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Related Experiment Videos

Two distinct O-methyltransferases in aflatoxin biosynthesis.

K Yabe1, Y Ando, J Hashimoto

  • 1National Institute of Animal Health, Ibaraki, Japan.

Applied and Environmental Microbiology
|September 1, 1989
PubMed
Summary

Sterigmatocystin derivatives are precursors to aflatoxins. Methylation of demethylsterigmatocystin (DMST) and dihydrodemethylsterigmatocystin (DHDMST) by specific O-methyltransferases produces aflatoxins B1, G1, B2, and G2 in Aspergillus parasiticus.

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Area of Science:

  • Mycology
  • Biochemistry
  • Food Safety

Background:

  • Sterigmatocystins are structurally related to aflatoxins, potent mycotoxins.
  • Aspergillus parasiticus is a known producer of aflatoxins.
  • Understanding the biosynthetic pathway is crucial for controlling mycotoxin contamination.

Purpose of the Study:

  • To investigate the role of sterigmatocystin derivatives in aflatoxin biosynthesis.
  • To identify and characterize the enzymes involved in the methylation steps.
  • To elucidate the sequential methylation reactions leading to aflatoxin production.

Main Methods:

  • Feeding experiments using demethylsterigmatocystin (DMST) and dihydrodemethylsterigmatocystin (DHDMST) to Aspergillus parasiticus mutant NIAH-26.
  • Cell-free experiments utilizing S-adenosyl-[methyl-3H]methionine to track methylation.

Related Experiment Videos

  • Enzyme inhibition assays using N-ethylmaleimide to differentiate methyltransferase activities.

    • Main Results:

    • DMST and DHDMST were converted to aflatoxins B1/G1 and B2/G2, respectively, by Aspergillus parasiticus.
    • Two distinct O-methyltransferases (OMT I and OMT II) were identified, catalyzing sequential methylations.
    • OMT I methylated the C-6-OH group, while OMT II methylated the C-7-OH group; OMT I was sensitive to N-ethylmaleimide, OMT II was not.

    Conclusions:

    • Demethylsterigmatocystin and dihydrodemethylsterigmatocystin are direct precursors in aflatoxin biosynthesis.
    • Two distinct O-methyltransferases sequentially methylate sterigmatocystin precursors to form aflatoxins.
    • The identified O-methyltransferases are distinct proteins involved in specific methylation steps of aflatoxin formation.