市瀬 浩志

The increasing prevalence of dermatophyte resistance to terbinafine, a key drug in the treatment of dermatophytosis, represents a significant obstacle to treatment. Trichophyton rubrum is the most commonly isolated fungus in dermatophytosis. In T. rubrum, we identified TERG_07844, a gene encoding a previously uncharacterized putative protein kinase, as an ortholog of budding yeast Saccharomyces cerevisiae polyamine transport kinase 2 (Ptk2), and found that T. rubrum Ptk2 (TrPtk2) is involved in terbinafine tolerance. In both T. rubrum and S. cerevisiae, Ptk2 knockout strains were more sensitive to terbinafine compared with the wild types, suggesting that promotion of terbinafine tolerance is a conserved function of fungal Ptk2. Pma1 is activated through phosphorylation by Ptk2 in S. cerevisiae. Overexpression of T. rubrum Pma1 (TrPma1) in T. rubrum Ptk2 knockout strain (ΔTrPtk2) suppressed terbinafine sensitivity, suggesting that the induction of terbinafine tolerance by TrPtk2 is mediated by TrPma1. Furthermore, omeprazole, an inhibitor of plasma membrane proton pump Pma1, increased the terbinafine sensitivity of clinically isolated terbinafine-resistant strains. These findings suggest that, in dermatophytes, the TrPtk2-TrPma1 pathway plays a key role in promoting intrinsic terbinafine tolerance and may serve as a potential target for combinational antifungal therapy against terbinafine-resistant dermatophytes.

A plethora of dimeric natural products exist with diverse chemical structures and biological activities. A major strategy for dimerization is aryl coupling reactions catalyzed by cytochrome P450 or laccase. Actinorhodin (ACT) from Streptomyces coelicolor has a dimeric pyranonaphthoquinone structure connected by a C-C bond. Here, we identified a NmrA-family dimerizing enzyme, ActVA-ORF4, and a cofactor independent oxidase, ActVA-ORF3, both involved in the last step of ACT biosynthesis. ActVA-ORF4 is a unique  NAD(P)H-dependent enzyme that catalyzes the inter-molecular C-C bond formation using 8-hydroxydihydrokalafungin (DHK-OH) as the sole substrate. On the other hand, ActVA-ORF3 was found to be a quinone-forming enzyme that produces the coupling substrate, DHK-OH, and the final product, ACT. Consequently, the functional assignment of all essential enzymes in ACT biosynthesis was completed, which would be a landmark in our understanding of the entire biosynthetic pathway for one of the best-known model natural products, ACT.

Actinorhodin (ACT) is a benzoisochromanequinone antibiotic produced by Streptomyces coelicolor A3(2), which has served as a favored model organism for comprehensive studies of antibiotic biosynthesis and its regulation. (S)-DNPA undergoes various modifications as an intermediate in the ACT biosynthetic pathway, including enoyl reduction to DDHK. It has been suggested that actVI-ORF2 encodes an enoyl reductase (ER). However, its function has not been characterized in vitro. In this study, biochemical analysis of recombinant ActVI-ORF2 revealed that (S)-DNPA is converted to DDHK in a stereospecific manner with NADPH acting as a cofactor. (R)-DNPA was also reduced to 3-epi-DDHK with the comparable efficacy as (S)-DNPA, suggesting that the stereospecificity of ActVI-ORF2 was not affected by the stereochemistry at the C-3 of DNPA. ActVI-ORF2 is a new example of a discrete ER, which is distantly related to known ERs according to phylogenetic analysis.

Nuclear factor-kappa B (NF-κB) signaling is an intracellular signaling pathway involved in inflammatory responses and the pathogenesis of various cancers, including ependymoma, which is a rare and chemotherapy-resistant glioma. Several isoforms of fusion proteins that consist of a nuclear protein, zinc finger translocation associated (ZFTA), and RELA (ZFTA-RELA), an NF-κB-signaling effector transcription factor, cause excessive activation of the NF-κB signaling pathway and result in supratentorial ependymomas (ST-EPN-RELA). As inhibitors of NF-κB activity induced by ZFTA-RELA are expected to be therapeutic agents for ST-EPN-RELA, we established an NF-κB responsive luciferase reporter cell line that expresses the most common isoform of ZFTA-RELA in a doxycycline-dependent manner. Using this reporter cell line, we screened fungus extracts for compounds that inhibit the NF-κB activity induced by ZFTA-RELA expression and identified aszonalenin, an alkaloid from Aspergillus novofumigatus. We also purified analogs of aszonalenin, namely acetylaszonalenin and epi-aszonalenin B and C. In a luciferase assay using cells constitutively expressing luciferase (counter assay), acetylaszonalenin and epi-aszonalenin C showed non-specific inhibition of the luciferase activity. Aszonalenin and epi-aszonalenin B inhibited the NF-κB responsive luciferase activity by expressing ZFTA-RELA more strongly than the luciferase activity in the counter assay. The upregulation of endogenous NF-κB responsive genes, such as CCND1, ICAM1, and L1CAM, by ZFTA-RELA expression was inhibited by epi-aszonalenin B, but not by aszonalenin. This study suggests that epi-aszonalenin B may be a lead compound for the therapeutic development of ST-EPN-RELA.

