Structural Basis for Cyclic Terpene Biosynthesis by Tobacco 5-Epi-Aristolochene Synthase

Starks, Courtney M.; Back, Kyoungwhan; Chappell, Joseph; Noel, Joseph P.

doi:10.1126/science.277.5333.1815

Cited by 676 publications

(799 citation statements)

References 24 publications

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“…Similar deprotonation/reprotonation sequences have been reported for other Class I TPS‐catalyzed cyclizations, including sesquiterpene synthases (for example, for tobacco 5‐epi‐aristolochene synthase (TEAS), and more recently for fungal STS astellifadiene synthase) 2c, 5a, 10. To support our proposed cyclization mechanism, we also conducted in vivo feeding and time course experiments whereby we harvested N. benthamiana leaves expressing the plant STS genes at different time points (4 d, 5 d, 8 d, and 10 d) after watering the plant with pure D 2 O for seven days, starting from the third day post‐infiltration,11 and analyzed the leaf extracts by GC‐MS.…”

supporting

confidence: 67%

Diverged Plant Terpene Synthases Reroute the Carbocation Cyclization Path towards the Formation of Unprecedented 6/11/5 and 6/6/7/5 Sesterterpene Scaffolds

et al. 2017

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Sesterterpenoids are a relatively rare class of plant terpenes. Sesterterpene synthase (STS)‐mediated cyclization of the linear C25 isoprenoid precursor geranylfarnesyl diphosphate (GFPP) defines sesterterpene scaffolds. So far only a very limited number of STSs have been characterized. The discovery of three new plant STSs is reported that produce a suite of sesterterpenes with unprecedented 6/11/5 and 6/6/7/5 fused ring systems when transiently co‐expressed with a GFPP synthase in Nicotiana benthamiana. Structural elucidation, feeding experiments, and quantum chemical calculations suggest that these STSs catalyze an unusual cyclization path involving reprotonation, intramolecular 1,6 proton transfer, and concerted but asynchronous bicyclization events. The cyclization is diverted from those catalyzed by the characterized plant STSs by forming unified 15/5 bicyclic sesterterpene intermediates. Mutagenesis further revealed a conserved amino acid residue implicated in reprotonation.

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supporting

confidence: 67%

Diverged Plant Terpene Synthases Reroute the Carbocation Cyclization Path towards the Formation of Unprecedented 6/11/5 and 6/6/7/5 Sesterterpene Scaffolds

et al. 2017

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“…In contrast, the class II enzymes initiate cyclization via protonation of the terminal carbon-carbon double bond in GGPP and contain a separately placed DXDD sequence rather than the class I associated DDXXD motif (Sun and Kamiya, 1994). Notably, prototypical class I enzymes are similar in size and contain two structurally defined domains (Starks et al, 1997;Whittington et al, 2002). However, some terpene synthases, in particular all of those involved in labdane-related diterpenoid biosynthesis (Fig.…”

mentioning

confidence: 99%

“…A, Domain schematic for prototypical class I terpene synthases (tpsI) and the class I and class II (tpsII) enzymes involved in labdane-related diterpene biosynthesis. Modeled on the structures determined for the typical class I epi-aristolochene and bornyl diphosphate synthases (Starks et al, 1997;Whittington et al, 2002), along with the additional insertional sequence element. Approximate locations of the Asp-rich motifs are also indicated.…”

mentioning

confidence: 99%

Identification of Syn-Pimara-7,15-Diene Synthase Reveals Functional Clustering of Terpene Synthases Involved in Rice Phytoalexin/Allelochemical Biosynthesis

