Induction of secondary metabolite production by hygromycin B and identification of the 1233A biosynthetic gene cluster with a self-resistance gene.

We found that the protein synthesis inhibitor hygromycin B induced the production of secondary metabolites, including lucilactaene, NG-391, fusarubin, 1233A, and 1233B, in the filamentous fungus, Fusarium sp. RK97-94. We identified the biosynthetic gene cluster for 1233A, an HMG-CoA synthase inhibitor. The biosynthetic gene cluster consisted of four genes, one of which was involved in conferring self-resistance to 1233A.

Biosynthetic gene cluster identification and biological activity of lucilactaene from Fusarium sp. RK97-94.

We identified the biosynthetic gene cluster for lucilactaene, a cell cycle inhibitor from a filamentous fungus Fusarium sp. RK 97-94. The luc1 knockout strain accumulated demethylated analogs, indicating the involvement of Luc1 methyltransferase in lucilactaene biosynthesis. Lucilactaene showed potent antimalarial activity. Our data suggested that methylation and ether ring formation are essential for its potent antimalarial activity.

Structure-function analyses of cytochrome P450revI involved in reveromycin A biosynthesis and evaluation of the biological activity of its substrate, reveromycin T.

Numerous cytochrome P450s are involved in secondary metabolite biosynthesis. The biosynthetic gene cluster for reveromycin A (RM-A), which is a promising lead compound with anti-osteoclastic activity, also includes a P450 gene, revI. To understand the roles of P450revI, we comprehensively characterized the enzyme by genetic, kinetic, and structural studies. The revI gene disruptants (ΔrevI) resulted in accumulation of reveromycin T (RM-T), and revI gene complementation restored RM-A production, indicating that the physiological substrate of P450revI is RM-T. Indeed, the purified P450revI catalyzed the C18-hydroxylation of RM-T more efficiently than the other RM derivatives tested. Moreover, the 1.4 Å resolution co-crystal structure of P450revI with RM-T revealed that the substrate binds the enzyme with a folded compact conformation for C18-hydroxylation. To address the structure-enzyme activity relationship, site-directed mutagenesis was performed in P450revI. R190A and R81A mutations, which abolished salt bridge formation with C1 and C24 carboxyl groups of RM-T, respectively, resulted in significant loss of enzyme activity. The interaction between Arg(190) and the C1 carboxyl group of RM-T elucidated why P450revI was unable to catalyze both RM-T 1-methyl ester and RM-T 1-ethyl ester. Moreover, the accumulation of RM-T in ΔrevI mutants enabled us to characterize its biological activity. Our results show that RM-T had stronger anticancer activity and isoleucyl-tRNA synthetase inhibition than RM-A. However, RM-T showed much less anti-osteoclastic activity than RM-A, indicating that hemisuccinate moiety is important for the activity. Structure-based P450revI engineering for novel hydroxylation and subsequent hemisuccinylation will help facilitate the development of RM derivatives with anti-osteoclast activity.

RK-1355A and B, novel quinomycin derivatives isolated from a microbial metabolites fraction library based on NPPlot screening.

Two novel quinomycin derivatives, RK-1355A (1) and B (2), and one known quinomycin derivative, UK-63,598 (3), were isolated from a microbial metabolites fraction library of Streptomyces sp. RK88-1355 based on Natural Products Plot screening. The structural elucidation of 1 and 2 was established through two-dimensional NMR and mass spectrometric measurements. They belong to a class of quinomycin antibiotics family having 3-hydroxyquinaldic acid and a sulfoxide moiety. They are the first examples for natural products as a quinoline type quinomycin having a sulfoxide on the intramolecular cross-linkage. They showed potent antiproliferative activities against various cancer cell lines and they were also found to exhibit moderate antibacterial activity.

Isolation of new polyketide metabolites, linearolides A and B, from Streptomyces sp. RK95-74.

Although all Streptomyces strains are now thought to have 20-30 gene clusters for secondary metabolite biosynthesis, we cannot actually identify so many kinds of metabolites from one strain by conventional methods. Using Streptomyces sp. RK95-74, previously found as a cytotrienin producer, we searched new metabolites other than cytotrienin derivatives. Following the cultivation with new media and the peak-guided fractionation, we have found new compounds with new polyketide scaffold, named linearolides A and B.

Spirotoamides A and B, novel 6,6-spiroacetal polyketides isolated from a microbial metabolite fraction library.

