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Kelly GT, Washburn LA, Watanabe CMH. The Fate of Molecular Oxygen in Azinomycin Biosynthesis. J Org Chem 2019; 84:2991-2996. [PMID: 30680995 DOI: 10.1021/acs.joc.8b03007] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
The azinomycins are a family of aziridine-containing antitumor antibiotics and represent a treasure trove of biosynthetic reactions. The formation of the azabicyclo[3.1.0]hexane ring and functionalization of this ring system remain the least understood aspects of the pathway. This study reports the incorporation of 18O-labeled molecular oxygen in azinomycin biosynthesis including both oxygens of the diol that ultimately adorn the aziridino[1,2- a]pyrrolidine moiety. Likewise, two other sites of heavy atom incorporation are observed.
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Affiliation(s)
- Gilbert T Kelly
- Department of Chemistry , Texas A&M University , College Station , Texas 77843 , United States
| | - Lauren A Washburn
- Department of Chemistry , Texas A&M University , College Station , Texas 77843 , United States
| | - Coran M H Watanabe
- Department of Chemistry , Texas A&M University , College Station , Texas 77843 , United States
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2
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Abstract
Oxidative rearrangements are key reactions during the biosyntheses of many secondary metabolites in fungi.
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Affiliation(s)
- Russell Cox
- Institute for Organic Chemistry
- Leibniz University of Hannover
- 30167 Hannover, Germany
- School of Chemistry
- University of Bristol
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3
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Yu J. Current understanding on aflatoxin biosynthesis and future perspective in reducing aflatoxin contamination. Toxins (Basel) 2012; 4:1024-57. [PMID: 23202305 PMCID: PMC3509697 DOI: 10.3390/toxins4111024] [Citation(s) in RCA: 197] [Impact Index Per Article: 16.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2012] [Revised: 10/08/2012] [Accepted: 10/09/2012] [Indexed: 01/20/2023] Open
Abstract
Traditional molecular techniques have been used in research in discovering the genes and enzymes that are involved in aflatoxin formation and genetic regulation. We cloned most, if not all, of the aflatoxin pathway genes. A consensus gene cluster for aflatoxin biosynthesis was discovered in 2005. The factors that affect aflatoxin formation have been studied. In this report, the author summarized the current status of research progress and future possibilities that may be used for solving aflatoxin contamination.
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Affiliation(s)
- Jiujiang Yu
- Southern Regional Research Center, Agricultural Research Service, United States Department of Agriculture (USDA/ARS), New Orleans, LA 70112, USA.
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Yan S, Liang Y, Zhang J, Liu CM. Aspergillus flavus grown in peptone as the carbon source exhibits spore density- and peptone concentration-dependent aflatoxin biosynthesis. BMC Microbiol 2012; 12:106. [PMID: 22694821 PMCID: PMC3412747 DOI: 10.1186/1471-2180-12-106] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2011] [Accepted: 06/13/2012] [Indexed: 11/27/2022] Open
Abstract
BACKGROUND Aflatoxins (AFs) are highly carcinogenic compounds produced by Aspergillus species in seeds with high lipid and protein contents. It has been known for over 30 years that peptone is not conducive for AF productions, although reasons for this remain unknown. RESULTS In this study, we showed that when Aspergillus flavus was grown in peptone-containing media, higher initial spore densities inhibited AF biosynthesis, but promoted mycelial growth; while in glucose-containing media, more AFs were produced when initial spore densities were increased. This phenomenon was also observed in other AF-producing strains including A. parasiticus and A. nomius. Higher peptone concentrations led to inhibited AF production, even in culture with a low spore density. High peptone concentrations did however promote mycelial growth. Spent medium experiments showed that the inhibited AF production in peptone media was regulated in a cell-autonomous manner. mRNA expression analyses showed that both regulatory and AF biosynthesis genes were repressed in mycelia cultured with high initial spore densities. Metabolomic studies revealed that, in addition to inhibited AF biosynthesis, mycelia grown in peptone media with a high initial spore density showed suppressed fatty acid biosynthesis, reduced tricarboxylic acid (TCA) cycle intermediates, and increased pentose phosphate pathway products. Additions of TCA cycle intermediates had no effect on AF biosynthesis, suggesting the inhibited AF biosynthesis was not caused by depleted TCA cycle intermediates. CONCLUSIONS We here demonstrate that Aspergillus species grown in media with peptone as the sole carbon source are able to sense their own population densities and peptone concentrations to switch between rapid growth and AF production. This switching ability may offer Aspergillus species a competition advantage in natural ecosystems, producing AFs only when self-population is low and food is scarce.
