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Zhang SY, Wang H, Yang M, Yao DS, Xie CF, Liu DL. Versicolorin A is a potential indicator of aflatoxin contamination in the granary-stored corn. Food Addit Contam Part A Chem Anal Control Expo Risk Assess 2018; 35:972-984. [PMID: 29337658 DOI: 10.1080/19440049.2017.1419579] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
The objective of this study was to evaluate the feasibility of the predictive monitoring of aflatoxin B1 (AFB1) under granary conditions, since mycotoxin contamination of the stored grain represents an important issue. Using the storage test, we investigated the relationship between versicolorin A (Ver A, an intermediate in AFB1 biosynthesis) levels and the levels of aflatoxigenic fungi, and their relationship with aflatoxin production. All samples, except for one, were found to be contaminated with aflatoxigenic fungi using PCR analyses, while their AFB1 levels were not detectable before the storage test using an enzyme-linked immunosorbent assay (ELISA) method with an LOD of 2 μg/kg. Aflatoxigenic fungi levels were analysed, as well as Ver A levels prior to the accumulation of AFB1 (Levels were ≥5 μg/kg; the permissible levels of AFB1 in corn intended for direct consumption are <5 μg/kg (EC)). Statistical analyses demonstrated that aflatoxin levels after both actual storage and safe storage (AFB1˂5μg/kg) times are significantly correlated with the Ver A levels and the changes in Ver A levels (ΔVer A). Both high and variable Ver A levels were indicative of the vigorous metabolic activity of aflatoxigenic fungi. In contrast, steady Ver A levels showed that aflatoxin production by the fungi was not active. Monitoring Ver A levels and their changes may allow an earlier detection of harmful aflatoxin contamination in the stored grain. Additionally, the toxicity of Ver A should be further examined. The results of our study indicate that the monitoring of Ver A levels, even when the AFB1 levels are very low, may increase the safety of grain consumption, especially considering Ver A toxicity.
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Affiliation(s)
- Shu-Yao Zhang
- a Department of Biotechnology, College of Life Science and Technology , Jinan University , Guangzhou , China.,b State Key Laboratory of Applied Microbiology Southern China, Guangdong Provincial Key Laboratory of Microbial Culture Collection and Application , Guangdong Institute of Microbiology , Guangzhou , China.,c Institute of Microbial Biotechnology , Jinan University , Guangzhou , China
| | - Hao Wang
- a Department of Biotechnology, College of Life Science and Technology , Jinan University , Guangzhou , China.,c Institute of Microbial Biotechnology , Jinan University , Guangzhou , China
| | - Min Yang
- a Department of Biotechnology, College of Life Science and Technology , Jinan University , Guangzhou , China.,c Institute of Microbial Biotechnology , Jinan University , Guangzhou , China
| | - Dong-Sheng Yao
- a Department of Biotechnology, College of Life Science and Technology , Jinan University , Guangzhou , China.,c Institute of Microbial Biotechnology , Jinan University , Guangzhou , China.,d National Engineering Research Centre of Genetic Medicine , Guangzhou , China
| | - Chun-Fang Xie
- a Department of Biotechnology, College of Life Science and Technology , Jinan University , Guangzhou , China.,c Institute of Microbial Biotechnology , Jinan University , Guangzhou , China.,d National Engineering Research Centre of Genetic Medicine , Guangzhou , China
| | - Da-Ling Liu
- a Department of Biotechnology, College of Life Science and Technology , Jinan University , Guangzhou , China.,c Institute of Microbial Biotechnology , Jinan University , Guangzhou , China
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Wee J, Hong SY, Roze LV, Day DM, Chanda A, Linz JE. The Fungal bZIP Transcription Factor AtfB Controls Virulence-Associated Processes in Aspergillus parasiticus. Toxins (Basel) 2017; 9:toxins9090287. [PMID: 28926946 PMCID: PMC5618220 DOI: 10.3390/toxins9090287] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2017] [Revised: 08/24/2017] [Accepted: 09/07/2017] [Indexed: 12/14/2022] Open
Abstract
