Abstract
Catalytic versatility is an inherent property of many enzymes. In nature, terpene cyclases comprise the foundation of molecular biodiversity as they generate diverse hydrocarbon scaffolds found in thousands of terpenoid natural products. Here, we report that the catalytic activity of the terpene cyclases AaTPS and FgGS can be switched from cyclase to aromatic prenyltransferase at basic pH to generate prenylindoles. The crystal structures of AaTPS and FgGS provide insights into the catalytic mechanism of this cryptic function. Moreover, aromatic prenyltransferase activity discovered in other terpene cyclases indicates that this cryptic function is broadly conserved among the greater family of terpene cyclases. We suggest that this cryptic function is chemoprotective for the cell by regulating isoprenoid diphosphate concentrations so that they are maintained below toxic thresholds.
Highlights
Catalytic versatility is an inherent property of many enzymes
To confirm the predicted coding sequence of AaTPS, genomic DNA of this gene was put under the control of the alcA promoter and transformed into A. alternata TPF6 via the Agrobacterium tumefaciens-mediated transformation method to generate mutant Alternaria alternata GB17117
AaTPS was purified and an in vitro assay was performed to evaluate the ability of the enzyme to utilize alltrans-polyisoprenoid diphosphates geranyl diphosphate (GPP), farnesyl diphosphate (FPP), and geranylgeranyl diphosphate (GGPP) as substrates
Summary
Catalytic versatility is an inherent property of many enzymes. In nature, terpene cyclases comprise the foundation of molecular biodiversity as they generate diverse hydrocarbon scaffolds found in thousands of terpenoid natural products. The reactions catalyzed by terpene cyclases are largely responsible for the expansive chemodiversity of terpenoid natural products In addition to their utility as substrates for terpene cyclases, isoprenoid diphosphates serve as co-substrates for aromatic prenyltransferases. To provide insight on catalytic mechanism in these bifunctional enzymes, we report crystal structures of the class I terpene cyclases AaTPS and FgGS. These structural and functional studies illuminate a dynamic regulation strategy for the utilization of indole prenylation to mitigate elevated DMAPP concentrations that could otherwise be toxic to the cell
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