Publications

• Identification of a flavin-monooxygenase as the S-oxygenating enzyme in aliphatic glucosinolate biosynthesis in Arabidopsis.

  Hansen B.G., Kliebenstein D.J., Halkier B.A.

  The cancer-preventive activity of cruciferous vegetables is commonly attributed to isothiocyanates resulting from the breakdown of the natural products glucosinolates (GSLs). Sulforaphane, the isothiocyanate derived from 4-methylsulfinylbutyl GSL, is thought to be the major agent conferring cancer ... >> More

  The cancer-preventive activity of cruciferous vegetables is commonly attributed to isothiocyanates resulting from the breakdown of the natural products glucosinolates (GSLs). Sulforaphane, the isothiocyanate derived from 4-methylsulfinylbutyl GSL, is thought to be the major agent conferring cancer-preventive properties, whereas the isothiocyanate of 4-methylthiobutyl GSL does not have the same activity. We report the identification of an Arabidopsis flavin-monooxygenase (FMO) enzyme, FMO(GS-OX1), which catalyzes the conversion of methylthioalkyl GSLs into methylsulfinylalkyl GSLs. This is evidenced by biochemical characterization of the recombinant protein, and analyses of the GSL content in FMO(GS-OX1) overexpression lines and an FMO(GS-OX1) knock-out mutant of Arabidopsis. The FMO(GS-OX1) overexpression lines show almost complete conversion of methylthioalkyl into methylsulfinylalkyl GSLs, with an approximately fivefold increase in 4-methylsulfinylbutyl GSL in seeds. Identification of FMO(GS-OX1) provides a molecular tool for breeding of Brassica vegetable crops with increased levels of this important GSL, which has implications for production of functional foods enriched with the cancer-preventive sulforaphane. << Less

  Plant J. 50:902-910(2007) [PubMed] [EuropePMC]

• Subclade of flavin-monooxygenases involved in aliphatic glucosinolate biosynthesis.

  Li J., Hansen B.G., Ober J.A., Kliebenstein D.J., Halkier B.A.

  Glucosinolates (GSLs) are amino acid-derived secondary metabolites with diverse biological activities dependent on chemical modifications of the side chain. We previously identified the flavin-monooxygenase FMO(GS-OX1) as an enzyme in the biosynthesis of aliphatic GSLs in Arabidopsis (Arabidopsis ... >> More

  Glucosinolates (GSLs) are amino acid-derived secondary metabolites with diverse biological activities dependent on chemical modifications of the side chain. We previously identified the flavin-monooxygenase FMO(GS-OX1) as an enzyme in the biosynthesis of aliphatic GSLs in Arabidopsis (Arabidopsis thaliana) that catalyzes the S-oxygenation of methylthioalkyl to methylsulfinylalkyl GSLs. Here, we report the fine mapping of a quantitative trait locus for the S-oxygenating activity in Arabidopsis. In this region, there are three FMOs that, together with FMO(GS-OX1) and a fifth FMO, form what appears to be a crucifer-specific subclade. We report the identification of these four uncharacterized FMOs, designated FMO(GS-OX2) to FMO(GS-OX5). Biochemical characterization of the recombinant protein combined with the analysis of GSL content in knockout mutants and overexpression lines show that FMO(GS-OX2), FMO(GS-OX3), and FMO(GS-OX4) have broad substrate specificity and catalyze the conversion from methylthioalkyl GSL to the corresponding methylsulfinylalkyl GSL independent of chain length. In contrast, FMO(GS-OX5) shows substrate specificity toward the long-chain 8-methylthiooctyl GSL. Identification of the FMO(GS-OX) subclade will generate better understanding of the evolution of biosynthetic activities and specificities in secondary metabolism and provides an important tool for breeding plants with improved cancer prevention characteristics as provided by the methylsulfinylalkyl GSL. << Less

  Plant Physiol. 148:1721-1733(2008) [PubMed] [EuropePMC]