Functional characterization of promiscuous tryptophan decarboxylase from indole alkaloids producing Rauvolfia tetraphylla L.

Abstract

The enzyme Tryptophan decarboxylase (TDC, EC 4.1.1.28) gene facilitates the conversion of tryptophan to tryptamine. A new gene encoding TDC was identified from the alkaloid producing plant Rauvolfia tetraphylla by transcriptome analysis, termed as RtTDC. It contains 1,500 base pair which encodes an open reading frame for 499-amino-acid polypeptide with molecular mass of 55729.29 kDa and isoelectric point of 5.37. Multiple sequence alignment and phylogenetic tree analysis showed the closest similarity (95.3 %) with the TDC from the Rauvolfia verticillata. This enzyme has property of recombinant tryptophan decarboxylase from R. tetraphylla was characterized. The potential activity of tryptophan decarboxylase specific to L-tryptophan may contribute to the biosynthesis of indole alkaloids in R. tetraphylla. The finding of tryptophan metabolites in R. tetraphylla plants is a novel report, lead to hypothesize the existence of TDC enzymatic activity, from which aromatic amino acid decarboxylases is formed. These results support the in-silico annotation of the examined protein sequences of R. tetraphylla as TDC and suggest the involvement of TDC enzymatic activity in this plant. Molecular modeling of the TDC gene evidencing the reliability, stability and the structural similarities of the R. tetraphylla TDC gene with R. verticillata TDC gene. The L-tryptophan used as ligand in docking analysis to verify the TDC gene enzymatic activity for synthesis of Indole alkaloids. High performance liquid chromatography data analyses of RtTDC catalyzed reaction mixture confirmed the catalytically decarboxylative activity of RtTDC.