et al. 2004

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Rice (Oryza sativa) produces momilactone diterpenoids as both phytoalexins and allelochemicals. Accordingly, the committed step in biosynthesis of these natural products is catalyzed by the class I terpene synthase that converts syn-copalyl diphosphate to the corresponding polycyclic hydrocarbon intermediate syn-pimara-7,15-diene. Here, a functional genomics approach was utilized to identify a syn-copalyl diphosphate specific 9b-pimara-7,15-diene synthase (OsDTS2). To our knowledge, this is the first identified terpene synthase with this particular substrate stereoselectivity and, by comparison with the previously described and closely related ent-copalyl diphosphate specific cassa-12,15-diene synthase (OsDTC1), provides a model system for investigating the enzymatic determinants underlying the observed difference in substrate specificity. Further, OsDTS2 mRNA in leaves is up-regulated by conditions that stimulate phytoalexin biosynthesis but is constitutively expressed in roots, where momilactones are constantly synthesized as allelochemicals. Therefore, transcription of OsDTS2 seems to be an important regulatory point for controlling production of these defensive compounds. Finally, the gene identified here as OsDTS2 has previously been mapped at 14.3 cM on chromosome 4. The class II terpene synthase producing syn-copalyl diphosphate from the universal diterpenoid precursor geranylgeranyl diphosphate was also mapped to this same region. These genes catalyze sequential cyclization steps in momilactone biosynthesis and seem to have been evolutionarily coupled by physical linkage and resulting cosegregation. Further, the observed correlation between physical proximity and common metabolic function indicates that other such class I and class II terpene synthase gene clusters may similarly catalyze consecutive reactions in shared biosynthetic pathways.Plants produce a vast and diverse array of low-molecular weight organic compounds, the overwhelming majority of which are secondary metabolites with nonessential, yet important, functions such as defense . For example, phytoalexins are produced in response to microbial infections and exhibit antimicrobial activity (VanEtten et al., 1994), while allelochemicals are secreted to the rhizosphere and suppress the growth of neighboring plants (Bais et al., 2004). Often found serving in such roles are terpenoids, which are particularly abundant in plant metabolism and form the largest class of natural products, exhibiting wide diversity in chemical structure and biological function . Much of the structural variation within this class arises from the diverse carbon backbones formed by terpene synthases (cyclases). These divalent metal dependent enzymes carry out complex electrophilic cyclizations/ rearrangements to create these diverse skeletal structures from relatively simple acyclic precursors (Davis and Croteau, 2000). Notably, production of a specific backbone structure either dictates, or at least severely restricts, the metabolic fate of that particular molecule. Thus,...

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“…2). It has been established from mechanistic studies and crystal structures of several class I enzymes that the associated DDXXD motif is involved in binding divalent metal ions, generally Mg 21 (Lesburg et al, 1997;Starks et al, 1997;Rynkiewicz et al, 2001). These divalent metal ions are involved in both binding the pyrophosphate group and catalyzing ionization and, therefore, are required for class I pyrophosphate ionization-initiated catalysis (Christianson, 2006).…”

mentioning

confidence: 99%

Synergistic Substrate Inhibition of ent-Copalyl Diphosphate Synthase: A Potential Feed-Forward Inhibition Mechanism Limiting Gibberellin Metabolism

2007

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Gibberellins (GAs) or gibberellic acids are ubiquitous diterpenoid phytohormones required for many aspects of plant growth and development, including repression of photosynthetic pigment production (i.e. deetiolation) in the absence of light. The committed step in GA biosynthesis is catalyzed in plastids by ent-copalyl diphosphate synthase (CPS), whose substrate, (E,E,E,)-geranylgeranyl diphosphate (GGPP), is also a direct precursor of carotenoids and the phytol side chain of chlorophyll. Accordingly, during deetiolation, GA production is repressed, whereas flux toward these photosynthetic pigments through their common GGPP precursor is dramatically increased. How this is accomplished has been unclear because no mechanism for regulation of CPS activity has been reported. We present here kinetic analysis of recombinant pseudomature CPS from Arabidopsis (Arabidopsis thaliana; rAtCPS) demonstrating that Mg 21 and GGPP exert synergistic substrate inhibition effects on CPS activity. These results suggest that GA metabolism may be limited by feed-forward inhibition of CPS; in particular, the effect of Mg 21 because light induces increases in plastid Mg 21 levels over a similar range as that observed here to affect rAtCPS activity. Notably, this effect is most pronounced in the GA-specific AtCPS because the corresponding activity of the resin acid biosynthetic enzyme abietadiene synthase is 100-fold less sensitive to [Mg 21 ]. Furthermore, Mg 21 allosterically activates the plant porphobilinogen synthase involved in chlorophyll production. Hence, Mg 21 may have a broad role in regulating plastidial metabolic flux during deetiolation. Finally, the observed synergistic substrate/feed-forward inhibition of CPS also seems to provide a novel example of direct regulation of enzymatic activity in hormone biosynthesis.

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Structural Basis for Cyclic Terpene Biosynthesis by Tobacco 5-Epi-Aristolochene Synthase

Cited by 676 publications

References 24 publications

Diverged Plant Terpene Synthases Reroute the Carbocation Cyclization Path towards the Formation of Unprecedented 6/11/5 and 6/6/7/5 Sesterterpene Scaffolds

Diverged Plant Terpene Synthases Reroute the Carbocation Cyclization Path towards the Formation of Unprecedented 6/11/5 and 6/6/7/5 Sesterterpene Scaffolds

Identification of Syn-Pimara-7,15-Diene Synthase Reveals Functional Clustering of Terpene Synthases Involved in Rice Phytoalexin/Allelochemical Biosynthesis

Synergistic Substrate Inhibition of ent-Copalyl Diphosphate Synthase: A Potential Feed-Forward Inhibition Mechanism Limiting Gibberellin Metabolism

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