生薬成分のTLC分析中の呈色反応に関する基礎研究を実習教育に応用し、実際の体験が学修効果の向上に及ぼす影響について検討した。薬学科所属の3年生124名を2群に分け、実習内容を解説する際に、サンシシからgeniposideを単離・精製する工程でTLC板上に検出される青色呈色物質gardenosideの構造情報を与えた群と、与えなかった群のレポート内容を比較した。その結果、情報を与えた群ではTLCのスポットに関する記載および色調・構造に関する用語の記載、化合物名や構造の記載、色調変化の原因に対する考察などが有意に増加し、学生が構造と物性変化などの実習結果についてより深く考察するようになったことが推察された。生薬学分野の基礎研究で得た知見を薬学教育に応用することは「化合物の構造と物性の関係性」を理解する機会となり、学修効果の向上につながると考えられた。

ブラジル産ゴオウ16検体、オーストラリア産ゴオウ5検体、コロンビア産ゴオウ1検体を用いた。ODSカラムを用いたHPLCによるビリルビン定量法を確立した。標準溶液につき6回繰り返し分析を行い、ピーク面積値についてシステムの再現性を確認し、相対標準偏差は0.48%であった。定量法の注意点として、ビリルビンは光により分解するため、操作時には充分な遮光が必要であった。また、試験環境温度が30℃を超える条件下では、標準溶液のピーク面積が経時的に低下し、ビリルビンの分解が促進していく現象が見られたため、常温(15〜25℃)で行うべきである。ゴオウ市場品22検体について、HPLCによるビリルビン定量法と日局17に規定されている成分含量測定法による結果の相関関係を確認し、両者には良好な相関が見られた。日局17成分含量測定法による結果がHPLCによるビリルビン定量法の結果より高い値が得られた理由として、HPLCによる定量法ではビリルビンのみを測定しているのに対し、成分含量測定法ではクロロホルムに溶解する全ての成分を測定しているためと考えられた。

The biosynthesis of aromatic polyketides derived from type II polyketide synthases (PKSs) is complex, and it is not uncommon that highly similar gene clusters give rise to diverse structural architectures. The act biosynthetic gene cluster (BGC) of the model actinomycete Streptomyces coelicolor A3(2) is an archetypal type II PKS. Here we show that the act BGC also specifies the aromatic polyketide GTRI-02 (1) and propose a mechanism for the biogenesis of its 3,4-dihydronaphthalen-1(2H)-one backbone. Polyketide 1 was also produced by Streptomyces sp. MBT76 after activation of the act-like qin gene cluster by overexpression of the pathway-specific activator. Mining of this strain also identified dehydroxy-GTRI-02 (2), which most likely originated from dehydration of 1 during the isolation process. This work shows that even extensively studied model gene clusters such as act of S. coelicolor can still produce new chemistry, offering new perspectives for drug discovery.

Mining of microbial genomes has revealed that actinomycetes harbor far more biosynthetic potential for bioactive natural products than anticipated. Activation of (cryptic) biosynthetic gene clusters and identification of the corresponding metabolites has become a focal point for drug discovery. Here, we applied NMR-based metabolomics combined with bioinformatics to identify novel C-glycosyl-pyranonaphthoquinones in Streptomyces sp. MBT76 and to elucidate the biosynthetic pathway. Following activation of the cryptic qin gene cluster for a type II polyketide synthase (PKS) by constitutive expression of its pathway-specific activator, bioinformatics coupled to NMR profiling facilitated the chromatographic isolation and structural elucidation of qinimycins A-C (1-3). The intriguing structural features of the qinimycins, including 8-C-glycosylation, 5,14-epoxidation, and 13-hydroxylation, distinguished these molecules from the model pyranonaphthoquinones actinorhodin, medermycin, and granaticin. Another novelty lies in the unusual fusion of a deoxyaminosugar to the pyranonaphthoquinone backbone during biosynthesis of the antibiotics BE-54238 A and B (4, 5). Qinimycins showed weak antimicrobial activity against Gram-positive bacteria. Our work shows the utility of combining bioinformatics, targeted activation of cryptic gene clusters, and NMR-based metabolic profiling as an effective pipeline for the discovery of microbial natural products with distinctive skeletons.

