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1.
Polyketide biosynthesis is catalyzed by polyketide synthase (PKS) and three types of bacterial PKS are known to date. Feeding experiments with isotope-labeled precursors established the polyketide origin of the macrotetrolides, but the labeling pattern cannot be rationalized according to the established PKS paradigm. Genetic analysis of the macrotetrolide biosynthesis unveiled an unprecedented organization for a polyketide gene cluster that features five genes encoding discrete ketoacyl synthase (KS) and four genes encoding discrete ketoreductase (KR) but lacking an acyl carrier protein (ACP). Macrotetrolide biosynthesis is proposed to involve a novel type II PKS that acts directly on acyl CoA substrates, functions noniteratively, and catalyzes both C-C and C-O bond formation. These findings demonstrate once again Nature's versatility in making complex molecules and suggests new strategies for PKS engineering to further expand the scope and diversity of polyketide library. They also should serve as an inspiration in searching for PKS with novel chemistry for combinatorial biosynthesis.  相似文献   

2.
The chalcone synthase (CHS) superfamily of type III polyketide synthases (PKSs) produces a variety of plant secondary metabolites with remarkable structural diversity and biological activities (e.g., chalcones, stilbenes, benzophenones, acrydones, phloroglucinols, resorcinols, pyrones, and chromones). Here we describe an octaketide-producing novel plant-specific type III PKS from aloe (Aloe arborescens) sharing 50-60% amino acid sequence identity with other plant CHS-superfamily enzymes. A recombinant enzyme expressed in Escherichia coli catalyzed seven successive decarboxylative condensations of malonyl-CoA to yield aromatic octaketides SEK4 and SEK4b, the longest polyketides known to be synthesized by the structurally simple type III PKS. Surprisingly, site-directed mutagenesis revealed that a single residue Gly207 (corresponding to the CHS's active site Thr197) determines the polyketide chain length and product specificity. Small-to-large substitutions (G207A, G207T, G207M, G207L, G207F, and G207W) resulted in loss of the octaketide-forming activity and concomitant formation of shorter chain length polyketides (from triketide to heptaketide) including a pentaketide chromone, 2,7-dihydroxy-5-methylchromone, and a hexaketide pyrone, 6-(2,4-dihydroxy-6-methylphenyl)-4-hydroxy-2-pyrone, depending on the size of the side chain. Notably, the functional diversity of the type III PKS was shown to evolve from simple steric modulation of the chemically inert single residue lining the active-site cavity accompanied by conservation of the Cys-His-Asn catalytic triad. This provided novel strategies for the engineered biosynthesis of pharmaceutically important plant polyketides.  相似文献   

3.
Fungal aromatic polyketides show remarkable structural diversity fundamentally derived from variations in chain length and cyclization pattern. Their basic skeletons are synthesized by multifunctional iterative type I polyketide synthases (PKSs). Recently, we have found that the C-terminal thioesterase (TE)-like domain of Aspergillus nidulans WA catalyzes Claisen-type cyclization to form the B-ring of naphthopyrone YWA1. Here we report the unprecedented mechanism of chain length determination by the C-terminal TE-like domain of Colletotrichum lagenarium PKS1, which, in addition to catalyzing Claisen-type cyclization, intercepts the polyketomethylene intermediate from the acyl carrier protein domain during the condensation reaction to produce shorter chain length products. This chain length determination system is novel among PKSs, including bacterial and plant PKSs. The functional diversity of the TE-like domain directly influences the structural diversity of aromatic polyketides in C. lagenarium PKS1.  相似文献   

