Engineering Escherichia coli for High-Yielding Hydroxytyrosol Synthesis from Biobased l-Tyrosine.

Hydroxytyrosol (HT) is a natural antioxidant with many associated health benefits. In this study, we established efficient enzymatic cascades for the synthesis of HT from biobased l-tyrosine. First, a dopamine-mediated route for HT production was investigated. The combination of native hydroxylase (HpaBC) from Escherichia coli and l-DOPA decarboxylase (DODC) from Pseudomonas putida could efficiently convert 5 mM l-tyrosine into dopamine with conversion above 90%. However, further incorporation of monoamine oxidase (MAO) from Micrococcus luteus and phenylacetaldehyde reductase (PAR) from Solanum lycopersicum only resulted in 3.47 mM HT with 69.4% conversion. Therefore, a second enzyme cascade that comprises HpaBC from E. coli, l-amino acid deaminase (LAAD) from Proteus mirabilis, α-keto acid decarboxylase (ARO10) from Saccharomyces cerevisiae, and PAR from S. lycopersicum was designed. This enzymatic route showed higher catalytic activity and efficiently synthesized HT. The 24.27 mM HT was obtained from 25 mM l-tyrosine with a high conversion of 97.1%, and 32.35 mM HT was produced using 50 mM l-tyrosine, which represents the highest HT titer using l-tyrosine as a substrate reported to date. In summary, we have developed a green and sustainable platform for efficient HT enzymatic synthesis.