Ben Shen

The Scripps Research Institute, لا هویا, California, United States

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Publications (168)1103.79 Total impact

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    ABSTRACT: Leinamycin (LNM) is a potent antitumor antibiotic produced by Streptomyces atroolivaceus S-140, featuring an unusual 1,3-dioxo-1,2-dithiolane moiety that is spiro-fused to a thiazole-containing 18-membered lactam ring. Upon reductive activation in the presence of cellular thiols, LNM exerts its antitumor activity by an episulfonium ion-mediated DNA alkylation. Previously, we have cloned the lnm gene cluster from S. atroolivaceus S-140 and characterized the biosynthetic machinery responsible for the 18-membered lactam backbone and the alkyl branch at C3 of LNM. We now report the isolation and characterization of leinamycin E1 (LNM E1) from S. atroolivacues SB3033, a ΔlnmE mutant strain of S. atroolivaceus S-140. Complementary to the reductive activation of LNM by cellular thiols, LNM E1 can be oxidatively activated by cellular reactive oxygen species (ROS) to generate a similar episulfonium ion intermediate, thereby alkylating DNA and leading to eventual cell death. The feasibility of exploiting LNM E1 as an anticancer prodrug activated by ROS was demonstrated in two prostate cancer cell lines, LNCaP and DU-145. Because many cancer cells are under higher cellular oxidative stress with increased levels of ROS than normal cells, these findings support the idea of exploiting ROS as a means to target cancer cells and highlight LNM E1 as a novel lead for the development of anticancer prodrugs activated by ROS. The structure of LNM E1 also reveals critical new insights into LNM biosynthesis, setting the stage to investigate sulfur incorporation, as well as the tailoring steps that convert the nascent hybrid peptide-polyketide biosynthetic intermediate into LNM.
    Proceedings of the National Academy of Sciences 06/2015; DOI:10.1073/pnas.1506761112 · 9.81 Impact Factor
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    ABSTRACT: Platensimycin (PTM) and platencin (PTN) are members of a new class of promising drug leads that target bacterial and mammalian fatty acid synthases. We previously cloned and sequenced the PTM and PTN gene clusters, discovered six additional PTM-PTN dual producing strains, and demonstrated the dramatic overproduction of PTM and PTN by inactivating the pathway-specific regulators ptmR1 or ptnR1 in four different strains. Our ability to utilize these PTM-PTN dual overproducing strains was limited by their lack of genetic amenability. Here we report the construction of Streptomyces platensis SB12029, a genetically amenable, in-frame ΔptmR1 dual PTM-PTN overproducing strain. To highlight the potential of this strain for future PTM and PTN biosynthetic studies, we created the ΔptmR1 ΔptmO4 double mutant S. platensis SB12030. Fourteen PTM and PTN congeners, ten of which were new, were isolated from SB12030, shedding new insights into PTM and PTN biosynthesis. PtmO4, a long-chain acyl-CoA dehydrogenase, is strongly implicated to catalyze β-oxidation of the diterpenoid intermediates into the PTM and PTN scaffolds. SB12029 sets the stage for future biosynthetic and bioengineering studies of the PTM and PTN family of natural products.
    Molecular BioSystems 06/2015; DOI:10.1039/C5MB00303B · 3.18 Impact Factor
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    ABSTRACT: Leinamycin (LNM, 1) is a novel antitumor antibiotic produced by Streptomyces atroolivaceus S-140 and features an unusual 1,3-dioxo-1,2-dithiolane moiety that is spiro-fused to a thiazole-containing 18-membered lactam ring. The 1,3-dioxo-1,2-dithiolane moiety of LNM is essential for its antitumor activity via an episulfonium ion-mediated DNA alkylation upon reductive activation in the presence of cellular thiols. We recently isolated leinamycin E1 (LNM E1, 2) from an engineered strain S. atroolivaceus SB3033, which lacks the 1,3-dioxo-1,2-dithiolane moiety. Here we report the chemical synthesis of 8,4'-dideshydroxy-LNM (5) from 2 and determination of the cytotoxicity of 5 against selected cancer cell lines in comparison with 1; 5 exhibits comparable activity as 1 with the EC50 values between 8.21 and 275nM. This work reveals new insight into the structure-activity relationship of LNM and highlights the synergy between metabolic pathway engineering and medicinal chemistry for natural product drug discovery. Copyright © 2015 Elsevier Ltd. All rights reserved.