Type II polyketide synthases iteratively generate a nascent polyketide thioester of the acyl carrier protein (ACP) this is structurally modified to produce an ACP-free intermediate towards the final metabolite. However, the timing of ACP off-loading is not well defined because of the lack of an apparent thioesterase (TE) among relevant biosynthetic enzymes. Here, ActIV, which had been assigned as a second ring cyclase (CYC) in actinorhodin (ACT) biosynthesis, was shown to possess TE activity in vitro with a model substrate, anthraquinone-2-carboxylic acid-N-acetylcysteamine. In order to investigate its function further, the ACT biosynthetic pathway in Streptomyces coelicolor A3(2) was reconstituted in vitro in a stepwise fashion up to (S)-DNPA, and the product of ActIV reaction was characterized as an ACP-free bicyclic intermediate. These findings indicate that ActIV is a bifunctional CYC-TE and provide clear evidence for the release timing of the intermediate from the ACP anchor.

A new shunt product was isolated from a actVA4 mutant strain of Streptomyces coeliclor A3(2). Its structure was elucidated based on stectrocipic data. Its biosynthetic implication in the actinorhodin pawathway was also presented.

Information on gene clusters for natural product biosynthesis is accumulating rapidly because of the current boom of available genome sequencing data. However, linking a natural product to a specific gene cluster remains challenging. Here, we present a widely applicable strategy for the identification of gene clusters for specific natural products, which we name natural product proteomining. The method is based on using fluctuating growth conditions that ensure differential biosynthesis of the bioactivity of interest. Subsequent combination of metabolomics and quantitative proteomics establishes correlations between abundance of natural products and concomitant changes in the protein pool, which allows identification of the relevant biosynthetic gene cluster. We used this approach to elucidate gene clusters for different natural products in Bacillus and Streptomyces, including a novel juglomycin-type antibiotic. Natural product proteomining does not require prior knowledge of the gene cluster or secondary metabolite and therefore represents a general strategy for identification of all types of gene clusters.

We previously demonstrated that ethyl acetate extracts of Kaempferia parviflora Wall. Ex Baker (KPE) improve insulin resistance in TSOD mice and showed that its components induce differentiation and adipogenesis in 3T3-L1 preadipocytes. The present study was undertaken to examine whether KPE and its isolated twelve components suppress further lipid accumulation in 3T3-L1 mature adipocytes. KPE reduced intracellular triglycerides in mature adipocytes, as did two of its components, 3,5,7,3',4'-pentamethoxyflavone and 5,7,4'-trimethoxyflavone. Shrinkage of lipid droplets in mature adipocytes was observed, and mRNA expression levels of adipose tissue triglyceride lipase (ATGL) and hormone-sensitive lipase (HSL) were up-regulated by these two polymethoxyflavonoids (PMFs). Furthermore, the protein expression level of ATGL and the release level of glycerol into the cell culture medium increased. In contrast, the peroxisome proliferator-activated receptor γ (PPARγ) agonist, troglitazone, did not decrease intracellular triglycerides in mature adipocytes, and the mRNA expression level of PPARγ was not up-regulated in mature adipocytes treated with the two active PMFs. Therefore, suppression of lipid accumulation in mature adipocytes is unlikely to be enhanced by transcriptional activation of PPARγ. These results suggest that KPE and its active components enhance lipolysis in mature adipocytes by activation of ATGL and HSL independent of PPARγ transcription, thus preventing adipocyte hypertrophy. On the other hand, the full hydroxylated flavonoid quercetin did not show the suppressive effects of lipid accumulation in mature adipocyte in the same conditions. Consequently, methoxy groups in the flavones are important for the activity.

Garlic (Allium sativum L.) has been used worldwide as a food and for medicinal purposes since early times. Garlic cultivars exhibit considerable morphological diversity despite the fact that they are mostly sterile and are grown only by vegetative propagation of cloves. Considerable recombination occurs in garlic genomes, including the genes involved in secondary metabolites. We examined the genomic DNAs (gDNAs) from garlic, encoding alliinase, a key enzyme involved in organosulfur metabolism in Allium plants. The 1.7-kb gDNA fragments, covering three exons (2, 3, and 4) and all four introns, were amplified from total DNAs prepared from garlic samples produced in Asia and Europe, leading to 73 sequences in total: Japan (JPN), China (CHN), India (IND), Spain (ESP), and France (FRA). The exon sequences were highly conserved among all the sequences, probably reflecting the fully functional alliinase associated with the flavor quality. Distinct intraspecific variations were detected for all four intron sequences, leading to the haplotype classifications. A close relationship between JPN and CHN was observed for all four introns, whereas IND showed a more divergent distribution. ESP and FRA afforded clearly different variants compared with those from Asian sequences. The present study provides information that could be useful in the development of an additional molecular marker for garlic authentication and quality control.

