Thioesterase domain swapping of a linear polyketide tautomycetin with a macrocyclic polyketide pikromycin in <Emphasis Type="Italic">Streptomyces</Emphasis> sp. CK4412

Tautomycetin (TMC) is a linear polyketide metabolite produced by Streptomyces sp. CK4412 that has been reported to possess multiple biological functions including T cell-specific immunosuppressive and anticancer activities that occur through a mechanism of differential inhibition of protein phosphatases such as PP1, PP2A, and SHP2. We previously reported the characterization of the entire TMC biosynthetic gene cluster constituted by multifunctional type I polyketide synthase (PKS) assembly and suggested that the linear form of TMC could be generated via free acid chain termination by a narrow TMC thioesterase (TE) pocket. The modular nature of the assembly presents a unique opportunity to alter or interchange the native biosynthetic domains to produce targeted variants of TMC. Herein, we report swapping of the TMC TE domain sequence with the exact counterpart of the macrocyclic polyketide pikromycin (PIK) TE. PIK TE-swapped Streptomyces sp. CK4412 mutant produced not only TMC, but also a cyclized form of TMC, implying that the bioengineering based in vivo custom construct can be exploited to produce engineered macrolactones with new structural functionality.     

Biosynthesis of an engineered tautomycetin analogue via disruption of tmcK-encoding terminal decarboxylase in Streptomyces CK4412

Tautomycetin (TMC), produced by Streptomyces sp. CK4412, is an antifungal secondary metabolite with an unusual ester bond linkage between a terminal cyclic anhydride moiety and a linear polyketide chain bearing an unusual terminal alkene. Recently, TMC was identified to possess additional biological functions including T cell-specific immunosuppressive and anti-cancer activities through differential inhibition of protein phosphatases, such as PP1, PP2A, and SHP2. These findings led us to isolate and characterize its entire biosynthetic and regulatory pathway gene cluster. In silico database comparisons revealed that the deduced products of two translationally coupled genes, a 666-bp tmcJ and a 1458-bp tmcK located on the 3′-terminus of the polyketide synthase gene, were found to have amino acid sequence homologies with putative bacterial decarboxylase genes. Targeted gene disruption of tmcK, but not tmcJ, from the Streptomyces sp. CK4412 chromosome resulted in production of a 5-deoxy-3″-carboxylic TMC. The tmcK mutant strain was functionally complemented using an integrative plasmid carrying tmcK and/or tmcJ–tmcK in order to restore TMC biosynthesis, a result suggesting that only TmcK is a functional TMC terminal decarboxylase. Unlike an authentic TMC, this engineered 5-deoxy-3″-carboxylic TMC analogue failed to show PP1 selectivity over PP2A, and it showed significantly reduced cytotoxicity against a human lung cancer cell line. These results imply that regio-specific modifications of TMC polyketide moiety, such as C3″-terminal carboxylation and/or C5-deketonization, could differentiate multiple biological activities in TMC produced from Streptomyces sp. CK4412.     

Biosynthesis,regulation, and engineering of a linear polyketide tautomycetin: a novel immunosuppressant in <Emphasis Type="Italic">Streptomyces</Emphasis> sp. CK4412

Tautomycetin (TMC) is a natural product with a linear structure that includes an ester bond connecting a dialkylmaleic moiety to a type I polyketide chain. Although TMC was originally identified as an antifungal antibiotic in the late 1980s, follow-up studies revealed its novel immunosuppressant activity. Specifically, TMC exhibited a mechanistically unique immunosuppressant activity about 100 times higher than that of cyclosporine A, a widely used immunosuppressant drug. Interestingly, a structurally close relative, tautomycin (TTM), was reported to not possess TMC-like immunosuppressant activity, suggesting that a distinctive polyketide moiety of TMC plays a critical role in immunosuppressant activity. Cloning and engineering of a TMC polyketide biosynthetic gene cluster generated several derivatives showing different biological activities. TMC was also found to be biosynthesized as a linear structure without forming a lactone ring, unlike the most polyketide-based compounds, implying the presence of a unique polyketide thioesterase in the cluster. Although TMC biosynthesis was limited due to its tight regulation by two pathway-specific regulatory genes located in the cluster, its production was significantly stimulated through homologous and heterologous expression of its entire biosynthetic gene cluster using a Streptomyces artificial chromosome vector system. In this mini-review, we summarize recent advances in the biosynthesis, regulation, and pathway engineering of a linear polyketide, TMC, in Streptomyces sp. CK4412.     