Fungal basic leucine zipper (bZIP) transcription factors mediate responses to oxidative stress. The ability to regulate stress response pathways in Aspergillus spp. was postulated to be an important virulence-associated cellular process, because it helps establish infection in humans, plants, and animals. Previous studies have demonstrated that the fungal transcription factor AtfB encodes a protein that is associated with resistance to oxidative stress in asexual conidiospores, and AtfB binds to the promoters of several stress response genes. Here, we conducted a gene silencing of AtfB in Aspergillus parasiticus, a well-characterized fungal pathogen of plants, animals, and humans that produces the secondary metabolite and carcinogen aflatoxin, in order to determine the mechanisms by which AtfB contributes to virulence. We show that AtfB silencing results in a decrease in aflatoxin enzyme levels, the down-regulation of aflatoxin accumulation, and impaired conidiospore development in AtfB-silenced strains. This observation is supported by a decrease of AtfB protein levels, and the down-regulation of many genes in the aflatoxin cluster, as well as genes involved in secondary metabolism and conidiospore development. Global expression analysis (RNA Seq) demonstrated that AtfB functionally links oxidative stress response pathways to a broader and novel subset of target genes involved in cellular defense, as well as in actin and cytoskeleton arrangement/transport. Thus, AtfB regulates the genes involved in development, stress response, and secondary metabolism in A. parasiticus. We propose that the bZIP regulatory circuit controlled by AtfB provides a large number of excellent cellular targets to reduce fungal virulence. More importantly, understanding key players that are crucial to initiate the cellular response to oxidative stress will enable better control over its detrimental impacts on humans.
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Affiliation(s)
- Josephine Wee
- Department of Food Science and Human Nutrition, Michigan State University, East Lansing, MI 48824, USA.
- Center for Integrative Toxicology, Michigan State University, East Lansing, MI 48824, USA.
| | - Sung-Yong Hong
- Department of Food Science and Human Nutrition, Michigan State University, East Lansing, MI 48824, USA.
| | - Ludmila V Roze
- Department of Plant Biology, Michigan State University, East Lansing, MI 48824, USA.
| | - Devin M Day
- Department of Food Science and Human Nutrition, Michigan State University, East Lansing, MI 48824, USA.
| | - Anindya Chanda
- Department of Environmental Health Sciences, University of South Carolina, Columbia, SC 29208, USA.
| | - John E Linz
- Department of Food Science and Human Nutrition, Michigan State University, East Lansing, MI 48824, USA.
- Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, MI 48824, USA.
- Center for Integrative Toxicology, Michigan State University, East Lansing, MI 48824, USA.
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Abstract
Oxidative cyclizations are important transformations that occur widely during natural product biosynthesis. The transformations from acyclic precursors to cyclized products can afford morphed scaffolds, structural rigidity, and biological activities. Some of the most dramatic structural alterations in natural product biosynthesis occur through oxidative cyclization. In this Review, we examine the different strategies used by nature to create new intra(inter)molecular bonds via redox chemistry. This Review will cover both oxidation- and reduction-enabled cyclization mechanisms, with an emphasis on the former. Radical cyclizations catalyzed by P450, nonheme iron, α-KG-dependent oxygenases, and radical SAM enzymes are discussed to illustrate the use of molecular oxygen and S-adenosylmethionine to forge new bonds at unactivated sites via one-electron manifolds. Nonradical cyclizations catalyzed by flavin-dependent monooxygenases and NAD(P)H-dependent reductases are covered to show the use of two-electron manifolds in initiating cyclization reactions. The oxidative installations of epoxides and halogens into acyclic scaffolds to drive subsequent cyclizations are separately discussed as examples of "disappearing" reactive handles. Last, oxidative rearrangement of rings systems, including contractions and expansions, will be covered.