    Bioorganic & medicinal chemistry letters 05/2015; DOI:10.1016/j.bmcl.2015.05.078 · 2.33 Impact Factor
  • The Journal of Antibiotics 03/2015; DOI:10.1038/ja.2015.22 · 2.04 Impact Factor
  • ChemInform 02/2015; 46(6). DOI:10.1002/chin.201506306
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    ABSTRACT: Cells have evolved exquisite mechanisms to fine-tune the rate of protein synthesis in response to stress. Systemic mapping of start-codon positions and precise measurement of the corresponding initiation rate would transform our understanding of translational control. Here we present quantitative translation initiation sequencing (QTI-seq), with which the initiating ribosomes can be profiled in real time at single-nucleotide resolution. Resultant initiation maps not only delineated variations of start-codon selection but also highlighted a dynamic range of initiation rates in response to nutrient starvation. The integrated data set provided unique insights into principles of alternative translation and mechanisms controlling different aspects of translation initiation. With RiboTag mice, QTI-seq permitted tissue-specific profiling of initiating ribosomes in vivo. Liver cell-specific ribosome profiling uncovered a robust translational reprogramming of the proteasome system in fasted mice. Our findings illuminated the prevalence and dynamic nature of translational regulation pivotal to physiological adaptation in vivo.
    Nature Methods 12/2014; 12(2). DOI:10.1038/nmeth.3208 · 25.95 Impact Factor
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    ABSTRACT: Next-generation transcriptome sequencing is increasingly integrated with mass spectrometry to enhance MS-based protein and peptide identification. Recently, a breakthrough in transcriptome analysis was achieved with the development of ribosome profiling (ribo-seq). This technology is based on the deep sequencing of ribosome-protected mRNA fragments, thereby enabling the direct observation of in vivo protein synthesis at the transcript level. In order to explore the impact of a ribo-seq-derived protein sequence search space on MS/MS spectrum identification, we performed a comprehensive proteome study on a human cancer cell line, using both shotgun and N-terminal proteomics, next to ribosome profiling, which was used to delineate (alternative) translational reading-frames. By including protein-level evidence of sample-specific genetic variation and alternative translation, this strategy improved the identification score of 69 proteins and identified 22 new proteins in the shotgun experiment. Furthermore, we discovered 18 new alternative translation start sites in the N-terminal proteomics data and observed a correlation between the quantitative measures of ribo-seq and shotgun proteomics with a Pearson correlation coefficient ranging from 0.483 to 0.664. Overall, this study demonstrated the benefits of ribosome profiling for MS-based protein and peptide identification and we believe this approach could develop into a common practice for next-generation proteomics.This article is protected by copyright. All rights reserved
    Proteomics 12/2014; 14(23-24). DOI:10.1002/pmic.201400180 · 3.97 Impact Factor
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    ABSTRACT: Lactimidomycin (LTM, 1) and iso-migrastatin (iso-MGS, 2) belong to the glutarimide-containing polyketide family of natural products. We previously cloned and characterized the mgs biosynthetic gene cluster from Streptomyces platensis NRRL 18993. The iso-MGS biosynthetic machinery featured an acyltransferase (AT)-less type I polyketide synthase (PKS) and three tailoring enzymes (MgsIJK). We now report cloning and characterization of the ltm biosynthetic gene cluster from Streptomyces amphibiosporus ATCC 53964, which consists of nine genes that encode an AT-less type I PKS (LtmBCDEFGHL) and one tailoring enzyme (LtmK). Inactivation of ltmE or ltmH afforded the mutant strains SB15001 or SB15002 that abolished the production of 1, as well as the three co-metabolites 8,9-dihydro-LTM (14), 8,9-dihydro-8S-hydroxy-LTM (15), and 8,9-dihydro-9R-hydroxy-LTM (13). Inactivation of ltmK yielded the mutant strain SB15003 that abolished the production of 1, 13, and 15 but accumulated 14. Complementation of the ΔltmK mutation in SB15003 by expressing ltmK in trans restored the production of 1, as well as 13 and 15. These results support the model for 1 biosynthesis, featuring an AT-less type I PKS that synthesizes 14 as the nascent polyketide intermediate and a cytochrome P450 desaturase that converts 14 to 1, with 13 and 15 as minor co-metabolites. Comparative analysis of the LTM and iso-MGS AT-less type I PKSs revealed several unusual features that deviate from the collinear type I PKS model. Exploitation of the tailoring enzymes for 1 and 2 biosynthesis afforded two analogues 8,9-dihydro-8R-hydroxy-LTM (16) and 8,9-dihydro-8R-methoxy-LTM (17) that provided new insights into the structure-activity-relationship of 1 and 2. While 12-membered macrolides, featuring a combination of a hydroxyl group at C-17 and a double bond at C-8/C-9 as found in 1, exhibit the most potent activity, analogues with a single hydroxyl or methoxy group at C-8 or C-9 retain most of the activity whereas analogues with double substitutions at C-8/C-9 lose significant activity.