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Affiliation(s)
- Shijuan Yan
- Practaculture College, Gansu Agricultural University, Lanzhou, 730070, China
- Key Laboratory of Plant Molecular Physiology, Institute of Botany, Chinese Academy of Sciences, 20 Nanxincun, Fragrant Hill, Beijing,, 100093, China
| | - Yating Liang
- Practaculture College, Gansu Agricultural University, Lanzhou, 730070, China
- School of Biology and Basic Medical Sciences, Soochow University, Suzhou, 215000, China
| | - Jindan Zhang
- Key Laboratory of Plant Molecular Physiology, Institute of Botany, Chinese Academy of Sciences, 20 Nanxincun, Fragrant Hill, Beijing,, 100093, China
| | - Chun-Ming Liu
- Key Laboratory of Plant Molecular Physiology, Institute of Botany, Chinese Academy of Sciences, 20 Nanxincun, Fragrant Hill, Beijing,, 100093, China
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5
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Leisch H, Morley K, Lau PCK. Baeyer−Villiger Monooxygenases: More Than Just Green Chemistry. Chem Rev 2011; 111:4165-222. [DOI: 10.1021/cr1003437] [Citation(s) in RCA: 317] [Impact Index Per Article: 24.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Affiliation(s)
- Hannes Leisch
- Biotechnology Research Institute, National Research Council Canada, 6100 Royalmount Avenue, Montreal, Quebec H4P 2R2, Canada
| | - Krista Morley
- Biotechnology Research Institute, National Research Council Canada, 6100 Royalmount Avenue, Montreal, Quebec H4P 2R2, Canada
| | - Peter C. K. Lau
- Biotechnology Research Institute, National Research Council Canada, 6100 Royalmount Avenue, Montreal, Quebec H4P 2R2, Canada
- Department of Microbiology and Immunology, McGill University, 3775 University Street, Montreal, Quebec H3A 2B4, Canada
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6
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Walsh CT, Fischbach MA. Natural products version 2.0: connecting genes to molecules. J Am Chem Soc 2010; 132:2469-93. [PMID: 20121095 DOI: 10.1021/ja909118a] [Citation(s) in RCA: 318] [Impact Index Per Article: 22.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Natural products have played a prominent role in the history of organic chemistry, and they continue to be important as drugs, biological probes, and targets of study for synthetic and analytical chemists. In this Perspective, we explore how connecting Nature's small molecules to the genes that encode them has sparked a renaissance in natural product research, focusing primarily on the biosynthesis of polyketides and non-ribosomal peptides. We survey monomer biogenesis, coupling chemistries from templated and non-templated pathways, and the broad set of tailoring reactions and hybrid pathways that give rise to the diverse scaffolds and functionalization patterns of natural products. We conclude by considering two questions: What would it take to find all natural product scaffolds? What kind of scientists will be studying natural products in the future?
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Affiliation(s)
- Christopher T Walsh
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, 240 Longwood Avenue, Boston, Massachusetts 02115, USA.
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Ehrlich KC, Chang PK, Scharfenstein LL, Cary JW, Crawford JM, Townsend CA. Absence of the aflatoxin biosynthesis gene, norA, allows accumulation of deoxyaflatoxin B1 in Aspergillus flavus cultures. FEMS Microbiol Lett 2010; 305:65-70. [PMID: 20158523 DOI: 10.1111/j.1574-6968.2010.01914.x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
Abstract
Biosynthesis of the highly toxic and carcinogenic aflatoxins in select Aspergillus species from the common intermediate O-methylsterigmatocystin has been postulated to require only the cytochrome P450 monooxygenase, OrdA (AflQ). We now provide evidence that the aryl alcohol dehydrogenase NorA (AflE) encoded by the aflatoxin biosynthetic gene cluster in Aspergillus flavus affects the accumulation of aflatoxins in the final steps of aflatoxin biosynthesis. Mutants with inactive norA produced reduced quantities of aflatoxin B(1) (AFB(1)), but elevated quantities of a new metabolite, deoxyAFB(1). To explain this result, we suggest that, in the absence of NorA, the AFB(1) reduction product, aflatoxicol, is produced and is readily dehydrated to deoxyAFB(1) in the acidic medium, enabling us to observe this otherwise minor toxin produced in wild-type A. flavus.