Actinorhodin (ACT) produced by Streptomyces coelicolor A3(2) belongs to the benzoisochromanequinone (BIQ) class of antibiotics. ActVA-ORF5, a flavin-dependent monooxygenase (FMO) essential for ACT biosynthesis, forms a two-component enzyme system in combination with a flavin:NADH oxidoreductase, ActVB. The genes for homologous two-component FMOs are found in the biosynthetic gene clusters for two other BIQs, granaticin (GRA) and medermycin (MED), and a closely related antibiotic, alnumycin (ALN). Our functional analysis of these FMOs (ActVA-ORF5, Gra-ORF21, Med-ORF7, and AInT) in S. coelicolor unambiguously demonstrated that ActVA-ORF5 and Gra-ORF21 are bifunctional and capable of both p-quinone formation at C-6 in the central ring and C-8 hydroxylation in the lateral ring, whereas Med-ORF7 catalyzes only p-quinone formation. No p-quinone formation on a BIQ substrate was observed for AInT, which is involved in lateral p-quinone formation in ALN.

An oxygenated derivative of dihydrokalafungin (DHK) was isolated from a deletion mutant of the actVA-ORF4 gene involved in the biosynthesis of a dimeric benzoisochromanequinone (BIQ) antibiotic, actinorhodin (ACT), in Streptomyces coelicolor A3(2). Spectroscopic analysis elucidated its structure as 8-hydroxy-DHK, corresponding to the monomeric unit of ACT. Further metabolite analysis identified its related compound, clearly derived from the reduction of 8-hydroxy-DHK. The structures of these metabolites indicate the essential role of ActVA-ORF4 in ACT biosynthesis, specifically in dimerization of a BIQ intermediate via C-C bond formation. (c) 2012 Elsevier Ltd. All rights reserved.

We previously reported that Kaempferia parviflora WALL. ex BAKER (KP) and its ethyl acetate extract (KPE) improve various metabolic disorders in obesity-model mice. However the mechanism is not certain, and, in this study, in order to elucidate the mechanism of the suppressive effect of KP on fat accumulation, we focused on adipocytes, which are closely linked to metabolic diseases. The finding was that KPE and its components, 3,5,7,4′- tetramethoxyflavone and 3,5,7,3′,4′-pentamethoxyflavone, strongly induced differentiation of 3T3-L1 preadipocytes to adipocytes. The above two polymethoxyflavonoids (PMFs) also induced adiponectin mRNA levels, and release of adiponectin into the medium. In addition, these PMFs enhanced the expression of peroxisome proliferator-activated receptor γ (PPARγ), but did not show PPARγ ligand activity. We then investigated the expression of the differentiation-regulator located upstream of PPARγ. Expression of CCAAT/enhancer-binding protein (C/EBP) β and -δ mRNA, a transcriptional regulator of PPARγ, was induced, and expression of GATA-2 mRNA, a down-regulator of adipogenesis, was suppressed by these PMFs. These functions of the KP PMFs that enhance adipogenesis and secretion of adiponectin are, to some extent at least, involved in the mechanisms of anti-metabolic disorders effects. © 2012 The Pharmaceutical Society of Japan.

The biosynthetic gene cluster of the aromatic polyketide antibiotic actinorhodin (ACT) in Streptomyces coelicolor A3(2) carries a pair of genes, actVA-ORF5 and actVB, that encode a two-component flavin-dependent monooxygenase (FMO). Our previous studies have demonstrated that the ActVA-ORF5/ActVB system functions as a quinone-forming C-6 oxygenase in ACT biosynthesis. Furthermore, we found that this enzyme system exhibits an additional oxygenation activity with dihydrokalafungin (DHK), a proposed intermediate in the ACT biosynthetic pathway, and generates two reaction products. These compounds were revealed to be monooxygenated derivatives of kalafungin, which is spontaneously formed through oxidative lactonization of DHK. Their absolute structures were elucidated from their NMR spectroscopic data and by computer modeling and X-ray crystallography as (5S,14R)-epoxykalafungin and (5R,14S)-epoxykalafungin, demonstrating an additional epoxyquinone-forming activity of the ActVA-ORF5/ActVB system in vitro.