    Biochemistry 11/2014; 53(49). DOI:10.1021/bi501396v · 3.19 Impact Factor
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    ABSTRACT: The bleomycin (BLM) family of glycopeptide-derived antitumor antibiotics consists of BLMs, tallysomycins (TLMs), phleomycins (PLMs), and zorbamycin (ZBM). The self-resistant elements BlmB and TlmB, discovered from the BLM- and TLM-producing orgranisms Streptomyces verticillus ATCC15003 and Streptoalloteichus hindustanus E465-94 ATCC31158, respectively, are N-acetyltransferases that provide resistance to the producers by disrupting the metal-binding domain of the antibiotics required for activity. Although each member of the BLM family of antibiotics possesses a conserved metal-binding domain, the structural differences between each member, namely the bithiazole moiety and C-terminal amine of BLMs, have been suggested to instill substrate specificity within BlmB. Here we report that BlmB and TlmB readily accept and acetylate BLMs, TLMs, PLMs, and ZBM in vitro but only in the metal-free forms. Kinetic analysis of BlmB and TlmB reveals there is no strong preference or rate enhancement for specific substrates, indicating that the structural differences between each member of the BLM family play a negligible role in substrate recognition, binding, or catalysis. Intriguingly, the zbm gene cluster from Streptomyces flavoviridis ATCC21892 does not contain an N-acetyltransferase, yet ZBM is readily acetylated by BlmB and TlmB. We subsequently established that S. flavoviridis lacks the homologue of BlmB and TlmB, and ZbmA, the ZBM binding protein, alone is sufficient to provide ZBM resistance. We further confirmed that BlmB can indeed confer resistance to ZBM in vivo in S. flavoviridis, introduction of which into the wild-type S. flavoviridis further increases the level of resistance.
    Biochemistry 10/2014; DOI:10.1021/bi501121e · 3.19 Impact Factor
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    ABSTRACT: Natural products offer unmatched chemical and structural diversity compared to other small-molecule libraries, but traditional natural product discovery programs are not sustainable, demanding too much time, effort, and resources. Here we report a strain prioritization method for natural product discovery. Central to the method is the application of real-time PCR, targeting genes characteristic to the biosynthetic machinery of natural products with distinct scaffolds in a high-throughput format. The practicality and effectiveness of the method were showcased by prioritizing 1911 actinomycete strains for diterpenoid discovery. A total of 488 potential diterpenoid producers were identified, among which six were confirmed as platensimycin and platencin dual producers and one as a viguiepinol and oxaloterpin producer. While the method as described is most appropriate to prioritize strains for discovering specific natural products, variations of this method should be applicable to the discovery of other classes of natural products. Applications of genome sequencing and genome mining to the high-priority strains could essentially eliminate the chance elements from traditional discovery programs and fundamentally change how natural products are discovered.
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    ABSTRACT: PKSE biosynthesizes an enediyne core precursor from decarboxylative condensation of eight malonyl-CoAs. The KR domain of PKSE is responsible for iterative β-ketoreduction in each round of polyketide chain elongation. KRs from selected PKSEs were investigated in vitro with β-ketoacyl-SNACs as substrate mimics. Each of the KRs reduced the β-ketoacyl-SNACs stereoselectively, all affording the corresponding β-d-hydroxyacyl-SNACs, and the catalytic efficiencies (kcat/KM) of the KRs increased significantly as the chain length of the β-ketoacyl-SNAC substrate increases.
