Substrate specificities of E- and Z-farnesyl diphosphate synthases with substrate analogs

Prenyltransferases catalyzes the basic isoprenoid chain elongation to produce prenyl diphosphates, which led to upward of 30,000 diverse isoprenoids as steroids, carotenoids, natural rubbers, and prenyl proteins. Here, we determined the reactivities of E- and Z-farnesyl diphosphate synthases (E- and Z-FPP synthases) isolated from Bacillus stearothermophilus and Thermobifida fusca, respectively. For this purpose we use the synthetic substrate analogs, 8-tetrahydropyran-2-yloxy-, 8-hydroxy- and 8-acetoxygeranyl diphosphates. Z-FPP synthase catalyzed the reaction between 8-hydroxygeranyl diphosphate (HOGPP) and isopentenyl diphosphate (IPP), which produced (2Z)-12-hydroxyfarnesyl diphosphate (yield: 16.7%) and (2Z, 6Z)-16-hydroxygeranylgeranyl diphosphate (yield: 6.6%). Neither E- nor Z-farnesyl diphosphate synthases detectably catalyzed reactions between 8-tetrahydropyran-2-yloxygeranyl diphosphate (8-THPOGPP) and IPP. However, a mutated E-FPP synthase (Y81S), did catalyze this reaction, producing 12-tetrahydropyran-2-yloxyfarnesyl diphosphate (12-THPOFPP) with a yield of 12.3%. Wild-type E-FPP synthase catalyzed the reaction of 8-acetoxygeranyl diphosphate (8-AcOGPP) with IPP, which produced 12-acetoxyfarnesyl diphosphate (12-AcOFPP) (yield, 21.8%). Mutant E-FPP synthase catalyzed the reaction between 8-AcOGPP with IPP, producing 12-AcOFPP and 16-acetoxygeranylgeranyl diphosphate (16-AcOGGPP) with respective yields of 55.3% and 1.7%. We believe our results contribute to a better understanding of the catalytic properties of these key enzymes and illustrate their use in the stereo-specific syntheses of compounds that may have significant biotechnological and medical applications.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► We describe the synthesis of novel allylic substrates for studying the enzymology of bacterial E- and Z-farnesyl diphosphate synthases (E- and Z-FPP synthases). ► Using these substrates we compared the catalytic specificities of recombinant bacterial E- and Z-FPP synthases isolated, respectively, from Bacillus stearothermophilus and Thermobifida fusca. ► Z-FPP synthase catalyzed the reaction between 8-hydroxygeranyl diphosphate (HOGPP) and isopentenyl diphosphate (IPP) but not between IPP and 8-tetrahydropyran-2-yloxygeranyl diphosphate (THPOGPP). ► Wild-type E- and Z-FPP synthases did not utilize 8-THPOGPP and IPP as substrates, whereas mutant (Y81S) E-FPP synthase produced two products using a mechanism characteristic of geranylgeranyl diphosphate synthase. ► Wild-type and mutant E-enzymes differed markedly with respect to utilization of other allylic substrates and the resulting products.