New red pigments were isolated from a lichen thallus, Lethariella sinensis by Wei & Jiang. The structures of the red pigments, rubrosinensiquinones A (1), B (2), and C (3), were determined by spectroscopic analyses.

Streptomyces sp. AM-7161 is a producer of an aromatic polyketide medermycin with strong antibacterial and antitumor activity. It has been inefficient to perform genetic manipulations in this strain, which heavily hinders the genetic analysis of some interesting problems concerning tailoring modifications in medermycin biosynthesis. Here, condition optimizations of sporulation and mycelium growth of this strain as well as protoplast preparation and regeneration were conducted systematically. Based on these results, protoplast transformation system was established, and two types of foreign plasmids (integrative and auto-replicating) were efficiently introduced into this strain. Additionally, a conjugation system to mediate plasmid transfer between Escherichia con and Streptomyces sp. AM-7161 was also optimized and established. These results provide the practical procedures to perform more convenient genetic analysis of medermycin biosynthesis in this strain.

All known benzoisochromanequinone (BIQ) biosynthetic gene clusters carry a set of genes encoding a two-component monooxygenase homologous to the ActVA-ORF5/ActVB system for actinorhodin biosynthesis in Streptomyces coelicolor A3(2). Here, we conducted molecular genetic and biochemical studies of this enzyme system. Inactivation of actVA-ORF5 yielded a shunt product, actinoperylone (ACPL), apparently derived from 6-deoxy-dihydro-kalafungin. Similarly, deletion of actVB resulted in accumulation of ACPL, indicating a critical role for the monooxygenase system in C-6 oxygenation, a biosynthetic step common to all BIQ biosyntheses. Furthermore, in vitro, we showed a quinone-forming activity of the ActVA-ORF5/ActVB system in addition to that of a known C-6 monooxygenase, ActVA-ORF6, by using emodinanthrone as a model substrate. Our results demonstrate that the act gene cluster encodes two alternative routes for quinone formation by C-6 oxygenation in BIQ biosynthesis.

Actinorhodin, an antibiotic produced by Streptomyces coelicolor, is exported from the cell by the ActA efflux pump. actA is divergently transcribed from actR, which encodes a TetR-like transcriptional repressor. We showed previously that ActR represses transcription by binding to an operator from the actA/actR intergenic region. Importantly, actinorhodin itself or various actinorhodin biosynthetic intermediates can cause ActR to dissociate from its operator, leading to derepression. This suggests that ActR may mediate timely self-resistance to an endogenously produced antibiotic by responding to one of its biosynthetic precursors. Here, we report the structural basis for this precursor-mediated derepression with crystal structures of homodimeric ActR by itself and in complex with either actinorhodin or the actinorhodin biosynthetic intermediate (S)-DNPA [4-dihydro-9-hydroxy-1-methyl-10-oxo-3-H-naphtho-[2,3-c]-pyran-3-(S)-acetic acid]. The ligand-binding tunnel in each ActR monomer has a striking hydrophilic/hydrophobic/hydrophilic arrangement of surface residues that accommodate either one hexacyclic actinorhodin molecule or two back-to-back tricyclic (S)-DNPA molecules. Moreover, our work also reveals the strongest structural evidence to date that TetR-mediated antibiotic resistance may have been acquired from an antibiotic-producer organism. (c) 2007 Elsevier Ltd. All rights reserved.

A novel shunt product, actinoperylone, has been isolated from a deletion mutant of the actVA-ORF5 and ORF6 genes involved in the biosynthesis of a benzoisochromanequinone (BIQ) antibiotic actinorhodin (ACT) in Streptomyces coelicolor A3(2). Spectroscopic analysis revealed its perylenequinone-type skeleton with the four chiral centers, obviously derived from the dimerization of an ACT intermediate. The structure of actinoperylone indicates the essential role of ActVA-0RF5 in the oxygen introduction at C-6, which is common to the formation of BIQ chromophore. The present results also agree with the distribution of the actVA-ORF5 homologues in all known BIQ biosynthetic clusters in streptomycetes. (c) 2007 Elsevier Ltd. All rights reserved.

