Efficient Synthesis of Hydroxytyrosol from <scp>l</scp>-3,4-Dihydroxyphenylalanine Using Engineered <i>Escherichia coli</i> Whole Cells

Abstract

Hydroxytyrosol is a high-value-added compound with a variety of biological and pharmacological activities. In this study, a whole-cell catalytic method for the synthesis of hydroxytyrosol was developed: aromatic amino acid aminotransferase (TyrB), l-glutamate dehydrogenase (GDH), α-keto acid decarboxylase (PmKDC), and aldehyde reductase (YahK) were co-expressed in Escherichia coli to catalyze the synthesis of hydroxytyrosol from l-3,4-dihydroxyphenylalanine (l-DOPA). The plasmids with different copy numbers were used to balance the expression of the four enzymes, and the most appropriate strain (pRSF-yahK-tyrB and pCDF-gdh-Pmkdc) was identified. After determination of the optimum temperature (35 °C) and pH (7.5) for whole-cell catalysis, the yield of hydroxytyrosol reached 36.33 mM (5.59 g/L) and the space-time yield reached 0.70 g L–1 h–1.