Two new 6,6-spiroacetal polyketides, spirotoamides A (1) and B (2), were isolated from a microbial metabolite fraction library of Streptomyces griseochromogenes JC82-1223 by screening of structurally unique compounds based on a search of spectral database. The fraction library was constructed using a systematic separation method to efficiently discover new metabolites from microbial sources such as actinomycetes and fungi. The structures of 1 and 2 were elucidated by 2D-NMR and mass spectrometric measurements. They belong to a class of polyketides, and contain a 6,6-spiroacetal core structure and a carboxamide group. The biosynthetic pathway of 1 and 2 is discussed in the text.

Reveromycin A biosynthesis uses RevG and RevJ for stereospecific spiroacetal formation.

Spiroacetal compounds are ubiquitous in nature, and their stereospecific structures are responsible for diverse pharmaceutical activities. Elucidation of the biosynthetic mechanisms that are involved in spiroacetal formation will open the door to efficient generation of stereospecific structures that are otherwise hard to synthesize chemically. However, the biosynthesis of these compounds is poorly understood, owing to difficulties in identifying the responsible enzymes and analyzing unstable intermediates. Here we comprehensively describe the spiroacetal formation involved in the biosynthesis of reveromycin A, which inhibits bone resorption and bone metastases of tumor cells by inducing apoptosis in osteoclasts. We performed gene disruption, systematic metabolite analysis, feeding of labeled precursors and conversion studies with recombinant enzymes. We identified two key enzymes, dihydroxy ketone synthase and spiroacetal synthase, and showed in vitro reconstruction of the stereospecific spiroacetal structure from a stable acyclic precursor. Our findings provide insights into the creation of a variety of biologically active spiroacetal compounds for drug leads.

Genetic safeguard against mycotoxin cyclopiazonic acid production in Aspergillus oryzae.

Aspergillus oryzae is a fungus widely used in traditional Japanese fermentation industries. Its inability to produce mycotoxins, due to mutation or transcriptional repression of the genes responsible for their biosynthesis, is consistent with the hypothesis that A. oryzae is a domesticated species derived from A. flavus, a wild species that is a well-known producer of aflatoxin. In contrast, the cyclopiazonic acid (CPA) biosynthetic gene (cpa) cluster in A. oryzae contains genes that have been lost in A. flavus. Through targeted gene inactivation, isolation of the corresponding metabolite, and evaluation of biological activity of the metabolite, we demonstrated that an A. oryzae-specific gene-cpaH-mediates the conversion of CPA into the less toxic 2-oxocyclopiazonic acid, a new analogue of CPA. The detoxifying properties of cpaH, which have been lost in the A. flavus pathway, reflect the relationship of the two species.

Furaquinocins I and J: novel polyketide isoprenoid hybrid compounds from Streptomyces reveromyceticus SN-593.

Two novel furaquinocin (FQ) analogues, I (1) and J (2), were isolated from Streptomyces reveromyceticus SN-593 strain NRM2. Their structures were elucidated by MS and NMR analyses. Similar to the previously described FQ D (3), both 1 and 2 possessed a dihydrofuran ring fused to a polyketide naphthoquinone skeleton. The main difference between 1, 2 and 3 was the type of residue attached to C-13; these were a carboxyl, a carboxamide and a methyl residue, respectively.

Verticilactam, a new macrolactam isolated from a microbial metabolite fraction library.

Systematic isolation of microbial metabolites has been performed to construct microbial metabolite libraries or fraction libraries. A novel macrolactam, verticilactam (1), was isolated from a library of Streptomyces spiroverticillatus JC-8444. The structure was determined on the basis of NMR and mass spectrometric measurements. 1 had a unique 16-membered macrolactam skeleton including a ß-keto-amide moiety.

Biochemical characterization of a novel indole prenyltransferase from Streptomyces sp. SN-593.

