Molecular cloning and functional characterization of tyrosine decarboxylases from galanthamine-producing Lycoris radiata

Tyrosine decarboxylase (TyDC), a pyridoxal-5′-phosphate (PLP)-dependent aromatic amino acid decarboxylase, catalyzes the decarboxylation of l-tyrosine (Tyr) to generate the important biogenic tyramine. This amine was reported to be a biosynthetic precursor of the Amaryllidaceae alkaloids, a group of pharmaceutically important natural products. Herein, we cloned two TyDC-encoding genes from Lycoris radiata, a galanthamine (GAL, a characteristic Amaryllidaceae alkaloid)-producing and medicinally and ornamentally important perennial herbaceous plant. Heterologous expression of LrTyDCs in Escherichia coli and the following purification gave recombinant LrTyDCs to homogeneity for enzymatic reactions. Tyramine was detected and validated by HPLC–DAD and HRESIMS analyses of the LrTyDC-catalyzed reaction mixture, which revealed the catalytic decarboxylation activity of LrTyDCs. The transcriptional LrTyDCs were detected in all tissues of L. radiata by quantitative real-time PCR analyses. The present works demonstrated that TyDC-catalyzed decarboxylation reaction is a key step to generate the non-catechol biosynthetic precursor of the Amaryllidaceae alkaloids.