Characterization flavanone 3β-hydroxylase expressed from Populus euphratica in Escherichia coli and its application in dihydroflavonol production

Abstract

Flavanone 3β-hydroxylase plays very important role in the biosynthesis of flavonoids. A putative flavanone 3β-hydroxylase gene (Pef3h) from Populus euphratica was cloned and over-expressed in Escherichia coli. Induction performed with 0.1 mM IPTG at 20°C led to localization of PeF3H in the soluble fraction. Recombinant enzyme was purified by Ni-NTA affinity. The optimal activity of PeF3H was revealed at pH 7.6 and 35°C. The purified enzyme was stable over pH range of 7.6–8.8 and had a half-life of 1 h at 50°C. The activity of PeF3H was significantly enhanced in the presence of Fe2+ and Fe3+. The K M and V max for the enzyme using naringenin as substrate were 0.23 mM and 0.069 μmoles mg–1min-1, respectively. The K m and V max for eriodictyol were 0.18 mM and 0.013 μmoles mg–1min–1, respectively. The optimal conditions for naringenin bioconversion in dihydrokaempferol were obtained: OD600 of 3.5 for cell concentration, 0.1 mM IPTG, 5 mM α-ketoglutaric acid and 20°C. Under the optimal conditions, naringenin (0.2 g/L) was transformed into 0.18 g/L dihydrokaempferol within 24 h by the recombinant E. coli with a corresponding molar conversion of 88%. Thus, this study provides a promising flavanone 3β-hydroxylase that may be used in biosynthetic applications.