A global positive regulator afsR2 stimulates tautomycetin production via pathway-specific regulatory gene over-expression in Streptomyces sp. CK4412

Tautomycetin (TMC) is a T cell-specific immunosuppressant with a unique ester bond linkage between a terminal cyclic anhydride and a linear polyketide chain. Since an afsR2 was proved to be a global antibiotics-stimulating regulatory gene in various Streptomyces species, an afsR2-induced TMC productivity stimulation was investigated in a TMC-producing Streptomyces sp. CK4412 strain. An afsR2 gene was cloned under the influence of a strong constitutive ermE* promoter in an integrative expression vector, followed by its conjugation into the Streptomyces sp. CK4412. Comparing TMC productivity and antifungal activity of the wild type and the afsR2-containing ex-conjugant revealed that afsR2 over-expression stimulated TMC production approximately 2.4-fold in Streptomyces sp. CK4412. Based on both RT-PCR and real-time RT-PCR analyses, an afsR2 over-expression significantly stimulated the expression of a TMC-specific positive regulatory gene, tmcN. This implies that the stimulatory effect of afsR2 functions in Streptomyces sp. CK4412 via up-regulation of a TMC pathway-specific positive regulatory gene over-expression.     

Biosynthesis of a natural polyketide-isoprenoid hybrid compound, furaquinocin A: identification and heterologous expression of the gene cluster

Furaquinocin (FQ) A, produced by Streptomyces sp. strain KO-3988, is a natural polyketide-isoprenoid hybrid compound that exhibits a potent antitumor activity. As a first step toward understanding the biosynthetic machinery of this unique and pharmaceutically useful compound, we have cloned an FQ A biosynthetic gene cluster by taking advantage of the fact that an isoprenoid biosynthetic gene cluster generally exists in flanking regions of the mevalonate (MV) pathway gene cluster in actinomycetes. Interestingly, Streptomyces sp. strain KO-3988 was the first example of a microorganism equipped with two distinct mevalonate pathway gene clusters. We were able to localize a 25-kb DNA region that harbored FQ A biosynthetic genes (fur genes) in both the upstream and downstream regions of one of the MV pathway gene clusters (MV2) by using heterologous expression in Streptomyces lividans TK23. This was the first example of a gene cluster responsible for the biosynthesis of a polyketide-isoprenoid hybrid compound. We have also confirmed that four genes responsible for viguiepinol [3-hydroxypimara-9(11),15-diene] biosynthesis exist in the upstream region of the other MV pathway gene cluster (MV1), which had previously been cloned from strain KO-3988. This was the first example of prokaryotic enzymes with these biosynthetic functions. By phylogenetic analysis, these two MV pathway clusters were identified as probably being independently distributed in strain KO-3988 (orthologs), rather than one cluster being generated by the duplication of the other cluster (paralogs).     

Draft genome sequence of marine Streptomyces sp. strain W007, which produces angucyclinone antibiotics with a benz[a]anthracene skeleton

A series of angucyclinone antibiotics have been isolated from marine Streptomyces sp. strain W007 and identified. Here, a draft genome sequence of Streptomyces sp. W007 is presented. The genome contains an intact biosynthetic gene cluster for angucyclinone antibiotics, which provides insight into the combinatorial biosynthesis of angucyclinone antibiotics produced by marine streptomycetes.     

Beta-lactam antibiotic biosynthetic genes have been conserved in clusters in prokaryotes and eukaryotes.

