase the relative intensity of target genes without affecting the expression of other genes; as a result, it could alleviate the cellular burden compared to other regulatory elements such as promoters. In addition, we obtained a PigF variant with improved activity and stability by the introduction of disulfide bonds into PigF. Collectively, we demonstrate here a novel approach for improving mRNA/enzyme stability using PNFs, which results in enhanced prodigiosin production in S. marcescens at 30°C.

Improved Prodigiosin Production by Relieving CpxR Temperature-Sensitive Inhibition

Prodigiosin (PG) is a typical secondary metabolite mainly produced by Serratia marcescens. CpxR protein is an OmpR family transcriptional regulator in Gram-negative bacteria. Firstly, it was found that insertion mutation of cpxR in S. marcescens JNB 5-1 by a transposon Tn5G increased the production of PG. Results from the electrophoretic mobility shift assay (EMSA) indicated that CpxR could bind to the promoter of the pig gene cluster and repress the transcription levels of genes involved in PG biosynthesis in S. marcescens JNB 5-1. In the ΔcpxR mutant strain, the transcription levels of the pig gene cluster and the genes involved in the pathways of PG precursors, such as proline, pyruvate, serine, methionine, and S-adenosyl methionine, were significantly increased, hence promoting the production of PG. Subsequently, a fusion segment composed of the genes proC, serC, and metH, responsible for proline, serine, and methionine, was inserted into the cpxR gene in S. marcescens JNB 5-1. On fermentation by the resultant engineered S. marcescens, the highest PG titer reached 5.83 g/L and increased by 41.9%, relative to the parental strain. In this study, we revealed the role of CpxR in PG biosynthesis and provided an alternative strategy for the engineering of S. marcescens to enhance PG production.

Streptomyces spp. in the biocatalysis toolbox

About 20,100 research publications dated 2000-2017 were recovered searching the PubMed and Web of Science databases for Streptomyces, which are the richest known source of bioactive molecules. However, these bacteria with versatile metabolism are powerful suppliers of biocatalytic tools (enzymes) for advanced biotechnological applications such as green chemical transformations and biopharmaceutical and biofuel production. The recent technological advances, especially in DNA sequencing coupled with computational tools for protein functional and structural prediction, and the improved access to microbial diversity enabled the easier access to enzymes and the ability to engineer them to suit a wider range of biotechnological processes. The major driver behind a dramatic increase in the utilization of biocatalysis is sustainable development and the shift toward bioeconomy that will, in accordance to the UN policy agenda "Bioeconomy to 2030," become a global effort in the near future. Streptomyces spp. already play a significant role among industrial microorganisms. The intention of this minireview is to highlight the presence of Streptomyces in the toolbox of biocatalysis and to give an overview of the most important advances in novel biocatalyst discovery and applications. Judging by the steady increase in a number of recent references (228 for the 2000-2017 period), it is clear that biocatalysts from Streptomyces spp. hold promises in terms of valuable properties and applicative industrial potential.

Substrate Scope of O-Methyltransferase from Streptomyces peucetius for Biosynthesis of Diverse Natural Products Methoxides

Methylation is a common post-modification reaction that is observed during the biosynthesis of secondary metabolites produced by plants and microorganisms. Based on the sequence information from Streptomyces peucetius ATCC27952, a putative O-methyltransferase (OMT) gene SpOMT7740 was polymerase chain reaction amplified and cloned into E. coli BL21 (DE3) host to test the substrate promiscuity and conduct functional characterization. In vitro and in vivo reaction assays were carried out over various classes of substrates: flavonoids (flavonol, flavones, and isoflavonoid), chalcones, anthraquinones, anthracyclines, and sterol molecules, and the applications in synthesizing diverse classes of O-methoxy natural products were also illustrated. SpOMT7740 catalyzed the O-methylation reaction to form various natural and non-natural O-methoxides, includes 7-hydroxy-8-O-methoxy flavone, 3-O-methoxy flavone, three mono-, di-, and tri-O-methoxy genistein, mono-O-methoxy phloretin, mono-O-methoxy luteolin, 3-O-methoxy β-sitosterol, and O-methoxy anthraquinones (emodin and aloe emodin) and O-methoxy anthracycline (daunorubicin) exhibiting diverse substrate flexibility. Daunorubicin is a native secondary metabolite of S. peucetius. Among the compounds tested, 7,8-dihydroxyflavone was the best substrate for bioconversion to 7-hydroxy-8-O-methoxy flavone, and it was structurally elucidated. This enzyme showed a flexible catalysis over the given ranges of temperature, pH, and divalent cationic conditions for O-methylation.

