Crocins are highly valuable medicinal compounds for treating human disorders, and they also serve as spices and coloring agents. However, the supply of crocins from plant extractions is insufficient for current demands, and using synthetic biology to produce crocins remains a big challenge. Here, we report the in vivo production of five types of crocins in E. coli with GjUGT94E13 and GjUGT74F8, which are responsible for the glycosylation of crocetin, from the crocin-producing plant Gardenia jasminoides. Subsequently, native UDP-glucose biosynthesis in E. coli is strengthened by the overexpression of pgm and galU. The optimization of catalytic reactions has demonstrated that 50 mM NaH2PO4-Na2HPO4 buffer (pH 8.0) plus 5% glucose is the best medium to use for the efficient glycosylation of crocetin. In engineered E. coli, the conversion rate of crocin III and crocin V from crocetin (50 mg/L) by the catalysis of GjUGT74F8 was increased to 66.1%, and the conversion rate of five types of crocins from crocetin (50 mg/L) via GjUGT94E13 and GjUGT74F8 was 59.6%, much higher than the catalytic activity of the reported microbial UGTs. This study not only sheds light on the in vivo biosynthesis of crocins in E. coli, but also provides important genetic tools for the de novo synthesis of crocins.
Keywords: UDP-glycosyltransferase; crocetin; synthetic biology, crocins.