放線菌抗生物質actinorhodin(ACT)生合成遺伝子クラスターには <I>act</I>VA‐5の相同遺伝子があるのに対して <I>act</I>VA‐6の相同遺伝子は存在しない。新たにactVA-5,6 の遺伝子破壊体を作成し、表現型や代謝産物のプロフィール解析から <I>in vivo</I> での両酵素の機能を検討した。翻訳共役している <I>act</I>VA-5,6 を併せて破壊した菌体は ACT の代わりに黄色色素を生産し、新規shunt productである actinoperyloneを同定した。市瀬は本研究の研究総括者として、研究指導並びに論文執筆に関わった。

Two new compounds, 8'-phospho derivatives of amicoumacins A and B, were isolated from the culture broth of a strain of Bacillus pumilus together with amicoumacins A and B. Their structures were elucidated on the basis of spectroscopic methods and alkaline phosphatase treatments. Comparison of the antibacterial activities against methicillin-resistant Staphylococcus aureus (MRSA) of these compounds suggested that C-8' hydroxyl and C-12' amide group of amicoumacin A played a critical role for anti-MRSA activity.

Actinorhodin (ACT) produced by Streptomyces coelicolor A3(2) is an aromatic polyketide antibiotic, whose basic carbon skeleton is derived from type II polyketide synthase (PKS). Although an acyl carrier protein (ACP) serves as an anchor of nascent intermediates during chain elongation in the type II PKS complex, it generally remains unknown when an ACP-free intermediate is released from the complex to post-PKS modification ("tailoring") steps. In ACT biosynthesis, a stereospecific ketoreductase (RED1) encoded by actVI-ORF1 reduces the 3 beta-keto group of a proposed bicyclic intermediate to an (S) secondary alcohol. The bicyclic intermediate is formed from the steps of PKS and its closely associated enzymes and lies at the interface toward ACT-tailoring steps. To clarify whether RED1 recognizes the ACP-bound bicyclic intermediate or the ACP-free bicyclic intermediate, recombinant RED1 was purified for enzymatic characterization. RED1 was heterologously expressed in Escherichia coli and purified using Ni-chelate and gel filtration column chromatographies to homogeneity in soluble form. Enzymatic studies in vitro on RED1 with synthetic analogues, in place of an unstable bicyclic intermediate, showed that RED1 recognizes 3-oxo-4-naphthylbutyric acid (ONBA) as a preferred substrate and not its N-acetylcysteamine thioester. This strongly suggests that RED1 recognizes ACP-free bicyclic beta-keto acid as the first committed intermediate of tailoring steps. Kinetic studies of RED1 showed high affinity with ONBA, consistent with the requirement for an efficient reduction of a labile beta-keto carboxylic acid. Interestingly, the methyl ester of ONBA acted as a competitive inhibitor of RED1, indicating the presence of strict substrate recognition toward the terminal acid functionality.

The actinorhodin biosynthetic gene (act) cluster in Streptomyces coelicolor carries a functionally unknown gene, actVI-ORFA. We have characterized an ActVI-ORFA disruptant by functional complementation and reverse transcriptase polymerase chain reaction analysis of the expression profiles of the act genes. Introduction of the functional actVI-ORFA gene into the disruptant restored actinorhodin production to an extent similar to that seen in the wild-type cells and abolished the accumulation of actinorhodin biosynthetic intermediates and shunt products specific for actVI mutants. Thus, unique phenotypes observed in the mutant are solely dependent on the function of actVI-ORFA. The disruptant was shown to yield significantly lower levels of the transcripts for certain act genes, especially for the actVI-ORF1-VA-ORF2 transcription unit, leading to the accumulation of the intermediates and shunt products. The functional actVI-ORFA gene restored expression of actVI-ORF1, which encodes a key reductase in the actinorhodin tailoring step, in the mutant cells, indicating a possible regulatory role of ActVI-ORFA.

大学関係者だけでなく、高校生や高校教員も読者とする本誌に連載された｢薬･香料の不思議｣シリーズの第2報として執筆。天然香料中に含まれる微量香気成分の有するキラリテォーの相違が香りの変化に及ぼす影響について、キラル香気成分を生成する酵素の存在に注目して解説した総説。

Medermycin shows the same trans (3S,15R) configuration as actinorhodin in the pyran ring crucial for its bioactivity. One medermycin biosynthetic gene, ined-ORF12, is assumed to be involved in the stereochemical control at C-3. Functional complementation suggested that it plays a similar role as actVI-ORFI previously proved to determine the stereospecificity at C-3 in actinorhodin biosynthesis. Co-expression of med-ORF12 with actinorhodin early biosynthetic genes further demonstrated that med-ORF12 encodes a ketoreductase responsible for the enantioselective reduction at C-3 in the formation of the pyran ring. (c) 2005 Elsevier Ltd. All rights reserved.