Biotransformations and biological activities of hop flavonoids

Female hop cones are used extensively in the brewing industry, but there is now increasing interest in possible uses of hops for non-brewing purposes, especially in the pharmaceutical industry. Among pharmaceutically important compounds from hops are flavonoids, having proven anticarcinogenic, antioxidant, antimicrobial, anti-inflammatory and estrogenic effects. In this review we aim to present current knowledge on the biotransformation of flavonoids from hop cones with respect to products, catalysis and conversion. A list of microbial enzymatic reactions associated with gastrointestinal microbiota is presented. A comparative analysis of the biological activities of hop flavonoids and their biotransformation products is described, indicating where further research has potential for applications in the pharmaceutical industry.

Characterization of streptonigrin biosynthesis reveals a cryptic carboxyl methylation and an unusual oxidative cleavage of a N-C bond

Streptonigrin (STN, 1) is a highly functionalized aminoquinone alkaloid with broad and potent antitumor activity. Here, we reported the biosynthetic gene cluster of STN identified by genome scanning of a STN producer Streptomyces flocculus CGMCC4.1223. This cluster consists of 48 genes determined by a series of gene inactivations. On the basis of the structures of intermediates and shunt products accumulated from five specific gene inactivation mutants and feeding experiments, the biosynthetic pathway was proposed, and the sequence of tailoring steps was preliminarily determined. In this pathway, a cryptic methylation of lavendamycin was genetically and biochemically characterized to be catalyzed by a leucine carboxyl methyltransferase StnF2. A [2Fe-2S](2+) cluster-containing aromatic ring dioxygenase StnB1/B2 system was biochemically characterized to catalyze a regiospecific cleavage of the N-C8' bond of the indole ring of the methyl ester of lavendamycin. This work provides opportunities to illuminate the enzymology of novel reactions involved in this pathway and to create, using genetic and chemo-enzymatic methods, new streptonigrinoid analogues as potential therapeutic agents.

Analysis of a parallel branch in the mitomycin biosynthetic pathway involving the mitN-encoded aziridine N-methyltransferase

Mitomycin C is a natural product with potent alkylating activity, and it is an important anticancer drug and antibiotic. mitN, one of three genes with high similarity to methyltransferases, is located within the mitomycin biosynthetic gene cluster. An inframe deletion in mitN of the mitomycin biosynthetic pathway was generated in Streptomyces lavendulae to produce the DHS5373 mutant strain. Investigation of DHS5373 revealed continued production of mitomycin A and mitomycin C in addition to the accumulation of a new mitomycin analog, 9-epi-mitomycin C. The mitN gene was overexpressed in Escherichia coli, and the histidine-tagged protein (MitN) was purified to homogeneity. Reaction of 9-epi-mitomycin C with MitN in the presence of S-adenosylmethionine yielded mitomycin E showing that the enzyme functions as an aziridine N-methyltransferase. Likewise, MitN was also shown to convert mitomycin A to mitomycin F under the same reaction conditions. We conclude that MitN plays an important role in a parallel biosynthetic pathway leading to the subclass of mitomycins with 9alpha-stereochemistry but is not involved directly in the biosynthesis of mitomycins A and C.