Genome sequencing of Streptomyces species has highlighted numerous potential genes of secondary metabolite biosynthesis. The mining of cryptic genes is important for exploring chemical diversity. Here we report the metabolite-guided genome mining and functional characterization of a cryptic gene by biochemical studies. Based on systematic purification of metabolites from Streptomyces sp. SN-593, we isolated a novel compound, 6-dimethylallylindole (DMAI)-3-carbaldehyde. Although many 6-DMAI compounds have been isolated from a variety of organisms, an enzyme catalyzing the transfer of a dimethylallyl group to the C-6 indole ring has not been reported so far. A homology search using known prenyltransferase sequences against the draft sequence of the Streptomyces sp. SN-593 genome revealed the iptA gene. The IptA protein showed 27% amino acid identity to cyanobacterial LtxC, which catalyzes the transfer of a geranyl group to (-)-indolactam V. A BLAST search against IptA revealed much-more-similar homologs at the amino acid level than LtxC, namely, SAML0654 (60%) from Streptomyces ambofaciens ATCC 23877 and SCO7467 (58%) from S. coelicolor A3(2). Phylogenetic analysis showed that IptA was distinct from bacterial aromatic prenyltransferases and fungal indole prenyltransferases. Detailed kinetic analyses of IptA showed the highest catalytic efficiency (6.13 min(-1) microM(-1)) for L-Trp in the presence of dimethylallyl pyrophosphate (DMAPP), suggesting that the enzyme is a 6-dimethylallyl-L-Trp synthase (6-DMATS). Substrate specificity analyses of IptA revealed promiscuity for indole derivatives, and its reaction products were identified as novel 6-DMAI compounds. Moreover, DeltaiptA mutants abolished the production of 6-DMAI-3-carbaldehyde as well as 6-dimethylallyl-L-Trp, suggesting that the iptA gene is involved in the production of 6-DMAI-3-carbaldehyde.

Deamino-hydroxy-phoslactomycin B, a biosynthetic precursor of phoslactomycin, induces myeloid differentiation in HL-60 cells.

During the screening for novel differentiation inducers, we found that a culture broth of Streptomyces sp. HK-803 induced myeloid differentiation of HL-60 cells. The active substance was identified as deamino-hydroxy-phoslactomycin B (HPLM) by mass spectrometry, and synthesized HPLM also induced the differentiation of HL-60 cells. HPLM showed greater inhibition of protein phosphatase 2A (PP2A) activity than phoslactomycin B (PLMB); however, PLMB and okadaic acid did not induce differentiation. Moreover, treatment with ATRA and 1alpha, 25(OH)2D3 induced retinoic acid receptor-beta and 1alpha, 25(OH)2D3 24-hydroxylase, respectively, whereas HPLM did not, suggesting that HPLM is a novel differentiation inducer.

Identification of cytochrome P450s required for fumitremorgin biosynthesis in Aspergillus fumigatus.

Fumitremorgin C, a diketopiperazine mycotoxin produced by Aspergillus fumigatus, is a potent and specific inhibitor of breast cancer resistance protein (BCRP). Elucidation of the fumitremorgin C biosynthetic pathway provides a strategy for new drug design. A structure-activity relationship study based on metabolites related to the ftm gene cluster revealed that the process most crucial for inhibitory activity against BCRP was cyclization to form fumitremorgin C. To determine the gene involved in the cyclization reaction, targeted gene inactivation was performed with candidate genes in the ftm cluster. Analysis of the gene disruptants allowed us to identify ftmE, one of the cytochrome P450 genes in the cluster, as the gene responsible for the key step in fumitremorgin biosynthesis. Additionally, we demonstrated that the other two cytochrome P450 genes, ftmC and ftmG, were involved in hydroxylation of the indole ring and successive hydroxylation of fumitremorgin C, respectively.

Fungal metabolite, epoxyquinol B, crosslinks proteins by epoxy-thiol conjugation.

Epoxyquinol B (EPQB) is a fungal metabolite, containing two alpha,beta-epoxy ketones. We previously showed that EPQB inhibited the signal transduction involved in angiogenesis through the binding to cysteine residues of receptor kinases. However, the inhibitory mechanism was undefined. In this report, we found that one EPQB molecule is covalently bound to two L-cysteine molecules through two epoxide residues on EPQB. Furthermore, EPQB crosslinked binding proteins through the cysteine residues. These results suggest that EPQB inhibits receptor kinases by crosslinking with other protein or by intramolecular crosslinking.

SNA-60-367 components, new peptide enzyme inhibitors of aromatase: structure of the fatty acid side chain and amino acid sequence by mass spectrometry.

SNA-60-367 components, new peptide enzyme inhibitors of aromatase, were isolated from the culture broth of soil bacterium, Bacillus sp. SNA-60-367. These inhibitors are a family of acylated decapeptides that differ from each other in terms of amino acid composition and the nature of the fatty acid side chain. The structures of the fatty acid moieties were shown to be (3-hydroxy)heptadecanoic acid and (3-hydroxy)hexadecanoic acid that possess normal-, iso- or anteiso-type alkyl groups. The amino acid sequence of the open form of the lactone ring of the acylpeptides is RCO-L-Glu-D-Orn-L(or D)-Tyr3-D-allo-Thr-L-Glu-D-X1 (Ala, Aba or Val)-L-Pro-L-Gln-D(or L)-Tyr-L-X2(10)(Ile or Val)-OH. The lactone ring of SNA-60-367 components is formed between Tyr3 and X2(10).