4.
5.
BACKGROUND: Modular polyketide synthases catalyse the biosynthesis of medically useful natural products by stepwise chain assembly, with each module of enzyme activities catalysing a separate cycle of polyketide chain extension. Domain swapping between polyketide synthases leads to hybrid multienzymes that yield novel polyketides in a more or less predictable way. No experiments have so far been reported which attempt to enlarge a polyketide synthase by interpolating additional modules. RESULTS: We describe here the construction of tetraketide synthases in which an entire extension module from the rapamycin-producing polyketide synthase is covalently spliced between the first two extension modules of the erythromycin-producing polyketide synthase (DEBS). The extended polyketide synthases thus formed are found to catalyse the synthesis of specific tetraketide products containing an appropriate extra ketide unit. Co-expression in Saccharopolyspora erythraea of the extended DEBS multienzyme with multienzymes DEBS 2 and DEBS 3 leads to the formation, as expected, of novel octaketide macrolactones. In each case the predicted products are accompanied by significant amounts of unextended products, corresponding to those of the unaltered DEBS PKS. We refer to this newly observed phenomenon as 'skipping'. CONCLUSIONS: The strategy exemplified here shows far-reaching possibilities for combinatorial engineering of polyketide natural products, as well as revealing the ability of modular polyketide synthases to 'skip' extension modules. The results also provide additional insight into the three-dimensional arrangement of modules within these giant synthases.  相似文献   

6.
A synthetic metabolic pathway has been constructed in vitro consisting of the type III polyketide synthase from Streptomyces coelicolor and peroxidases from soybean and Caldariomyces fumago (chloroperoxidase). This has resulted in the synthesis of the pentaketide flaviolin and its dimeric derivative, and a wide range of pyrones and their coupled derivatives with flaviolin, as well as their halogenated derivatives. The addition of acyl-CoA oxidase to the pathway prior to the polyketide synthase resulted in unsaturated pyrone side chains, further broadening the product spectrum that can be achieved. The approach developed in this work, therefore, provides a new model to exploit biocatalysis in the synthesis of complex natural product derivatives.  相似文献   

7.
BACKGROUND: A single modular polyketide synthase (PKS) gene cluster is responsible for production of both the 14-membered macrolide antibiotic picromycin and the 12-membered macrolide antibiotic methymycin in Streptomyces venezuelae. Building on the success of the heterologous expression system engineered using the erythromycin PKS, we have constructed an analogous system for the picromycin/methymycin PKS. Through heterologous expression and construction of a hybrid PKS, we have examined the contributions that the PKS, its internal thioesterase domain (pikTE) and the Pik TEII thioesterase domain make in termination and cyclization of the two polyketide intermediates. RESULTS: The picromycin/methymycin PKS genes were functionally expressed in the heterologous host Streptomyces lividans, resulting in production of both narbonolide and 10-deoxymethynolide (the precursors of picromycin and methymycin, respectively). Co-expression with the Pik TEII thioesterase led to increased production levels, but did not change the ratio of the two compounds produced, leaving the function of this protein largely unknown. Fusion of the PKS thioesterase domain (pikTE) to 6-deoxyerythronolide B synthase (DEBS) resulted in formation of only 14-membered macrolactones. CONCLUSIONS: These experiments demonstrate that the PKS alone is capable of catalyzing the synthesis of both 14- and 12-membered macrolactones and favor a model by which different macrolactone rings result from a combination of the arrangement between the module 5 and module 6 subunits in the picromycin PKS complex and the selectivity of the pikTE domain.  相似文献   

8.
A tetraketide synthase containing a loading module (LM), the extension modules erythromycin module 1, rapamycin module 2, and erythromycin module 2 (LM-Ery1-Rap2-Ery2-TE), when expressed in Saccharopolyspora erythraea strain JC2, produced as previously reported a mixture of tetraketide lactones (minor products) and triketide lactones (major products). Several alternative plausible mechanisms by which this "skipping" phenomenon might occur may be proposed. Site-directed mutagenesis of the ketosynthase (KS) and acylcarrier protein (ACP) domains in the interpolated module has shown that skipping within the hybrid PKS involves passage of the growing polyketide through the interpolated module, by direct ACP-to-ACP transfer of the polyketide chain.  相似文献   

