Heterologous Expression, Purification, and Biochemical Characterization of α-Humulene Synthase from Zingiber zerumbet Smith

The α-humulene synthase from Zingiber zerumbet Smith was expressed as a polyhistidine-tagged protein in an E. coli BL21(DE3) strain. Induction time and inductor (isopropyl-β-D-thiogalactopyranoside) concentration were optimized. The enzyme was successfully purified directly from cell lysate by NTA affinity column chromatography and careful selection of coordinated metal ion and imidazole elution conditions. Bioactivity assays were conducted with the natural substrate farnesyl diphosphate (FDP) in a two-phase system with in situ extraction of products. The conversion of FDP to α-humulene (~94.5 %) and β-caryophyllene (~5.5 %) could be monitored by gas chromatography-flame ionization detection (GC-FID). Optimal pH and temperature as well as kinetic parameters KM and kcat were determined using a discontinuous kinetic assay.