Development of a Multienzyme Cascade for Salvianolic Acid A Synthesis from l-Tyrosine

Salvianolic acid A (SAA) has an important application value for preventing and treating cardiovascular diseases. In this study, we developed a novel multienzyme cascade system for the efficient biosynthesis of SAA, utilizing l-tyrosine (l-Tyr) as a cost-effective and stable starting material. The cascade system incorporated four enzymes: membrane-bound l-amino acid deaminase from Proteus vulgaris (Pvml-AAD), d-lactate dehydrogenase from Pediococcus acidilactici (Pad-LDH), 4-hydroxyphenylacetate 3-hydroxylase from Escherichia coli (EcHpaBC), and formate dehydrogenase from Mycobacterium vaccae N10 (MvFDH). All reaction steps in the cascade system were thermodynamically favorable. In addition, to avoid generating an unstable intermediate (3,4-dihydroxyphenyl-pyruvate, DHPPA), which was produced owing to the promiscuity of EcHpaBC and Pad-LDH, we performed the cascade system according to the reaction sequence of deamination, chiral reduction, and ortho-hydroxylation. Under optimized conditions, the developed cascade system yielded 81.67 mM SAA from an initial concentration of 100 mM l-Tyr, corresponding to a yield of 81.67%.