    Organic Letters 07/2014; 16(15). DOI:10.1021/ol501767v · 6.32 Impact Factor
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    ABSTRACT: Carrier proteins (CPs) play a critical role in the biosynthesis of various natural products, especially in nonribosomal peptide synthetase (NRPS) and polyketide synthase (PKS) enzymology, where the CPs are referred to as peptidyl-carrier-proteins (PCPs) or acyl-carrier-proteins (ACPs), respectively. CPs can either be a domain in large multifunctional polypeptides or stand-alone proteins, termed type I and type II, respectively. There have been many biochemical studies of the type I PKS and NRPS CPs, and of type II ACPs. However, recently a number of type II PCPs have been found and biochemically characterized. In order to understand the possible interaction surfaces for combinatorial biosynthetic efforts we crystallized the first characterized and representative type II PCP member, BlmI, from the bleomycin biosynthetic pathway from Streptomyces verticillus ATCC 15003. The structure is similar to CPs in general, but most closely resembles PCPs. Comparisons with previously determined PCP structures in complex with catalytic domains reveals a common interaction surface. This surface is highly variable in charge and shape, which likely confers specificity for interactions. Previous NMR analysis of a prototypical type I PCP excised from the multimodular context revealed three conformational states. Comparison of the states with the structure of BlmI and other PCPs reveals that only one of the NMR states is found in other studies, suggesting the other two states may not be relevant. The state represented by the BlmI crystal structure can therefore serve as a model for both type I and type II PCPs. © Proteins 2013;. © 2013 Wiley Periodicals, Inc.
    Proteins Structure Function and Bioinformatics 07/2014; 82(7). DOI:10.1002/prot.24485 · 2.92 Impact Factor
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    ABSTRACT: The ability of the radiomimetic anti-tumor enediyne C-1027 to induce DNA inter-strand crosslinks (ICLs), in addition to the expected DNA strand breaks, is unique among traditional DNA targeted cancer therapies. Importantly, radiation therapy and most radiomimetic drugs have diminished effect in hypoxic environments due to decreased induction of DNA strand breaks, which is an oxygen requiring process. However, C-1027's induction of ICLs is enhanced under hypoxia and it is actually more potent against hypoxic cells, overcoming this common tumor resistance mechanism. In this study, an analog of C-1027, 20'-deschloro-C-1027 was examined for its ability to induce DNA ICLs under hypoxic conditions. Deschloro-induced ICLs were detected under hypoxic cell-free conditions, with a concomitant reduction in the induction of DNA strand breaks. In cells deschloro behaved similarly, inducing cellular ICLs under hypoxic conditions with a reduction in DNA breaks. The cytotoxicity of deschloro treatment was similar in normoxic and hypoxic cells, suggesting that the ICL induction allows deschloro to retain its cytotoxic activity under hypoxia. It appears that rational engineering of the C-1027 family of radiomimetics holds promise toward overcoming the radioresistance associated with the hypoxic environment associated with solid tumors.
    DNA Repair 06/2014; DOI:10.1016/j.dnarep.2014.06.001 · 3.36 Impact Factor
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    ABSTRACT: Cycloheximide (1) and actiphenol (2) have been isolated from numerous Streptomyces species. Cloning, sequencing, and characterization of a gene cluster from Streptomyces sp. YIM65141 now establish that 1 and 2 production is governed by single biosynthetic machinery. Biosynthesis of 1 features an acyltransferase-less type I polyketide synthase to construct its carbon backbone but may proceed via 2 as a key intermediate, invoking a provocative reduction of a phenol to a cyclohexanone moiety in natural product biosynthesis.
    Organic Letters 05/2014; 16(11). DOI:10.1021/ol501179w · 6.32 Impact Factor
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    ABSTRACT: Platensimycin (PTM) and platencin (PTN) are potent inhibitors of bacterial fatty acid synthases and have emerged as promising antibacterial drug leads. We previously characterized the PTM and PTN biosynthetic machineries in the Streptomyces platensis producers. We now identify two mechanisms for PTM and PTN resistance in the S. platensis producers-the ptmP3 or ptnP3 gene within the PTM-PTN or PTN biosynthetic cluster and the fabF gene within the fatty acid synthase locus. PtmP3/PtnP3 and FabF confer PTM and PTN resistance by target replacement and target modification, respectively. PtmP3/PtnP3 also represents an unprecedented mechanism for fatty acid biosynthesis in which FabH and FabF are functionally replaced by a single condensing enzyme. These findings challenge the current paradigm for fatty acid biosynthesis and should be considered in future development of effective therapeutics targeting fatty acid synthase.
