Temperature-dependent modulation of farnesyl diphosphate/geranylgeranyl diphosphate synthase from hyperthermophilic archaea

Enzyme characteristics of trans-prenyl diphosphate synthase ( Tk-IdsA) from Thermococcus kodakaraensis, which catalyzes the consecutive trans-condensation of isopentenyl diphosphate (C 5) units with allylic diphosphate, were examined. Product analysis revealed that Tk-IdsA is a bifunctional enzyme, farnesyl diphosphate (FPP, C 15)/geranylgeranyl diphosphate (GGPP, C 20) synthase, and mainly yields both C 15 and C 20. The FPP/GGPP product ratio increases with the rise of the reaction temperature. The kinetic parameters obtained at 70 and 90 °C demonstrated that the rise of the temperature elevates the k 0 value for the C 10 allylic substrate to more than those for the C 5 and C 15 allylic substrates. These data suggest that Tk-IdsA contributes to adjust the membrane composition to the cell growth temperature by modulating its substrate and product specificities. Mutation study indicated that the aromatic side chain of Tyr-81 acts as a steric hindrance to terminate the chain elongation and defines the final product length.