Catechol-O-methyltransferase and its inhibitors in Parkinson's disease

Parkinson's disease (PD) is a neurological disorder characterized by the degeneration of dopaminergic neurons, with consequent reduction in striatal dopamine levels leading to characteristic motor symptoms. The most effective treatment for this disease continues to be the dopamine replacement therapy with levodopa together with an inhibitor of aromatic amino acid decarboxylase (AADC). The efficacy of this therapy, however, decreases with time and most patients develop fluctuating responses and dyskinesias. The last decade showed that the use of catechol-O-methyltransferase inhibitors as adjuvants to the levodopa/AADC inhibitor therapy, significantly improves the clinical benefits of this therapy. The purpose of this article is to review the current knowledge on the enzyme catechol-O-methyltransferase (COMT) and the role of COMT inhibitors in PD as a new therapeutic approach to PD involving conversion of levodopa to dopamine at the target region in the brain and facilitation of the continuous action of this amine at the receptor sites. A historical overview of the discovery and development of COMT inhibitors is presented with a special emphasis on nebicapone, presently under clinical development, as well as entacapone and tolcapone, which are already approved as adjuncts in the therapy of PD. This article reviews human pharmacokinetic and pharmacodynamic properties of these drugs as well as their clinical efficacy and safety.

Flavanone metabolism in healthy and tumor-bearing rats

Flavanones, the main polyphenols of citrus fruits, are thought to contribute to the protective effects of these fruits against cardiovascular diseases and cancer. The metabolism of naringin (naringenin 7-O-neohesperidoside) is studied here in healthy (sham-operated, ShO) and tumor-bearing (TuB) rats. The tumor was induced by implanting Yoshida's sarcoma in hindlimb. Both groups received for 7 days a semi-synthetic diet containing 0.5% naringin in per feeding conditions. Flavanones were analyzed in plasma, liver, kidney and urine by tandem mass spectrometry. Naringenin conjugates (essentially glucuronides) accounted for up to 98% of the total flavanones in plasma. Low amounts of hesperetin (4'-O-methyl naringénine) and isosakuranetin (3'-hydroxy-4'-O-methylnaringenin) were also detected in all biological samples and accounted for 2% of the total flavanones in plasma. They were largely present as aglycones. The in vivo hydroxylation of flavanones is described here for the first time. Total concentrations of naringenin metabolites reached 17.3+/-2.7 microM in plasma 6 hours after the beginning of the meal in healthy rats and only 10.6+/-1.3 microM in TuB rats. The nature of metabolites was similar in both healthy and TuB rats and in plasma, tissues and urine. The lower concentration of flavanones in the TuB rats suggests that disease and more particularly cancer, may affect the bioavailability of flavonoids.

Biochemical characterization of MelJ and MelK

Melithiazol and myxothiazol are two myxobacterial metabolites that are highly efficient electron transport inhibitors of the respiratory chain. MelJ and MelK encoded in the melithiazol biosynthetic gene cluster were recently shown to be involved in the formation of the methyl ester from a hypothetical amide intermediate. In vivo studies suggest that the structurally highly similar amide myxothiazol A can be used as a substrate mimic of the hypothetical melithiazol amide to characterize the hydrolase MelJ. Both enzymes were produced in Escherichia coli as intein chitin fusion proteins and were purified using affinity chromatography. MelJ was found to catalyse the conversion of the amide myxothiazol to free myxothiazol acid. The formerly unknown myxothiazol acid was purified and used as a substrate for the methyl transferase MelK which methylates the compound using S-adenosyl-methionine as cosubstrate. Sequence analyses suggest that MelJ and MelK are members of the amidase signature family and of a new subclass of methyltransferases, respectively. Kinetic analyses point at a very high substrate specificity for both enzymes. Furthermore, the in vitro reconstitution of a unique mechanism of methyl ester formation found in myxobacteria is reported.

Microbial degradation of sulfur, nitrogen and oxygen heterocycles

Sulfur (S), nitrogen (N) and oxygen (O) heterocycles are among the most potent environmental pollutants. Microbial degradation of these pollutants is attracting more and more attention because such bioprocesses are environmentally friendly. The biotechnological potential of these processes is being investigated, for example, to achieve better sulfur removal by immobilized biocatalysts with magnetite nanoparticles or by solvent-tolerant bacteria, and to obtain valuable intermediates from these heterocycles. Other recent advances have demonstrated the mechanisms of angular dioxygenation of nitrogen heterocycles by microbes. However, these technologies are not yet available for large-scale applications so future research must investigate proper modifications for industrial applications of these processes. This review focuses on recent progress in understanding how microbes degrade S, N and O heterocycles.