    Chemistry & biology 02/2014; DOI:10.1016/j.chembiol.2014.01.005 · 6.59 Impact Factor
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    ABSTRACT: Natural products remain the best sources of drugs and drug leads and serve as outstanding small-molecule probes to dissect fundamental biological processes. A great challenge for the natural product community is to discover novel natural products efficiently and cost effectively. Here we report the development of a practical method to survey biosynthetic potential in microorganisms, thereby identifying the most promising strains and prioritizing them for natural product discovery. Central to our approach is the innovative preparation, by a two-tiered PCR method, of a pool of pathway-specific probes, thereby allowing the survey of all variants of the biosynthetic machineries for the targeted class of natural products. The utility of the method was demonstrated by surveying 100 strains, randomly selected from our actinomycete collection, for their biosynthetic potential of four classes of natural products, aromatic polyketides, reduced polyketides, nonribosomal peptides, and diterpenoids, identifying 16 talented strains. One of the talented strains, Streptomyces griseus CB00830, was finally chosen to showcase the discovery of the targeted classes of natural products, resulting in the isolation of three diterpenoids, six nonribosomal peptides and related metabolites, and three polyketides. Variations of this method should be applicable to the discovery of other classes of natural products.
    Journal of Natural Products 01/2014; 77(2). DOI:10.1021/np401063s · 3.95 Impact Factor
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    ABSTRACT: Nine-membered enediyne antitumor antibiotics C-1027, neocarzinostatin (NCS), and kedarcidin (KED) possess enediyne cores to which activity-modulating peripheral moieties are attached via (R)- or (S)-vicinal diols. We have previously shown that this stereochemical difference arises from hydrolysis of epoxide precursors by epoxide hydrolases (EHs) with different regioselectivities - the "inverting" EH, such as SgcF, hydrolyzes an (S)-epoxide substrate to yield an (R)-diol in C-1027 biosynthesis, while the "retaining" EHs, such as NcsF2 and KedF, hydrolyze an (S)-epoxide substrate to yield an (S)-diol in NCS and KED biosynthesis. We now report the characterization of a series of EH mutants and provide a predictive model for EH regioselectivity in the biosynthesis of the 9-membered enediyne antitumor antibiotics. A W236Y mutation in SgcF increased the retaining activity towards (S)-styrene oxide 3-fold, and a W236Y/Q237M double mutation in SgcF, mimicking NcsF2 and KedF, resulted in a 20-fold increase in the retaining activity. To test the predictive utility of these mutations, two putative enediyne biosynthesis-associated EHs were identified by genome mining and confirmed as inverting enzymes - SpoF from Salinospora tropica CNB-440 and SgrF (SGR_625) from Streptomyces griseus IFO 13350. Finally, phylogenetic analysis of EHs revealed a familial classification according to inverting versus retaining activity. Taken together, these results provide a predictive model for the vicinal diol stereochemistry in enediyne biosynthesis and set the stage for further elucidating the origins of EH regioselectivity.
    Biochemistry 07/2013; 52(31). DOI:10.1021/bi400572a · 3.19 Impact Factor
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    ABSTRACT: We have recently isolated tirandamycin (TAM) B from Streptomyces sp. 17944 as a Brugia malayi AsnRS (BmAsnRS) inhibitor that efficiently kills the adult B. malayi parasites and does not exhibit general cytotoxicity to human hepatic cells. We now report (i) the comparison of metabolite profiles of S. sp. 17944 in six different media, (ii) identification of a medium enabling the production of TAM B as essentially the sole metabolite, and with improved titer, and (iii) isolation and structural elucidation of three new TAM congeners. These findings shed new insights into the structure-activity relationship of TAM B as a BmAsnRS inhibitor, highlighting the δ-hydroxymethyl-α,β-epoxyketone moiety as the critical pharmacophore, and should greatly facilitate the production and isolation of sufficient quantities of TAM B for further mechanistic and preclinical studies to advance the candidacy of TAM B as an antifilarial drug lead. The current study also serves as an excellent reminder that traditional medium and fermentation optimization should continue to be very effective in improving metabolite flux and titer.The Journal of Antibiotics advance online publication, 29 May 2013; doi:10.1038/ja.2013.50.