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Affiliation(s)
- Man-Cheng Tang
- Department of Chemical and Biomolecular Engineering, Department of Chemistry and Biochemistry, University of California, Los Angeles, 420 Westwood Plaza, Los Angeles, CA 90095, USA
| | - Yi Zou
- Department of Chemical and Biomolecular Engineering, Department of Chemistry and Biochemistry, University of California, Los Angeles, 420 Westwood Plaza, Los Angeles, CA 90095, USA
| | - Kenji Watanabe
- Department of Pharmaceutical Sciences, University of Shizuoka, Shizuoka 422-8526, Japan
| | - Christopher T. Walsh
- Stanford University Chemistry, Engineering, and Medicine for Human Health (ChEM-H), Stanford University, 443 Via Ortega, Stanford, CA 94305
| | - Yi Tang
- Department of Chemical and Biomolecular Engineering, Department of Chemistry and Biochemistry, University of California, Los Angeles, 420 Westwood Plaza, Los Angeles, CA 90095, USA
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Arroyo-Manzanares N, Diana Di Mavungu J, Uka V, Malysheva SV, Cary JW, Ehrlich KC, Vanhaecke L, Bhatnagar D, De Saeger S. Use of UHPLC high-resolution Orbitrap mass spectrometry to investigate the genes involved in the production of secondary metabolites inAspergillus flavus. Food Addit Contam Part A Chem Anal Control Expo Risk Assess 2015; 32:1656-73. [DOI: 10.1080/19440049.2015.1071499] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
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Roze LV, Chanda A, Wee J, Awad D, Linz JE. Stress-related transcription factor AtfB integrates secondary metabolism with oxidative stress response in aspergilli. J Biol Chem 2011; 286:35137-48. [PMID: 21808056 DOI: 10.1074/jbc.m111.253468] [Citation(s) in RCA: 87] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
In filamentous fungi, several lines of experimental evidence indicate that secondary metabolism is triggered by oxidative stress; however, the functional and molecular mechanisms that mediate this association are unclear. The basic leucine zipper (bZIP) transcription factor AtfB, a member of the bZIP/CREB family, helps regulate conidial tolerance to oxidative stress. In this work, we investigated the role of AtfB in the connection between oxidative stress response and secondary metabolism in the filamentous fungus Aspergillus parasiticus. This well characterized model organism synthesizes the secondary metabolite and carcinogen aflatoxin. Chromatin immunoprecipitation with specific anti-AtfB demonstrated AtfB binding at promoters of seven genes in the aflatoxin gene cluster that carry CREs. Promoters lacking CREs did not show AtfB binding. The binding of AtfB to the promoters occurred under aflatoxin-inducing but not under aflatoxin-noninducing conditions and correlated with activation of transcription of the aflatoxin genes. Deletion of veA, a global regulator of secondary metabolism and development, nearly eliminated this binding. Electrophoretic mobility shift analysis demonstrated that AtfB binds to the nor-1 (an early aflatoxin gene) promoter at a composite regulatory element that consists of highly similar, adjacent CRE1 and AP-1-like binding sites. The five nucleotides immediately upstream from CRE1, AGCC(G/C), are highly conserved in five aflatoxin promoters that demonstrate AtfB binding. We propose that AtfB is a key player in the regulatory circuit that integrates secondary metabolism and cellular response to oxidative stress.
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Affiliation(s)
- Ludmila V Roze
- Department of Food Science and Human Nutrition, Michigan State University, East Lansing, Michigan 48824, USA
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Huffman J, Gerber R, Du L. Recent advancements in the biosynthetic mechanisms for polyketide-derived mycotoxins. Biopolymers 2010; 93:764-76. [PMID: 20578001 PMCID: PMC2894268 DOI: 10.1002/bip.21483] [Citation(s) in RCA: 85] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Polyketides (PKs) are a large group of natural products produced by microorganisms and plants. They are biopolymers of acetate and other short carboxylates and are biosynthesized by multifunctional enzymes called polyketide synthases (PKSs). This review discusses the biosynthesis of four toxic PK, aflatoxins, fumonisins, ochratoxins (OTs), and zearalenone. These metabolites are structurally diverse and differ in their mechanisms of toxicity. However, they are all of concern in food safety and agriculture because of their toxic properties and their frequent accumulation in crops used for food and feed. The focus is on the recent advancements in the understanding of the molecular mechanisms for the biosynthesis of these mycotoxins. Several of the mycotoxin PKSs have been genetically and biochemically studied while other PKSs remain to be investigated. Multiple post-PKS modifications are often required for the maturation of the mycotoxins. Many of these modification steps for aflatoxins and fumonisins are well established while the post-PKS modifications for zearalenone and OTs remain to be biochemically characterized. More efforts are needed to completely illustrate the biosynthetic mechanisms for this important group of PKs.