Microbial and enzymatic transformations of flavonoids

Flavonoids are among the most ubiquitous phenolic compounds found in nature. These compounds have diverse physiological and pharmacological activities such as estrogenic, antitumor, antimicrobial, antiallergic, and anti-inflammatory effects. They are well-known antioxidants and metal ion-chelators. In the present review, biotransformations of numerous flavonoids catalyzed mainly by microbes and few plant enzymes are described in four different flavonoid classes, viz., chalcones, isoflavones, catechins, and flavones. Both phase I (oxidative) and phase II (conjugative) biotransformations representing a variety of reactions including condensation, cyclization, hydroxylation, dehydroxylation, alkylation, O-dealkylation, halogenation, dehydrogenation, double-bond reduction, carbonyl reduction, glycosylation, sulfation, dimerization, or different types of ring degradations are elaborated here. In some cases, the observed microbial transformations mimic mammalian and/or plant metabolism. This review recognizes Norman Farnsworth, who through his fascination and hard work in pharmacognosy has fostered the excitement of discovery by numerous students and faculty far and beyond the halls of the University of Illinois at Chicago. It is with grateful thanks for these efforts that we dedicate this review to him.

Characterization of O-methyltransferase ScOMT1 cloned from Streptomyces coelicolor A3(2)

The roles of O-methyltransferases (OMTs) in microorganisms are not well understood, and are suggested to increase antimicrobial activity. Studies on OMTs cloned from microorganisms may help elucidate their roles. Streptomyces coelicolor A3(2) produces many useful natural antibiotics such as actinorhodin. Based on sequence information from S. coelicolor A3(2) genome, it was possible to clone several methyltransferases. An OMT cloned from Streptomyces coelicolor A3(2), ScOMT1 was characterized by in vivo and in vitro assays. Of 23 compounds tested, 13 were found to serve as its substrates. Of the 13 substrates, the methylated positions of 7 compounds were determined by HPLC, NMR, and MS analyses. This OMT favored ortho-dihydroxyflavones. Among the compounds tested here, the best substrate is 6,7-dihydroxyflavone.

Metabolism of daidzein by Nocardia species NRRL 5646 and Mortierella isabellina ATCC 38063

The phytoestrogen daidzein was metabolized by Nocardia species NRRL 5646 to give two metabolites obtained by hydroxylation and methylation. These metabolites were spectrally characterized as 7-methoxy-4'-hydroxyisoflavone (isoformononetin) and 7,8-dimethoxy-4'-hydroxyisoflavone. Mortierella isabellina ATCC 38063 was able to metabolize daidzein to the unusual metabolite daidzein-4'-rhamnopyranoside.

Isolation and characterization of 27-O-demethylrifamycin SV methyltransferase provides new insights into the post-PKS modification steps during the biosynthesis of the antitubercular drug rifamycin B by Amycolatopsis mediterranei S699

