Conversion of a new metabolite to aflatoxin B2 by Aspergillus parasiticus

Bhatnagar, Deepak; Foell, C. J.; McCormick, Susan P.

doi:10.1128/aem.53.12.2804-2807.1987

Cited by 20 publications

(13 citation statements)

References 16 publications

(25 reference statements)

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“…The enzymes required for the latter stages of aflatoxin biosynthesis (ST --OMST -. aflatoxin B1) are present in this strain (12).…”

Section: Materuils and Methodsmentioning

confidence: 80%

“…Although preliminary sequencing data indicate that their N termini differ, this does not rule out the possibility that the 40-kDa protein has some sequence homology to the 168-kDa protein. Antibodies raised against a preparation of the larger protein (12) reacted weakly with the 40-kDa protein (data not shown); antibodies against the 40-kDa protein need to be tested with the 168-kDa protein.…”

Section: Discussionmentioning

confidence: 99%

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Purification of a 40-kilodalton methyltransferase active in the aflatoxin biosynthetic pathway

Keller

Dischinger

Bhatnagar

et al. 1993

Appl Environ Microbiol

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The penultimate step in the aflatoxin biosynthetic pathway of the filamentous fungi Aspergilusflavus and A. parasiticus involves conversion of sterigmatocystin to O-methylsterigmatocystin. An S-adenosylmethioninedependent methyltransferase that catalyzes this reaction was purified to homogeneity (>90,%) from 78-hold mycelia of A. parasiticus SRRC 163. Purification of this soluble enzyme was carried out by five soft-gel chromatographic steps: cell debris remover treatment, QMA ACELL chromatography, hydroxylapatite-Ultrogel chromatography, DEAE-Spherodex chromatography, and Octyl Avidgel chromatography, followed by MA7Q high-performance liquid chromatography. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the protein peak from this step on silver staining identified a single band of approximately 40 kDa. This purified protein was distinct from the dimeric 168-kDa methyltransferase purified from the same fungal strain under identical growth conditions (D. Bhatnagar, A. H. J. Ullah, and T. E. Cleveland, Prep. Biochem. 18:321-349, 1988). The chromatographic behavior and N-terminal sequence of the 40-kDa enzyme were also distinct from those of the 168-kDa methyltransferase. The molar extinction coefficient of the 40-kDa enzyme at 278 nm was estimated to be 4.7 x 104 M-1 cm-' in 50 mM potassium phosphate buffer (pH 7.5).

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“…The enzymes required for the latter stages of aflatoxin biosynthesis (ST --OMST -. aflatoxin B1) are present in this strain (12).…”

Section: Materuils and Methodsmentioning

confidence: 80%

Section: Discussionmentioning

confidence: 99%

Purification of a 40-kilodalton methyltransferase active in the aflatoxin biosynthetic pathway

Keller

Dischinger

Bhatnagar

et al. 1993

Appl Environ Microbiol

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“…After submission of this manuscript, Cleveland et al (8) on September 5, 2020 by guest http://aem.asm.org/…”