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Affiliation(s)
- Justin Huffman
- Department of Chemistry, University of Nebraska-Lincoln, NE 68588, USA
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Roze LV, Chanda A, Linz JE. Compartmentalization and molecular traffic in secondary metabolism: a new understanding of established cellular processes. Fungal Genet Biol 2010; 48:35-48. [PMID: 20519149 DOI: 10.1016/j.fgb.2010.05.006] [Citation(s) in RCA: 113] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2010] [Revised: 05/11/2010] [Accepted: 05/12/2010] [Indexed: 01/15/2023]
Abstract
Great progress has been made in understanding the regulation of expression of genes involved in secondary metabolism. Less is known about the mechanisms that govern the spatial distribution of the enzymes, cofactors, and substrates that mediate catalysis of secondary metabolites within the cell. Filamentous fungi in the genus Aspergillus synthesize an array of secondary metabolites and provide useful systems to analyze the mechanisms that mediate the temporal and spatial regulation of secondary metabolism in eukaryotes. For example, aflatoxin biosynthesis in Aspergillus parasiticus has been studied intensively because this mycotoxin is highly toxic, mutagenic, and carcinogenic in humans and animals. Using aflatoxin synthesis to illustrate key concepts, this review focuses on the mechanisms by which sub-cellular compartmentalization and intra-cellular molecular traffic contribute to the initiation and completion of secondary metabolism within the cell. We discuss the recent discovery of aflatoxisomes, specialized trafficking vesicles that participate in the compartmentalization of aflatoxin synthesis and export of the toxin to the cell exterior; this work provides a new and clearer understanding of how cells integrate secondary metabolism into basic cellular metabolism via the intra-cellular trafficking machinery.
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Affiliation(s)
- Ludmila V Roze
- Department of Food Science and Human Nutrition, Michigan State University, East Lansing, MI-48824, USA
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Abstract
Eukaryotes have evolved highly conserved vesicle transport machinery to deliver proteins to the vacuole. In this study we show that the filamentous fungus Aspergillus parasiticus employs this delivery system to perform new cellular functions, the synthesis, compartmentalization, and export of aflatoxin; this secondary metabolite is one of the most potent naturally occurring carcinogens known. Here we show that a highly pure vesicle-vacuole fraction isolated from A. parasiticus under aflatoxin-inducing conditions converts sterigmatocystin, a late intermediate in aflatoxin synthesis, to aflatoxin B(1); these organelles also compartmentalize aflatoxin. The role of vesicles in aflatoxin biosynthesis and export was confirmed by blocking vesicle-vacuole fusion using 2 independent approaches. Disruption of A. parasiticus vb1 (encodes a protein homolog of AvaA, a small GTPase known to regulate vesicle fusion in A. nidulans) or treatment with Sortin3 (blocks Vps16 function, one protein in the class C tethering complex) increased aflatoxin synthesis and export but did not affect aflatoxin gene expression, demonstrating that vesicles and not vacuoles are primarily involved in toxin synthesis and export. We also observed that development of aflatoxigenic vesicles (aflatoxisomes) is strongly enhanced under aflatoxin-inducing growth conditions. Coordination of aflatoxisome development with aflatoxin gene expression is at least in part mediated by Velvet (VeA), a global regulator of Aspergillus secondary metabolism. We propose a unique 2-branch model to illustrate the proposed role for VeA in regulation of aflatoxisome development and aflatoxin gene expression.
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Functional expression and subcellular localization of the aflatoxin pathway enzyme Ver-1 fused to enhanced green fluorescent protein. Appl Environ Microbiol 2008; 74:6385-96. [PMID: 18757582 DOI: 10.1128/aem.01185-08] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Aflatoxin, a mycotoxin synthesized by Aspergillus spp., is among the most potent naturally occurring carcinogens known. Little is known about the subcellular organization of aflatoxin synthesis. Previously, we used transmission electron microscopy and immunogold labeling to demonstrate that the late aflatoxin enzyme OmtA localizes primarily to vacuoles in fungal cells on the substrate surface of colonies. In the present work, we monitored subcellular localization of Ver-1 in real time in living cells. Aspergillus parasiticus strain CS10-N2 was transformed with plasmid constructs that express enhanced green fluorescent protein (EGFP) fused to Ver-1. Analysis of transformants demonstrated that EGFP fused to Ver-1 at either the N or C terminus functionally complemented nonfunctional Ver-1 in recipient cells. Western blot analysis detected predominantly full-length Ver-1 fusion proteins in transformants. Confocal laser scanning microscopy demonstrated that Ver-1 fusion proteins localized in the cytoplasm and in the lumen of up to 80% of the vacuoles in hyphae grown for 48 h on solid media. Control EGFP (no Ver-1) expressed in transformants was observed in only 13% of the vacuoles at this time. These data support a model in which middle and late aflatoxin enzymes are synthesized in the cytoplasm and transported to vacuoles, where they participate in aflatoxin synthesis.