The gene rif orf14 in the rifamycin biosynthetic gene cluster of Amycolatopsis mediterranei S699, producer of the antitubercular drug rifamycin B, encodes a protein of 272 amino acids identified as an AdoMet: 27-O-demethylrifamycin SV methyltransferase. Frameshift inactivation of rif orf14 generated a mutant of A. mediterranei S699 that produces no rifamycin B, but accumulates 27-O-demethylrifamycin SV (DMRSV) as the major new metabolite, together with a small quantity of 27-O-demethyl-25-O-desacetylrifamycin SV (DMDARSV). Heterologous expression of rif orf14 in Escherichia coli yielded a 33.8-kDa polyhistidine-tagged polypeptide, which efficiently catalyzes the methylation of DMRSV to rifamycin SV, but not that of DMDARSV or rifamycin W. 27-O-Demethylrifamycin S was methylated poorly, if at all, by the enzyme to produce rifamycin S. The purified enzyme does not require a divalent cation for catalytic activity. While Ca(2+) or Mg(2+) inhibits the enzyme activity slightly, Zn(2+), Ni(2+), and Co(2+) are strongly inhibitory. The K(m) values for DMRSV and S-adenosyl-L-methionine (AdoMet) are 18.0 and 19.3 microM, respectively, and the K(cat) is 87s(-1). The results indicate that DMRSV is a direct precursor of rifamycin SV and that acetylation of the C-25 hydroxyl group must precede the methylation reaction. They also suggest that rifamycin S is not the precursor of rifamycin SV in rifamycin B biosynthesis, but rather an oxidative shunt-product.

Glutathione S-transferase isoenzymes from Streptomyces griseus

An inducible, cytosolic glutathione S-transferase (GST) was purified from Streptomyces griseus. GST isoenzymes with pI values of 6.8 and 7.9 used standard GST substrates including 1-chloro-2,4-dinitrobenzene. GST had subunit and native M(r)s of 24 and 48, respectively, and the N-terminal sequence SMILXYWDIIRGLPAH.

Analysis of dibenzothiophene metabolic pathway in Mycobacterium strain G3

The dibenzothiophene (DBT) metabolic pathway in Mycobacterium strain G3, which is classified as a desulfurizing microorganism with the 4S pathway, was analyzed. 2-Hydroxybiphenyl (HBP), which is an end metabolite in the DBT desulfurization reaction, and 2-methoxybiphenyl (MBP) were found in the reaction mixture, and the methoxylation pathway from HBP to MBP was clarified. Although the substrate in the methoxylation reaction was HBP, there was no relationship between expression of the methoxylation activity and that of the desulfurization activity. Then, 4,6-dimethyl DBT, 4,6-diethyl DBT and benzo[b]naphtho[2,1-d]thiophene were metabolized to their methoxy forms via the desulfurization pathway. We established the methoxylation pathway in Mycobacterium G3.

Biotransformation of 2,7-dichloro- and 1,2,3,4-tetrachlorodibenzo-p-dioxin by Sphingomonas wittichii RW1

Aerobic biotransformation of the diaryl ethers 2,7-dichlorodibenzo-p-dioxin and 1,2,3,4-tetrachlorodibenzo-p-dioxin by the dibenzo-p-dioxin-utilizing strain Sphingomonas wittichii RW1, producing corresponding metabolites, was demonstrated for the first time. Our strain transformed 2,7-dichlorodibenzo-p-dioxin, yielding 4-chlorocatechol, and 1,2,3,4-tetrachlorodibenzo-p-dioxin, producing 3,4,5,6-tetrachlorocatechol and 2-methoxy-3,4,5,6-tetrachlorophenol; all of these compounds were unequivocally identified by mass spectrometry both before and after N,O-bis(trimethylsilyl)-trifluoroacetamide derivatization by comparison with authentic standards. Additional experiments showed that strain RW1 formed a second metabolite, 2-methoxy-3,4,5,6-tetrachlorophenol, from the original degradation product, 3,4,5,6-tetrachlorocatechol, by methylation of one of the two hydroxy substituents.

Hydroxylations and methylations of quercetin, fisetin, and catechin by Streptomyces griseus

Preparative-scale biotransformation of quercetin (1), fisetin (7), and (+)-catechin (12) with Streptomyces griseus (ATCC 13273) resulted in the isolation and characterization of nine known hydroxylated and/or methylated (2--6, 8, 9, 11, 13a) metabolites and two previously unknown (10 and 14) metabolites. S.griseus catalyzed aromatic hydroxylations of rings A and B of quercetin and fisetin. Mono- and dimethoxy ring-B metabolites were obtained with all three substrates. Methylation appeared to occur only when catechol functional groups were present. Metabolite structures were established by FABMS, EIMS, and 1D and 2D NMR analysis.