9.
Zhao Q  He Q  Ding W  Tang M  Kang Q  Yu Y  Deng W  Zhang Q  Fang J  Tang G  Liu W 《Chemistry & biology》2008,15(7):693-705
Azinomycin B is a complex natural product containing densely assembled functionalities with potent antitumor activity. Cloning and sequence analysis of the azi gene cluster revealed an iterative type I polyketide synthase (PKS) gene, five nonribosomal peptide synthetases (NRPSs) genes and numerous genes encoding the biosynthesis of unusual building blocks and tailoring steps for azinomycin B production. Characterization of AziB as a 5-methyl-naphthoic acid (NPA) synthase showed a distinct selective reduction pattern in aromatic polyketide biosynthesis governed by bacterial iterative type I PKSs. Heterologous expression established the PKS-post modification route from 5-methyl-NPA to reach the first building block 3-methoxy-5-methyl-NPA. This proposed azinomycin B biosynthetic pathway sets the stage to investigate the enzymatic mechanisms for building structurally unique and pharmaceutically important groups, including the unprecedented azabicyclic ring system and highly active epoxide moiety.  相似文献   

10.
Phenolic glycolipids (PGLs) are polyketide-derived virulence factors produced by Mycobacterium tuberculosis, M. leprae, and other mycobacterial pathogens. We have combined bioinformatic, genetic, biochemical, and chemical biology approaches to illuminate the mechanism of chain initiation required for assembly of the p-hydroxyphenyl-polyketide moiety of PGLs. Our studies have led to the identification of a stand-alone, didomain initiation module, FadD22, comprised of a p-hydroxybenzoic acid adenylation domain and an aroyl carrier protein domain. FadD22 forms an acyl-S-enzyme covalent intermediate in the p-hydroxyphenyl-polyketide chain assembly line. We also used this information to develop a small-molecule inhibitor of PGL biosynthesis. Overall, these studies provide insights into the biosynthesis of an important group of small-molecule mycobacterial virulence factors and support the feasibility of targeting PGL biosynthesis to develop new drugs to treat mycobacterial infections.  相似文献   

11.
Streptomyces coelicolor CH999/pJRJ2 harbors a plasmid encoding DEBS(KS1 degrees ), a mutant form of 6-deoxyerythronolide B synthase that is blocked in the formation of 6-deoxyerythronolide B (1, 6-dEB) due to a mutation in the active site of the ketosynthase (KS1) domain that normally catalyzes the first polyketide chain elongation step of 6-dEB biosynthesis. Administration of (2E,4S,5R)-2,4-dimethyl-5-hydroxy-2-heptenoic acid, N-acetylcysteamine thioester (6) an unsaturated triketide analogue of the natural triketide chain elongation intermediate to cultures of S. coelicolor CH999/pJRJ2 results in formation of a 16-membered macrolactone, which is isolated in the hemiketal form 33. The formation of the octaketide 33 indicates that the triketide substrate has been processed by DEBS module 2 as if it were a diketide analogue. The substrate specificity of this novel reaction has been explored by the incubation of three additional analogues of the unsaturated triketide 6, compounds 18, 31, and 32, with S. coelicolor CH999/pJRJ2, resulting in the formation of the corresponding macrolactones 34, 35, and 36. By contrast, the unsaturated triketide 10, lacking a methyl group at C-2, did not give rise to any detectable macrolactone product when incubated with S. coelicolor CH999/pJRJ2.  相似文献   

12.
A versatile approach for the enantioselective synthesis of functionalised beta-hydroxy N-acetylcysteamine thiol esters has been developed which allows the facile incorporation of isotopic labels. It has been shown that a remarkable reversal of selectivity occurs in the titanium mediated aldol reaction of acyloxazolidinone using either (S)- or (R)-tert-butyldimethylsilyloxybutanal. The aldol products are valuable intermediates in the synthesis of 4-hydroxy-6-substituted delta-lactones.  相似文献   

