Biochemistry, Biophysics and Molecular Biology, Roy J. Carver Department of
Journal or Book Title
Vascular plants invariably contain a class II diterpene cyclase (EC 5.5.1.x), as an ent-copalyl diphosphate synthase is required for gibberellin phytohormone biosynthesis. This has provided the basis for evolution of a functionally diverse enzymatic family. These biocatalysts fold their substrate, the general diterpenoid precursor (E,E,E)-geranylgeranyl diphosphate (GGPP), to bring the terminal three carbon-carbon double bonds into proximity with each other, and then carry out bicyclization via a protonation-initiated carbocation cascade reaction. The resulting labda-15-en-8-yl+ diphosphate intermediate is most commonly quenched by deprotonation at an exocyclic methyl, as in the production of labdadienyl/copalyl diphosphate (Scheme 1). Alternatively, the bicyclized labda-15-en-8-yl+ diphosphate intermediate can be captured by water prior to deprotonation, to form hydroxylated compounds such as labda-15-en-8-ol diphosphate. In addition, this intermediate can undergo subsequent rearrangement via 1,2-hydride and/or methyl shifts, starting with the hydrogen substituent on the neighboring endocyclic methine (C9). However, terminating deprotonation at the neighboring endocyclic methylene (C7) has not previously been observed. Here we report that the lycophyte Selaginella moellendorffii contains a bifunctional diterpene synthase, SmCPSKSL1, which catalyzes just such a class II cyclization reaction. In particular, SmCPSKSL1 produces an endocyclic double bond isomer of copalyl diphosphate (CPP), as well as carries out subsequent replacement of the diphosphate by a hydroxyl group to form labda-7,13E-dien-15-ol. Although this is a known plant metabolite, and a small family of bioactive derived natural products is known from a phylogenetically diverse group of plants,[4-5] its biosynthesis has not been previously investigated. Our results demonstrate that this diterpenoid can be generated by a single bifunctional diterpene synthase that directly generates the endocyclic double bond, as well as hydroxyl group.
WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Mafu, Sibongile; Hillwig, Matthew L.; and Peters, Reuben J., "A Novel Labda-7,13E-dien-15-ol-Producing Bifunctional Diterpene Synthase from Selaginella moellendorffii" (2011). Biochemistry, Biophysics and Molecular Biology Publications. 108.