Cloning, characterization, and enzymatic identification of a new tryptophan decarboxylase from Ophiorrhiza pumila

Tryptophan decarboxylase (TDC, EC 4.1.1.28) catalyzes tryptophan decarboxylation to form tryptamine through the cofactor pyridoxal-5′-phosphate (PLP), a crucial stage in the production of the terpenoid indole alkaloids like camptothecin (CPT). A new gene encoding TDC was identified from the CPT-producing plant Ophiorrhiza pumila by transcriptome analysis, termed OpTDC2. It contained a 1,536 bp open reading frame that encodes a 511 amino acid protein with a molecular mass of 57.01 kDa and an isoelectric point of 6.39. Multiple sequence alignment and phylogenetic tree analysis showed the closest similarity (85%) with the TDC from Mitragyna speciosa . Moreover, the highest expression of OpTDC2 was observed in the O. pumila root. To achieve high-efficiency expression of OpTDC2 in Escherichia coli , we fused the TF tag onto the N-terminal of the OpTDC2. Optimum enzymatic activity was observed at 45 °C, pH 8 and cofactor concentration of 0.1 mM. The catalytic reaction was strongly inhibited by metal ions of Cu 2+ , Zn 2+ , and Fe 2+ . The l -tryptophan was particularly catalyzed compared with d -tryptophan. Besides, the K m and k cat of the OpTDC2 were 1.08 mM and 0.78 Sec −1 , respectively. The results provided information on new functional OpTDC2 that might be used in synthetic biology for the enhanced biosynthesis of CPT in O. pumila .