A cosmid clone containing closely linked beta-lactam antibiotic biosynthetic genes was isolated from a gene library of Flavobacterium sp. SC 12,154. The location within the cluster of the DNA thought to contain the gene for delta-(L-alpha-aminoadipyl)-L-cysteinyl-D-valine synthetase (ACVS), the first step in the beta-lactam antibiotic biosynthetic pathway, was identified by a novel method. This DNA facilitated the isolation, by cross-hybridization, of the corresponding DNA from Streptomyces clavuligerus ATCC 27064, Penicillium chrysogenum Oli13 and Aspergillus nidulans R153. Evidence was obtained which confirmed that the cross-hybridizing sequences contained the ACVS gene. In each case the ACVS gene was found to be closely linked to other beta-lactam biosynthetic genes and constituted part of a gene cluster.     

Cloning and identification of saprolmycin biosynthetic gene cluster from Streptomyces sp. TK08046

Saprolmycins A–E are anti-Saprolegnia parasitica antibiotics. To identify the gene cluster for saprolmycin biosynthesis in Streptomyces sp. TK08046, polymerase chain reaction using aromatase and cyclase gene-specific primers was performed; the spr gene cluster, which codes for angucycline biosynthesis, was obtained from the strain. The cluster consists of 36 open reading frames, including minimal polyketide synthase, ketoreductase, aromatase, cyclase, oxygenase, and deoxy sugar biosynthetic genes, as defined by homology to the corresponding genes of the urdamycin, Sch-47554, and grincamycin biosynthetic gene clusters in Streptomyces fradiae, Streptomyces sp. SCC-2136, and Streptomyces lusitanus, respectively. To establish the function of the gene cluster, an expression cosmid vector containing all 36 open reading frames was introduced into Streptomyces lividans TK23. The transformant was confirmed to express the biosynthetic genes and produce saprolmycins by liquid chromatography–mass spectrometry analysis of the extract.     

东乡野生稻内生放线菌Streptomyces sp. PRh5的全基因组测序及序列分析

【目的】Streptomyces sp. PRh5是从东乡野生稻(Oryza rufipogon Griff.)中分离获得的一株对细菌和真菌都具有较强抗菌活性的内生放线菌。为深入研究PRh5菌株抗菌机制及挖掘次级代谢产物基因资源,有必要解析PRh5菌株的基因组序列信息。【方法】采用高通量测序技术对PRh5菌株进行全基因组测序,然后使用相关软件对测序数据进行基因组组装、基因预测与功能注释、直系同源簇(COG)聚类分析、共线性分析及次级代谢产物合成基因簇预测等。【结果】基因组组装获得290 contigs,整个基因组大小约11.1 Mb,GC含量为71.1%,序列已提交至GenBank数据库,登录号为JABQ00000000。同时,预测得到50个次级代谢产物合成基因簇。【结论】将为Streptomyces sp. PRh5的功能基因组学研究及相关次级代谢产物的生物合成途径与异源表达研究提供基础。     

1株土壤放线菌的分类鉴定及其抗菌活性的研究

对从土壤微生物中筛选到的放线菌菌株1356进行分类学和抗菌活性的研究。采用多相分类法,对菌株的形态特征、培养特征、生理生化特性及16 SrRNA基因序列进行了研究。结果表明:该菌株的形态特征、培养特征、生理生化特性为链霉菌属的特征;16S rDNA序列分析及系统进化树分析表明其序列与灰色产色链霉菌的同源性最高;该菌株的发酵产物对番茄叶霉、白色念珠菌、小麦根腐菌等17种真菌均有不同程度的抑制作用。放线菌1356菌株具有广谱抗真菌活性而对细菌无作用;初步确定其为链霉菌属灰色产色链霉菌的一个亚种。     

Analysis of clustered genes encoding both early and late steps in daunomycin biosynthesis by Streptomyces sp. strain C5.