The reaction mechanism of chemical conversion of (E)-β-[2-hydroxylphenylethylene]benzeneethanol into 2-phenylbenzofuran by DDQ, which involves loss of one carbon unit, was characterized and described. Five naturally occurring 2-phenylbenzofurans of not only the isoflavonoid but also stilbenoid origin were synthesized by use of this chemical scheme, which proved that this new scheme is a useful tool for quick synthesis of 2-phenylbenzofurans. © 2005 The Japan Institute of Heterocyclic Chemistry All rights reserved.

放線菌抗生物質代謝経路中で機能する還元酵素RED1に。ベータケトエステル部分を有する１１種類の人工基質を合成し、RED1の放線菌における効率的な発現系を利用し、バイオトランスフォーメーション法による還元性を検証したところ１０種の人工基質については９５～９９％eeの選択性で対応するキラルアルコールに還元されることが判明した。市瀬は本研究の共同研究者として、論文執筆に関わった。

Two ketoreductases, RED1 and RED2, are involved in the biosynthesis of actinorhodin in Streptomyces coelicolor A3(2) and dihydrogranaticin in S. violaceoruher Tu22 respectively. They are responsible for the stereospecific reductions of the bicyclic intermediate to give (S)- or (R)-DNPA although there is no similarity between their amino acid sequences. Biotransformation using synthetic analogous substrates revealed that the substrate specificities are quite different. Homology modelling studies and site directed mutagenesis showed remarkable differences in three-dimensional structures and catalytic mechanisms between RED1 and RED2. (C) 2004 Elsevier Ltd. All rights reserved.

Neocarzilins (NCZs) are antitumor chlorinated polyenones produced by "Streptomyces carzinostaticus" var. F-41. The gene cluster responsible for the biosynthesis of NCZs was cloned and characterized. DNA sequence analysis of a 33-kb region revealed a cluster of 14 open reading frames (ORFs), three of which (ORF4, ORF5, and ORF6) encode type I polyketide synthase (PKS), which consists of four modules. Unusual features of the modular organization is the lack of an obvious acyltransferase domain on modules 2 and 4 and the presence of longer interdomain regions more than 200 amino acids in length on each module. Involvement of the PKS genes in NCZ biosynthesis was demonstrated by heterologous expression of the cluster in Streptomyces coelicolor CH999, which produced the apparent NCZ biosynthetic intermediates dechloroneocarzillin A and dechloroneocarzilin B. Disruption of ORF5 resulted in a failure of NCZ production, providing further evidence that the cluster is essential for NCZ biosynthesis. Mechanistic consideration of NCZ formation indicates the iterative use of at least one module of the PKS, which subsequently releases its product by decarboxylation to generate an NCZ skeleton, possibly catalyzed by a type II thioesterase encoded by ORF7. This is a novel type I PKS system of bacterial origin for the biosynthesis of a reduced polyketide chain. Additionally, the protein encoded by ORF3, located upstream of the PKS genes, closely resembles the FADH(2)-dependent halogenases involved in the formation of halometabolites. The ORF3 protein could be responsible for the halogenation of NCZs, presenting a unique example of a halogenase involved in the biosynthesis of an aliphatic halometabolite.

Overexpression of the landomycin glycosyltransferase gene lanGT4 in Streptomyces fradiae Tu2717 resulted in the conversion of the urdamycin trisaccharide into an unnatural tetrasaccharide by transfer of an L-rhodinose unit. We propose that LanGT4 is able to act iteratively on growing saccharide chains.

A review on biosynthetic studies of the antibiotic actinorhodin and structurally related benzoisochromanequinone. The metabolic engineering is described of deoxysugar moieties of polyketide glycosides, focusing on urdamycins (URDs) from <I>Streptomyces fradiae </I>Tu2717, since URDs contain D-?olivose and L-?rhodinose attached via <I>C</I>- and<I> O</I>-glyosylations.

A novel shunt product was isolated from a disruptant of the actVI-ORFA gene involved in the biosynthesis of actinorhodin (ACT) in Streptomyces coelicolor A3(2). Its structure was elucidated as 1,4-naphthoquinone-8-hydroxy-3-[3(S)-acetoxy-butyric acid], (S)-NHAB, based on NMR, MS. and CD spectroscopic data as well as a single crystal X-ray crystallographic analysis. The formation of (S)-NHAB involves a retro-Claisen type C-C bond cleavage of an ACT biosynthetic intermediate. Feeding experiments with [1-C-13] and [2-C-13] acetates indicated its biosynthetic origin as a single octaketide chain. The relevant gene product, Act-ORFA, which is a functionally unknown protein. is proposed to play a regulatory role related to the multi-enzymatic steps to ACT production, based on the metabolic profile of its disruptant and the wide distribution of actVI-ORFA homologues in the gene clusters for Streptomyces aromatic polyketides. (C) 2003 Elsevier Ltd. All rights reserved.