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Affiliation(s)
- Kenneth C Ehrlich
- Southern Regional Research Center, ARS/USDA, New Orleans, LA 70179, USA.
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Sharma V, Kelly GT, Watanabe CMH. Exploration of the Molecular Origin of the Azinomycin Epoxide: Timing of the Biosynthesis Revealed. Org Lett 2008; 10:4815-8. [DOI: 10.1021/ol8018852] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Affiliation(s)
- Vasudha Sharma
- Department of Chemistry, Texas A&M University, College Station, Texas 77842
| | - Gilbert T. Kelly
- Department of Chemistry, Texas A&M University, College Station, Texas 77842
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9
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Gengan RM, Chuturgoon AA, Dutton MF. Kinetics of the oxidoreductase involved in the conversion of O-methylsterigmatocystin to aflatoxin B1. Prep Biochem Biotechnol 2006; 36:297-306. [PMID: 16971301 DOI: 10.1080/10826060600912435] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
Abstract
Among the enzymatic steps in the aflatoxin biosynthetic pathway, the conversion of O-methylsterigmatocystin (OMST) to the potent environmental carcinogen aflatoxin B1 (AFB1), has been proposed to be catalysed by an oxidoreductase (OR) that requires a cytochrome P-450 type of oxidoreductase activity. This enzyme displays relative specificity towards OMST homologues in fungal whole cells. These studies were extended to the action of a cell-free enzyme system (CFES), on five OMST homologues, with a view to establish the kinetics. In the current study a CFES, containing an oxidoreductase, was derived from a blocked mutant of Aspergillus parasiticus (Wh1-11-105). The key experimental steps involved rapid concentration and efficient dialysis by membrane filtration to remove small biomolecules (MW<10,000), co-factors, primary and secondary metabolites. The kinetic parameters of the enzyme-substrate reactions indicated that the reaction follows a Michealis-Menten kinetics and OR activity decreased in the order: O-butylsterigmatocystin>O-propylsterigmatocystin>O-ethylsterigmatocystin>O-methylsterigmatocystin>O-acetylsterigmatocystin>O-benzoylsterigmatocystin. The 7-O-alkyl homologues were the best substrate for the CFES, thereby substantially supporting that the 7-O-methyl group of OMST is preferred for OR catalytic activity in the absence of any other alkylating groups in vitro. The Km was calculated as 5.65 microM for this CFES and varied marginally among the OMST homologues studied.
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Affiliation(s)
- Robert M Gengan
- Department of Chemistry, Faculty of Engineering, Science and the Built Environment, Durban University of Technology, Durban, South Africa.
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10
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Ehrlich KC, Chang PK, Yu J, Cotty PJ. Aflatoxin biosynthesis cluster gene cypA is required for G aflatoxin formation. Appl Environ Microbiol 2005; 70:6518-24. [PMID: 15528514 PMCID: PMC525170 DOI: 10.1128/aem.70.11.6518-6524.2004] [Citation(s) in RCA: 112] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Aspergillus flavus isolates produce only aflatoxins B1 and B2, while Aspergillus parasiticus and Aspergillus nomius produce aflatoxins B1, B2, G1, and G2. Sequence comparison of the aflatoxin biosynthesis pathway gene cluster upstream from the polyketide synthase gene, pksA, revealed that A. flavus isolates are missing portions of genes (cypA and norB) predicted to encode, respectively, a cytochrome P450 monooxygenase and an aryl alcohol dehydrogenase. Insertional disruption of cypA in A. parasiticus yielded transformants that lack the ability to produce G aflatoxins but not B aflatoxins. The enzyme encoded by cypA has highest amino acid identity to Gibberella zeae Tri4 (38%), a P450 monooxygenase previously shown to be involved in trichodiene epoxidation. The substrate for CypA may be an intermediate formed by oxidative cleavage of the A ring of O-methylsterigmatocystin by OrdA, the P450 monooxygenase required for formation of aflatoxins B1 and B2.