We recently described the isolation and sequence analysis of the daunomycin polyketide synthase biosynthesis genes of Streptomyces sp. strain C5 (J. Ye, M. L. Dickens, R. Plater, Y. Li, J. Lawrence, and W. R. Strohl, J. Bacteriol. 176:6270-6280, 1994). Contiguous to the daunomycin polyketide synthase biosynthesis gene region in Streptomyces sp. strain C5 are four additional genes involved in daunomycin biosynthesis, two of the products of which show similarity to different types of methyltransferases. The dauC gene, encoding aklanonic acid methyltransferase (AAMT), complements dauC-blocked mutants of Streptomyces sp. strain C5, restores in vitro AAMT activities to the mutant strains, and confers in vitro AAMT activity on Streptomyces lividans. Partial purification through gel filtration, followed by photoaffinity labeling of enriched AAMT with S-adenosyl-L-[3H-methyl]methionine, indicates that AAMT is a homodimer with an M(r) of ca. 48,000 (subunit M(r) of ca. 24,000), which corresponds with the size of the deduced gene product. The dauD gene, encoding aklanonic acid methyl ester cyclase, is divergently arranged with respect to dauC. Immediately downstream and apparently translationally coupled with dauD is the dauK gene, encoding carminomycin 4-O-methyltransferase. The dauK gene confers in vitro carminomycin 4-O-methyltransferase activity on S. lividans and is nearly identical to a similar gene isolated from Streptomyces peucetius and characterized. Directly downstream of dauK lies a gene encoding a deduced protein that is similar to the methyl esterases.     

Cloning, Expression, and Biological Function of a dTDP-Deoxyglucose Epimerase (gerF) Gene from Streptomyces sp. GERI-155

GERI-155 is a macrolide antibiotic containing two deoxyhexose molecules which has antimicrobial activities against gram-positive bacteria. The deoxyhexose biosynthetic gene cluster of GERI-155 from Streptomyces sp. GERI-155 genome has now been isolated. Four orf were identified and a putative orf, supposed to code for the dTDP-deoxyglucose epimerase gene, was designated as gerF. gerF was expressed in E. coli using recombinant expression vector pHJ3. The recombinant protein expressed in a soluble form. The enzyme was purified by Ni-affinity column using imidazole buffer as eluents. The molecular mass of the expressed protein correlated with the predicted mass (36,000 Da) deduced from the cloned gene sequence data. The purified enzyme produced maltol from dTDP-4-keto-6-deoxyglucose and it was confirmed that the expressed protein was dTDP-deoxyglucose epimerase catalyzing epimerization of C-3 and C-5 or C-3 of dTDP-4-keto-6-deoxyglucose.     

Biosynthesis of the red antibiotic, prodigiosin, in Serratia: identification of a novel 2-methyl-3-n-amyl-pyrrole (MAP) assembly pathway, definition of the terminal condensing enzyme, and implications for undecylprodigiosin biosynthesis in Streptomyces

The biosynthetic pathway of the red-pigmented antibiotic, prodigiosin, produced by Serratia sp. is known to involve separate pathways for the production of the monopyrrole, 2-methyl-3-n-amyl-pyrrole (MAP) and the bipyrrole, 4-methoxy-2,2'-bipyrrole-5-carbaldehyde (MBC) which are then coupled in the final condensation step. We have previously reported the cloning, sequencing and heterologous expression of the pig cluster responsible for prodigiosin biosynthesis in two Serratia sp. In this article we report the creation of in-frame deletions or insertions in every biosynthetic gene in the cluster from Serratia sp. ATCC 39006. The biosynthetic intermediates accumulating in each mutant have been analysed by LC-MS, cross-feeding and genetic complementation studies. Based on these results we assign specific roles in the biosynthesis of MBC to the following Pig proteins: PigI, PigG, PigA, PigJ, PigH, PigM, PigF and PigN. We report a novel pathway for the biosynthesis of MAP, involving PigD, PigE and PigB. We also report a new chemical synthesis of MAP and one of its precursors, 3-acetyloctanal. Finally, we identify the condensing enzyme as PigC. We reassess the existing literature and discuss the significance of the results for the biosynthesis of undecylprodigiosin by the Red cluster in Streptomyces coelicolor A3(2).     

