Production of bioactive hydroxyflavones by using monooxygenase from Saccharothrix espanaensis

Biocatalysts are a valuable tool for the structural modification of fine chemicals. Flavonoids possess several biological activities, which are correlated to their antioxidant activity. The numbers of hydroxyl groups in flavonoids are critical for their antioxidant activity. Development of biocatalysts for hydroxylation of flavonoids is challenging because of the difficulty in expressing flavonoid hydroxylase in Escherichia coli. In this study, a monooxygenase from Saccharothrix espanaensis (Sam5) was used for regioselective hydroxylation of flavonoids. We found that Sam5 hydroxylated isoflavones, flavanones, and flavones but did not produce any detectable hydroxylated product with flavonols. In addition, coexpression of P450 reductase with Sam5 in E. coli enhanced hydroxylation by approximately from 34 to 50%, depending on the flavonoid used. The production of two bioactive flavonoids, 8-hydroxyluteolin and 3′-hydroxydaidzein was optimized using this Sam5 system. Approximately 88 mg/L of 8-hydroxyluteolin and 75 mg/L of 3′-hydroxydaidzein were obtained. These results indicate that the Sam5 system could be used for the production of bioactive hydroxylated flavonoids.