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Affiliation(s)
- Kenneth C Ehrlich
- Southern Research Center, Agricultural Regional Research Service, U.S. Department of Agriculture, New Orleans, Louisiana 70179, USA.
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11
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Keller NP, Watanabe CM, Kelkar HS, Adams TH, Townsend CA. Requirement of monooxygenase-mediated steps for sterigmatocystin biosynthesis by Aspergillus nidulans. Appl Environ Microbiol 2000; 66:359-62. [PMID: 10618248 PMCID: PMC91830 DOI: 10.1128/aem.66.1.359-362.2000] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Sterigmatocystin (ST) and aflatoxin B(1) (AFB(1)) are two polyketide-derived Aspergillus mycotoxins synthesized by functionally identical sets of enzymes. ST, the compound produced by Aspergillus nidulans, is a late intermediate in the AFB(1) pathway of A. parasiticus and A. flavus. Previous biochemical studies predicted that five oxygenase steps are required for the formation of ST. A 60-kb ST gene cluster in A. nidulans contains five genes, stcB, stcF, stcL, stcS, and stcW, encoding putative monooxygenase activities. Prior research showed that stcL and stcS mutants accumulated versicolorins B and A, respectively. We now show that strains disrupted at stcF, encoding a P-450 monooxygenase similar to A. parasiticus avnA, accumulate averantin. Disruption of either StcB (a putative P-450 monooxygenase) or StcW (a putative flavin-requiring monooxygenase) led to the accumulation of averufin as determined by radiolabeled feeding and extraction studies.
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Affiliation(s)
- N P Keller
- Department of Plant Pathology and Microbiology, Texas A&M University, College Station, Texas 77843, USA.
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12
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Yabe K, Nakamura M, Hamasaki T. Enzymatic formation of G-group aflatoxins and biosynthetic relationship between G- and B-group aflatoxins. Appl Environ Microbiol 1999; 65:3867-72. [PMID: 10473388 PMCID: PMC99713 DOI: 10.1128/aem.65.9.3867-3872.1999] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
We detected biosynthetic activity for aflatoxins G(1) and G(2) in cell extracts of Aspergillus parasiticus NIAH-26. We found that in the presence of NADPH, aflatoxins G(1) and G(2) were produced from O-methylsterigmatocystin and dihydro-O-methylsterigmatocystin, respectively. No G-group aflatoxins were produced from aflatoxin B(1), aflatoxin B(2), 5-methoxysterigmatocystin, dimethoxysterigmatocystin, or sterigmatin, confirming that B-group aflatoxins are not the precursors of G-group aflatoxins and that G- and B-group aflatoxins are independently produced from the same substrates (O-methylsterigmatocystin and dihydro-O-methylsterigmatocystin). In competition experiments in which the cell-free system was used, formation of aflatoxin G(2) from dihydro-O-methylsterigmatocystin was suppressed when O-methylsterigmatocystin was added to the reaction mixture, whereas aflatoxin G(1) was newly formed. This result indicates that the same enzymes can catalyze the formation of aflatoxins G(1) and G(2). Inhibition of G-group aflatoxin formation by methyrapone, SKF-525A, or imidazole indicated that a cytochrome P-450 monooxygenase may be involved in the formation of G-group aflatoxins. Both the microsome fraction and a cytosol protein with a native mass of 220 kDa were necessary for the formation of G-group aflatoxins. Due to instability of the microsome fraction, G-group aflatoxin formation was less stable than B-group aflatoxin formation. The ordA gene product, which may catalyze the formation of B-group aflatoxins, also may be required for G-group aflatoxin biosynthesis. We concluded that at least three reactions, catalyzed by the ordA gene product, an unstable microsome enzyme, and a 220-kDa cytosol protein, are involved in the enzymatic formation of G-group aflatoxins from either O-methylsterigmatocystin or dihydro-O-methylsterigmatocystin.
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Affiliation(s)
- K Yabe
- National Food Research Institute, Tsukuba, Ibaraki 305-8642, Japan.