    The Journal of Antibiotics 05/2013; 67(1). DOI:10.1038/ja.2013.50 · 2.04 Impact Factor
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    ABSTRACT: 4-Methylideneimidazole-5-one (MIO)-containing aminomutases catalyze the conversion of l-α-amino acids to β-amino acids with either an (R) or an (S) configuration. l-Phenylalanine and l-tyrosine are the only two natural substrates identified to date. The enediyne chromophore of the chromoprotein antitumor antibiotic kedarcidin (KED) harbors an (R)-2-aza-3-chloro-β-tyrosine moiety reminiscent of the (S)-3-chloro-5-hydroxy-β-tyrosine moiety of the C-1027 enediyne chromophore, the biosynthesis of which uncovered the first known MIO-containing aminomutase, SgcC4. Comparative analysis of the KED and C-1027 biosynthetic gene clusters inspired the proposal for (R)-2-aza-3-chloro-β-tyrosine biosynthesis starting from 2-aza-l-tyrosine, featuring KedY4 as a putative MIO-containing aminomutase. Here we report the biochemical characterization of KedY4, confirming its proposed role in KED biosynthesis. KedY4 is an MIO-containing aminomutase that stereospecifically catalyzes the conversion of 2-aza-l-tyrosine to (R)-2-aza-β-tyrosine, exhibiting no detectable activity toward 2-aza-l-phenylalanine or l-tyrosine as an alternative substrate. In contrast, SgcC4, which stereospecifically catalyzes the conversion of l-tyrosine to (S)-β-tyrosine in C-1027 biosynthesis, exhibits minimal activity with 2-aza-l-tyrosine as an alternative substrate but generating (S)-2-aza-β-tyrosine, a product with the opposite stereochemistry of KedY4. This report of KedY4 broadens the scope of known substrates for the MIO-containing aminomutase family, and comparative studies of KedY4 and SgcC4 provide an outstanding opportunity to examine how MIO-containing aminomutases control substrate specificity and product enantioselectivity.
    Proceedings of the National Academy of Sciences 04/2013; DOI:10.1073/pnas.1304733110 · 9.81 Impact Factor
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    ABSTRACT: The iso-migrastatin (iso-MGS) biosynthetic gene cluster from Streptomyces platensis NRRL 18993 consists of 11 genes, featuring an acyltransferase (AT)-less type I polyketide synthase (PKS) and three tailoring enzymes MgsIJK. Systematic inactivation of mgsIJK in S. platensis enabled us to (i) identify two nascent products (10 and 13) of the iso-MGS AT-less type I PKS, establishing an unprecedented novel feature for AT-less type I PKSs, and (ii) account for the formation of all known post-PKS biosynthetic intermediates (10-17) generated by the three tailoring enzymes MgsIJK, which possessed significant substrate promiscuities.
    Journal of the American Chemical Society 02/2013; 135(7). DOI:10.1021/ja4002635 · 11.44 Impact Factor

Publication Stats

4k Citations
1,103.79 Total Impact Points


  • 2012–2015
    • The Scripps Research Institute
      • • Department of Chemistry
      • • Department of Molecular Therapeutics
      لا هویا, California, United States
  • 2002–2014
    • University of Wisconsin–Madison
      • • Division of Pharmaceutical Sciences
      • • Department of Chemistry
      Madison, Wisconsin, United States
  • 2010–2013
    • Cornell University
      Итак, New York, United States
  • 2008
    • University of Kentucky
      • Department of Pharmaceutical Sciences
      Lexington, KY, United States
  • 2006
    • University of Illinois, Urbana-Champaign
      • Department of Chemistry
      Urbana, Illinois, United States
  • 1999–2004
    • University of California, Davis
      • Department of Chemistry
      Davis, CA, United States
  • 2003
    • University of Nebraska at Lincoln
      • Department of Chemistry
      Lincoln, NE, United States