Abstract
Polyphenols, which include phenolic acids, flavonoids, stilbenes, and phenylethanoids, are generally known as useful antioxidants. Tyrosol, hydroxytyrosol, and salidroside are typical phenylethanoids. Phenylethanoids are found in plants such as olive, green tea, and Rhodiola and have various biological activities, including the prevention of cardiovascular diseases, cancer, and brain damage. We used Escherichia coli to synthesize three phenylethanoids, tyrosol, hydroxytyrosol, and salidroside. To synthesize tyrosol, the aromatic aldehyde synthase (AAS) was expressed in E. coli. Hydroxytyrosol was synthesized using E. coli harboring AAS and HpaBC, which encodes hydroxylase. In order to synthesize salidroside, 12 uridine diphosphate-dependent glycosyltransferases (UGTs) were screened and UGT85A1 was found to convert tyrosol to salidroside. Using E. coli harboring AAS and UGT85A1, salidroside was synthesized. Through the optimization of these three E. coli strains, we were able to synthesize 531 mg/L tyrosol, 208 mg/L hydroxytyrosol, and 288 mg/L salidroside, respectively.
Highlights
Many countries have traditional foods or medicines; olive oil in southern Europe and the Middle East and green tea from Asia are considered regional traditional foods
For the synthesis of tyrosol in E. coli, we constructed the pathway from tyrosine to tyrosol using aldehyde synthase (AAS)
Tyrosol has been synthesized in E. coli using tyrosine decarboxylase (TDC) and TYO14 or using Aro[10] from yeast[13]
Summary
Many countries have traditional foods or medicines; olive oil in southern Europe and the Middle East and green tea from Asia are considered regional traditional foods. Hydroxytyrosol, and salidroside belong to a group of plant phenolic compounds called phenylethanoids. The synthesis of C6-C1 phenolic compounds, such as benzoic acid relies on the coenzyme A-dependent β-oxidation of cinnamoyl-CoA11 These results support that tyrosol is synthesized through tyrosine decarboxylation. Bai et al.[13] used aro[10] and other genes for the biosynthesis of tyrosine, in addition to several E. coli mutants to produce tyrosol. This group introduced UGT into the tyrosine producing E. coli strain to synthesize salidroside[13]. We used plant AAS to synthesize tyrosol, hydroxytyrosol, and salidroside in E. coli. Using engineered E. coli harboring AAS and the identified UGT, we could synthesize 288 mg/L salidroside
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