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10
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Roze LV, Arthur AE, Hong SY, Chanda A, Linz JE. The initiation and pattern of spread of histone H4 acetylation parallel the order of transcriptional activation of genes in the aflatoxin cluster. Mol Microbiol 2007; 66:713-26. [PMID: 17919289 DOI: 10.1111/j.1365-2958.2007.05952.x] [Citation(s) in RCA: 88] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The 27 genes involved in aflatoxin biosynthesis are clustered within a 70 kb region in the Aspergillus parasiticus genome. Using chromatin immunoprecipitation, we demonstrated a positive correlation between the initiation and spread of histone H4 acetylation in aflatoxin promoters and the onset of accumulation of aflatoxin proteins and aflatoxin. Histone H4 acetylation in the pksA (encodes an 'early' biosynthetic pathway enzyme) promoter peaked at 30 h, prior to the increased acetylation in the omtA and ordA (encode 'late' enzymes) promoters detected at 40 h. The specific order in which pksA, ver-1 (encodes a 'middle' enzyme) and omtA transcripts accumulated in cells paralleled the pattern of spread of histone H4 acetylation. Binding of AflR, a positive regulator of aflatoxin biosynthesis, to the ordA promoter showed a positive correlation with the spread of histone H4 acetylation. The data suggest that the order of genes within the aflatoxin cluster determines the timing and order of transcriptional activation, and that the site of initiation and spread of histone H4 acetylation mediate this process. Our data indicate that the aflatoxin and adjacent sugar utilization clusters are part of a larger 'regulatory unit'.
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Affiliation(s)
- Ludmila V Roze
- Department of Food Science and Human Nutrition, Michigan State University, East Lansing, Michigan 48824, USA
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Schwelm A, Barron NJ, Zhang S, Bradshaw RE. Early expression of aflatoxin-like dothistromin genes in the forest pathogen Dothistroma septosporum. ACTA ACUST UNITED AC 2007; 112:138-46. [PMID: 18262779 DOI: 10.1016/j.mycres.2007.03.018] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2007] [Revised: 02/22/2007] [Accepted: 03/20/2007] [Indexed: 11/30/2022]
Abstract
The forest pathogen Dothistroma septosporum produces the polyketide dothistromin, a mycotoxin very similar in structure to versicolorin B, a precursor of aflatoxin (AF). Dothistromin is a broad-range toxin and possibly involved in red-band needle blight disease. As the role of dothistromin in the disease is unknown the expression of dothistromin genes was studied to reveal clues to its function. Although the genes of AF and dothistromin biosynthesis are very similar, this study revealed remarkable differences in the timing of their expression. Secondary metabolites, like AF, are usually produced during late exponential phase. Previously identified dothistromin genes, as well as a newly reported versicolorin B synthase gene, vbsA, showed high levels of expression during the onset of exponential growth. This unusual early expression was also seen in transformants containing a green fluorescent protein (GFP) gene regulated by a dothistromin gene promoter, where the highest GFP expression occurred in young mycelium. Two hypotheses for the biological role of dothistromin are proposed based on these results. The study of dothistromin genes will improve current knowledge about secondary metabolite genes, their putative biological roles, and their regulation.