Section: Discussionmentioning

confidence: 99%

Biosynthetic relationship among aflatoxins B1, B2, G1, and G2

Yabe

Ando

Hamasaki

1988

Appl Environ Microbiol

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Aspergillus parasiticus NIAH-26, a UV-irradiated mutant of A. parasiticus SYS-4 (NRRL 2999), produces neither aflatoxins nor precursors. When sterigmatocystin (ST) or O-methylsterigmatocystin was fed to this mutant in YES medium, aflatoxins B, (AFBI) and G, (AFG,) were produced. When dihydrosterigmatocystin (DHST) or dihydro-O-methylsterigmatocystin was fed to this mold, aflatoxins B2 (AFB2) and G2 (AFG2) were produced. The reactions from ST to AFB1 and DHST to AFB2 were also observed in the cell-free system and were catalyzed stepwise by the methyltransferase and oxidoreductase enzymes. In the feeding experiments of strain NIAH-26, the convertibility from ST to AFB,-AFG, was found to be remarkably suppressed by the coexistence of DHST in the medium, and the convertibility from DHST to AFB2-AFG2 was also suppressed by the presence of ST. When some other mutants which endogenously produce a small amount of aflatoxins (mainly AFB, and AFG,) were cultured with DHST, the amounts of AFB1 and AFG, produced were significantly decreased, whereas AFB2 and AFG2 were newly produced. In similar feeding experiments in which 27 kinds of mutants including these mutants were used, most of the mutants which were able to convert exogenous ST to AFBI-AFG1 were also found to convert exogenous DHST to AFB2-AFG2. These results suggest that the same enzymes may be involved in the both biosynthetic pathways from ST to AFB,-AFG, and DHST to AFB2-AFG2. The reactions described herein were not observed when the molds had been cultured in the YEP medium. Aflatoxins B1 (AFBj), B, (AFB,), G1 (AFG1), and G, (AFG,) are toxic secondary metabolities produced by certain strains of the common molds Aspei-gillius flai'iis and A. par-asiticits (4, 22). The biosynthetic pathway of AFB1 has been extensively studied (4, 5, 22, 24), and it has been suggested that AFB1 is produced from sterigmatocystin (ST) and O-methylsterigmatocystin (OMST); also, some enzyme activities relating to several steps in the biosynthetic pathway have been reported (2, 4, 26-28). However, there are many conflicting hypotheses concerning the biosynthetic pathways of other aflatoxins (5, 6, 13-16, 20, 23), and the precise relationship between AFB1 and other aflatoxins is still unclear. Maggon and Venkitasubramanian suggested that AFB., AFG1, and AFG, may be metabolically related to AFB1 by a direct interconversion process (23). In contrast, Dutton et al. suggested that AFB1 and AFB, may arise independently via a branched pathway (13). Dihydrosterigmatocystin (DHST) and dihydro-O-methylsterigmatocystin (DHOMST) are fungal secondary metabolites that have been isolated from A. Versicolor (Vuill .) Tiraboshi (10, 17) and A.flavus (10, 11), respectively. These compounds are dihydroderivatives of ST and OMST and seemed to be precursors of AFB,, because AFB, is a dihydro derivative of AFB1. In this study, the biosynthetic relationship among four kinds of aflatoxins (AFB1, AFG1, AFB2 and AFG,) has been examined by both feeding experiments and a cell-free system.

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“…Dried residues were resuspended in 300 μl of chloroform. Twenty-five microliters of each extracts were separated by thin layer chromatography (TLC) as previously described [ 37 ] on silica plate (Si250F, J.T. Baker) using chloroform:acetone (85:15,v/v) as solvent system.…”

Section: Methodsmentioning

confidence: 99%

RmtA, a Putative Arginine Methyltransferase, Regulates Secondary Metabolism and Development in Aspergillus flavus

2016

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Aspergillus flavus colonizes numerous oil seed crops such as corn, peanuts, treenuts and cotton worldwide, contaminating them with aflatoxin and other harmful potent toxins. In the phylogenetically related model fungus Aspergillus nidulans, the methyltransferase, RmtA, has been described to be involved in epigenetics regulation through histone modification. Epigenetics regulation affects a variety of cellular processes, including morphogenesis and secondary metabolism. Our study shows that deletion of rmtA in A. flavus results in hyperconidiating colonies, indicating that rmtA is a repressor of asexual development in this fungus. The increase in conidiation in the absence of rmtA coincides with greater expression of brlA, abaA, and wetA compared to that in the wild type. Additionally, the rmtA deletion mutant presents a drastic reduction or loss of sclerotial production, while forced expression of this gene increased the ability of this fungus to generate these resistant structures, revealing rmtA as a positive regulator of sclerotial formation. Importantly, rmtA is also required for the production of aflatoxin B1 in A. flavus, affecting the expression of aflJ. Furthermore, biosynthesis of additional metabolites is also controlled by rmtA, indicating a broad regulatory output in the control of secondary metabolism. This study also revealed that rmtA positively regulates the expression of the global regulatory gene veA, which could contribute to mediate the effects of rmtA on development and secondary metabolism in this relevant opportunistic plant pathogen.

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Conversion of a new metabolite to aflatoxin B2 by Aspergillus parasiticus

Cited by 20 publications

References 16 publications

Purification of a 40-kilodalton methyltransferase active in the aflatoxin biosynthetic pathway

Purification of a 40-kilodalton methyltransferase active in the aflatoxin biosynthetic pathway

Biosynthetic relationship among aflatoxins B1, B2, G1, and G2

RmtA, a Putative Arginine Methyltransferase, Regulates Secondary Metabolism and Development in Aspergillus flavus

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