Cloning and Characterization of δ-Guaiene Synthase Genes Encoding a Sesquiterpene Cyclase from Aquilaria microcarpa Cell Cultures

Abstract

Three cDNA clones encoding δ-guaiene synthase, a sesquiterpene cyclase, were isolated from tissue cultures of Aquilaria microcarpa, and data mining analysis of the orthologous genes suggested that 10 and 9 amino acid residues of N- and C-terminal ends of the translated products of these clones remained undefined. The recombinant enzyme proteins, to which the putative missing Nand C-terminal amino acid sequences (MSSAKLGSAS and ALLRHAIEI, respectively) were ligated, exhibited the catalytic activities of sesquiterpene biosynthesis. Among these three δ-guaiene synthases, two isoforms were capable of liberating α-guaiene, δ-guaiene, β-elemene plus α-humulene as a minor product, while remaining one isoenzyme generated α-, δ-guaiene and β-elemene but not α-humulene. Although the enzyme protein solely lacking in the N-terminal 10 amino acid residues was capable of synthesizing the sesquiterpenoids, the protein without 9 amino acids at Cterminal did not exhibit the catalytic activity. These results suggest that two types of δ-guaiene synthase; α-, δ-guaiene, β-elemene-producing type, and α-, δ-guaiene, β-elemene plus α-humulene-producing type; concomitantly occur in A. microcarpa cell cultures, and several amino acid residues at C-terminal of the synthase protein are essential to exhibit the catalytic activities as the sesquiterpene cyclase.