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Affiliation(s)
- Arne Schwelm
- National Centre for Advanced Bio-Protection Technologies, Institute of Molecular BioSciences, Massey University, Private Bag 11222, Palmerston North, New Zealand
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Chiou CH, Lee LW, Owens SA, Whallon JH, Klomparens KL, Townsend CA, Linz JE. Distribution and sub-cellular localization of the aflatoxin enzyme versicolorin B synthase in time-fractionated colonies of Aspergillus parasiticus. Arch Microbiol 2004; 182:67-79. [PMID: 15258720 DOI: 10.1007/s00203-004-0700-6] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2004] [Revised: 06/17/2004] [Accepted: 06/18/2004] [Indexed: 10/26/2022]
Abstract
Aflatoxins are highly toxic and carcinogenic fungal secondary metabolites. At least 18 enzyme activities are required for aflatoxin biosynthesis in the filamentous fungus Aspergillus parasiticus. One of these enzymes, versicolorin B synthase (VBS), catalyzes bisfuran ring closure in versiconal hemiacetal (a reaction near the middle of the pathway) to form versicolorin B. This reaction is required for the subsequent activation to aflatoxin B1-8,9 epoxide, a highly reactive and toxic aflatoxin metabolite, and is important for aflatoxin toxicity. We analyzed the localization of VBS in the aflatoxin-producing strain A. parasiticus SU-1 grown on solid media using a colony fractionation technique developed previously. A highly specific polyclonal antibody, raised against a maltose-binding protein-VBS fusion protein synthesized in Escherichia coli, was used to detect VBS in SU-1 grown on a rich solid medium via immunofluorescence confocal laser scanning microscopy (CLSM) and immunogold transmission electron microscopy (TEM). VBS was detected in both vegetative hyphae and in asexual developmental structures, called conidiophores. Western blot and CLSM analyses demonstrated the highest abundance of VBS in colony fraction S2 consisting of cells that had grown for 24-48 h; this fraction also contained the highest levels of newly developed conidiophores and the highest abundance of aflatoxin B1, consistent with VBS abundance. At the subcellular level, CLSM and TEM detected VBS distributed throughout the cytoplasm and concentrated in ring-like structures surrounding nuclei. It is uncertain whether enzymatically active VBS is present in either or both locations.
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Affiliation(s)
- Ching-Hsun Chiou
- Department of Food Science and Human Nutrition, 234B GM Trout Food Science and Human Nutrition Building, Michigan State University (MSU), East Lansing, MI 48824, USA
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Yu J, Chang PK, Ehrlich KC, Cary JW, Bhatnagar D, Cleveland TE, Payne GA, Linz JE, Woloshuk CP, Bennett JW. Clustered pathway genes in aflatoxin biosynthesis. Appl Environ Microbiol 2004; 70:1253-62. [PMID: 15006741 PMCID: PMC368384 DOI: 10.1128/aem.70.3.1253-1262.2004] [Citation(s) in RCA: 553] [Impact Index Per Article: 27.7] [Reference Citation Analysis] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Affiliation(s)
- Jiujiang Yu
- Southern Regional Research Center, Agricultural Research Service, U.S. Department of Agriculture, New Orleans, Louisiana 70124, USA.
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Roze LV, Miller MJ, Rarick M, Mahanti N, Linz JE. A novel cAMP-response element, CRE1, modulates expression of nor-1 in Aspergillus parasiticus. J Biol Chem 2004; 279:27428-39. [PMID: 15054098 DOI: 10.1074/jbc.m400075200] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The level of aflatoxin accumulation in the filamentous fungus Aspergillus parasiticus is modulated by a variety of environmental cues. The presence of glucose (a preferred carbon source) in liquid and solid glucose minimal salts (GMS) growth media strongly stimulated aflatoxin accumulation. Peptone (a non-preferred carbon source) in peptone minimal salts (PMS) media stimulated only low levels of aflatoxin accumulation. Glucose stimulated transcription of the aflatoxin structural genes ver-1 and nor-1 to similar intermediate levels in liquid GMS, while on solid media, ver-1 transcription was stimulated to 20-fold higher levels than nor-1. PMS liquid and solid media stimulated very low or non-detectable levels of transcription of both genes. Electrophoretic mobility shift analysis using a nor-1 promoter fragment (norR) and A. parasiticus cell protein extracts revealed specific DNA-protein complexes of different mobility on GMS and PMS solid and liquid media. An imperfect cAMP-response element, CRE1, was identified in norR that mediated formation of the specific DNA-protein complexes. Mutation in CRE1 or AflR1 (AflR cis-acting site) caused up to a 3-fold decrease in cAMP-mediated stimulation of nor-1 promoter activity on GMS agar. South-Western blot analysis identified a 32-kDa protein that specifically bound to norR. p32 could be co-immunoprecipitated by anti-AflR antibody and co-purified with an AflR-maltose-binding protein fusion demonstrating a physical interaction between AflR and p32 in vitro. We hypothesize that p32 assists AflR in binding to the nor-1 promoter, thereby modulating nor-1 gene expression in response to environmental cues.
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Affiliation(s)
- Ludmila V Roze
- Department of Food Science and Human Nutrition, Michigan State University, East Lasing 48824, USA
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