Screening and heterologous expression of flavone synthase and flavonol synthase to catalyze hesperetin to diosmetin.

Abstract

In this study, 44 flavone synthases (FNS) and flavonol synthases (FLS) from different origins were collected. The instability index and conserved domain of the enzymes were analyzed through bioinformatics analysis, the results of which allowed us to screen suitable enzymes for constructing recombinant Escherichia coli. Defective enzymes were selected as controls. Native- and sodium dodecyl sulfate-polyacrylamide gel electrophoresis were conducted to isolate the heterologously expressed proteins. Liquid chromatography-mass spectrometry, 1H nuclear magnetic resonance, and ultra-performance liquid chromatography were performed to qualitatively and quantitatively analyze the products. The cellular transformation results showed that recombinant E. coli catalyzed the synthesis of diosmetin from hesperetin, and in vitro catalysis showed that heterologously expressed FNS/FLS played a catalytic role in this reaction. AnFNS (from Angelica archangelica) showed the highest substrate conversion (38.80% for cellular transformation, 12.93% for in vitro catalysis). The catalytic capacity of FNS/FLS from different origins exhibited the expected results, indicating that bioinformatics analysis is useful for screening enzymes. In addition, the catalytic properties of AnFNS and CaFLS (from Camellia sinensis) differed significantly, although these enzymes are structurally similar. Based on this difference, C-2 was predicted as the key site for FNS/FLS catalytic synthesis of diosmetin rather than C-3.