Medermycin is a Streptomyces aromatic C-glycoside antibiotic classified in the benzoisochromanequinones (BIQs), which presents several interesting biosynthetic problems concerning polyketide synthase (PKS), post-PKS tailoring and deoxysugar pathways. The biosynthetic gene cluster for medermycin (the med cluster) was cloned from Streptomyces sp. AIM-7161. Completeness of the clone was proved by the heterologous expression of a cosmid carrying the entire med cluster in Streptomyces coelicolor CH999 to produce medermycin. The DNA sequence of the cosmid (36 202 bp) revealed 34 complete ORFs, with an incomplete ORF at either end. Functional assignment of the deduced products was made for PKS and biosynthetically related enzymes, tailoring steps including strereochemical control, oxidation, angolosamine pathway, C-glycosylation, and regulation. The med cluster was estimated to be about 30 kb long, covering 29 ORFs. An unusual characteristic of the cluster is the disconnected organization of the minimal PKS genes: med-ORF23 encoding the acyl carrier protein is 20 kb apart from med-ORF1 and med-ORF2 for the two ketosynthase components. Secondly, the six genes (med-ORF1 4, 15, 16, 17, 18 and 20)-for the biosynthesis of the deoxysugar, angolosamine, are all contiguous. Finally, the finding of a glycosyltransferase gene, med-ORF8, suggests a possible involvement of conventional C-glycosylation in medermycin biosynthesis. Comparison among the three complete BIQ gene clusters - med and those for actinorhodin (act) and granaticin (gra) - revealed some common genes whose deduced functions are unavailable from database searches (the 'unknowns'). An example is med-ORF5, a homologue of actV/-ORF3 and gra-ORF18, which was highlighted by a recent proteomic analysis of S. coelicolor A3(2).

UrdGT2 is a d-olivosyltransferase from the metabolic pathway of urdamycin A, an angucycline antitumor and antimicrobial drug. The remarkable feature of this biocatalyst is its ability to set up C-glycosidic bonds. Using an in vivo system suitable to deliver the trideoxysugar rhodinose in both d- and l- configuration we could verify that both have been accepted as substrates and attached to the urdamycin polyketide backbone via a C-glycosidic bond. Regardless of the stereochemistry, these C-glycosides served as acceptor for a subsequent glycosylation step to yield the novel urdamycins R and S with di-rhodinosyl side chains at C-9 of the polyketide moiety.

Costus speciosus produces a large quantity of steroidal glycosides derived from the sole aglycone, diosgenin. Cycloartenol, a product of oxidosqualene cyclase (OSC), is postulated to be a common intermediate for phytosterols of primary metabolism and diosgenin of secondary metabolism, possibly providing a metabolic branch point. Two cDNAs, CSOSC1 and CSOSC2, were cloned from C. speciosus by RT-PCR and cDNA library screening. Both cDNAs encode 759 amino acids with high mutual identity (74%), resembling (>55% identity) the known OSCs. Phylogenetic tree analysis indicated that the gene products occupy distinct positions from those of cycloartenol synthases (CASs) and triterpene synthases from dicotyledonous plants. By functional expression in yeast, CSOSC1 and CSOSC2 were proved to encode a CAS and a multifunctional triterpene synthase, respectively. The present result is the first demonstration of the functional expression of OSCs from monocotyledonous plants.

Combinatorial biosynthesis is a promising technique used to provide modified natural products for drug development. To enzymatically bridge the gap between what is possible in aglycon biosynthesis and sugar derivatization, glycosyltransferases are the tools of choice. To overcome limitations set by their intrinsic specificities, we have genetically engineered the protein regions governing nucleotide sugar and acceptor substrate specificities of two urdamycin deoxysugar glycosyltransferases, UrdGT1b and UrdGT1c. Targeted amino acid exchanges reduced the number of amino acids potentially dictating substrate specificity to ten. Subsequently, a gene library was created such that only codons of these ten amino acids from both parental genes were independently combined. Library members displayed parental and/or a novel specificity, with the latter being responsible for the biosynthesis of urdamycin P that carries a branched saccharide side chain hitherto unknown for urdamycins.

<I>Streptomyces fradiae</I>由来抗生物質Urdamycin A (URD-A)構成デオキシ糖の４つの糖転移酵素 (GT) のうち，L-rhodinose及びD-olivoseの転移を特異的に触媒するGT1b及びGT1cの基質特異性に関する解析研究の紹介記事