The phosphinomethylmalate isomerase gene pmi, encoding an aconitase-like enzyme, is involved in the synthesis of phosphinothricin tripeptide in Streptomyces viridochromogenes

Streptomyces viridochromogenes Tü494 produces the antibiotic phosphinothricin tripeptide (PTT). In the postulated biosynthetic pathway, one reaction, the isomerization of phosphinomethylmalate, resembles the aconitase reaction of the tricarboxylic acid (TCA) cycle. It was speculated that this reaction is carried out by the corresponding enzyme of the primary metabolism (C. J. Thompson and H. Seto, p. 197-222, in L. C. Vining and C. Stuttard, ed., Genetics and Biochemistry of Antibiotic Production, 1995). However, in addition to the TCA cycle aconitase gene, a gene encoding an aconitase-like protein (the phosphinomethylmalate isomerase gene, pmi) was identified in the PTT biosynthetic gene cluster by Southern hybridization experiments, using oligonucleotides which were derived from conserved amino acid sequences of aconitases. The deduced protein revealed high similarity to aconitases from plants, bacteria, and fungi and to iron regulatory proteins from eucaryotes. Pmi and the S. viridochromogenes TCA cycle aconitase, AcnA, have 52% identity. By gene insertion mutagenesis, a pmi mutant (Mapra1) was generated. The mutant failed to produce PTT, indicating the inability of AcnA to carry out the secondary-metabolism reaction. A His-tagged protein (Hispmi*) was heterologously produced in Streptomyces lividans. The purified protein showed no standard aconitase activity with citrate as a substrate, and the corresponding gene was not able to complement an acnA mutant. This indicates that Pmi and AcnA are highly specific for their respective enzymatic reactions.     

Identification of 8-amino-2,5,7-trihydroxynaphthalene-1,4-dione, a novel intermediate in the biosynthesis of Streptomyces meroterpenoids

Furaquinocin is a natural polyketide-isoprenoid hybrid (meroterpenoid) produced by Streptomyces sp. strain KO-3988. All of the fur genes required for furaquinocin biosynthesis have been cloned, and the heterologous production of furaquinocin has been demonstrated in Streptomyces albus. Here, we report the identification of 8-amino-2,5,7-trihydroxynaphthalene-1,4-dione (8-amino-flaviolin) produced by the S. albus heterologous expression of the three contiguous genes encoding type III polyketide synthase (Fur1), monooxygenase (Fur2), and aminotransferase (Fur3) in the furaquinocin biosynthetic gene cluster. An S. albus transformant (S. albus/pWHM-Fur2_del3) harboring the fur gene cluster and lacking the fur3 gene did not produce furaquinocin, whereas furaquinocin production was restored when 8-amino-flaviolin was added to the culture medium of S. albus/pWHM-Fur2_del3. These results demonstrate that Fur3 aminotransferase is essential for furaquinocin biosynthesis and that 8-amino-flaviolin is an early-stage intermediate in furaquinocin biosynthesis. We propose that the biosynthetic pathway generating 8-amino-flaviolin is the common route for the biosynthesis of Streptomyces meroterpenoids.     

Identification of the gene encoding an N-acetylpuromycin N-acetylhydrolase in the puromycin biosynthetic gene cluster from Streptomyces alboniger.

The biologically inactive compound N-acetylpuromycin is the last intermediate of the puromycin antibiotic biosynthetic pathway in Streptomyces alboniger. Culture filtrates from either this organism or Streptomyces lividans transformants harboring the puromycin biosynthetic gene cluster cloned in low-copy-number cosmids contained an enzymic activity which hydrolyzes N-acetylpuromycin to produce the active antibiotic. A gene encoding the deacetylase enzyme was located at one end of this cluster, subcloned in a 2.5-kb DNA fragment, and expressed from a high-copy-number plasmid in S. lividans.