Construction of engineered bifunctional enzymes to improve the production of kaempferol in an in vitro synthetic biosystem

Kaempferol, an important flavonol, has numerous health-beneficial bioactivities and possesses a great potential for application in medicine, food, and cosmetics industries. To improve the production of kaempferol in an in vitro synthetic biosystem, we designed and constructed a panel of bifunctional enzymes by fusing the flavanone 3-hydroxylase (AtF3H) and the flavonol synthase (AtFLS1) of Arabidopsis thaliana with different orientation and different peptide linker type and length. By comparing the output of kaempferol, we obtained a highly active bifunctional enzyme AtF3H-(GGGGS)₂-AtFLS1 with a Km value of 0.129 ± 0.016 mM. After optimization of a series of reaction parameters, kaempferol was produced at 100.54 ± 0.54 mg/L, the currently highest kaempferol output in an in vitro synthetic biosystem, and the substrate conversion rate was 68.26% ± 0.05%. In addition, we observed substrate inhibition for the AtFLS1, which eventually limited the production of kaempferol. This study provides a highly active biocatalyst for production of kaempferol and an insight into biosynthesis of other valuable molecules.

Keywords:
kaempferol; flavanone 3-hydroxylase; flavonol synthase; bifunctional enzyme; peptide linker