13.
Abe I  Abe T  Wanibuchi K  Noguchi H 《Organic letters》2006,8(26):6063-6065
[Structure: see text] Benzalacetone synthase from Rheum palmatum efficiently catalyzed condensation of N-methylanthraniloyl-CoA (or anthraniloyl-CoA) with malonyl-CoA (or methylmalonyl-CoA) to produce 4-hydroxy-2(1H)-quinolones, a novel alkaloidal scaffold produced by a type III polyketide synthase (PKS). Manipulation of the functionally divergent type III PKSs by a nonphysiological substrate thus provides an efficient method for production of pharmaceutically important quinolone alkaloids.  相似文献   

14.
The biosynthesis of the potent environmental carcinogen aflatoxin B(1) is initiated by norsolorinic acid synthase (NorS), a complex of an iterative type I polyketide synthase and a specialized yeast-like pair of fatty acid synthases. NorS has been partially purified from Aspergillus parasiticus, has been found to have a mass of approximately 1.4 x 10(6) Da, and carries out the synthesis of norsolorinic acid in the presence of acetylCoA, malonylCoA, and NADPH where hexanoylCoA is not a free intermediate. The N-acetylcysteamine thioester of hexanoic acid can substitute for the catalytic functions of HexA/B to initiate norsolorinic acid synthesis by the complex in the presence of only malonylCoA. An alpha(2)beta(2)gamma(2) stoichiometry is proposed for NorS in keeping with its estimated mass and the observed dimeric or higher-order quarternary structures of PKS and FAS enzymes.  相似文献   

15.
16.
Zhang W  Wang L  Kong L  Wang T  Chu Y  Deng Z  You D 《Chemistry & biology》2012,19(3):422-432
Highlights? Cloning and sequencing of the complete xantholipin biosynthesis gene cluster ? Identification of genes for xanthone and methylenedioxy bridge formation ? An unusual C11 ketoreductase for the prearomatic reduction ? Multiple redox tailoring for type II PKS biosynthesis  相似文献   

17.
Isolation and sequencing of a PKS gene isolated from xenovulene-producing cultures of Acremonium strictum indicated the presence of NT-, KS-, AT-, PT-, C-MeT- and R-domains; heterologous expression in Aspergillus oryzae resulted in the production of 3-methylorcinaldehyde, demonstrating the role of the terminal reductase domain in product release.  相似文献   

18.
PCR primers designed to selectively amplify the unique C-methyltransferase domain of fungal polyketide synthases were used to selectively clone a polyketide synthase gene involved in the biosynthesis of the squalene synthase inhibitor squalestatin S1 , heterologous expression of which led to the biosynthesis of the squalestatin side-chain.  相似文献   

19.
Background: It has been proposed that Streptomyces malonyl CoA:holo acyl carrier protein transacylases (MCATs) provide a link between fatty acid and polyketide biosynthesis. Two recent studies have provided evidence that the presence of MCAT is essential for polyketide synthesis to proceed in reconstituted minimal polyketide synthases (PKSs). In contrast to this, we previously showed that the holo acyl carrier proteins (ACPs) from type II PKSs are capable of catalytic self -malonylation in the presence of malonyl CoA, which suggests that MCAT might not be necessary for polyketide biosynthesis.Results: We reconstituted a homologous actinorhodin (act) type II minimal PKS in vitro, When act holo-ACP is present in limiting concentrations, MCAT is required by the synthase complex in order for polyketide biosynthesis to proceed. When holo-ACP is present in excess, however, efficient polyketide synthesis proceeds without MCAT, The rate of polyketide production increases with holo-ACP concentration, but at low ACP concentration or equimolar ACP:KS:CLF (KS, ketosynthase; CLF, chain length determining factor) concentrations this rate is significantly lower than expected, indicating that free holo-ACP is sequestered by the KS/CLF complex.Conclusions: The rate of polyketide biosynthesis is dictated by the ratio of holo-ACP to KS and CLF, as well as by the total protein concentration, There is no absolute requirement for MCAT in polyketide biosynthesis in vitro, although the role of MCAT during polyketide synthesis in vivo remains an open question. MCAT might be responsible for the rate enhancement of malonyl transfer at very low free holo-ACP concentrations or it could be required to catalyse the transfer of malonyl groups from malonyl CoA to sequestered holo-ACP.  相似文献   

20.
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