Cloning, prokaryotic expression, and enzyme activity of a UDP-glucose flavonoid 3-o-glycosyltransferase from mulberry (Morus alba L.) leaves

Background: Mulberry leaves are traditional Chinese medicines, which have pharmacological activities such as anti-inflammation, anti-oxidation, antitumor, and hypoglycemic. Moreover, flavonol glycosides are one of the main functional ingredients. However, the biosynthetic pathway involved in mulberry flavonol glycosides has not been clear. UDP-glucose flavonoid 3-O -glycosyltransferase (UFGT) is a key enzyme in the biosynthesis pathway of flavonol glycosides, which can glycosylate unstable flavonols to form stable flavonol glycosides. Objectives: In this article, MaUFGT , a cDNA encoding the UFGT from mulberry leaves, was cloned, codon optimized, and expressed in Escherichia coli to study its effect in vitro . Materials and Methods: Mulberry UDP-Glucose flavonoid-3-O-glucanotransferase (MaUFGT) gene was reverse transcription-polymerase chain reaction amplified using the cDNA obtained from young leaves of mulberry, and the full-length MaUFGT gene was synthesized by codon-optimized whole-gene synthetic method. Then, the plasmid pCzn1/MaUFGT was constructed and heterologously expressed in E. coli . After denatured, renatured, and purified, the recombinant protein was used to evaluate its function in vitro by determining the final product by high-performance liquid chromatography. Results: The target protein was in the range of 45-66 KD and mainly present in the form of inclusion bodies. The obtained protein was found to transfer UDP-glucose glycosyl moieties to the 3-hydroxyl group of quercetin or kaempferol to form the corresponding products in vitro . Conclusion: The MaUFGT was preliminarily proved to be involved in flavonoid 3-O -glucoside biosynthesis.