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Silva JC, Minto RE, Barry CE, Holland KA, Townsend CA. Isolation and characterization of the versicolorin B synthase gene from Aspergillus parasiticus. Expansion of the aflatoxin b1 biosynthetic gene cluster. J Biol Chem 1996; 271:13600-8. [PMID: 8662689 DOI: 10.1074/jbc.271.23.13600] [Citation(s) in RCA: 51] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
Versicolorin B synthase catalyzes the side chain cyclization of racemic versiconal hemiacetal to the bisfuran ring system of(-)-versicolorin B, an essential transformation in the aflatoxin biosynthetic pathway of Aspergillus parasiticus. The dihydrobisfuran is key to the mutagenic nature of aflatoxin B1. The protein, which shows 58% similarity and 38% identity with glucose oxidase from Aspergillus niger, possesses an amino-terminal sequence homologous to the ADP-binding region of other flavoenzymes. However, this enzyme does not require flavin or nicotinamide cofactors for its cyclase activity. The 643-amino acid native enzyme contains three potential sites for N-linked glycosylation, Asn-Xaa-Thr or Asn-Xaa-Ser. The cDNA and genomic clones of versicolorin B synthase were isolated by screening the respective libraries with random-primed DNA probes generated from an exact copy of an internal vbs sequence. This probe was created through polymerase chain reaction by using nondegenerate polymerase chain reaction primers derived from the amino acid sequences of peptide fragments of the enzyme. The 1985-base genomic vbs DNA sequence is interrupted by one intron of 53 nucleotides. Southern blotting, nucleotide sequencing, and detailed restriction mapping of the vbs-containing genomic clones revealed the presence of omtA, a methyltransferase active in the biosynthesis, 3.3 kilobases upstream of vbs and oriented in the opposite direction from vbs. The presence of omtA in close proximity to vbs supports the theory that the genes encoding the aflatoxin biosynthetic enzymes in A. parasiticus are clustered.
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Affiliation(s)
- J C Silva
- Department of Chemistry, The Johns Hopkins University, Baltimore, Maryland 21218, USA
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Watanabe CM, Wilson D, Linz JE, Townsend CA. Demonstration of the catalytic roles and evidence for the physical association of type I fatty acid synthases and a polyketide synthase in the biosynthesis of aflatoxin B1. CHEMISTRY & BIOLOGY 1996; 3:463-9. [PMID: 8807876 DOI: 10.1016/s1074-5521(96)90094-0] [Citation(s) in RCA: 67] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
BACKGROUND Aflatoxin B1 (compound 5. ) is a potent environmental carcinogen produced by certain Aspergillus species. Its first stable biosynthetic precursor is the anthraquinone norsolorinic acid (compound 3. ), which accumulates in the Aspergillus mutant strain NOR-1. Biochemical and genetic evidence suggest that this metabolite is synthesized in vivo by a specialized pair of fatty acid synthases (FAS-1 and FAS-2) and a separately transcribed polyketide synthase (PKS-A). RESULTS The N-acetylcysteamine (NAC) thioester of hexanoic acid was shown to efficiently support the biosynthesis of norsolorinic acid (compound 3. ) in the NOR-1 strain. In contrast, the mutants Dis-1 and Dis-2, which are derived from NOR-1 by insertional inactivation of fas-1, produced unexpectedly low amounts of norsolorinic acid in the presence of hexanoylNAC. Controls eliminated defects in the parent strain or enhancement of degradative beta-oxidation activity as an explanation for the low level of production. Southern blots and restriction mapping of Dis-1 and Dis-2 suggested normal levels of expression of the PKS-A and FAS-2 proteins should be observed because the genes encoding these proteins are not physically altered by disruption of fas-1. CONCLUSIONS The impaired ability of Dis-1 and Dis-2, harboring modified FAS-1 enzymes, to carry out norsolorinic acid synthesis implies the need for FAS-1 (and possibly also FAS-2) to physically associate with the PKS before biosynthesis can begin. The failure of the unaffected PKS alone to be efficiently primed by hexanoylNAC, and the presumed requirement for at least one of the FAS proteins to bind and transfer the C6 unit to the PKS, is in contrast to behavior widely believed to occur for type I PKSs.
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Affiliation(s)
- C M Watanabe
- Department of Chemistry, The Johns Hopkins University, Baltimore, MD 21218, USA
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